Tag Archives: Cadwell park

Cadwell race report – September 2015

It’s been a quiet summer on the Scott racing front. All kinds of responsibilities and activities fill a Summer when you’ve got two very small children and I must admit to at least attempting to lead a balanced life, especially when the sun is out. Also, doing a bit of Scott work for other people does mean that I’m spending time on their engines rather than my own! It’s all good though and I was looking forward to getting to the September meeting at Cadwell park as this is my favourite meeting of all.

The Flying Squirrel (remember, it’s a Flying Squirrel and not a Super Squirrel as I discovered this year..) was still on the bench looking a little forlorn at the beginning of September. I had removed the top end after the seizures at Anglesey because I wanted to check the pistons and bores. The seizures had occurred on both pistons at the rear corners and the left hand piston was a little distorted because of it. I spent quite a bit of time filing the damage out carefully. The bores were fine, although I flex-honed them to freshen them up a bit.

The last time I had assembled the engine, I used a gasket compound called ‘three bond’ which has good gap filling properties and remains flexible. I used a tiny smear on various surfaces that I had scraped flat, just to ensure a good seal. I had a hell of a job getting things apart and in fact the bond was so good that it pulled the devcon epoxy out of some corrosion damage on one of the carburettor flange faces. There’s such a thing as too good! I think I’ll use it where a face isn’t good, but back to a silicone sealant where it’s needed.

So, with the engine back together and the repaired radiator back in (thank you again, Graham Moag), the bike just needed a few bits sorting out to get it ready. The front mudguard needed to be replaced and the L/H footrest needed straightening. A few other little bits as well.
Inevitably, some of these things ended up being left to the last minute, which was OK since I’d arranged to have the day free before I went to Cadwell just to make sure everything was finished. Unfortunately, my wife had a work deadline which meant that I had to look after our children on this day. This was an error in my calculations! Instead of an unhurried day and early afternoon departure to Cadwell, I frenetically worked on the bike from around 5pm till 9.00pm on the Friday night, then packed the van and went to bed at 10.30pm. At 1.00am I arose, drank coffee and set off to Cadwell… over 6 hours away.

The drive wasn’t so bad and the morning was crisp, with a low mist that hugged the warm ground. It was obvious that it would clear and clear it did. It was indeed a beautiful morning welcome from Cadwell Park.

I arrived pretty much as people were starting to get up and got the bike down to Scrutineering early. No problems here and I signed on and started to check the bike over myself.

Practice for solos was called and the bike started immediately. The twin carbs breathing without bellmouths because I knew I needed to make some that actually flowed properly and I hadn’t done testing to base a length on. I figured it would do at this point.

1" type 76s without bellmouths... yet!
1″ type 76s without bellmouths… yet!

The Scott seemed willing at low revs although I was concentrating on the clutch, given the seizures it had experienced at Anglesey. Sure enough, at the bottom of the park straight it came. I was quick to get the clutch in and coasted to the marshall’s post to wait for the end of the session and the recovery truck.

Back in the paddock I started to go through the fuel system. A gentleman called Peter, who was interested in the Scott, was kind enough to help as I went through the fuel system checking the flows through the taps, lines and banjos.
It’s dangerous to assume but sometimes you forget when you have assumed. I had the bike on the dyno at the beginning of the year and had thought that this would show up any problems with fuel supply. It wasn’t that I was expecting it to give problems.. and it didn’t. I’d made sure that the fuel lines were all of a descent size and had put the lot together being as careful as possible to avoid flow related issues. The dyno runs were completed without the suspicion of a seizure, so I hadn’t thought there was likely to be a problem.
I did flow tests all the way to the banjos that fit to the bottom of the carbs and was surprised at the results. They were barely able to flow the potential of the main jet. With my new found assistant’s help, I drilled every fitting out and found that I’d increased flow by a couple of hundred cc’s per minute to each carb. Part of the flow improvement was that I removed a connector pipe between the feeds to the two float chambers from my twin taps. I’d thought that this was was a good idea in case one tap became blocked but in effect the T- piece connectors were just another cause of a pressure drop. Amal main jets are rated by cc’s per minute flow (albeit under certain controlled conditions that I wasn’t trying to emulate) but at least now I had almost double the flow specified by each jet. I thought that should cover that as a possibility of seizure.
I was therefore hopeful when I got out in my first race, though aware that I still may be missing something.
It seized at the end of park straight on about the second lap. Bugger.

I started to think about the history of this problem. Roger had presented my future wife and myself with the exhaust as a wedding present in 2011. She was overjoyed of course :). It had been made by Gibsons in the south east and they’d had the bike to fit it to properly. They hadn’t run any calculations but had copied my dad’s pipe which he’d supplied them with for that purpose.
I went to the Prescott hill climb early in 2012 as the first outing with the bike and .. guess what.. it had seized at the first corner. It sound so hard edged and got so hot that I’d ended up fitting another head gasket at the next outing (BHR meeting at Lydden) simply to get it to stop overheating. It didn’t overheat (though it still got very hot) but it was slow. I thought perhaps that all this was a sign that if I wanted the power, it was a case that I’d need to make the engine dissipate heat better. Maybe my radiator, which is very small, was incapable or that my block (cast iron) was too slow in getting that heat away. It started to look very expensive.
That was why I switched to methanol in the first place…that I thought it might provide me with an easy alternative.
Methanol had worked, but was there another problem that it was hiding?

I had been wondering somewhere of course whether the pipe was in fact unsuitable for some reason. Since none of the problems existed before the pipe, it seems like a clear possibility. I talked to Rex Caunt (BSA Bantam tuner) on the Sunday and told him that I wondered whether the stinger outlet was too small and that it was the exhausts inability to get rid of the pressure quick enough that was causing the heat build up. He gave me a ‘rule of thumb’ to work out whether this was the case.
Apparently, the inside diameter of the ‘stinger’ pipe outlet is normally around 60% to 62% of the inside diameter of the beginning of the header pipe (around 50mm).

My Flying Squirrel's  Gibsons exhaust header pipes
My Flying Squirrel’s Gibsons exhaust header pipes
That would make it around 30 to 31mm ID. I couldn’t get to the stinger, but I could measure the silencer outlet and it was around 26.8mm. That’s under 54% of the ID.

When I start to think about it more, I think there’s another reason why it might need to be bigger. It’s a 2 into 1 pipe and although the operation of the phases are separated, there’s not the time to dissipate pressure that you get with a normal 1 pipe for 1 cylinder operation. In fact it makes sense to me that the outlet should be bigger than a standard pipe for this.

Silencer outlet
Silencer outlet

So in terms of racing it was a terrible weekend but in terms of development, I feel happy that I’ve got some new direction for the off season. I’m going back to basics with the fuel system and the exhaust and maybe even make some experimental pipes simply for the dyno. I also have started to realise what the dyno may or may not be useful for. I’ll still use the dyno to show what relative power I’ve achieved but I wont assume that it’s all I need for testing.

I’ve got lots of reasons to be excited about this winter. Roger finally took his bike to Motoliner in Maidstone to have the frame and forks checked and straightened after Steve Plater’s crash at the beginning of the year. It will be good to see that make progress.
The Moss Silk Scott needs to start moving to the next level… a dry build to see what kind of tank and seat unit it’s going to need and where the exhausts can go. I really look forward to moving forward with this.
I’ve got my lathe to finish scraping/ re-building, my milling machine to re-commission and tool up for and various other engines and gearboxes to work on in the meantime.

I still have a dream of making my Flying Squirrel the machine to beat in the vintage class and will be yet again edging toward that over the winter. I can but try!

July 2015 : an update

I’ve not written much recently but there’s plenty been going on.

My racer is still on the stand, although I now have a new front aluminium mudguard to replace the one damaged in the lowside crash at Anglesey earlier in the year. I also set about the paintwork on the headstock to try and find trace of a frame number, which would help me to register it for the road if I so desired. I found it in the end (but not before I’d removed a decent amount of perfectly decent paint) and amusingly it confirmed that the frame was never a Super Squirrel frame, but a 1932 Flying Squirrel. I have actually called it a Flying Squirrel in the past (and a Sprint Special when I was very young and simply wanted it to be one…) but the idea that it was a Super Squirrel stuck for some reason and I can’t even remember why. It’s not even that the engine type was the same.
So from this moment on I shall call my noble steed by its rightful title: My Flying Squirrel racer.

Although Anglesey was a while ago now, one of the other things that happened at the time was that my dad’s bike was due to be tested the following Tuesday for Classic racer magazine by Steve Plater, a former motorcycle racer and TT winner. I made the journey to Cadwell the day after getting back from Anglesey and we were very interested to see how he got on and what he made of the bike. He’s used to modern machines and I don’t think he’d ever ridden anything like it before. My dad advised caution through Charlies because of it’s tendency to get out of shape on the exit, but apart from that let him work it out himself.
We changed the bars to give him a different position and he seemed to be gaining confidence quite quickly through hall bends, where we were watching. He was certainly moving. However, maybe the confidence was a little premature as he lost it out of Charlies as a result of a tank-slapper that he couldn’t control.
Noticing that he hadn’t come round for another lap, I feared the worst and ran up to the van just in time to intercept the recovery vehicle. I took a deep breath when they opened the back door as the steel Vincent straight handlebars were bent vertically both sides, like bulls horns. I could see the top fork links had bent significantly before I even got it on the stand, and by the time Steve told me that it had gone over a couple of times I already had a mental picture of what, in all honesty, was the worst racing incident it had ever endured in over thirty years.
Of course, we were all relieved that Steve was ok. It could have been very nasty for him. On reflection, I think we were naive to think that even a highly successful professional modern rider might just sit on something with as lowly relative performance as my dad’s Scott and be able to work it out easily. Riding a rigid bike, or more to the point, racing a rigid bike requires a whole skill-set of its own. The feedback to the rider from a rigid chassis with girder (almost rigid) forks has little comparable in the modern motorcycling world. Racing with modern tyre compounds winds up the chassis and causes some instability that you get used to and some you know you can’t. Even though you ride a different line to avoid the ripples or the sudden dip in track surface etc, arse off the saddle.. damping with your knees like a jockey… there are some corners where you don’t want to try to push the line, and the exit of Charlies always has been one.
At the end of last year, Bill Swallow had a ride on my Dad’s bike in one of my races and he got into a tank-slapper coming out of Charlies which certainly caused him to wind it back it little. He knew he couldn’t push any further.
Maybe Steve felt a little under pressure to perform? Possibly, although he is obviously a great rider with a lot of experience of real racing pressure so it’s difficult to believe. I think the truth is, that he just didn’t know what the bike would do and assumed that he’d be able to tame it. It was a sad end to a day which promised some exposure for the British Historic Racing Club, plus a wonderful chance to see what a well respected modern champion might achieve with the bike in the way Paul Dobbs did with such style, ten years ago. Rest in peace, Paul.
In the end, it was a mistake, just unfortunately one which will take a while to sort out. Now stripped, his racer needs to have to frame checked for straightness, the bearings, the wheels etc. The fork blades are bent and most likely other parts of the assembly too.
Of course it will be done, but at 74 Roger has a lot of engine work for customers and it’s just difficult to find the time for minor developments, let alone complete re-alignment and rebuilding work. It won’t be done until next year, for certain. We have to remind ourselves that beyond the feelings of sadness and regret over the incident there must remain one clear point:
This is what racing is.

1960’s VMCC racing pictures from Cadwell

I was sent a box of 35mm slides recently, taken by the sender many years before at a VMCC Cadwell meeting. He thought it was the 1970’s, but I have an idea it’s the mid to late 1960’s because of the use of pudding basins and the car registrations. I might well be wrong. I have the use of a scanner and so have digitally converted them. They are a really interesting insight into the variety of machines being used back then. I’d like to identify the machines and the riders so if anyone can help with this or any other interesting information, please let me know.

Cadwell Park – September 2014 – part 1

I awoke at 7.30am. 3 1/2hours of actual sleep would indeed have been preferable to the energy drink induced, reclined wakefulness that I’d experienced. I was so tired when I woke up that I doubted I’d brought enough coffee to right the situation. Still, I was here, the bike was here.. all I had to do was to barely function and it would work out.

The identity of track days has changed a lot from what they once were. They used to be called practice days and were invariably for people who wanted to do some kind of set up work as part of their racing endeavours. When I started racing in 1988, I remember going to my first practice day at Cadwell and being blown away by RC30 Hondas. I was on the 1939 Tiger 100 for the first time, in fact it was the first time I’d ever ridden a bike with gears (excepting my 197cc Francis Barnett around the garden). I didn’t even know that you didn’t have to use the clutch every time you braked. I must have been all over the place. Makes me shudder a little to think of it. What these guys must have had to do in the middle of corners to avoid me…

This track day was specifically for classic bikes though and was, I believe, organised with the circuit by Tony Page who was involved in the Beezumph events for many years. Coming the day before the BHR meeting means that it’s well subscribed by competitors and spectators alike. People can make a really good weekend of it.

The format is pretty much the same for all trackdays. You have to sign on and sign a disclaimer. You then attend a riders briefing where they talk about how the day is run and safety on and off the circuit. They fit you with a wristband to say what group you are in; in this case the groups are self graded on your own assessed ability/ circuit knowledge / ego.
You get another wristband to say that you have actually attended the briefing and apart from getting your bike noise tested (105db max), that’s it.

The Scott doesn’t even have a rev counter.. they don’t really know what to do with it when you take it for noise testing. It’s quiet though, people always say with a little sadness that they can’t hear it when you are riding it. A Scott’s ‘yowling’ noise is unique to the marque and it’s a shame to stifle it with silencers. God knows what the yowl would sound like out the un-silenced end of a stinger though..

Then you have 15 or 20 minute sessions all day on a rotational basis. They just call out the colour of your wristband and you go down to the ‘assembly area’ and wait to be sent out.

Roger had bought the starting rollers and it was with significant crossing of fingers that I dropped the clutch that morning.
I needn’t have worried as after only a few seconds she spluttered into life and sounded pretty good. A moments contemplation of what we’d achieved passed over me before I realized that I’d yet to mix fuel and do some final wiring work. No rest indeed.

I think I’d definitely set the oiling a bit generously as the smoke screen was almost comical. It was as if the mist hadn’t risen that morning. I did wind it back later, but I thought I’d rather be safe than sorry initially.

On the track I arranged to circulate with Roger and then see what the relative performance was. At the Beezumph, the Super Squirrel had seemed to be faster than his on the straight and I was interested, having changed the head and the entire fuel system, in seeing what was going to happen now. Of course I had hopes of having to caress the throttle with the rear tyre spinning up as I backed into charlies, Moto GP style. It wasn’t quite like that. The first session, It seemed that my dad and I both circulated at low speed whilst waiting for the other one to catch up. There’s nothing like communication etc.

We actually managed it the next time, but instead of being able to pull away from him as before, I found him to be definitely stronger coming out of barn corner and I couldn’t catch him before we got into the top of Charlies, simply because I keep it on up the hill more than he does nowadays.

Not quite the overwhelming power increase I’d hoped for then, but still with so many un-tested changes it was working and working well.

Over the day I changed the timing a couple of degrees but did very little else apart from have fun. The front brake was starting to squeal a bit and felt like it was staying on a little after the lever had been released so after the last session I stripped and cleaned everything, copper-slipping the pivots, pivot bushes and cams and giving a bit more chamfer to the leading edge of the linings. They are still the old AM4 ‘Green’ linings on this brake, having been still available back in when i had them done over 10 years ago. They are great linings but they are so aggressive that they need a really good chamfer. The triumph has them also and five years ago when I was going into hall bends the front brake locked up solid… the chamfer on the leading edge wasn’t quite enough and it delaminated slightly shedding a sliver of lining which completely jammed the brake solid. Fortunately I wasn’t in the middle of Charlies but it wasn’t nice.

It was dark when I finished and just time to put everything away in readiness for the following day.

The push for the line – September 2014

As my second daughter was born on August 8th, a certain amount of sleep deprivation was bound to be involved in these final weeks prior to the September 28th/ 29th British Historic Racing Club’s meeting at Cadwell Park. Since my entire year’s work on the Scott Super Squirrel has really been focused on this meeting, I was determined that I was going to do everything in my power to get the bike as good as possible before I arrived, sleep or no sleep.
I had arranged with my dad, Roger, that we would attend the classic track day being laid on by the circuits organiser’s (MSV) on the Friday of that weekend and so it was with some relief that the bike was finished late on the Friday night before, almost a full week before I was due to be leaving for my Dad’s.

A sensible man would probably have looked at the improvements on the Dyno test results and decided to have left it at that for the year. I was not that man however, having tried and failed to have fitted the much anticipated twin carb conversion before the Beezumph in August, I was determined to have it ready for the last (and my only) BHR meeting of the year. The weeks of September had involved late nights flow testing the twin float chambers feeds to the carbs and setting the whole system up.

Twin carb set-up - september 2014
Twin carb set-up – september 2014

A fair amount of guesswork was involved in the choice (or manufacture) of main jets and I knew that the needles/ needle jets would be on the rich side, but I’d given it my best shot.
I had a moment though on that final Friday night when somewhere near 11 o’clock and undoubtedly tired, I dropped a washer whilst working to mount the inlet manifold. This was an awful thing to happen as the inlet was open at the time and I wasn’t sure where it had gone. I used a torch and a magnet to look into the inlet and couldn’t see anything. I then found a washer that met the description on the crankcase bottom deck.
I made a decision… this must be the washer.

Of course, it wasn’t.

The Scott fired up pretty easily (thank you easy start)in the yard of my friends farm, deep in Devon’s South Hams, the following morning. I had worried enough about the potential for ingested grit from his track to fit gauze filter bellmouths to the twin 276 carburettors and I was heartened by the seemingly strong pull of the motor as I headed up the track.
I don’t suppose I’ll ever forget the sound of the washer being bitten in two, twice.. not that I absolutely knew what it was at the time. It did stop the engine though.

As I put the bike back on the bench, I think I really knew somewhere as the first thing I did was to check the compressions on both sides.
Left, perfect .. no problem. Now right…wait.. I’m sure that should have been compression.

The transfer port cover was removed to reveal the kind of damage you would expect from a piston that had just sheared a 0.030″ washer in two using the top ring land and the edge of the port as cutting faces. The exhaust then told a similar story.

Damaged piston. September 2014
Damaged piston. September 2014

damaged piston exhaust - September 2014
damaged piston exhaust – September 2014

It was Saturday night. Five days before I was due to go up to Cadwell park via Roger’s.

Sunday morning my wife and I took my daughters swimming. It was peaceful, the calm before the storm I guess. I knew what I had to do in order to make this right and what kind of effort it was going to require and I also knew that I couldn’t do it in my workshop. I needed a little help from Roger.

So Sunday afternoon I call him. I tell him what’s happened and I know what his first reaction will be: ‘It can’t be done, have a ride on mine’.
It is the only sensible answer, after all I’ve got work and I look after the girls so my wife can work and that’s that… except that I still have the thing that fits so well with racing Scotts; The knowledge that if it is merely work and time standing between me and a functioning bike on the start line, then I can do it.
At 73, Roger’s initial enthusiasm for this kind of effort is less forthcoming but it doesn’t take long for him to come around. It is, after all, part of the game. It’s part of the deal of vintage racing, not to wreck engines, but immersion in this little drama requires an absolute agreement with oneself to work tirelessly to fix a problem when the odds are stacked against. Otherwise, there are always so many reasons to give up.

So, I gave him bore diameters so that he could grind oversize pistons ready for me and put everything in the van. I took an extra day off work and made the four hour trip on Tuesday night, arriving at midnight.

Wednesday 24th September.

Super Squirrel on stand at Roger's September 2014
Super Squirrel on stand at Roger’s September 2014

I put the bike on the ramp and gave Roger the cylinder block. The bores were pretty worn anyway and would definitely have appreciated a rebore, but not like this. There was fortunately no damage to the port edges so he started to set up on the big angle plate on his Thiel 162 horizontal jig mill.
He’d put the main ports in already before he’d ground the last of his old stock Silk pistons, 0.008″ undercut at the ring land and 0.004″ at the base of the skirt. I set them up to do the boost ports and cooling holes for the exhaust port bridge as well as the cutaways at the skirt for the extended inlet timing duration. This all sounds a lot quicker than it is.

After using an air grinder with a very small burr to oil groove the little end of the replacement right hand rod I handed it to Roger to hone to the pin size. All bores are done on fixtures to ensure accuracy as the alignments of the big and little ends on Scott rods are quite critical as as any out of squareness to the narrow big end tends to result in the 3/8″ rollers pitching themselves into the side of the rod with the tighter clearance and from then on (and with little chance for oil film) overheating themselves, the big end side plate, and the entire big end of the rod. Final assembly clearances are established with a hone.

After that, one side at a time, I used a tool Roger designed to establish the amount of back-facing required on the piston’s gudgeon pin bosses per side. Normally we aim to have a few thou clearance either side. The little end is therefore controlled but this controlled position is established using the free position of the big end assembly. It simply sits in the little end bush and, using a little knurled wheel, you wind out the centre which is on a fine thread until it touches the side of the bore. This gives a measurement from the side face of the little end bush to the bore face. Using a large set of vernier calipers you measure the gudgeon pin boss width and then you simply know that the difference is going to be about the right figure. Clever and relatively quick way to start the process.
Once you’ve got the figures you set the piston up on his vertical jig mill and very simply back face the bosses.

Backfacing gudgeon pin bosses
Backfacing gudgeon pin bosses
It’s a time consuming job to get it right as you need to do it several times and continue to measure the clearances but it is a great job when done.

With me working on the engine, Roger sets about one last modification for the day; the slugging of my bars to reduce the vibration I’d had at the Beezumph.
He turns down 6″ lengths of tungsten heavy metal and bangs them into the ends of the bars. Job done.

Turning down tungsten heavy metal for bar ends
Turning down tungsten heavy metal for bar ends

Those are serious bar ends.

Thursday 25th September

The work to the pistons and clearances go on into the early afternoon, when Roger starts to gap the rings for the new block. Care has to be made to clear the existing ring stops and Roger wants to knock them in a little further. It’s something he’s done so many times…
Suddenly I realise that something has happened. I go over to see him and look down at the piston. The ring land is broken… a moments slip.
Bugger.
We’ve gone too far to quit though… it can still be done. The grinder is still set up. Coffee and then Roger sets to work on grinding a new piston.

It’s early afternoon on the Thursday. We were going to leave by 4 for the 2 hour journey North.

Of course at this point we can’t actually continue with the build together. Roger comes up with the freshly ground piston in quick time and I start the rest of the work.

Knowing that I have to also measure all the piston clearances to the head, I tell Roger to get up to Cadwell whilst he’s still got energy to do it. It’s about 7.00pm.

I knew that it was a bit ambitious to want to fit a new cylinder head but I also knew that I would have probably needed to have done some work to the piston crown or the combustion chamber on the existing head anyway. One of my ambitions for the year was to have fitted a high compression head that we’d over skimmed to allow a closer matching to the piston crown. There’s a reasonable amount of work though but this was the place to do it. High speed air grinders with big cutting tools make short work of aluminium and, using the extending rod that tells us the point that the piston is hitting the head, I started to match the two.

I had measured the original head volume at around 29cc, which I had thought to have potential to be reduced. I know Colin heath once ran a head with 19cc, and I once did one with pretty much the same, maybe a couple more. I knew that the expansion chamber was going to (hopefully!) also contribute to the amount of compression here but I thought a bit more squeeze would increase the speed of the combustion process and the efficiency of the engine. If you haven’t got an engine that can be made to usefully rev, then the alternative is to extract more power out of each and every one of the lower revs that you have. That’s what I’ve picked up anyway.

There’s a lot of ‘taking off the head and putting it back on’ involved but finally I got the clearance I needed and started the build. A shade under 25cc, roughly a 15% increase.

Around midnight things were going pretty slowly but were certainly getting there and by 1.30am I had the bike finished and on the van. It took me another slow moving half and hour to pack everything else up and I rolled out at 2am, drinking the fizzless remnants of an energy drink I’d had the night before on the long way up from Devon.

The roads are quiet early in the morning and the Lincoln bypass certainly helps. The long single carriageway section at the end of the A46 North was always a jam when we used to go up to Cadwell as kids. The old derelict (obviously haunted) mansion somewhere outside of Nottingham is now a health spar. So many points of reference have disappeared with the bypass, but it is quicker.

I got to Cadwell and crawled into the sofa bed in Roger’s van just after 4am.

Super Squirrel racer – dyno test results – August 2014

I really enjoy taking the bike to the dyno. It’s so useful to see the results of changes prior to driving 300 miles to a race circuit and it gives you a deadline to get things done by.
The rolling road dyno I use is at Alan Jeffry’s engine tuning workshop on the Valley road in Plymouth. Alan’s a really nice guy but the main part of his work is cars so the motorcycle dyno is run by GT motorcycles (01752 485000). A single run (at time of writing) costs under £40 including VAT and Steve, who operates it, is a two stroke fanatic and a very experienced re-builder and tuner. He had an NSR 500 (GP bike) complete with carbon chassis on his stand when I saw him on Thursday. People with NSR 500s aren’t going to let just anybody work on them.
It was all the more enjoyable since I was joined by Roger who, having made the journey down to Devon to meet his new grand-daughters the day before, was interested to see the improvements I had made.
I was there at 9.30am as planned, and then again at 9.45am… this time with fuel!
As I said in the Beezumph report post, it didn’t feel any quicker to me in the way it was delivering power, but I thought that it was pulling through a higher rev range. This wasn’t actually the case since it is producing more power, in fact it’s almost exactly doing what I intended to do when I started planning the modifications at the beginning of this year.

The plan was to try and get the engine to breathe better with some carefully executed gas flowing and port modifications, and also to extend the inlet timing a little to see whether I could take advantage of any negative pressure pulled by the exhaust before the transfer closed. By using Jennings’ port time/area calculations I was trying to move the peak torque up the revs a little from the previous 3500RPM (ish) to nearer 4000rpm. I didn’t want to lose the bottom end and I knew that was too easily done.

See the graph below. The blue line (as indicated) is last years test after returning from the final Cadwell park BHR meeting.

August 28th 2014 Torque Curve
August 28th 2014 Torque Curve

How that translates into horsepower:

August 28th 2014 - hp graph
August 28th 2014 – hp graph

So, it shows that there’s a fair bit more power available and really well spread over the rev range. It may be that that’s why it didn’t actually feel more powerful, because it delivers it so smoothly over the range.
Whilst peak torque is up from 31.8 to 37.9 ft/lb (almost 20%), it’s interesting to see the change in revs that this occurs at. Previously it was around 3700 RPM and now it’s pretty much dead on 4000 RPM.
Also, driving out of corners should be much improved as low down torque is significantly better. I haven’t plotted the actual revs through the gears at corners for Cadwell, for example, but for slow corners like the Old Hairpin and the chicane after Mansfield this is where you really need that low down grunt, otherwise you get passed on the exit. At 3000 rpm, the torque is up from 23 to 31ft/lbs (35% increase). That’s pretty impressive to me.

So extrapolated from that, the peak power is up from 26 to 33hp, but still everything stops at 5000RPM. Steve said he could feel it wasn’t producing any more so he just shuts down. Whether it would actually rev any more anyway is another question. Unfortunately I have no idea what I am revving to because my Scitsu hasn’t worked since I converted to methanol. Apparently a common problem with inductive rev counters due to methanols highly conductive nature. Something I need to address sometime.
The main focus now is to fit the twin carbs to give me more intake mixture. The 30mm carb is definitely sized small and
I’ve got less than a month before the last Cadwell (27th and 28th September). It may well be that this will keep things going up toward the higher end of the rev range where the need for an easier ‘gulp’ comes into play. It may be that it loses some immediate pick up at low revs, but we will just have to see.
The other thing that I need to look at is the cylinder head. I’ve never worked on the head, it’s a standard ‘MOSS Engineering’ high compression head which is designed to raise the compression to a level acceptable on a fast road machine on petrol. Since I’m on methanol, I can deal with some extra squeeze and with a bit of time and effort I think I could get the compression a bit higher which would increase the burn speed. I’m then looking at 40 ft/lb as possible and maybe even a fraction more. I may even extend the rev range a little.
Ideally I need to get the work done in time to get to the dyno again before I go. Just over three weeks.. I’d better get a move on!

Beezumph 2014 report

Well, I tried to get the twin carb manifold completed before Beezumph 23, on the 12th July but it was not to be and I was glad that I’d made the decision to leave intact the entire single carb assembly, fuel lines and all, just in case I needed to put it back. It was a close run thing and I actually still hadn’t finished the bike when it went in the back of the van but in fact retaining the single carburettor gave me the opportunity to assess the changes I’d made on the engine with more certainty as to what had affected what.

Just to re-cap, the Beezumph is not a race meeting but a track day organised by the vibrant Trident and Rocket 3 Owners club, many of whose members bring their machines out for this spirited social occasion. I first went in 2001, I think, and Roger a couple of years before that. I think it was his first return with the Scott to the track after some years of working hard to build his workshop and business. I believe that first time he attended he was awarded the ‘man of the meeting’ award by Doug Hele after having caused great amusement having repeatedly passed very much more modern bikes invariably by diving up the inside of them into corners.

I got up early as I still needed to finish a few details. Rear chain tension and corresponding alignment of the rear wheel needed to done, followed by the wiring of the rear brake torque arms and wheel nuts. A good check over and then put the kettle on for the morning coffee.

The fog that had descended on Cadwell park the previous evening lingered for a while in the morning lending it a brigadoon-esque feeling of a world apart which I’ve always felt Cadwell somehow symbolised anyway. You can be a hero just for one day at a race meeting, away from normal sensible life, normally in battling to fix things in adverse conditions. Two years running I worked ’til two in the morning at the last vintage Cadwell meeting, stripping and rebuilding a jammed Scott clutch (having three gears is hard on a clutch). I’ve ridden hundreds of miles to fetch a replacement component to fit overnight. We fixed a hole punched through Rogers crankcase by a fallen transfer cover bolt with epoxy and underpants so that Paul Dobbs could continue to race the same day. It’s still the same today.
So the fog delayed a little the start of proceedings but when it did finally lift, it revealed a beautiful day which was at times almost too hot in racing leathers.
In short it was perfect.

Beezumph has become a family favourite, and until very recently (Babies have arrived) there were regularly several of us making an event of it. As it was, three Scotts and their owners turned up to support us and it made a very fine line up in the paddock. Richard Rawson and his fine Silk Scott and friend on his very nice Birmingham Scott, and then Alan Noakes on his beautifully detailed, girder forked, Flying Squirrel.

2014-07-12 12.54.06
2014-07-12 12.57.17
2014-07-12 12.55.03
2014-07-12 12.55.58

I hadn’t mixed my fuel and so set to work with the ingredients. The engine had not appeared to have enjoyed a surplus of oil in the bores from my inspections after the previous season and so I’d decided to reduce the acetone percentage in the mix in case this was simply stripping the lubrication out. Acetone is one of the things that came up in my research when I was looking at running on methanol and my understanding is that it’s used to help combat pre-ignition in leaner fuel mixtures and possibly aid starting. I had decided on a 5% Castrol M, 10% acetone and 85% Methanol mix previously but this weekend I reduced that to 5% Acetone to see whether that made a difference.

Not having even run the engine since I started working on it at the end of last year, I was glad to have an offer to use someones starting rollers.

With the drippers set high feeding Castrol R through the non return valves direct to the main bearings she turned over for a few seconds before gradually starting to fire. A tell tale hanging of mist in front of the carb opening showed the effect of the extra inlet duration I had applied. I expected that that would only be present at lower revs, but we would see. When cold she always carburates poorly and there’s a significant lag on the throttle as if the cable has a length of elastic in it. After the engine warms up, she’s immediately responsive. Methanol simply runs so cold that when the engine is also cold the atomisation seems to be quite poor. That’s what I imagine anyway.

So up and down the pit road a couple of times and then out in our session.

The beezumph has different categories and they range from beginner (marshall led laps) follwed by classic, fast classic, open (any age of bike) and then expert classic. We go in expert or equivalent normally simply because you can get problems with people being unused to being passed around a corner in other classes. Last year in fact, Roger decided to go in the fast classic group thinking that class more appropriate. He was 72 and on a 1934 bike and so thought he’d give it a try. He found, as is often the case, that he was being passed down the straight by more modern, faster bikes which then proceeded to brake very early where a corner was approached. Thinking that they may be stopping to attend to natures call or maybe a sandwich, he would pass them. Some take seeing a pensioner riding a vintage girder forked bike up the inside of you at a ridiculous angle of lean with great humour and enthusiasm, but not all. Roger would invariably pass, undoubtedly at a significantly higher (if not warp) speed, until their desire to storm by on the straight was diminished by a growing sense of futility in the action. There-after some are merely crest fallen, whilst for the special few indignance steps in to protect a fragile self esteem..
One rider was so affected by this (whether through genuine fear or critically injured vanity it’s not known) that he complained and Roger was informed that if he wasn’t able to pass on the straights then he should not pass.
This year he returned to the self appointed experts class, where passing on corners is in fact expected.

The first session out, I was obviously quite sensitive to the engine’s character as much work had been done since last season. It seemed to me to have less torque low down and be therefore slightly less drivable out of the corners. However, the engine seemed to be be pulling longer through the revs and although the majority of bikes (750 Tridents and Rocket 3’s) were easily faster down the straight, it wasn’t the difference I would have thought. I thought I felt the engine tighten a couple of times (though I might have been over sensitive) so I took it relatively steady.

I raised the needle before going out the second time and was not to feel any hesitation again. I kept behind Roger for a couple of laps to get a comparison between his and mine and he thinks that I have about 2 or 3 mph on him on the straight. maybe 5. It’s doesn’t feel quicker than last year in the way it delivers power, but I think that actually I’ve made it breathe so much better that it’s simply getting more in at higher revs and therefore revving longer. Extra vibration has come with this, but we’re going to slug the bars with tungsten heavy metal to help here. Although my dyno tests last year are compromised by the fact that I’d blown a head gasket, I think the torque curve will be broadly representative and a comparison will show me what has actually happened. I look forward to getting it on there and will not change to the twin carbs before I’ve tested with the single. I’ll then swap the carbs before going back for another test. It’s going to be interesting.

So in the end, the bike was flying and little was able to get past and stay past. True, it’s a track day and not everyone is wanting to ‘ride it like they stole it’ though some are. It’s easy to walk away from a track day thinking that the bike is a rocket and that you are riding at the edge of human ability then go to a vintage racing meeting and get lost in the wake of serious riders on seriously developed machines. Saying that, mine is a seriously developed machine. By the time I get to the last vintage Cadwell it will have been my only race meeting this year. Family and work commitments coupled with a realistic budget have prevented me from attending more, but not in idle have we stayed away and I am hoping that when we do turn up to the last Cadwell at the end of September that we are able to move further toward the front of the field than we have before.

I’ve never won at Cadwell, and whilst I do all this for so many reasons beyond achieving a position in a race; this is what drives my desire to develop of course. To win, one day on my Scott Super Squirrel against good men on good bikes at full circuit Cadwell park. Of course it’s a folly, but what a grand folly!

The head question

I’ve been trying to work out what to do regarding the Triumph cylinder head. I’ve not built this engine up as a 500 for years and it’s not really a ‘bolt together’ job as it is.
I started racing it in 1988 and at that point it had the bronze head. It was the first geared bike I’d ever ridden and the first time I rode it was at a Cadwell park practice day. I remember seeing these RC30s screaming by me at every corner of the track. It was dangerous of course as novices (and especially ones that can only just ride a bike) are completely unpredictable. I survived though.
After my first season, we stripped it and realised that the valve seats were quite sunken by many years of use (no seats.. straight on the bronze)IMAG0522 so we asked Owen Greenwood in Loughborough to have the bronze head seats built up ready for re-working and in the meantime I ported an iron head for that season. I obviously enjoyed using the air grinder as I definitely took enough metal out(!). In one place the seat is thin enough that I worried about overheating. No multi angles, no finesse! IMAG0516 We ran that head for another season or two and then it didn’t get run again until I rebuilt it to take to the Beezumph in 2001. I should have left it alone but I was obviously seized by the desire to improve it. This seemed to involve skimming 0.080″ of the head and the barrel spigot in order to increase the compression ratio.Doing this causes all kinds of issues as you have to deal with the sealing of the pushrod tubes and the lengths of the pushrods. IMAG0517It was misplaced endeavour, but it probably was fun at the time. Unfortunately There wasn’t enough clearance and the substantial 1.5″ inlet valves (Norton Atlas if you’re interested) contacted the pistons. It didn’t result in carnage, but we knew that it wasn’t really running right so I only did a couple of sessions.
I didn’t start racing with the VMCC again until around 2008-ish, twenty years after I first raced with the club, and this time it was with the Scott, but the following year we rebuilt the Triumph with the big motor (680cc) so the 500 has lain unused and unresolved.
I think considering that if I had no other options I’d be justified in re-working the skimmed head, but I think I’d keep my life as easy as I can. It’s not like I have a lot of time, so I think I’ll stick to either re-doing the bronze head or an iron one. Time to get some prices for hemisphere recutting!

Roger on the Triumph  with 680cc motor in mid 1970's rounding Mansfield corner at Cadwell Park
Roger on the Triumph with 680cc motor in mid 1970’s rounding Mansfield corner at Cadwell Park

Richard at the September Cadwell meeting in 2008 (or 2009?) on the Triumph. 680cc motor fitted.
Richard at the September Cadwell meeting in 2008 (or 2009?) on the Triumph. 680cc motor fitted.

Triumph cylinder head

I’ve decided to rebuild the Triumph this year, after being working engine-less since the last BHR Cadwell meeting in 2009 I think), when the 680cc motor blew the RH cylinder apart just above the base flange at the end of the start/finish line straight at Cadwell, just as I was going into Coppice. Fortunately, being used to a two stroke, I’m pretty quick on the clutch and I just pulled off.
The 680cc motor is very exciting in the Triumph, as it does make it bend in the middle a bit and that trait is at the heart of more than one story.
Although I’d probably prefer to keep the big motor in it, a change to classes in the BHR racing has meant that the old vintage class (up to 1934) has been joined to the post vintage class (up to 1948). The grids numbers became too low to run them separately. This meant that whilst before you could get two rides in the vintage with the Scott and two in the post vintage with the Triumph, I have only the ‘up to 48’ class and the ‘unlimited up to ’63 class’ that I can ride with either.
I thought since I can do those four with the same bike, it would be nice to have the Triumph running as a 500 to run in a separate class.
I’ve got a 500 iron head that I over-enthusiastically ported when I was about 15 years old and then later (over)skimmed to increase the compression. It’s an example in iron of what not to do if trying to make a bike go faster. I could possibly recover it, but I do actually have an unmolested one and it may be the wisest thing to start again with a bit more care.

Me and Triumph at Beezumph 2009
Me and Triumph at Beezumph 2009