The Stafford classic bike shows are apparently very popular and certainly this one was a good day out. Definitely oriented towards post vintage stuff and mostly 1960’s onwards really. I don’t go to shows that often, in fact the last time i went to Stafford was on my dad’s Ducati 750SS when I was 18 (he must have been mad). That’s 24 years ago. The best bit really was the opportunity to chat to the guys on the BHR (British Historic Racing) stand where Roger’s Scott was being displayed along with a number of other really interesting machines.
The Mogvin, a mightily impressive Vincent twin powered three wheeler with two wheels at the front and one at the rear drew a lot of interest and Robbie Browns highly developed 175cc championship winning BSA Bantam sounded fantastic when he started it up for a crowd. The Mogvin Robbie Browns BSA Bantam in 175cc guise.Mark and Sue Whittaker, hugely enthusiastic supporters of the club and campaigners of a BSA outfit were displaying their temporarily worse for wear Enfield Bullet, which they lend out to people who want to try their hand at racing with the club. Roger’s Scott Flying Squirrel racer with Mark and Sue Whittaker’s ‘Bullet for borrowing’
Tony Wooley’s purposeful Rocket 3, and a number of other club machines completed a very impressive display with Gerry Daine, John Lorriman, the Whittakers, my dad, Robbie Brown and others manning the stand for the weekend.
I started racing with the club back in 1988, but it’s neither been continuous through the intervening years nor am I as regular a competitor as I’d like. The best bit of the show for me was really the opportunity to talk with the guys on the stand. So much racing experience, so much tuning knowledge and such decent people. The BHR has still much of the family feeling to it that it always had. Sure, things change and the early classes aren’t as well supported anymore but I guess that’s what is bound to happen. Things change. Paddocks are still open and friendly to all who come to a meeting and anyone who fancies a go will find a welcoming reception.
There was one other notable thing which made my day.
They have a little ‘GP area’ which they bring notable bikes into so that the owner can talk about his machine and then they can start it up for all to listen to. Roger had been asked to show his Scott on the Saturday and the guy doing the interviewing, Steve Plater ( ex TT and NW200 winner) had given him the microphone. My dad occasionally likes playing to the crowd and put on a great show. I saw him present his bike on Sunday and I was very pleased to find that someone had videoed the occasion.
As with all good projects, you need a certain amount of momentum to get over the tricky bits. The first tricky bit for the Moss/Silk Scott racer is to rebuild the frame so that its strong and aligned.
I cut the front downtubes out about ten years ago, as we had intended to make the bike work as a test bed for engines we were rebuilding. The problem was that you couldn’t get the blinking engine out without having to partially strip it, or that’s what I remember anyway. Maybe others (Yuri Gellar?) would have had better luck. Paul Dobbs, who raced Roger’s bike at the time, agreed with my suggestion that we could have a detachable cradle… so I cut the front tubes out. I’ve often regretted it, mostly because of the extra effort required to get the thing back together. With some intelligent work though, it could be a really useful modification and it’s time that I pushed to get it sorted out.
As Roger is snowed under with engine work (and welding and brazing were never his thing anyway) I’ve been talking to Alan Noakes, an engineer and a Scott enthusiast, about the best way to approach this. Alan has considerable experience with welding and brazing and also has a frame jig for the duplex Scott frame which may just work with the Spondon frame.
Another reason that it’s great to be working on this with Alan is the fact that he has his own history with the Silk Scott. He sent me a wonderfully atmospheric photograph of him with a Silk Scott set up for racing when I first contacted him and after some encouragement he gave me some of the background.
The Spondon Silk (see below) you have pictured on your website could be Georges prototype but it does not have the double sided Fahron front brake which I would have expected as the first one was raced in the Manx GP by Stuart Hicken 2 years running either 71/72 or 72/73, by the way I believe Stuart Hicken is MD of Mallory Park now, I did meet him at a vintage meeting at Crystal Palace after his ride in the MGP and he said he was aquiring Scott parts to build a vintage racer with Georges (George Silk) help but I don`t recall ever seeing him racing after that.
The story of the Silk Racer in the photo is this, during the 1960s I met a local Scott owner by the name of John Farrar, we were both intent on tuning our Scotts to make them faster we also used to bother George Silk at race meetings hanging round his camp asking stupid questions etc. at some stage John had his crankcase fitted with Silk cranks and we carried on experimenting with different mods and sharing information with George, I did the engineering John paid for it. When George and Bob Stephenson shared a stand at a race bike show in London could have been 71/72 george had his racer and the first road bike on display, John had decided to order a racing chassis complete with gearbox but minus engine as he would use his existing engine and placed his order at the show this is the bike you see in the photo, on the day the photo was taken you can see that the bike was not finished no exhausts etc. we just wanted to make sure that the gearbox and clutch worked I had modified a Jawa speedway clutch to fit. The letters FNT on the bike stood for Farrar Noakes Tingley, Barry Tingley was a Local rider quite good had been given rides by Stan Shenton from Boyers of Bromley who later ran team Kawasaki. Our first race with this bike was at a Big international formula 750 meeting at Brands with the likes of Sheene Grant etc. we finished well down the field the following week saw us drawing up a completely uprated engine with reed valves flat top pistons alloy cylinder and heads etc. I did actually start making some bits for this engine but a change of job put a stop to progress and by that time John had decided that Georges new Silk engine would be a better option for the bike. John eventually sold the bike to Colin Heath.
Alan Noakes with FNT Silk Scott (1971/2)FNT Silk Scott racer with Alan Noakes. (1971/2)Silk Scott prototype
So, the last British Historic Racing club meeting of 2014 at Cadwell Park has been and gone. In our calendar that is the sign that winter is on it’s way. What normally happens is that you think you’ve got plenty of time to get on with your bike project(s) but all of a sudden, it’s Christmas. Then, no sooner than you’ve sung ‘auld lang syne’, January disappears too. You are then halfway through March before you know it and suddenly you realise that the season starts in April and you’ve a week before the first practice day and you are no-where near ready.
Even though I know this, it will still happen…
I had thought that the Super Squirrel wasn’t quite working as well as it should after the frenetic ‘development’ work I did just before the meeting, but was very happy that it was working at all. It certainly went well enough to be competitive enough to have some fun but I know it could be a lot better and it was with that thought that I took it to the dyno at the beginning of October.
October dyno run
Torque Super squirrel torque curve – October 2014
BHP
Super Squirrel BHP curve – October 2014
Steve, who runs the dyno said pretty much immediately that he could see it was massively rich… so much so that it’s just not able to run anything properly. He’s up for a longer set-up session, and with that in mind I am now trying to get everything together that I’ll need.
I’d talked to Rex Caunt at Cadwell Park. Rex is a friend of Roger’s and it was with his help that we fitted a PVL system to his Scott many years ago. He went on to fit a BTH magneto and I inherited the PVL system.
Rex is not just an expert on racing ignition systems, but he’s also very much involved with two stroke tuning and we had a long chat about my plans for development. He suggested analysing the exhaust gas temperature with some thermocouples to give me some idea of what was happening. Pressure waves behave differently in different gas densities, so temperature has an effect on the speed of the wave. I picked some up really cheaply on ebay.
I also bought some new needles and needle jets as the one I did are not suitable.
Once I’ve got everything ready, I’ll be booking a dyno slot.
The Saturday dawned a little blustery but the sky was clear. With so much work actually done to get to this point, it was quite odd to wake up knowing that there was no real rush. I’d been through scrutineering the preceding evening and had my leathers and helmet checked, and the Scott noise tested. Apart from getting a program and a transponder (used by race timekeepers to identify bike and sense when bike goes over the line) all I had to do was have my breakfast and wait for the first race.
Roger had felt a bit down on power by the end of the track day and had talked to Gerry Daine, the ACU steward for the BHR meeting, about the possibility of someone else having a ride. Bill Swallow was at the meeting and had enjoyed riding the Scott before (having 6 wins in 6 races) and Gerry would ask him whether he wanted to. Bills father had raced a Scott (which Bill still has) many years ago and I think he enjoys the connection. Bill Swallows family racing Scott – 2012
So it was that Bill lined up for the first of our races of the day, not our main class; ‘Up to 1948 unlimited capacity’ but the class we enter for an extra pair of races, the ‘up to 1963 unlimited’.
This is always a bit of an effort to stay involved in this race since we are in with 950cc Nortons and Tridents as well as the 750 triumph twins of the up to ’63 class. The winner was over 15 seconds quicker per lap than me… that’s a varied field.
Bill hadn’t had the time to practice on Roger’s bike and also wasn’t able to set it up for himself. Normally he’d change the bars from the very narrow set of curled in bars that my dad has favoured since a crash at Mallory park many years ago ‘designed’ them by accident. Having had problems with his right shoulder for years, Roger’s position is also very ‘sit up and beg’. He’s raced like that for years but it’s a very odd position for someone used to the Aermacchi/ Ducati stretched position.
I have straight bars as I feel like I need to muscle the Super Squirrel around, especially since we fitted the new Avon roadrider 21″ tyre in the harder race compound as its much harder to change direction. It’s a brilliant, confidence inspiring tyre but you really need to put the effort in to get it to change direction. I feel I’ve got much more control with the straights.
Anyway, Bill got off the line before me and I took chase in earnest. I managed to get fairly well behind him going through Charlies and stuck with him like glue down the straight and through Chris’s and then Gooseneck until Mansfield where I managed to out-brake him down the inside.
Although I didn’t see Bill again, I found out when I got back that Bill had had a massive tank slapper coming out of Charlies on the following lap and had ended up on the grass. He didn’t crash but it had diminished somewhat his inclination toward riding the Scott over the weekend (he already had lots of other rides lined up) and he decided to pass. If we’d set the bike up for him it would have been totally different. I’m sure I wouldn’t have seen him for dust, but that’s the importance of bike set-up and time to do it.
In the meantime, Roger was feeling a bit more ‘up for it’ and was glad to have the opportunity to get his leathers on again. He did let Rod Graham, who races a Ducati single and sits on the racing committee with him, have a couple of rides but he apart from that he rode the rest of the weekend.
The second race of Saturday came after lunch and was the up to 48 class, bundled in with the ‘BEARS 750’ class and the new ‘up to ’83 (?) 500cc Air cooled Japanese’ class. Crikey.
Most of the other bikes in the up to ’48 class are methanol burning singles with four speeds and they are quick off the line. Having only three gears does present a challenge getting off the line. Mervyn Stratford was unassailable over the weekend on his incredibly quick 250cc Rudge but I was much better matched with some of the others and I managed to have some great battles with some of the other two classes as well as Tony Perkins on his 500cc Rudge who at one point outbraked me into Park corner. He succumbed to my excellent front brakes at Mansfield the same lap and I didn’t see him again.
In the end, I was second in every race of the weekend in the ‘up to 48’ class, but I felt that I was down on power and that I definitely needed more power to get to Mervyn! He wasn’t just escaping on the corners but he was faster on the straight.. on a 250cc!. However, Mervyn is a very good and very competitive rider and has been developing his Rudges for over forty years. It takes more than a few extra bhp to get in front and stay in front of Mervyn. See his website here.
In the end though, it doesn’t matter whether you win, just that you have a race with someone and that’s why it’s nice to have a good sized grid of equalish machines. There are always going to be faster bikes, but the smaller your grid is, the more likely to be riding in a procession. Likewise, a big grid of Tridents and a small grid of our class does not provide great racing although people like to see a vintage bike hounding a 70’s Triple.
Though there were plenty of vintage racers not there, it was good to see Arron Rogers out for the first time on an International Norton. The ‘up to 48’ class, which now has absorbed the old ‘up to ’34’ class, is such an important link to the roots of the racing club that it’s heartening to see someone else join the grid. Stewart, Arron’s dad, raced very successfully for many years with the club and is well known for his work with cammy Nortons. I remember vividly Stewart passing me on the inside at Charlies in my first full season of racing in 1989. He was so quick I couldn’t believe it. He must have been lapping me.
Hopefully Stewart will return for some racing next year.
Considering the position I found myself in when my engine swallowed the washer, just one week on I was getting consistent second places on a completely untested set-up. We both had a very good time and saw lots of old friends who came to say hello and give their support. Thank you as always.
I will continue to push, and also start to move with the Moss/Silk Scott racer. I am determined to do what I can to get the Super Squirrel even better over the winter, to do more meetings in 2015 and hopefully encourage others to come out to do the same.
Scott Super Squirrel racer. Cadwell Park September 2014
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.
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
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 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
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 bossesIt’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
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.
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
How that translates into horsepower:
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!
The latest addition to the Moss family arrived on August 8th. A healthy little girl and we’re all very happy. She’s not been in the workshop yet but I intend to indoctrinate them both to make sure that their idea of a family holiday is to share a damp tent at a racing circuit. I’ve taken a couple of weeks off for paternity leave and as well as spending some enjoyable time with the family, I also managed to get the Norton model 18 gearbox shell down to a local machine shop to (hopefully) have it fixed.
I’m a little nervous about giving it to the guy, not because I think for a moment that he’s not capable of working a lathe or a mill, but that unless you are going to prepare and supply an entire op sheet that details every check, every measurement, the way you hold the component etc, you are relying on someone really working to engage with the context of a component to make sure that they actually address the problem.
It’s not that I’m a control freak, just that I’ve found that people who are sparky enough to really engage like that are the exception rather than the rule. Anyway, I’m very excited at the possibility that I’ll be overwhelmed with satisfaction at the job!
Tomorrow, the Norton will dismount the bench having used its quota of time unwisely by presenting me with damaged gears and casing, rather than allowing me to put it all together. The Scott Super Squirrel racer will go back on so that I can check it over prior to its appointment with the dyno next Thursday morning.
I don’t really have a clue what it’s going to tell me, but I’m thinking that it’s likely to be over 30 BHP. The most interesting thing though will be to see the actual torque curve as the one I got from the last dyno test I did, which was prior to all the flow and port work I did over the winter was really strong at 3500 rpm and then everything tailed off well before 5000 RPM. I think I’ve got more revs now, and have lost some at the bottom. It’s going to interesting to see.
Also, to recap, I know that my inlet port area is 25% bigger than the cross sectional area of the carb, so I’m going to try to get it all ready for twin carbs for the last meeting and get the extra gas in. I’ve got to have cables made, carb machining work, float chamber/ carb flow testing before that can be finished which is why I need to get it back on the bench! I also want to get it back on the dyno before I go.
Hopefully the rest of the bike will be ok. The rear tyre did suffer at the beezumph as it was quite hot and large chunks get ripped out if it starts to hop around. I’m pretty sure that the last meeting in September will not be so hot that this is exacerbated.
Anyway, loss of sleep is taking it’s toll so I’ll sign off.
The fact I’ve managed to do anything on the bikes in the last few weeks is a minor miracle. My wife is expecting our second child and with D-day approaching fast, I’ve had to focus on preparatory DIY.
I have managed to move forward with my projects though, if not at startling speed.
The Super Squirrel racer is sitting patiently, waiting for a trip to be organised to Alan Jeffries dynamometer in Plymouth. After that I’ll be trying to get the new fuel system completed for the final Cadwell park race meeting for the BHRC (British Historic Racing Club) at the end of September.
The Moss/Silk Scott racer is just about to enter a new stage, as I’ve found someone locally who will soda blast the frame. It’s about double the cost of normal media blast cleaning, but I wont have to plug every aperture in the vain attempt to stop the abrasive media ingress. I also don’t really want it in my workshop if I don’t have to. It gets everywhere. In terms of my own time, I think it’s worth the extra. I’m intending to take it up there this week along with the oil and water tanks.
Roger (my dad) has also given me the engine (in bits) to make a start on and I need to do a dummy build to look at timings. A couple of months ago contacted a guy who lives fairly locally to me who has done some very impressive expansion chambers for more modern machines and told him about this project. He’s interested in looking at what would be necessary (or possible) in terms of pipes and he needs provisional timing information to run through his calculation programme. I’ll write more about it all in a separate post.
The main subject of my attention at the moment is the Norton Model 18 which we’ve had in the family for over thirty years now. The last time the Norton was used was I think 2001, when I actually used it for daily transport through the winter. I’d come back from five years of travelling and working abroad and simply didn’t have anything else. It jumped out of third gear a lot and pulling the chair only managed 47mph top speed but I really liked riding it, once I’d got used to riding an outfit.
I brought it down to Devon sometime last year with the plan of returning it to the road. Unfortunately as I wrote in one of my first posts on this site, their was a problem with the engine and I’ve temporarily replaced it with a later one. This requires a conversion to run using coil ignition and alternator.
Only last week I also removed the gearbox to have a look at the jumping third gear issue and unfortunately the news wasn’t great. Damage to dogs on Norton four speed gearboxFive gears had reasonable damage to the dogs and I’ve ordered some (also secondhand) replacements from the Norton Owners club. Also the gearbox casting is cracked at the lower gearbox mounting pivot on the drive side. Apparently this is a common problem and I will have to get it welded. It’s a design weakness here I think so I’ll have a look at some possible improvements to the arrangement. I need to order a bunch of other things for it, but it’s a really nice bike and is too good to sit around for another 10 years. My grand plan is to get it recommissioned and use it my everyday road bike. It’s much more of a sensible option than in many other counties too. The route between here and work is about 50% tiny lanes where you often can’t do much more than 25mph anyway. The roads through Dartmoor are more open than the ‘lanes’ in the South Hams but the presence of sheep, cattle and ponies create an element of surprise. The undulating nature of the land favours a engine rich in low down torque and flexibility. This terrain is the ideal stamping ground for a big single more than anywhere else I know!
The virtual oily corkboard of a vintage motorcycle racing family
