Tag Archives: Cadwell classic track day

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.
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.