I emailed Colin a couple of days ago to ask him whether he knew of anyone who had cut the bridges out of the transfer successfully and he sent me this. Thanks Colin.
“Just a little more about the pictures. These are the barrels used by Martin Heath in that one glorious season when he won 12 events, including his first win. This was at Cadwell when he was left on the grid as the compression was so high the rear wheel just slid instead of turning the engine over, on the old downhill start by the timing/ commentary box. He managed to start it eventually by vaulting on from the greatest possible height and it fired up. The field were disappearing into Charlies by now, but he caught and passed them all to win. Proper Boys Own Paper stuff.
However, the point is that the barrel, as we had no other, was reclaimed by boring out the broken skirt from a damaged set and pressing in a flanged liner from the top. ( It sat in a machined recess). The machining had broken through into the jacket so good old Loctite sealed it all up and provided what I think is called a ‘wet liner’. We could not bring ourselves to put dividing bars back in the ports so made them elliptical as you see and relieved them to give the rings a softer time. You will also see that we needed to use a ‘detachable’ steel ring for the lower seal – and this located on a small step machined on the liner o/d.
Another simultaneous experiment was to make the liner full length down to the very bottom of the crankwell to see whether preventing any piston ‘rock’ would help. You can see the remains of this in the pics after it was later cut off. The rods had to be scalloped to clear the base of the liner, but we still use them to this day with no trouble.
The heads are a type you are familiar with and the drilled/tapped holes onder the dome on the exhaust side were so that we could use a head steady onto a frame cross tube. ( This was our super lightweight T45 frame, it was more of a frame steady than an engine steady. It was so light it sang like a tuning fork even after the engine was cut).”
I also sent him the pictures of my piston for his interest and to get his thoughts.
“As for the fuel pattern on the piston crown, by using a close profile high compression arrangement I expected that any ‘clean’ area on the side was trapped fuel ‘end gasses’ that got rudely pushed/ sucked out of the way before they had a chance to detonate.”
and of the photo of Martin:
I think it was taken at Mallory but expect Martin will correct me if necessary. Incidentally the silencer shown was our first effort after introduction of silencing regulations. This one is designed on the principle of ‘silencing by controlled leakage’ whereby multiple small outlets are provided under the crankcase all carefully pointed in different directions. From memory this set up has five intentional outlets including the official one. The theory is that one noise meter will have difficulty covering all directions at once. It worked well enough, for we would have been excluded on open pipes, and to my surprise the machine seemed, subjectively, to go just a little better than before.
I was intrigued that former Scott racer, Colin Heath’s name had come up as a subsequent owner for both the ‘prototype’ racing Silk Scott and ‘FNT’, the Silk Scott racer owned by John Farrar and co-developed with Alan Noakes and Barry Tin(g)ley. See Alan’s memories here.
I wondered whether this could be true.. did he really own both of these machines and what was the story?
Colin came to visit me a few months ago, as his daughter lives in the same town as I do, and upon seeing the picture of the white Silk Scott prototype on my wall noted that he’d owned it, having bought it from George Silk himself.
Only this week, Dave Whiteside contacted me to say that he’d bought it from Colin and that it was now in Sweden.
I thought I’d email Colin to ask about FNT, and he sent me a piece that he’d written for ‘Yowl’, the journal of the Scott Owners Club in 2005 but never sent to be published.
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.
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.
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.
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.
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. 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.
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.
The virtual oily corkboard of a vintage motorcycle racing family