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.