Colin Heaths racing barrels

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.

4 thoughts on “Colin Heaths racing barrels”

  1. Hi Richard all the 2 stroke tuning books that I have ever read state that straight edge ports should only have a chordal width equal to 62% of the bore diameter but elliptical ports may be up to 70% of the bore diameter. It is also a good idea to have a slight bevel on the top and bottom edge of the port to ease the rings back into their grooves. Alan Noakes.

    1. Hi Alan,

      I read the 70% figure as being top in Jennings’ book and figured that the shape of the ports would not give the rings an easy time. I don’t think I’ve seen the 62% figure, but it makes sense that it would be smaller. I did think that it would be possible to file an extremely shallow eliptical profile above the port into the cylinder wall to effect an oval port shape but you would effectively be raising it, which would obviously have repercussions. At about 50mm width, the transfer on a block bored for a Silk piston (mine is 75.93mm) would be about 66%. My transfer is already wider so I ruled it out.
      I did think about the possibility of grinding some small location grooves in the top right corners of the transfers and then using them as a way of keying some devcon deflectors to force the transfer flow into the deflector on the piston rather than around it. This would effectively reduce the aperture of the transfers though, and they are already restrictive. I’d have to be sure they’d keyed well though as I wouldn’t want them dropping into my transfer. I’m hoping not to go through that again!
      I think though, since the bores and pistons are good, I should just get the carburation sorted (and some changes to the shape of my cylinder head’s combustion chamber), and get the process of setting up underway. I might well look at the barrel question on the Super Squirrel again at some point, but I think I need to crack on otherwise I’ll have nothing to ride!

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