Gents, my 1921 532 is having an engine job done. There has been discussion previously about blow back and back firing and mine has suffered with both until I fitted the gauzes in both transfer ports. The problem was also attributed to possible port timing and /or the piston height and the position of the little end. These engines were somewhat primitive and I can accept that some learning might have taken place even though I hate to differ from the original AA Scott design and probably won’t. Roger has supplied us with the original specifications for the pistons yet in my previous exploits found that there are a few variants of the same design with differing dimensions of little end position which I can only attribute to the passing of time and experimentation etc where bikes have ended up with all sorts of components.
So my question is, of the folks out there with these bikes running nicely or otherwise, do you know the piston height, the little end position as measured from the base and this weeks winning lottery ticket numbers too. Martin, you sent over some photos a few years back and if you have still have them they would add to this process.
You can send your thoughts whatever they may be to the forum or to me at email@example.com or ring on 07531 781196. Insults appreciated.
Will, I think the most important thing to do & avoid “blowback” is to provide a splitter in the exhaust at the cylinder and exhaust stub to stop flames “tracking” from one cylinder into the other as there is a period when the pistons allow this as they allow the exhaust ports to be open at the same time.
I did this to my veteran and it utterly transformed it.Transfer gauzes might be able to be done away with.(I don’t know I never did this but the gauzes never required cleaning out ).
Hi Will. Assuming you have a standard 532 cc engine rather than a Squirrel engine, the design drawing for the pistons is in the technical section of this site. I referred to it when the engine on my 1923 was being rebuilt earlier in the year. It has sll of the diemensions.