Does boring weaken 500 cylinders?

jseng1 · May 1, 2026

How far can you bore a 500 without having to worry about the cylinders cracking just above the base flange?

johnm · May 1, 2026

My 500 Dommie generator barrels are still going with a 60 thou over bore , 10.25 CR and about 10 years of racing. So 60 thou seems OK.

I have never used sleeved 500 barrels but a fellow competitor told me his failed at the thin area above the studs when he sleeved and raced 500 barrels. He ended up casting new ones in NZ because at that time they were impossible to find. Casting in cast iron.

jseng1 · May 2, 2026

johnm said:
My 500 Dommie generator barrels are still going with a 60 thou over bore , 10.25 CR and about 10 years of racing. So 60 thou seems OK.

I have never used sleeved 500 barrels but a fellow competitor told me his failed at the thin area above the studs when he sleeved and raced 500 barrels. He ended up casting new ones in NZ because at that time they were impossible to find. Casting in cast iron.

This is exactly what I was worried about. I'm currently talkiing someone out of sleeving his cylinders. Personally I had 750 cylinders crack above the base flange when bored to .060" over.

He's putting in these 174 gram pistons:

johnm · May 2, 2026

I think its almost impossible to get liners in with breaking through the casting at some point.

Maybe if they converted it to through bolting??

Never done it myself but one of our competitors did through bolt a 500

jseng1 · May 2, 2026

johnm said:
I think its almost impossible to get liners in with breaking through the casting at some point.

Maybe if they converted it to through bolting??

Never done it myself but one of our competitors did through bolt a 500

Maybe you're talking about Rogers 57hp short stroke 500 w JS ultralight carrillo rods & lightweight pistons. See his shortened bolt through cylinders below.

johnm · May 2, 2026

Lyndsey Kyle in New Zealand. But about 15 years ago.

Would have been standard bore and stroke because he was running in NZMCRR Clubmans class.

Peteyoung75 · May 9, 2026

This has me worried as my 88 barrels have been sleeved and it cost a load of money. I won’t be racing the bike - just road riding and no doubt a bit spirited at times.

johnm · May 9, 2026

Peteyoung75 said:
This has me worried as my 88 barrels have been sleeved and it cost a load of money. I won’t be racing the bike - just road riding and no doubt a bit spirited at times.

It was racing with high compression pistons that blew the sleeved barrels I saw. Thickness of the sleeve would matter too.

Peteyoung75 · May 9, 2026

johnm said:
It was racing with high compression pistons that blew the sleeved barrels I saw. Thickness of the sleeve would matter too.

Thanks, not trying to tune mine above stock so hopefully will be good

Fast Eddie · May 9, 2026

Peteyoung75 said:
Thanks, not trying to tune mine above stock so hopefully will be good

Should be fine.

Making an extra heavy duty head steady will help if you wanna ease your anxiety.

Does boring weaken 500 cylinders?

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