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My sleeve is smaller than it should be?


I'm running late on being ready to run my long-suffering M20 road engine yet again at the Speed Week event at Lake Gairdner in South Australia. One of the delaying factors has been the local engine services I've used, as he puts back the small number of motorcycle barrels he has to work on whilst he clears his bread-and-butter work for much larger engines. In April last year whilst "refining" the set-up of the engine I went badly wrong and seized her. Totally my stuff up, I'd run-in and then had some fun times at an earlier rally in March (last year's Speed Week was washed out along with a good portion of the rest of SA). The engine wasn't running at full throttle, so on return from that rally I investigated, and also fitted an AFR / Oxygen sensor to the straight pipe exhaust. without thinking enough, I also re-checked the timing and found that was 9mm not 7/16inch and reset it "correctly" ignoring the fact that I'd found I didn't need full advance, 9mm is about 32-33degrees compared to about 36-37deg for 7/16 inch. Anyway, once I ran with the AFR the reason for not pulling to full throttle was that the main jet was far too big, I dropped back and resolved that issue. I didn't however pay attention to the far too lean midrange or the that I really didn't need full advance now. Hence far too hot on the second day of the rally and a run out resulted in the messed-up engine.

So, since the custom piston with standard stroke was 84mm which gives something a small amount under the maximum swept volume limit for the class I knew I need to replace the sleeve (liner), so I got that on order along with the custom piston. I think I had both of those with my local engine services before end July. Anyway, yesterday after I'd checked in for the umpteenth time and he'd said he was starting on it, about 30 mins later I get a call, the liner he'd taken out was 3 thou larger than the new liner. His view was the new liner would almost drop into the block, and this was before cleaning thoroughly. To keep me on track for Speed Week I got over to him with another block which was the original road engine, that has standard size valve, as I knew that could re-bore for the 84mm piston, which has modern rings and is lighter, forged, etc. So, he's working on that for me now, should have it next week.

I've sent an email to Westwood to ask about oversize liners. But I also want to double check with the knowledge here. I found a post from Ian, who I have huge faith in for this knowledge, indicating the need to measure replacement liners and the block and that there should be a 2-3.5 thou interference fit circa 7 tons to press the new liner in. So, I just want to check this out as a clear set of data so that once the block in question is out of cleaning, should be Monday, a re-check of measurements can be made to confirm the block internal diameter and the sleeve outside diameter and confirm the issue and what oversize I'd need.



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Re: My sleeve is smaller than it should be?

If westwood let you down Richard, I keep raw Mahle liner castings. So any size is easy.


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Re: My sleeve is smaller than it should be?

I can confirm the figures quoted for liner interference are correct...Ian

Re: My sleeve is smaller than it should be?

Thanks Ian

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