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Liner/Muff interference fit


Well Known and Active Forum Website User
VOC Member
I have to fit a new liner to a new muff.No problems there.
I have been reading in WhitakerPedia about having a 10 thou interference fit instead of the standard 6 thou.
Has anyone tried this and are there any real benefits from this tighter interference?..John

Simon Dinsdale

VOC Machine Registrar
VOC Member
VOC Forum Website Moderator
I've seen the results of approx 10 thou interference between muff and liner done by a friend years ago who thought better. It went together ok, but next day the muff had cracked, following the holes for the head studs. This was with an original Vincent muff that had been bored true for a oversize liner.

Personally ever had a problem with the factory spec of 6 thou.

chankly bore

Well Known and Active Forum Website User
Non-VOC Member
Slightly off topic, but make sure your muff is round, then fit liner. Check liner for roundness and for truth square to base of muff/ crankcase face. check conrod for centrality and twist (or check previous piston for unusual wear.) Me, I,d go for .005" bottom skirt clearance having had nip-ups with this modern "fuel." As I've said before the muff should have a registering diameter snug in the crankcase mouth. Cheers.


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VOC Member
I think we had a muff pop at .009", so those who wanted tighter muffs went lower. Just a little lower will distort the bore quite a bit, so there is an uneven liner that has to be made round by boring or honing. I went to aluminum liners and Nicasil for racing and street.



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VOC Member
I have heard of muffs cracking after new liners have been fitted. The article in WhitakerPedia was by Maughans,so I did not dismiss it out of hand..But I bored the muff to 6 thou as per standard anyway.
I have dismantled the last muff and liner assy that was on my Comet and found that although the parts where brand new when assembled,there has been poor contact between liner and muff.
This time I bought an oversize liner and faced the top and bottom parallel and then bored the muff square to the base face.It all went together well and I left it to cool in my hydraulic press so that there was no chance of the liner creeping up when it cooled.
Hopefully I will have the Comet back on the road in about a week after the liner has been bored for the new piston..John


Well Known and Active Forum Website User
VOC Member
If you are making an all-alloy cylinder, would it perhaps be better to make it one-piece?

On another tack, standard muffs. My barrels are part way through having new (thick) liners made. Do standard muffs have enough metal at the base of the fins? Would there be an advantage in new muffs, with thick fin roots cast for 90mm bore?
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