C15 oversized piston

[davet147]

Can anyone advise please? I have bought a second hand barrel for my C15 and I was told by the chap I purchased it from that it was a +0.020.  upon measuring the diameter it would not be a plus +0.020 it is in fact in between +0.040 +0.060, which would be the maximum that you could get a C15 piston unless you went up to 69mm and then I understand that I could fit a T100 piston which I believe was common practise at one point.

To fit a +0.040 piston the diameter would need to be 2.677 or to fit a +0.060 piston the diameter would need to be 2.697. The actual diameter I have within my barrel is 2.691.  Would I need to get a rebore on it to bring it up to the +0.060 or could I just fit a +0.040 as the rings would take up the difference. Hope this makes sense.

Dave

[cardan]

Hi Dave,
The key point here is that you need very accruate measurement of the bore to make a good decision. Often it's not the size of the bore that is so important, but the uniformity of size down the cylinder. Wear is never uniform, so you need to find the regions of greatest wear before you can decide what size to bore the the cylinder.
Re the measurements you mention: 2.691 is 14 thou greater than the +0.040 piston - way too much to consider.
Get some careful measurements, and with luck it might bore out to +0.060.
Good luck! Leon

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[davet147]

Thanks Leon, I am sending it off to Langcourts, who are going to rebore it to +0.060 and blast the fins ready for repaint for £50.00 for me. Thanks for the advice once again. 

Anyone have a +0.060 piston hanging around that they want to sell? Give me a shout.