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125 Posts
Discussion Starter · #1 ·
I got these off ebay for my 1972 T100R. I sent them and my jugs off for rebore and it came back +10 over. The guy said the were only just oversize, more like +7 really. He also noted the dome wasn't as high as my originals. To be (stupidly) honest.. I hadn't even noticed that. I was so pleased at getting them for 51$ shipped I guess I hadn't looked at the description to well. So my jugs are bored to +10 and I have these low dome pistons.

Will it be OK? I'm not gonna do any racing on this.


Premium Member
4,721 Posts
They'd be pre-'67 and suit a different head.Compression is not your biggest problem.You need to check valve-to-piston clearance.Your intake valves are bigger and at a different angle to the early head.
You might need to enlarge the valve pockets in the pistons.

Do a dummy assembly,no base gasket,no rings,no circlips,no pushrod tubes ;put a head gasket in place.
Take the valve springs out,but leave valves in the head.
With the pistons at TDC,bolt the head on lightly (enought to flatten the gasket).
See how much valve-lift you can get before the valves hit the piston.You'll need at least 3/16" on the exhausts,and maybe 0.020" more on the intakes.
Take the head off again and put some narrow strips of plasticene radially around the valve pockets.Put the head back on and push the valves into the plasticene.You need clearance around the valves,at least 1/32".

If that all works out,you'll be OK.Then you can do a proper assembly.If you leave out the cylinder base gasket and use Loctite 518,you"ll get back some (not all) compression.
Do a search on how to assemble with minimum oil and no oil on rings.Do a search on bedding in new rings.
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