I have had the bottom end rebuilt by SRM on my 1968 N15, with some NOS +060" dished pistons that I managed to find. I am now looking at putting the head on, but have a few queries relating to the clearances:
1. The pistons are proud of the cylinder by .043", is this normal? I unfortunately didn't take any notice of how the flat topped pistons looked when I stripped the engine. As the gasket is .040" thick, this will put the piston crowns just into the head recess, but there is sufficient height clearance in the recess.
2. With the +060" overbore, I have found that there is only .005" annular clearance between the piston crowns and the head recess, if the piston enters the head. This is a bit of a worry as the head recesses are unlikely to be in perfect alignment with the bores, so there is potential for contact on the edge of the piston crowns. Is this a common problem with the .060" overbore?
3. With reference to the above, what is the solution, do I open up the ID of the head recesses? Or do I fit a de-compression plate to lower the piston height, if it is the piston height that is wrong?
Thanks
Andy
Not enough. I would take…
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I think the left hand piston…
I think the left hand piston is reversed on its rod. How does the dished piston compare to the 750 pistons available now from the usual suppliers? It looks as if the top of the barrel has been machined as well. How much did they remove?
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Not enough. I would take the easy route and fit a compression plate under the barrel. And check the valve action .