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I was inspecting my 836 block and noticed that there was a step in the top of the bore. It measures 3.508″ in diameter and is about .215″ deep (towards the bottom of the bore. Below the step it is mic’ing 3.465″.
What I figure is that the block has been sleeved and not finished, which would be a good thing I guess. What I am worried about is the top .215″ of the bore that is oversized. Will it make any difference if I rebore the liner and leave the top?
Is there any evidence of a sleeve on the deck surface? I wouldn’t want a sleeve installed from the bottom even if it was possible.
Are all cylinders like this?
If you are going to bore it .020″ over it would clean up anyway. Jim”
I don’t remember the dimensions offhand, but Pierce factory machined a relief at the top of the bore, that I have found in several original engines, both 8’s and 12’s. Don’t know the reason. But the main bore was still around 3.500. Could go measure some tomorrow.
Bob
The step in the blocks was an attempt to make the engine run more quietly. I know at .040 over it goes away. I haven’t bothered to put the relief back in after a re-bore. The engines still run “Pierce” quiet.
Happy Motoring,
Rick
Rick is correct. We have several 836 blocks in the shop with the step. I have not seen it on the other series cars….. but with Pierce who knows?
My 845 is stepped like this, it has never been bored. I wondered if it was supposed to let the ring compressor slip into the bore on assembly to reduce the tendency of the rings – particularly the cast iron oil rings – from catching and breaking when being tapped in. Haven’t actually gotten to the point of trying it. Another theory: the step corresponds to the top of the ring travel and avoids having a ridge from wear that catches on the rings when trying to pull the pistons.
Jim