Thread: 350 rebuild piston issue

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Since the pistons fit freely into the bores w/o rings, all rings have been checked for end gap, and all piston grooves have been confirmed clean of carbon it might be interesting to see how much torque it takes to spin the crank alone, with no rods in place? It should turn with very little resistance. Seems it would be worth checking, given the specifics that have been stated. Have you checked the rod bearing clearances? Did you use inside & outside micrometers, or PlastiGuage? Did you measure your cylinders for tapered wear using an inside micrometer?

If the pistons will drop through without rings and the rings are the correct size, there remains only one problem. The rings are either too wide for the ring land or there is still carbon in the ring land, not allowing the rings to fully engage in the lands. And by the way, stop beating on engine parts with a hammer. Can you turn the crank with no pistons in the block?

I used to shoot for 35 ft/lbs on the torque wrench when turning the crank of a fresh short block from zero.

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Along Rogers question, Have you marked and made sure all your main caps & rods caps are on the corrisponding rods or mains with mic'd bearings?, are they the original main caps? different crank? Sounds like your getting close..

There should be no valve spring tension as the heads are usually off at this point, but a good point for rotating pressure. OP stated he was having trouble pushing the piston down once the compression ring entered the cylinder, so much so he was having to use a mallet. This leads me to the same conclusion as tech, something ain't right with the ring grooves or rings. Of course, if he's not using oil on the pistons and rings all bets are off.

Ok so I may have made a bone head mistake. Are the piston rings different between gen 1 and gen 2 blocks? I ordered rings for a gen 1 by accident while I believe mine is a gen 2 ('86 with a 1pc rear main seal)

It happens, you're not the only one to grab a wrong part. Yes, there is a difference in the ring grooves between gen 1 and gen 2 pistons. Examine your pistons ring lans closely for damage caused by the slightly larger rings.

the ring groove needs to be deeper than the depth of the ring--you should be able to push the ring completely into the groove with none sticking out----
over the years ring depth has gotten less to allow gas pressure behind the ring to force it against the wall for better sealing.

However you haven't answered about suggestion to remove top ring and try and then remove others and try------

also I looked at that part number from summit and it listed the oil groove at .200? also that rings were made by Hastings-they had a somewhat different oil expander and rails IIRC (haven't used a Hastings since early 60s)

Ok so I believe I have found my problem: wrong piston rings. I was trying to use gen 1 rings on a gen 2 block.

As to the rest of your questions:
... I have been turning the crank with an old flywheel
... the crank spins easily without an pistons
... all clearances have been checked with a plastigauge
... there is some tapered wear on the cylinder but the ring gaps were in spec all the way down the bore
... all rod caps and and main caps are where they're supposed to be with the fresh bearings in the correct places
... I am using the original crank and caps
... I have been using copious amounts of lubrication from the start
...and Jerry: I got the same amount of resistance when I had just the top ring in as I did when I had just the second compression ring in. This wasn't as much resistance as having all the rings on the piston but it was still too much. When only the oil ring was on the piston, sliding the piston down the bore was fairly easy. So the compression rings were definitely the problem.

Thanks for all your help. It was a pretty obvious mistake but I wouldn't have gone back to check the ring part number if one of you hadn't suggested it. I doubt this will be the last time that the learning curve will kick me in the nuts.

Be vigilant riffraff and trust NOBODY.

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Well, maybe just the Iraniuns

mispelled on purpose

Hey tech, I need to meet this Nobody guy before I trust him, do you have his first name and a number for him? Lol!

Jerry Nobody-----888-555=6969

Dying from laughter from that one!!!!

I have had problems with the oil control rings before. Try installing the pistons without those and see what happens .....ted

Originally Posted by jerry clayton

Well, maybe just the Iraniuns
mispelled on purpose

Hey Jerry, you misspelled misspelled.

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