350 rebuild piston issue

I'm currently rebuilding a sbc 350 with casting number 10054727. I'm trying reinstall the pistons with new rings and they are very hard to move once the compression rings are in the cylinder. The only way I can slide them further into the cylinder is by hitting it with mallet. The piston ring gaps are correct (checked with a feeler gauge) and the pistons are original to the engine. Every video I have seen of pistons being installed, the pistons can almost be pushed in by hand. Any ideas as to what I'm doing wrong?

I am not your expert here but you are not putting these in dry are you?

Should have some good grip, but a rap with the mallet handle should be all you need. I like some cheap 10W40 for assembly lube, on pistons.

Did you clean the piston ring grooves? Any build up in the grooves will prevent the rings from compressing completely.

Watching too many videos????????

Did you square the ring in the bore to check the gap?

Are the rings for oversized bore?

Remove top ring to verify its top ring problem, then remove other rings and try to install with just top ring to verify that it is top ring problem

AND, as already posted by 36------did you clean out the ringgrooves-they get a carbon buildup behind the ring as time wears on---------

And does the ring rotate easily in the groove??


And I am assuming that you removed the top ridge and honed the cylinder wall?

Welcome to CHR

OK riffraff, now that you have our attention, first question that has already been addressed by Jerry is: did you ridge ream the cylinders?
https://www.youtube.com/watch?v=79i-_-u3HzA

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Hi guys. Thanks for responding. I have the correct ring size and I checked the gap and it is within spec. Yes, I reamed the cylinders. I will try cleaning the ring grooves with a scraper to see if that helps.

Sorry it took me a day to respond, I've been in the garage all day.

For a scraper you can use a section of an old ring-just sharpen the end to make it sharp? and rotate arounf the grove-if you get black stuff out its probably the reason why--------

I scraped out the ring grooves and I did get a lot of carbon out but it didn't seem to do anything. I installed the piston nearest the back of the block and that went in as easily as before... I had to beat it in with a mallet. With that piston installed and torqued to spec, I could still rotate the crank shaft with much difficulty. When I installed another piston, I couldn't move the crank at all.

Is this even remotely normal? I still need to be able rotate the crank to install the rest of the pistons.

No, this is not normal. The piston once in the cylinders should only require light tapping if any to move them, and you should be able to rotate the crank with al cylinders loaded, although a large wrench may be required to turn the crank.
Check your ring grooves again, when cleaned properly you should see shinny metal at the bottom of the grooves, very important to get all the carbon out. Also check the ring gap in the cylinder as Jerry suggested being sure the ring is square in the cylinder by pushing the ring down slightly with a piston top.
You either have a build up in the piston ring grooves or the wrong rings.

Here is a summary of all of the responders questions. Answer them BEFORE the next step:
1. Will piston slide into its corresponding bore when there are NO rings on the piston? (yes/no answer)
2. Do you know how to tell if a ring is upside down? (yes/no answer)
3. Did you square the compression ring in bore with the piston and measure the end gap? (yes/no answer)
4. Did you do this measurement with ALL of the other rings for that piston? (yes/no answer)
5. How much did you cut off the end of the ring? (measurement answer)
6. Did the block get the ridge removed? (yes/no answer)
7. Did the block get honed with the proper crosshatch? (yes/no answer)
8. Did the pistons get the carbon removed from the ring grooves using a sharp tool (not a wire brush)? (yes/no answer)

Until you answer ALL of these questions, we are still on step 1 of the troubleshooting process.

Post the exact part number of the ring set your using -and I mean to include the last 3 numbers----------

and take off the top ring to install a test fit on the other rings, then reverse to just the top ring to verify that its a top ring problem---------

can you see the end gap of the top ring when its in the hole? should be aprox .020 gap visable


sorry robot------probly typing at same time

1. Yes, the pistons will slide into their bore without the rings
2. Yes, I followed the diagrams on the box they came in
3. Yes, I squared the ring in the bore and found the gaps to be in spec (.016 for second and .020 for top ring)
4. Yes, I measured the gap on all the rings
5. 0.0, all rings were in spec out of the box
6. Yes, I reamed the cylinder ridge during teardown
7. The block hasn't been honed.
8. Yes, I removed all the carbon in the ring grooves so that you can see the metal at the bottom of the groove

The rings are part number SUM-133-139-00

You may be confusing cylinder hone with boring. The cylinders need to be cross hatched for the rings to seat, this is sometimes called glaze breaking. It can be done with a hone attached to a drill motor.
Assuming the honing has been done along with all other procedures and you have liberally oiled the piston and rings prior to insert. The only thing left is how much force is required.
How are you turning the crank?

THANKS, Rif, this is a good start to confirm exactly what you had done so far. Too many times, the answer is hidden in an unanswered question.
Good point about the liberal oiling and the breaking of the glaze.
In the old days, I typically saw 50ish ft lbs to rotate the entire setup including pistons, all torqued to specs. Some would be a little tighter but I never saw a motor hit 100 ft lbs unless I had a main bearing/crank straightness problem. I suppose a too-tight rod bearing could contribute to the problem but it sounds as if the piston/rings/bore is the culprit. Lots of oil on the rings/piston skirts. We used to use the freebie STP for this but it attracted too much lint from the shop towels so we stopped.

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

Quote:

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Originally Posted by jerry clayton

Well, maybe just the Iraniuns
mispelled on purpose

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Hey Jerry, you misspelled misspelled.

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Rollin on floor laughing!
But Tech, Jerry didn't say what he misspelled on purpose....
You guys are kiiilling me, lol!

Check oil ring there are two different ring depths shallow and normal . you can not mix normal with shallow ring grooves in piston .