Hello-
I am assembling a .030" 400 Smallblock, using SRP pistons and the Speed-Pro file fit rings reccomended by them.

The problem I have is installing the pistons. I have installed and positioned the thin oil ring upper and lower "rails" as they call them to specs. When I push the piston into the bore, the bottom rail will consistantly go into the bore with the expander ring, but the top rail will pop out of the ring compressor and hang outside the bore before it goes in to the chamfer at the top edge of the cylinder.

I have tried three different designs of ring compressor- a band type that clamps together with locking pliars such as used on an aircooled engine, and two circular band type that use an allen key to clamp them around the rings on the piston. Niether one works.

When the ring pops out, I have to remove the ring compressor and use a tiny screwdriver to push the thin rail in while pushing down on top of the piston to get it to pop into the bore. Then I clamp the ring compressor back on for the top and second compression rings and push it down. I had a bud who is a GM master tech helping me and he had never had this happen before. I have put together probably a hundred or so engines of all types and NEVER had this problem, but, they were all one piece oil rings too.

This is annoying, and I am afraid I will damage either my oil ring land or put small gouges (which it is doing) where the fire ring on the head gasket will seal at the top of the bore.

I sill have three to put in. Any words of wisdom other than suck it up and accept it?

 

Wow, never had that happen. Usually when the OCR is compressed it says compressed and the two retaining rings are the easyest to install since they have the lowest amount of tension. Is this the type of ring compressor you are using?

 

Yes, that is one of the types I have tried. Only have the problem with the top rail, the compression rings go in fine. There is definitley a slight chamfer to the top of the bore as is done normally when a block is honed just to allow the rings to go in. This is a PITA I tell ya.

 

Make sure you're pressing the compressor tight against the deck.

 

Yep.

Also speed affects it. You dont want to go nuts and slam the piston into the bore because if it does happen to let go of one of those rings it can get nasty real quick. Definitely dont go at a snail pace though, or that ring will pop every time.

 

I like to go around the ring compressor tapping very lightly with a small hammer to make sure it's completely flush aginst the block then push piston in just firm enough so it will go in completely with 1 smooth motion. Not all the way down the bore, but far enough to get the rings in.

By the time you get to the 8th piston, you'll have it down!!

 

Is your expander ring the right thickness for the oil ring groove? No chance someone threw a slightly-too-thin metric expander in there instead of the one you really need for the piston (3/16" or whatever)?

And just how much chamfer at the top of the bore? Maybe a little too much- enough a skinny oil ring can pop out after the ring compressor but before it gets in the bore?

I've built a lot of engines and I have not run into this problem either.

 

The wraparound band type compressor like the one in the picture above is an example of the type to avoid.

 

Wow! Go out of town on a suprize ski trip from my wife and look at all the responses I get-

As far as it being an incorrect ring, they are all out of a complete Speed-Pro set.

I am tapping the top of the compressor to square it against the bore, then tapping firmly but not wailing on the top of the slug (piston) to push it down.

As I have said, I have tried THREE different types of ring compressor, one a band type as pictured that wraps around the piston with an allen key and ratchet mechanism to tighten it, one is a clamp around band type that uses a turnbuckle and lever to snug it against the piston, and the third type is a motorcycle or aircooled engine type, it uses a band that has a ratcheting pliars to tighten it, and once the piston is in (or in the case of an aircooled engine with studs that the cylinder slides over the piston)you release the pliars and remove the band.

Ain't one of them workin', and I am not trying to blow my own horn here but I have put a LOT of pistons in in my life, though most are in V12 diesels with a 6" bore and stroke!

Oh well only three to go and I guess I will just deal with the situation. Thanks for all the replies and tips guys!

Eric