I am reassembling my LT1 block and need help with the ring gap. I had the block decked and the heads milled to eliminate some pitting from a blown head gasket. About 80,000 miles ago the block was bored .030. The cylinders were honed but not rebored this time. The cylinders still look good.

The machine shop ordered me a set of Hastings standard .030 moly rings. I am checking the ring gap and here is what I found:

Top Compression Ring - .022 typical
Bottom Compression Ring - .025 typical
Oil Scrapers - .033 typical

According to the GM manual, the ranges should be:

Top Compression Ring - .010 - .020
Bottom Compression Ring - .018 - .026
Oil Scrapers - .010 - .030

The manual also lists a service limit for the compression rings as .035 MAX and the oil rings as .065 MAX.

Before the rebuild, I suspected there was a lot of oil getting pushed through the PCV into the intake because my idle air bypass port got clogged causing idle problems. I suspected a blowby problem. I had to clean the intake and install an oil separator. I started finding water in the oil separator which lead me to the leaking head gasket.

Am I OK with these ring gaps? Do you think that blowby was or could be a problem? Should I get a set of rings and custom grind them to the appropriate gap or am I being to picky? It looks like my gaps are all about .005 too large.

Any advice would be appreciated. I am going to contact the machine shop tomorrow for their opinion too.

 

Realistically those ring gaps are not going to create a problem...they're just loose for your application - but I would be curious to know how loose your piston to wall clearance is if that's where a set of rings that should be at ~ .013" top ring out of the box end up at...

Are you getting the rings squared up properly?

What kind of pistons are they?

Do you have a build sheet with tolerances?

 

Blowby contains water.... that's a major component of the burned fuel, along with carbon dioxide.

 

I am using a tool from summit to place the ring square about 1" from the deck. I don't have a bore guage or a micrometer to check the piston to cylinder clearance. I am trying to buy one on ebay. I am using the same sealed power hypeuretectic pistons (.030 over) that the original machine shop put in 4 years ago so I am trusting that the clearances were right then. The machine shop I am using now said the cylinder bores were OK and they just needed dressing. They also said the standard .030 rings were OK to use now but I check the clearances myself and see that the gap is a little too big.

Fred, I get your point that the water I saw might have been from blow by. I did find that the head gasket was leaking into the #7 cylinder which is why I started this project. I had the block decked because of some pitting and there was a slight groove in the Edelbrock aluminum heads where the armor ring in the head gasket was located so I had the heads shaved a little too.

I don't have a build sheet. Should I use these rings or go the extra distance and grind my own rings? I'll need to buy a grinder and figure out what rings to buy if you think this is the best route.

 

Update:

I purchased Total Seal file fit gapless rings. The instructions say to follow manufacturer spec for hypeuretectic pistons, which I am still using. Since I have no power adders, do you all agree I should be using the GM stock specs:

Top Compression Ring - .010 - .020
Bottom Compression Ring - .018 - .026
Oil Scrapers - .010 - .030

Also, I have the book "How to rebuild an LT1/LT4 engine" and it says the top compression ring should be between .010 - .016. I have managed to keep all of them around .012 - .014 so they are within spec of both books. I was having blowby issues with the old rings (gap was around .029) so I am looking to keep these on the tighter side.

Do you guys think this is acceptable? I am planning to use the Quick Seat dry lubricant on the cylinders for break in.

 

To the tight side of

.016"
.018"
.025"

is what I would put them at.

Make sure to de-burr the edges so you don't score the cylinder walls.

 

Thanks. I have deburred them and they look good. Can't wait to put this back together this weekend.