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Pistons dont fit in block.

6K views 12 replies 9 participants last post by  prumora1 
#1 ·
Hello i decided to re ring my chevy 350. I honed the cylinders with 400grit stones and bought new sealed power moly rings ze251k, now i tried to install the pistons in the block but couldnt. i bought the piston ring compressor and applied light oil to both the piston skirts and cylinders.

I noticed that piston stopped at the second compression ring. I hit it alittle hard and forced all the piston in but stopped, i didnt want to break anything. I then decided to pull the piston out. now there is a grey mark on the cylinder wall were the piston rings were.

I made sure i had boots on the bolts and not hitting the crankshaft. Also i made sure the rod wasnt hitting anywhere. And there was plenty of oil on these parts.

Help is really appreciated.
 
#3 ·
Most after market piston rings are 'file to fit'. To say that, they are manufactured .015 to .020 oversize to fit differences in the way each cylinder is bored.

I don't have photos handy, but you take each cylinder individually and each piston (I use that cylinders piston) and a set of the three rings that you intend on using in that cylinder. I then push the top two, one at a time, about an inch into the piston bore, using the top of the inverted piston itself and measure the end clearance with a feeler gauge. This should end up being be.005/.007 per inch of piston diameter(4" piston would be .020 gap) for the top two rings AFTER YOU FILE TO SIZE. This may entail several 'trips' into that cylinder and several passes with a file or special filer tool (Summit and others will have that tool). The bottom and usually 3 piece ring doesn't get any fitting (normally) and is installed as supplied.

There are many write ups on the internet, but if you have conventional cast/moly rings, will all use this kind of assembly. There are other kinds that are installed differently, but are specials with those 'special' high buck prices.

Dave W
 
#13 ·
just like other post stated you need to file fit the rings, unless they are gapless, there should be a paper with your rings that give you the equation for figuring on your gap. it will have a multiplier for different applications such as street, racing, supercharged and even your types of fuel you plan to use.
all of these things make a difference when your putting your motor together. also there is a top and bottom to the rings, the top will be indicated by either a dot or a taper on the ring its self
 
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