1988 Force 125 hp OB piston ring orientation

Hi. I'm installing rings on this engine, and the new Sierra ring pack has one beveled ring, and one flat ring. Clymer's says bevels point up on EACH ring. the OLD rings look flat. ( Both of them on each piston). Is this a parts improvement? If so, does the beveled, or flat ring go on the top groove?

Thanx,
Bob List

Re: 1988 Force 125 hp OB piston ring orientation

You're not getting many answers here, so here's mine. The old ones came out flat,so flat is important, put that one on top. The beveled one is next. ? Can't figure the use for the bevel so up or down is up to you.

Re: 1988 Force 125 hp OB piston ring orientation

Are you saying that the new ring is beveled or semi-keystone?

Beveled refers to the inside top of the rings having a small chamfer. Semi-keystone refers to the ring tapering from full thickness at the outside to very thin on the inside--almost triangular in cross section. Not all engines used them. Most Chrysler and Force engines that do use them have the keystone on the top and the flat ring as the lower or second ring.

Semi-keystone will not fit in a flat ring groove. If this is the set you have and if your piston has two flat grooves, the ring set is incorrect for your piston. You probably will not be able to fit the piston with rings into the cylinder. If you can fit it, the top ring will be destroyed and most likely will destroy the piston and damage the cylinder walls in a very short period of running.

If you have two flat rings, the internal chamfer or bevel faces up on each ring. The theory is that combustion pressure leaks through the chamfer and gets behind the ring, forcing it outward for a better wall seal.

If indeed you have two flat rings and only one is chamfered, then that one goes in the top ring groove.

Re: 1988 Force 125 hp OB piston ring orientation

yes, one of the rings in each pack is triangular... it tapers to a sharp edge towards the inside of the ring.. funny thing, there is only one ring set listed for the .312 piston... the lands are square cut. I'll be calling Iboats store tomorrow, possibly Sierra to get it figgered out.. thing is, what does the land look like on a piston that uses keystone style?.. is it tapered as well?
Bob

Re: 1988 Force 125 hp OB piston ring orientation

piston part# is 18-4629 (sierra)
rings part # is 18-39010.. the only set listed for the only piston listed for this engine..
however, the package for the pistons says: "fits 18-4269 piston". ( note the reversal of the 6 and the 2! )
There IS no 18-4269 piston part #. I wonder if it's a dsylexic misprint on the bag.

Re: 1988 Force 125 hp OB piston ring orientation

My second question is: Why do you need rings? If you are using a stock bore piston, rings seldom wear out. Almost the only reason to re-ring an engine is if it has been bored. Rarely, a ring willbreak and cathch in the exhaust port, but that usually damaged the cylinder wall too.

The piston for the semi-keystone ring is cut with the top groove tapered to match the ring, tapered side up. Two different versions were made. One had the ring right at the top of the piston and the other had the ring about 1/8 inch down. The ones at the top tend to break rings a little easier than the ones set down a bit. Again, the theory of the semi-keystone ring is that compustion pressure gets behind the ring and forces it out for a better seal.

Contact franzmarine@aol for new rings to fit your piston. He will be a bit more expensive but he will send the correct parts.