87 Force 85 HP Piston rings.

[drowningworm]

New to iboats, I have a question regarding an 87 Bayliner with an 85 HP Force outboard.
Model 856X7A.
Engine had low compression on cyl #2, did a leak down test, the test indicated leakage past rings. I pulled the engine apart and found that the rings were stuck in the ring lands due to excessive carbon. I ordered new rings and a complete gasket / seal kit(s) off of iboats site ( piston rings part number 18-39010). All of the parts look correct EXCEPT for the piston rings, they do not match the ones that are on the pistons in my outboard. My outboard has two rings that are seemingly identical, the rings I received are a set of two but are different thickness and one of them is a "v" shape. The "V" shapped ring is also quite a bit thicker and will not fit into the ring land in the piston.. I am not sure what piston rings I need to order as this seems to be the only part number that Iboats has for this year of outboard.. HELP!

 

[Frank Acampora]

Re: 87 Force 85 HP Piston rings.

This problem popped up before and I sold the guy may last set of rings and a used piston. For some reason, iboats does not list the correct rings for earlier Force engines. On these engines, the lower and upper rings are the same square shape, exact same ring. The set you received contain one regular square edged lower ring (which is the same in all engines) and one "semi-keystone" upper ring. The upper groove of the piston is machined to match and the theory is that combustion pressure gets behind the ring, expands it against the cylinder wall, and seals more pressure. In reality, those uppers are a bit more prone to breakage and I don't see any real improvement in power. You can return those rings and order a set of 3.3125 late Chrysler rings or early Force rings from franzmarine@aol.com. This assumes that the cylinder is stock and not overbored.

Outboard rings usually do not get a lot of wear. If you can free up the original rings without breaking them, you can clean them and the ring grooves and re-use them. Compression will be fine. The only time I buy new rings is if I replace a piston with an aftermarket type which uses different rings.

When you do install the rings, the chamfer on the inner edge goes UP in the piston--same theory, combustion pressure gets behind them for a better seal.

 

[drowningworm]

Re: 87 Force 85 HP Piston rings.

Frank,
Thank you very much. Unfortunately the rings were stuck pretty bad and could not be removed without breaking them. I appreciate the help and the prompt response, this forum has been a wealth of information! I will return the rings and get the proper ones.