View Full Version : Piston rings???

flying tomato
11-06-2010, 12:35 PM
Need help deciding on piston rings for a stout 540.

Are the zero gaps "all that"?

Any info is appreciated.

Flying Tomato, Lee

farmer tx
11-06-2010, 08:42 PM
Don't think I would use zero gap in a boat, infact in a marine engine I think you increase end gap. I will try to look at the service manual tomorrow.

11-06-2010, 09:12 PM
IMO, I like the zero gaps, they usually have overlapping butts and not faced end butts, there are more than one manufacturer of these styles

will you gain any power? I seriously doubt it

11-06-2010, 09:13 PM
The amount of ring end gap is dependent on the amount of heat developed in the combustion chamber. When combustion heat is high causing the rings to expand and the block temperature is cool preventing cylinder expansion sometimes additional end gap is needed in a boat motor
Most piston suppliers should give you an idea of what gap you should use.
I dont like the idea of gapless rings in a boat.
Just my 2 cents.

Dr. David Fleming
11-06-2010, 11:17 PM
Piston rings are one of the most important parts of the engine. They cause friction and seal the cylinder combustion gasses. The best piston rings are not good enough for your engine. They need to be installed the way they were engineered with as tight an end gap as you can get away with and side clearances within spec.

Boats run under power and load not usually encountered in automotive - I would follow Merc specs exactly and use their piston rings. Now if you know a major engine builder and they tell you to do something different - well go ahead.

Piston rings must be broken in and seated to the cylinder bore. Most performance engine builders use a honing plate bolted onto the cylinder block to keep the engine stressed while the cylinders are sized. Proper grade cross-hatch of the hone job is important. Merc service tells you to break in new piston rings by running the engine easy and not at a constant speed. Piston rings not seated in the cylinder bore properly may never seat and always leak.

I watched Tyler Crockett seat piston rings on the dyno in a few minutes by loading up the engine in a fashion of his own choosing - he has the reputation as a performance builder to set his own method - because its all about power.

11-06-2010, 11:40 PM
Get total seal rings,,you wont be sorry..top ring gapless..

The Hedgehog
11-07-2010, 12:50 AM
Got zero gaps. I run lots of cyl pressure. They are the way to go.

11-07-2010, 09:31 PM
I have used lots of gapless rings in theory they make a lot of sense in a marine engine since marine engines put lots of heat into the rings you can run a wide gap on the top rings and not have any leakage as long as the rings don't ever line up with each other. The new style with the slanted gap on the skinny ring would still seal better than standard rings if the two gaps ever lined up. I think the most important consideration is the distance the ring is down from the top of the piston. Steel top rings take more temperature therefore less crevice volume and better economy but more thermal load on the ring so sticking with a 1/16th or larger is probably a good idea. Also if you have oil squirters a napier scraper second helps.