boat vs car engine
 

Ive heard there are differences, but what about rebuilding a boat engine. can you use car parts? pistons and rings specifically?

Sure, as long as you use high-quality parts. Take SpeedPro pistons as an example. An L2399F piston really doesn't care whether it's in a car or a boat engine. The piston-to-wall clearance might be just a touch larger on the marine engine but the parts are the same.

the basic parts are the same but some of the specs are different.

whn biulding them clearances are different. Cam specs are different. Like eth 502/502 cam in the 502 crate engien tends to casue reversion in a wet exhaust. YOu have to use brass freeze plug in eth block, Marine distributors, starters and alternators are NOT interchangeable. DO NOT run car parts in a boat. The marien version aredesigned not to create sparks. ANd if you get soem gas fume settled in yoru bilge and you have automotive elctricals parts possible BAM!!!!!!

also marine carbs have "j" tubes so any excess fuel from eth fule bowls gets dumped into the carb down into et engein as opposed to all over the place (half in eth engien/half ON the engine) with the standard overflow tubes.

im with you on the alternator/starter etc. im just checking on piston and ring clearance

Depending on the ring package, marine engines may require an additional .002-.004 top ring end gap. Aftermarket piston to wall clearance and gauge points will vary per manufacturer and material.
Bob

sorry if a stupid question but why the larger ring gap on marine motors? Young mind wanting to know.:confused:

I think its because these motors run cooler than car motors

The larger gap is required due to the prolonged (relatively) high rpm marine engines routinely encounter. The .002-.004 allows for additional thermal expansion needed from increased cylinder temps that build under these conditions. It decreases the possibility of ring ends butting.
Bob

Thanks for the aknowledge! Just goes to show how good oso really is:p

Funny thing, I just talked with JE Pistons this afternoon about end gap on my 4.500-bore supercharged marine engines and they said .022 on the top ring, .025 on the second. I would have guessed a little bigger than that but JE ought to know.

If you toast an impeller, you might end up wishing you'd have gone a touch bigger on the gap..

mcoll, why is that?

Crazyhorse,
JMHO but .022 top gap seems "snug" for a forced induction marine engine. Thats .0048" gap per inch cylinder bore. These numbers are from JE installation guidelines.
High-Perf. Street-Strip Bore x .0045"
Street Moderate Turbo/Nitrous Bore x .0050"
Late Model Stock Bore x .0050"
Circle Track / Drag Race Bore x .0055"
Nitrous Race Only Bore x .0070"
Blown Race Only Bore x .0060"

Bob

end gap on my 598" project??
 

So in my case with a 4.600 bore JE pistons naturally aspirated would it be smart to use their recommendation for Street Moderate Turbo / Nitrous and set the top ring at bore X .005" (.023) and the second ring at bore X .0055" (.025")? Is that still slightly to tight on top? It sure would be nice if JE would list some marine applications on their end gap table. I guess us boaters are still only a small percentage of the racer industry. Thanka for the opinions in advance!!
Craig

Ive never heard of the second ring needing a larger gap. Whats up with that?

Puder,

Ring heat closes the end gap.
Cylinder sleeve heat opens the bores which opens end gap.

Problem is, the ring heat is transferred to the cylinder liner and it is then absorbed into the cooling water.

While lack of coolant will indeed allow the liners to get hot and grow, the rings heat more quickly than the liners, and the gap closes. If the gap completely closes, the rings try to lock up in the bore. At a minimum, this scores the cylinder walls. At worst, the rings try to seize up and while there is plenty of piston meat to push the rings UP the bore, when the piston tries to some DOWN, it rips the top of the piston off (usually partially, not completely which allows the ring to peel out and lose tension). New parts will be required...

F-31, the new school of thought on a larger 2nd-ring gap concerns the ability of air passage through that gap. If the second ring has a tighter gap than the top ring it causes a restriction in the airflow between the top and second ring, reducing the sealing effect of the top ring. Pressure differential is what causes ring sealing. The greater the pressure differential, the greater the sealing effect.

This is the answer Back4More gave in another tread about the difference between automotive crate engines and marine, I thought it was pretty good and clear.
The thread;
http://www.offshoreonly.com/forums/s...threadid=61488