Cast vs Moly Rings

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mopowers

mopowers

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In a stock rebuild, is it worth it to go with Moly rings? What are the differences moly vs cast?

My dad's putting together a stock 360 LA. His machinist recommends cast rings and I understand moly rings require a different surface finish. I've had good luck with moly rings in the past. What do you folks think?
 
Cast rings are good for stock or near stock applications with lower compression and lower engine requirements.

Moly rings are for engines with higher cylinder pressure and or heavier pulling requirements that will put extra heat in the rings.

Each ring requires a different ring and specific cylinder wall finish in order to seal correctly,so make sure your machinist uses the correct finish for whichever rings you decide on.

IMO, with today's ethanol blended fuel, I would not run anything less than a moly ring. The blended ethanol burns at a higher temperature and puts more heat in the engine.

That's just my personal preference.
 
Moly for sure! That is all i ever use. Never smokes or anything. I use Sealed Power moly rings. Have them in a hopped up 360 with Keith Black pistons. Gapped top ring to .35 I believe!:thumbsup:
 
Thanks guys. If the block isn't honed with a torque plate, will Moly rings have issues seating? This is just a stock rebuild and the machinist wasn't going to plate hone it.
 
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I'd prefer moly just from the sealing benefits.

Plenty of cast rings have gone a bunch of miles as well.
 
Moly doesn't seal any better than cast iron. Doesn't last any longer either. In fact, beat on them a bit and the moly comes out.

So, we are again dealing with decades old nonsense about ring seal and why something was done the way it was.

I don't know of a serious engine build that uses moly any more. There have been entire firsts cut down to manufacture the paper and rivers of ink expended to explain the story of moly rings. Most of it is Madison Avenue bullcrap.

If you can't afford a set of gapless top rings from Total Seal, just do the cast iron rings. Finish the bores to 280 grit, hit them with a plateau hone for 8-10 strokes and forget it.


Sometimes you have to get off Broadway to see the show.
 
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Yup.
"Moly" rings are iron rings, with a molybdenum coating applied to the wear surface that contacts the cylinder wall. It's only the top ring that gets it, because that's the one that is designed to seal compression. Moly faced rings need a smoother wall finish than iron faced. Much smoother to really do what they are supposed to, which is seat immediately. Moly does nothing else but seat much faster with the right wall finish. If the wall is too rough, the moly is scraped off (think like using a brillo pad on a Teflon pan), and then it's an iron faced ring that takes a while to seat. Any shop doing performance work should have the equipment to properly finish the bores to the right finish for them. It's way smother than dingle ball hones or the typical flex hone stones so if you're using those, just buy iron faced and expect to give them time to seat.
 
moper said:
Yup.
"Moly" rings are iron rings, with a molybdenum coating applied to the wear surface that contacts the cylinder wall. It's only the top ring that gets it, because that's the one that is designed to seal compression. Moly faced rings need a smoother wall finish than iron faced. Much smoother to really do what they are supposed to, which is seat immediately. Moly does nothing else but seat much faster with the right wall finish.
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You beat me to it.... moly rings are just a iron ring with a different facing. But I have used them for years to get the benefit of a faster seal. My engines are all street or rally use engines.

Any shop should be able to finish to either type. BTW, Hastings makes very little differentiation in grit fibish between moly faced and plain iron rings. Untitled Document
 
Thanks guys. I never really knew too much about the differences. I just got off the phone with my dad. Apparently the shop already ordered the cast rings. I guess they'll work for what he's gonna be doing.
 
Didn't MOPAR use moly faced top rings on HP/police/truck motors starting way back in the 70's if not earlier?
 
cast rings will work fine,they seat quick ,usually have less cyl wall tension,and are cheaper.But they dont seem to last as long as moly.
 
joec said:
cast rings will work fine,they seat quick ,usually have less cyl wall tension,and are cheaper.But they dont seem to last as long as moly.
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hi, the advantage of moly rings , is they will seal at wide open throttle. fuel washes the bores down, no oil , cast rings then loose their seal. moly ring is self lubricating, it will seal. as for wall tension, you will find moly ring usually has less tension. there is power in a good moly ring combo. we use them in our stocker and street engines. just food for thought.
 
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