This is topic 5.0 Engine Rebuild Cast VS Moly Piston Rings in forum Tech Talk at Northern California Ford Owners .
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Posted by CoyoteCoupe (Member # 9621) on
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Just a rebuild on a stock 5.0 out of an 90 mustang. Which rings work the best? Cast or moly.
Posted by Duncan Motors (Member # 7045) on
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cast is old school grocery gutter stuff. the 5.0 came stock with a chromoly top ring at least, so dont under cut what at least came stock
Posted by Tom Renzo (Member # 13165) on
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No such thing as a CHROME MOLLY RING!!! What you mean is the first ring is MOLLY and the second is chrome. This is one of the most miss understood thing in a car engine and the myth has been going on for years. Just wanted to post the info correctly.What you want is a MOLLY first an iron second and a standard tension oil. Or another words a premium set of rings. Chrome molley ring sets were big years ago because the molly seated fast and is resistant to high heat. The second chrome ring broke in harder but when it did made a good combination. A chrome top ring is good for non paved tracks and dusty areas as chrome holds up better in dusty environments. So basically you have 3 choices CHROME MOLLY OR IRON. Go with a top Molly and an iron second!!
[ 2014-04-10, 05:49 PM: Message edited by: Tom Renzo ]
Posted by Duncan Motors (Member # 7045) on
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did u just say rings where set up for dusty tracks?
Posted by CoyoteCoupe (Member # 9621) on
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The parts store has the standard ones which are iron and the premium ones which are moly. Which should I go with just for a fresh rebuild. Small difference in price.
Posted by koupe377 (Member # 13461) on
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If it's just a small difference in price go with the premium.
Posted by Tom Renzo (Member # 13165) on
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Premium Molly first ring set is the way to go!!
Posted by Duncan Motors (Member # 7045) on
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theres a lot more then whats being said on here about ring differences, or pros or cons, i dont have enough time to explain nor am going too, but nothing here explained has anything about them, what ever u do make sure your block is honed right for the rings your using. power adders and your use of the motor matters greatly
Posted by Tom Renzo (Member # 13165) on
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The machinist will know the proper honing procedure. But just for kicks and giggles the hone has to be correct for the molly rings. If he is going to hone it himself i would strongly not recommend that. Most people including mechanics do not hone a block correctly.No need to explain it as in dought leave the block alone. Modern rings are pre lapped from the manufacturer. Rings are something that there is a lot of misconceptions about, Like CHROME MOLLY which is a combination of rings not a material of a top ring.
Dirt track engines injest dirt particles and should use a TOP CHROME RING
Boats that do not have to deal with dust or dirt can use MOLLY TOP
Street engines are best suited for Mollie top and either a chrome second or a cast second.
Most premium sets are a Molly top and an iron second. As i explained above Honing is something left to professionals. Most do it yourself and some professional mechanics do not know how to hone a block properly. In most cases if the block is good and no ridge on the top do not hone it if it has no gouges or low spots to speak of. I have been in this business quite a long time and have seen professional people mess up a hone like you would not believe. Remember busting a glaze and honing is two completely different things. Remember modern rings are pre lapped and some have a fast break in costing. So if in doubt do not hone a block.
Note honing is the key to good sealing. If you mess it up your are finished. I have seen many an engine with the molly stripped out of the rings with an improper hone job. Remember a Molly ring uses very fine stones like 400 ETC
[ 2014-04-13, 07:43 PM: Message edited by: Tom Renzo ]
Posted by Duncan Motors (Member # 7045) on
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chrome moly is or stands for molly,,,or thats what i meant, yeah no such thing as a true full chrome molly ring its coated with the m word though. i dont think anybody but yourself would of took THAT literally, OR EVEN THOUGHT THAT DEEP. i if was u i would read more than one book, other than getting stuck on one guys work, an beliefs. the boat, dirt, applications are just weird, or they would be called boat rings, open dirt in your motor rings lol common man lol. the 5.0 comes stock with a chrome molly <coated just for u> top ring. second is cast. so just for u guys your motor will run in dirt and water an will now be ok lol. AGAIN THERES ALOT OF STUFF ON HERE THAT GUYS WILL JUST PUT UP THAT JUST REALLY SHOULDN'T.
Posted by Tom Renzo (Member # 13165) on
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OK Thanks.
The single most important factor to be considered in selecting the proper top compression ring face coating material is the service requirements the engine will be operated under. Will the engine be subjected to unusual speed or load operation, stop and go - short trip driving, or operating in a high dust or dirt environment? if, for example, the vehicle is a passenger car operated by family members for what could be termed the average driver, it really doesn't matter which type is selected from a standpoint of the life of the engine and piston rings. On the other hand if one of the above mentioned conditions is going to exist on a regular basis then no doubt one type of ring face coating will be more appropriate than the others.
The three popular types of top compression ring face coatings, chrome, moly, and cast iron, each has advantages of its own with respect to operating conditions. Moly has a very high resistance to scuff. Chrome has good resistance to scuff but does not exhibit moly's oil retention capabilities. Plain cast iron is a durable wear surface in normal operating conditions and is less costly than the moly or chrome faced ring.
[ 2014-04-14, 04:10 AM: Message edited by: Tom Renzo ]
Posted by Duncan Motors (Member # 7045) on
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your last paragraph was perfect and answered everything i think as gd as it could get.
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