I got my 0.030" oversize pistons and rings from RockAuto, but then I broke a 2nd ring installing them and now the size is out of stock everywhere I look. Question: these are moly rings (Enginetech M34056)--can I replace the 2nd ring with one from a set of cast iron rings? Which rings are actually moly in a moly set?

Well...you'd never know the difference if that is what you're asking. It's more of a 'can I sleep at night knowing that out in the garage there is a cast iron ring in my ring land that should be moly?' Some people can, some people can't.

I would really not worry about it and just get a cast replacement. Hey, are these 0.060" over? I may have an extra piston-set or two of that size, in Moly, from 1992...

Lou

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Home of Slant6-powered fun machines since 1988

The moly coating is there to reduce scuffing during the break in process.
Top rings will have more tension then the second ring so the moly coating is
more important on the top ring. Less important on the second ring.
The moly coating will also provide a bit of lubrication at each start up, but again,
your plain ring is the lower tension second ring.
There have been lots of motors built using plain rings, follow an easy warm up
on the motor and you and the motor will be fine.

Concerning being able to sleep at night,
remember that the slant that you are working on was built with all plain rings when it was new.
It survived.

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The second ring is almost always a plain iron ring. If you buy Moly it's on the top ring. You can look at the ring face and see it there in the middle. Molybdenum is micro-porous and retains oil better than plain cast iron to improve upper cylinder lubrication and reduce ring and cylinder wear.

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Joshua

Thanks everyone. I thought it would be OK to get a cast iron set, but those are hard to find in the 0.030" oversize too. In the end I ordered a new set direct from EngineTech. Now I can break 5 more and still be OK.

Wish you hadn't jumped the gun. I should have 1/2 set of .030 molly, and a 1/2 set of .060 mollys. I had a motor one time running three .030 pistons and three .060 pistons. I could have sent you what you needed.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I think Joshie is right. IIRC, when the second ring is also molly they are called "double moly."

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