Engine rebuild - piston rings and LPG

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liteon
Posts: 21
Joined: Mon Oct 15, 2012 6:07 am
Location: The Netherlands

Engine rebuild - piston rings and LPG

Post by liteon »

Hey all,

I'm currently rebuilding my Pontiac 1963 389 engine.
I'm trying to find some info about piston rings, as i'm going to do the break-in process on LPG.
Some months I thought i've read somewhere that the break in process on LPG requires different rings, but I really have no idea if that's really true.
So does anyone over here know if it really matters which kind of piston rings i'm using?
I can choose about 2 different sets. One has a cast iron top ring, the other a moly facing top ring.

Thanks :)

C3H8
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Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Engine rebuild - piston rings and LPG

Post by C3H8 »

Either of these selections is fine.

The rings that LPG users had to stay away from were sets with chrome rings. These were used in some dodge engines (slant six 2V in the 70's and 80's come to mind). Also some of the heavy duty truck engines like Ford 429's In the F700 and 800's. When a chrome ring was used it was almost impossible to get it to seal properly. These sets even took a long time to seat on gasoline. Eventually they would wear in since gasoline washed the oil off the walls. On LPG this washing action does not occur and these rings take forever to break in. During this period the engine also uses oil in larger amounts then normal. The IMPCO manual back in the 60's to 80's even had a procedure to force these rings to wear. They used a cleaning powder called Bon Ami mixed with oil. The plugs were removed and the solution was sprayed into the cylinders and then the engine was rotated several times manually. This could also be done with the heads removed. It is not a procedure I would suggest as getting all the powder out is difficult. If any of the powder is left it gets into the oil in the oil pan and can damage the bearings. It has been used successfully though if done very carefully.

BigBlockMopar
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Re: Engine rebuild - piston rings and LPG

Post by BigBlockMopar »

The words 'moly' and 'chrome' are often used to describe "Chrome Moly" pistonrings.
Unless you will be breaking in the engine on gasoline I would stick with castiron pistonrings for quick ringseating.
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C3H8
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Re: Engine rebuild - piston rings and LPG

Post by C3H8 »

Thanks for the clarification Bigblock. It's been so long since I used the terminology I forgot that Moly and chrome moly were the same thing. Good catch.

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