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Hi all... I picked up a non-running 94 LWB dirt cheap a while back, and couldn't get it started. Turned out to be no compression on several cylinders.. I pulled one head, and its obvious I need some new pistons, at least one of them is chipped. I've yet to pull the other head.

Looking around, I don't see much in the way of 4.2 pistons for sale. Would 3.9 pistons work? Because they are taller, would they be too tall, or make my compression insanely high?
 

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Hi all... I picked up a non-running 94 LWB dirt cheap a while back, and couldn't get it started. Turned out to be no compression on several cylinders.. I pulled one head, and its obvious I need some new pistons, at least one of them is chipped. I've yet to pull the other head.

Looking around, I don't see much in the way of 4.2 pistons for sale. Would 3.9 pistons work? Because they are taller, would they be too tall, or make my compression insanely high?
Firstly, if you pistons are damaged your bores are also likely to be damaged. If so, your engine is toast unless you want to put all new liners in it. This is because you cannot rebore these motors and they do not make oversize pistons for them.

I believe that the pistons between the 3.9 and 4.2 are similar. The 4.2 pistons are likely to have a larger dome in them to keep the compression ratio under control. I would think that you would be OK if you got 3.9 low compression pistons.
 

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Firstly, if you pistons are damaged your bores are also likely to be damaged.
Yeah, I get that. A little background about the truck. I bought it after it sat in a (desert) field for 4 years. Engine would only turn about 10 degrees. Eventually freed the engine. For all I know, I damaged the pistons it when i freed it.

I plan on pulling the engine (have to get a hoist) sometime in the next few months, then I'll do more investigation.
 
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