Anyone know if I can install a 318 cast crank in to a 5.2 magnum, is the balance the same? Have a magnum with a bad crank and a machinde 318 LA crank...

Swap away.

Even the same casting in many cases.

R.

Isn't the balance different? I know the Magnum rods are narrower. Casting number isn't the same as part number BTW, just means the initial casting used is the same, machining can be different, or balance, or both.

That's exactly what I would like to know. Can I just install the LA cam and expect the balance to be as good (or as bad) as in any production 318?

don't know, I do know that the piston part numbers are different, but haven't been able to find weights.

The cranks are interchangeable. It has been done thousands of times.
The pin end of the Mag rod is narrower, but just a little. The rods otherwise are very similar.

Several years ago I researched 318 pistons on the hope that the 5.2 pistons were lighter and had a higher compression height. Nope. Piston weights are the same, and compression heights maxed out at 1.755 and then retreated to 1.745 or so. Piston catalogs show the same pistons as applicable for both styles of engines. The only change in piston design was the adoption of thinner rings somewhere in the late '80s.

Let's not get another false rumor started. You know how hard it is to stop disinformation.

R.

Not starting a rumor, just trying to figure out if the claim was a rumor is all. Never heard of it, but then again that doesn't mean anything either.

Problem I ran into is not seeing a piston application that spans the LA and Magnum versions. Also, my understanding is that the narrower magnum rod pin end is accounted for in the magnum pistons and an LA rod needs narrowed to fit the stock magnum piston, which means there is not a piston that spans LA and Magnum versions.

I still don't know the weight of the magnum rod or piston versus the LA versions. For all I know the difference, if any, is small enough not to matter, but then again some like to balance their engine to substantially tighter tolerances than OEM.

The rod is maybe 10 grams lighter on average. You can find that much variation in stock rods in one stock engine easily so for a stock build don't sweat it. On the other hand they do run smoother even balancing a stock engine so... sure would't hurt.

The pistons are the same in 318 and 5.2, they made the rod standard between the 5.2 and 5.9 and the 5.9 needed a thinner rod to make up for the lighter piston and its narrower boss, the 318 just happened to get a slightly lighter rod for no reason.

Thanks for the explanation, makes sense.