I can hear the "why?" questions forming on keyboards right off but I'd rather not get sidetracked... this question is for a non-road application with no particular performance targets other than cost and reliability.

The question simply stated is- can I take the crank, rods, and pistons right out of an LA 318 and bolt them into a Magnum 318 engine block? ...keeping the Magnum cam, valvetrain, and heads but carbureted fuel system so no sensors etc.

-LA crank, rods, and pistons into the Magnum block- that's the question.

Assuming they are the same bore size, then in theory yes.

Rings on the two different design pistons may ride at different locations, So unless the bores are pristine I would suggest a hone to make sure you don't have the rings crashing into a ridge left by the Magnum setup.

Deck heights between the LA and Magnum blocks are also different, so double check piston to head and piston to valve clearance.

HUH ?

intakes interchanges ( with the bolts angle diff ), so I think that's a wrong statement

Can't speak for the rods and pistons, but that is a no on the crank. There is two different main sizes in LA motors: 273/318/340 had one, and the 360 had its own. With the Magnum motors the 5.2L and 5.9L shared the same main size as the LA 360.

The 5.2L Magnum uses the same bearing size of the early 318. Where the confusion comes in is the pan.. The new 5.2L mag engine uses the same oil pan and gasket a the 5.9L . But the main bearing are the same.

Go check the main bearings part numbers...the 5.2L does not show up with any of the 5.9L main bearing size.

So the answer to the OP is YES...the Deck height on the Mag blocks is about .020 less then the LA....but the blocks are never at manufacturers specs to begin with.

Balance will be off too.
Both LA 360 and Magnum 5.9 are externally balanced, but LA parts are heavier and require more balance weight. Early and later Mag 5.9 put the transmission side external weights in different spots.

True, but OP is talking about LA 318 guts and Magnum 5.2 block. Both internal balance.

early magnum block are drilled for LA rocker shaft oiling but oil thru the lifter/hollow PR.

early LA roller lifters are not oil thru and have sold PR. in 89-91 LA roller lifters went oil thru with hollow PR.

LA & magnum can use the same OEM roller lifter but need to watch for the non oil thru lifter.

I have swapped a few pre-magnum roller blocks over to roller valve train with magnum roller lifters/spider plate/dog bones & pre-mag roller cam PR.

my LA pre-mag 318 is oiling thru the lifter & hollow PR "AND" thru the LA heads/shafts/rockers LA style.

I found a few stock 89-91 318s oiling this way from factory and does not seem to be too much oil in the VC area.

you can fit a magnum piston to the LA rod by thinning the small end width (LA rod is thicker)

IMHO, lot of work and 2 steps backwards.

better to go with a pre-magnum roller cam 318 block with magnum heads. you can find a lot of the pre-mag roller blocks in trucks with flat tappet cams.

Good info! I gotta get my printer up & running.

My bad, I stand corrected.

good info guys, thanks.

So what I took away from the discussion is that "yes" I can take the lower reciprocating assembly (crank, rods, pistons) out of a Magnum engine and bolt in the same parts from a same displacement LA engine. Power production not being a part of the discussion, and assuming reasonable comparisons for wear, it should run.

I also interpret that to mean I could keep the crank in the Magnum engine and just swap the rod & piston assemblies in.


For the curious, I am playing with applications where high heat tolerance is the primary concern. The LA versions are unreal for their ability to absorb thermal abuse, but the Magnum versions suffer piston meltdown fairly easy. I thought I would try swapping some LA guts in and see what happens.