1940 LaSalle 50 using 346 pistons?...

[csearider]

I have a LaSalle 50 322 block and want to put oversize pistons 346 pistons in block....years ago read some tips on this but cannot find topic now...any technical advice or experience appreciated

[z3skybolt]

Bore the engine out to 346. They are the same block.

Bob R.

[Bob Schuman]

The only difference in the rotating parts of the 322 and 346 is the pistons and piston pins. New 346 pistons should come with new pins. The 322 pistons are lighter than the 346 because they are smaller, so Cadillac engineering compensated by making the 322 pins heavier than the 346 pins. This was done by boring a smaller hole through the length of the pin, making it heavier to compensate for the lighter piston. That is something to watch out for when making this change.
Also, the LaSalle did not use a harmonic balancer on the front of the crankshaft like Cadillac did. I have had a stock 346, and a LaSalle with its original block enlarged to 346 by a previous owner, and could detect no difference in smoothness, so I would not worry about the harmonic balancer.

[csearider]

Thanks all postees...really appreciate your responses

[LaSalle5019]

When I rebuilt the 322 in my 1939 LaSalle it had previously been bored 0.010" over so I decided to just increase the bore to 3-1/2" (vs the 3-3/8" bore in the LaSalle). I used a 346 rebuild kit and the piston/pin weights were the same as the 322 piston/pin assemblies for the reasons Bob mentioned above. One other benefit going to the bigger bore is that you cannot find the smaller bore 322 head gaskets so everyone uses the 346 gaskets and this keeps your compression ratio the same (you get a very small reduction using 346 gaskets on a 322).

I had my engine fully balanced but noticed a little vibration at certain engine rpms so I decided to add a Cadillac torsional harmonic balancer and did notice an improvement in vibration. All piston engines have crankshaft torsional vibrations and the spring/mass/damper assembly helps to reduce those which is why the more expensive Cadillacs got them.

I do have a spare one - $120 plus shipping. PM me if interested.
Scott

[Chopper1942]

I know it is an extra expense that may not be needed, but since you are doing a complete rebuild, I would do as LaSalle5019 did and install a harmonic balancer and have the engine balanced.  If it is a manual trans, also have the flywheel and pressure plate balanced separately so they can be replaced later if necessary and not effect the actual engine balance.  You will have a very smooth running engine.