A novice question about the 346 cu. in engine in my 1940 LaSalle

[z3skybolt]

I learned recently that the engine in my 1940 LaSalle is actually a 346 from a 1940 Cadillac. No concern there.  I have a "knock" in the number 2 cyl. Goes "mostly" away if I pull the spark plug. One "old engine" guy says it is a lifer the other guy says it is a wrist pin.  Both say it is not a rod. I have an engine rebuidler guy with a machine shop, "some" old engine experience and 40 years in the rebuilding business who will pull the pan and head early winter to find the problem.  Here is the question. Is it possible/likely that I could have a lose rod or worn bearing that is making the sound?  My oil pressure is 35 lbs when hot or cold and nearly 35lbs indicated even at idle.  Assuming these pressures are accurate....does that eliminate the rod or bearing as a culprit?  Of course there are no absolutes....but just question the possibility.  I've been told that continuing to drive it gently until the tear down this fall is O.K. What do you knowledgeable  folks think?  The engine has 5,300 miles on it since a partial overhaul of "clean up" bearings,rings,cam and one piston.  Otherwise runs great. I have driven it about 1,200 miles with no change in the sound.  It can be heard even when driving slowly on a quiet road, especially when accelerating.



Thank you,

bob

[Tom Beaver]

Bob,

I've had the same issue with an engine that was also partially rebuilt.  The parts that seem to be forgotten in a partial rebuild seems to be the wrist pins.  Mine was the number 7 cylinder.  Your oil pressure probably precludes the bearings being bad and the fact that the sound goes away when the spark is shorted out is a pretty sure sign of a bad wrist pin.

As for continuing to drive it, I don't know, but sooner or later the connecting rod will probably be damaged.  It's not a to bad job dropping the pan, removing the head and popping out the offending rod and piston.  You will know for sure right away.

Tom Beaver

[ebuliavac]

Tom,

Does your car smoke at all?  My 1940 6227C does under hard acceleration, and probably needs a rebuild.  I too have a sound like that; it goes away after the car warms up.  I can't hear it when I am in the car.  If I drive the car too long, the lifters start getting noisy. 

My question regarding smoke is to get at maybe a loose piston/rings.  Keep us posted.

Ed Buliavac

[Tom Beaver]

Ed,

The engine in question had just been bored with new pistons, rings and bearings they just didn't check the wrist pins.  So the engine didn't smoke, it just knocked.  A knock that goes away after the engine warms up would not be from a wrist pin but will have something to do with thermal expansion of parts like the pistons in the bore or other parts where the clearance changes.  Smoking under hard acceleration could be worn out rings.  Noisy lifters after the engine gets warm could be caused by oil that is to thin.  What viscosity oil are you running?

Tom Beaver

[MikeGerman]

Hey guys, sorry I can not help but have a question about the engine, too. You mentioned the correct piston order. Which one is it? Where do I start counting? (Also got a 40 LaSalle)
Thanks for the help,
Mike

[Bobby B]

Hey guys, sorry I can not help but have a question about the engine, too. You mentioned the correct piston order. Which one is it? Where do I start counting? (Also got a 40 LaSalle)
Thanks for the help,
Mike

Driver's side front to back- 1,3,5,7.
Passenger side front to back- 2,4,6,8.
Whether you're going to work on the car or not, you should really get a shop manual for reference.
                                                   Bobby

[MikeGerman]

THANK YOU VERY MUCH!
Yes, I am looking around for one, but they`re kinda hard to find in Germany lol :/

[Steve Passmore]

THANK YOU VERY MUCH!
Yes, I am looking around for one, but they`re kinda hard to find in Germany lol :/

You can buy them on USA eBay and have them shipped to you. Its where most of my library here in the UK came from.

[ebuliavac]

Tom,

I have 20W in there now.  Almost undoubtedly needs a rebuild.  Has been sitting since 1984 or '86 but it fires up immediately and drives around OK.

Ed

[Tom Beaver]

Ed,

Try putting some 20W 50 in the engine and see what that does to the lifter noise and smoke.

Tom Beaver