322 flathead has a slight knocking.

[jos1270]

Hello there I have a 1938 La Salle. I have a question about the engine. I just started hearing a slight knocking in it. Its not loud. And it may be that it had been there and i just noticed it, and just never payed attention to it. I just did the oil change in the car and in the process I added Marvel Mystery Oil. I wouldnt think that that would make it sound like that. But Im not sure. So my questions are. Does anyone have an engine like this and does it sound similar to that and is it normal? If not normal what could be the problem and how can i fix it? Please someone help me out so i can get it fixed and not have a bigger problem later on with my engine. I don't want to have to fix something worse later on. Also does anyone know who messes with flathead engines here in North Carolina?


                            J. Aranda

[Alan Harris CLC#1513]

Without hearing it I don't know how anybody can say one way or the other. If the car never made this noise before and just now started, you probably have a problem.

How is your oil pressure?

[Tom Beaver]

Where is the knocking loudest, up top or down by the pan and crankshaft?  Does the knocking vary with engine speed or not?  Is the knocking intermittent or continuous?  Can you hear it with the engine under load or when decelerating?   We would need a fuller description of the problem to make any useful suggestions.

Tom Beaver

[dadscad]

Marvel Mystery Oil will thin the oil from its normal viscosity. How much MMO did you add to the crankcase? I would do another oil change, with filter if there is one, and see if that stops your engine noise. The oil may be too thin with the MMO added.

Name brand quality motor oils do not need an additive. They are formulated to supply all the protection a mechanically sound engine needs, without the additive. Adding an oil supplement to the crankcase, may actually cause adverse reactions with the additive package your oil manufacture has in their recipe, causing more harm than good. MMO in the fuel is OK, but it can/will thin out the motor oil and possibly reduce the motor oil film strength, causing metal to metal contact. Not to mention the possible chemical reaction to your oil manufacturers recipe.

Good luck, HTH. David

[pauldridge]

If changing the oil doesn't solve the problem, then you may need to inspect the rod bearings.  It's a pretty quick and simple job on these cars, the oil pan slips right off from underneath (just make sure the crank throws for the 2 forward pistons are at the top of their stroke, otherwise the pan won't clear the crank).

It's pretty easy to remove each rod bearing cap in turn and inspect the journals, to see if you have any serious damage (and, as well, use Plastigage to check your clearances)

Good luck

[jos1270]

The knocking is louder towards the back (closer to the firewall). I cant tell if its louder up top or at the bottom. And when i accelerate the knocking gets faster not louder. And is continuous. It is the first time i have used it on any of my cars. I started using it cus it smoked a little bit, and i read on a forum that MMO would help it not smoke as much. I used 20% of MMO on the whole oil change. Like it says on the instructions. And used pennzoil straight 30w engine oil. Is that a good oil to use in it? cus it hard to find it and more expensive. can i use a different weigh of oil? Or what oil do you recommend for an engine that old? Im going to try the oil change ones again and see if that helps it or goes away (hopping it does). I can't really think of anything else that might make it knock. except that it overheats in the hot weather. But i wouldn't think that has to do with the knocking. And witch by the way i'm trying to fix the overheating. Theres many things wrong with this engine. I might have to rebuild it and so that i don't have to worry to much about it. What do you all think?


                          J. Aranda

[buicksplus]

Sounds like you're dealing with an older engine with plenty of wear.  If you want to delay rebuild, try draining the oil and refilling with a decent brand of 20W-50.  This may increase the viscosity enough to cut down on the knocking.

I'm not a fan of additives to reduce oil consumption or smoking -- like MMO or bon-ami down the carburetor.  I have heard anecdotes about great improvements from this sort of stuff but I am a bit skeptical.  I think just keeping decent clean oil topped up in the engine is the best way to keep an old engine alive -- even if it continues to smoke a bit.  I have heard that putting detergent oil in an engine that has lived for years on non-detergent can be a problem.  The detergent can stir up sleeping sludge.  It is not hard to remove the oil pan on these cars.   This would let you clean out the sludge in the bottom of the pan if you are concerned about that.

Rebuilding a flathead is not particularly difficult and parts are readily available for them.  You just need to find a shop that enjoys working on older engines.  Keep asking around, I am sure there are shops in NC with that sort of interest.  Hardest part may be removing the engine.  The front end clip needs to come off to get the engine out.  It can be quite difficult if the attachment bolts to the cowl are rusted (they usually are).

Good luck! 

[jos1270]

Thank you very much for you time and information. So a 20w-50 would be fine for an engine that old? is there none detergent oils 20w-50?

[buicksplus]

I used 20W-50 in mine for years without any problems.  Don't think you can get 20W-50 as non-detergent.    I had cleaned out my oil pan of sludge (there was some there) before using the oil.  Suggest you do the same if you are concerned about it.

I think you can buy straight 50 weight non-detergent oil.  That might be another option if you don't want to drop the pan. The only problem with that may be for winter driving.  Probably not a problem in your area.

Chances are the heavier oil won't make a lot of difference but it may quiet it down enough to let you be comfortable driving the car for a few more miles before rebuilding.

Good luck!