Engine Knock

At 35,000 miles, my 1948 New Yorker is experiencing some knocking in the engine and slow to accelerate from a dead stop. I had a tune up less than 1,000 miles ago. Could this be from not using a lead additive or using low octane gas? Or could it be a more serious problem? I'm not a gearhead so any sound advice is very appreciated.

How is your oil pressure? What kind of knock?

The 1948 New Yorker has a low compression flathead engine. It should run perfectly on the cheapest regular, no additive necessary.

There is something wrong that needs to be checked out. If I was closer I would have a look.

Who did the tuneup?

Oil pressure usually runs at 60 but the guages are not trustworthy. It's kind of a rattling knock while the car is idling. The tune-up was done by a local mechanic.

I have no idea what the trouble is. That motor should be dead silent at idle, quieter than most new cars.

Have you asked your mechanic? Is he an old bald head or gray haired guy who knows the old models? A lot of the younger guys have no clue about cars that old. Sad but true. They don't even know their way around a carburetor or points ignition. This is understandable since such things have been obsolete now for 25 years so it isn't really their fault. But you really need to find someone who is sympathetic to your car.

If you have 60 PSI oil pressure it's not your bearings, on the other hand if the gauge is on the fritz that leaves us back where we started.

A kind of rattling knock when the engine is idling. Could be any one of a million things none of them good. No other symptoms at all?

All I can suggest is to have it looked at by someone who knows what he is doing. But you probably already figured that out.

That oil pressure is actually on the high side. I hope some sap head did not talk you into using good ol' non detergent, single weight, heavy oil.

I would check the timing.

All good suggestions... thanks.

Reading this again, are we talking about only when you are driving or is the knocking there all the time the engine is running?

If its there all the time then at 35000 there should be no knocking at all - period

We might be able to identify where its coming from with a few simple checks:

1. with engine at idle remove each spark plug wire one at a time, does the noise vary/disappear on a particular cylinder? if so we have at least pinpointed the area (you might want a decent pair of gloves or well insulated pliers to avoid a hefty shock during this excecise).

2. if the above hasnt revealed anything then get yourself a piece of wooden dowel or plastic conduit and position it against the forward part of your ear, now place the other end against various parts of the engine, like a stethoscope, and see if you can isolate where the noise is coming from. Careful here that you dont get the probe tangled up in the drive belts or fan and do yourself a nasty injury.

Let us know your findings and we take from there.

I have a '49 1st series New Yorker, which is the same car as yours.

I have a problem with an exhaust leak around the exhaust manifold somewhere. I have yet to figure out just where it is coming from but have not yet removed the mainfold. Now the noise is really more of a ticking noise; it's not a knocking noise. But if your description of the noise is not quite correct (i.e.-it's really more of a ticking) then your car may have the same problem mine does. Mine is noticeable at idle and going down the road up to about 40 mph. Above that, all the other noise drowns it out.

Keep us posted. By the way, where are you?

Jim

Ft. Worth, TX

I have a '49 1st series New Yorker, which is the same car as yours.

I have a problem with an exhaust leak around the exhaust manifold somewhere. I have yet to figure out just where it is coming from but have not yet removed the mainfold. Now the noise is really more of a ticking noise; it's not a knocking noise. But if your description of the noise is not quite correct (i.e.-it's really more of a ticking) then your car may have the same problem mine does. Mine is noticeable at idle and going down the road up to about 40 mph. Above that, all the other noise drowns it out.

Keep us posted. By the way, where are you?

Jim

Ft. Worth, TX

Ticking straight 8 Chrysler noises from the exhaust manifold area usually means a cracked exhaust manifold at the center section down low and at the back of the manifold in a thinner area of the manifold-and is very hard to see.

Bob

I have a "37 DeSoto 6 with the same problem. It is more of a deep rattle knock and only at slow idle....it seems to disappear once the engine rpm increase's. The knock seemed to be coming from right under the oil pump area, so replaced the oil pump however, the knock is still there.

The car has great oil pressure, uses no oil, and runs very strong. No one has come up with a cure to date.

If it's a tap tap tap or knock knock knock sound in time with the engine it could be a wrist pin. They sometimes make a noise at idle that disappears when you rev up. If you have good oil pressure that pretty much eliminates a bad rod or main bearing but of course, we can't even go that far until he puts a good oil gauge on there and finds out if he has oil pressure.

While you are checking things, check the belt. That would be more like a chirpping sound.

Any time you are trying to find a noise try to determine if it is internal or external. As others have said internal noises can sometimes be heard with a dowel rod , stethoscope, or long screwdriver. However, if the noise is external like an exhaust leak or rattling heat riser for example, get a 3 ft length of garden hose or heater hose. Put one end to your best ear and search with the other end. It works wonderful.

I went crazy trying to diagnose the ticking in my old Dodge. Good oil pressure, low compression (80-90 lbs.) I decided to go for the rebuild. The ticking was a piece of broken piston ring that broke its way through the top piston edge to the combustion chamber! The tired old motor had broken top compression rings on all six pistons, and #3 was the first to go.

Good luck with your search.