Engine Noise When Cold

[YukonJack]

My 47 P15 engine has a noise when cold, more of a tapping than a knock. When the engine warms up the noise is gone. I pulled the plug wires one at a time with engine running and cold thinking if it were a rod the noise would go away when the correct wire was pulled. No difference, noise still there regardless of which cylinder I pulled. I read a previous thread about piston slap when cold but it goes away when engine warms up. If it were piston slap wouldn't the noise go away when the plug wire was removed (like testing for a bad rod) I'm running an electric fuel pump with the old pump still on the engine. I recall reading that the stock fuel pumps are loud when they are run dry. Also, my gasket between the intake & exhaust manifolds is bad (the square one). Engine runs good when warm. Any ideas on what could be causing my noise? Thanks in advance.

[Norm's Coupe]

The fuel pump will make that kind of noise. If you aren't using it, I'd remove it altogether and put a plate with a gasket over the hole in the block. You can make a plate using a piece of steel.

Probably should replace the manifold gasket too.

[james curl]

Wrist pin bushings in the upper rod make a loud noise much like a loose lifter when they get loose. They do not always get quiter when the engine warms up.

[blueskies]

My engine was making a similar noise...

It started at about 7,000 miles after the rebuild, as a faint tick noise when cold. It would go away when warmed up, but over time and miles it took longer to go away, and got louder when it was there. Eventually it got to the point that it would not go away when warmed up, but was continuous.

Early on, I tried pulling plug wires to see if the sound would stop, to isolate the noise to one cylinder, and it seemed to make no difference. I decided to drive it till something broke, because I couldn't figure it out.

I went through every possible external part that could make the noise, listened to the engine all over with a mechanic's stethascope. Still couldn't find the source of the noise. After the noise got much worse, I finally pulled the pan to inspect every bearing, piston, and moving part that could be seen from the bottom end. Still couldn't see anything visibly wrong.

Put it all back together, and drove it some more. I did the plug wire test again at about 10,000 miles, and sure as hell, the sound went away when I removed the #4 wire.

Once I knew which hole the sound was coming from, I knew it was either the piston, or wrist pin because I had already inspected all the bearings.

I removed the head, pan, and dropped the #4 piston and found that the wrist pin bushing had come loose in the rod, had split, and was rotating in the rod end.

You can read the fix thread by clicking here... Pics of the bushing, etc.

After I got the engine back together and drove it around for a few days to make sure it was all good, I drove the car 3,300 miles to Tulsa and back for a test run. Purred like a lion all the way. I was worried that the other five wrist pin bushings may develop the same problem, but they seem to be fine at this point.

Hope your noise is an easy fix, I know how frustrating and time consuming this can be...

Pete

[DLK]

I hope this thread can help solve the problem I have had with my 53 DeSoto Powermaster 251 CI six for the entire four years I have owned it. The prior owner's son rebuilt the engine and it runs smoothly and doesn't burn a drop of oil. However ever since I bought it there is a tapping noise (knock) especially pronounced at idle. Hot or cold it doesn't matter. It is definitely louder than when I bought the car.

My problem is I haven't torn down an engine since my '31 Model A in 1968 so I will probably have to go the a shop for this. Since it will involve tearing down the engine I can only imagine the cost even to fix one wrist pin. At the same time I realize driving the car at 55 mph with the knock is inviting bigger trouble.

[Young Ed]

If you can do what Pete did and diagnose it to a specific cylinder its not that difficult to get a piston/rod out. Have to drop the pan and pull the head. I know a good engine shop in the Blaine area but I'm not sure he wants whole cars in there.

[blueskies]

I hope this thread can help solve the problem I have had with my 53 DeSoto Powermaster 251 CI six for the entire four years I have owned it. The prior owner's son rebuilt the engine and it runs smoothly and doesn't burn a drop of oil. However ever since I bought it there is a tapping noise (knock) especially pronounced at idle. Hot or cold it doesn't matter. It is definitely louder than when I bought the car.

My problem is I haven't torn down an engine since my '31 Model A in 1968 so I will probably have to go the a shop for this. Since it will involve tearing down the engine I can only imagine the cost even to fix one wrist pin. At the same time I realize driving the car at 55 mph with the knock is inviting bigger trouble.

I think you should have a look inside the pan. You can pull the oil pan with the engine in the car, up on a good set of jack stands (saftey first!). Once you have the pan off, you can pull bearing caps, one at a time, and check then for wear, and plastiguage them at the same time. All you need is a socket set, a torque wrench, and a new pan gasket. Your old gasket is probably leaking anyway . I would also suggest getting a mechanic's stethoscope to narrow down the noise. It's amazing what you can hear inside the engine with one of these things.

I did the wrist pin repair on my 230 with the engine in the car. Once I knew what it was, I pulled the head and pan, and popped out the offending piston. Didn't take but a leisurely weekend's time to get it all done.

Problem with taking it to a shop, aside from the $$$, is you won't really know what is in there, or if they did the right thing to fix it.

There is Zen in the art of flathead six maintenance, take the leap...

Pete

[Normspeed]

I would use a mechanic's stethoscope, or a long wood dowel to zero in on the location. The mechanical fuel pumps, even new out of the box, can make quite a knocking noise, especially if the pivot area for the activating arm is out of spec. This can get louder as the pivot pin hole wears. I had a brand new Airtex pump that knocked. Sounded like a rod knocking.

[bob westphal]

A small exhaust leak can also sound like a knock and go away when warmed up because of expansion. Could be that leaky gasket between the intake/ exhaust.

[DLK]

Thanks for the suggestions. I do have a new pan gasket so after the stethescope test I will drop the pan and start from the bottom. I did buy a set of heavy duty jack stands last year that came in handy for replacing my leaf springs.