Engine noise only when hot

Ken MA

Ken MA

Junior Member
I'm tracking this tapping sound that starts after the engine runs for about 10 minutes. Checking with stethoscope sound is most noticeable near right side of timing cover.Loud tap on every other crank revolution.I suspect exhaust valve #1 or #2 but I would expect noise to diminish as the valve heats up.
Engine is quiet on cold startup. Compression is 64 psi 1-4. rods and mains were plastigauged last year, leakdown teat did not indicate a stuck valve.
I'd appreciate any suggestions
 
Can you put the timing pin in while running, don't cut your hand off with the fan, and press in to see if the noise changes with pressure on the timing gear.
 
Already ran the motor without fan belt to isolate the noise with no effect, also used dowel in timing pin hole but made no difference
Ken
 
When did this start? Has it been running fine for awhile after the engine work and then just started? I am having a hard time since it does it after warm up. Are the pistons all clean when you look in the plug holes?
 
Long shot is a bad lifter bore,most likely its a sticking valve..next time its tapping short out the cylinder thats you think is tapping,see if you get a big change.A crapshoot fix if its sticking is a pint of marvel mystery oil on the next change..or pull head,valve cover and suspect valve,inspect for galling.
 
Or it could be a noisy one piece distributor, I just rebuilt my dizzy and a tapping noise went away !
I replaced the single shaft with the original type two piece shaft.
 
This winter I replaced a leaky rope seal with modern style. Had to drop the pan and remove timing cover for that job. I also had the valve cover off to check valve clearance. All in spec. Last year I noticed heavy carbon on plug #1, and repaired a leaky intake manifold, changed to a hotter plug. The puzzle is why this noise starts when the motor heats up.I plan to pull valve cover again but would rather not pull the head if possible. Thanks to all for the suggestions.
Ken
 
Ken,
My ‘30 tudor has about the same thing right now . I’m so busy working on every else’s I haven’t gotten to it but had it going this last weekend and listened to it again. The Distributor shaft noise is different knocking as opposed to a tapping. My engine has quite a few miles on it. I’m going to recheck my lifter clearances and hope that is it. Usually it’s the other way as when they warm up it gets better. Pulling the valve cover and doing a check is pretty easy. Doing main check tonight on one so it’s not a big deal. Sometimes noises can be other issues like pistons issues, etc,
I know you said you just checked them a while back but I’d do it again. You may have a clearance out and it’s worth a check. While you are in there you can check your distributor shafts and drive gear for any issues. I would set the valves at .012-.013 across the board.

It’s worth s shot . I’ll keep you posted on mine as I hope to check mine maybe later in the week.
Larry shepard
 
The noise is not pronounced when I use the stethoscope on the distributer , the distributer retaining screw or the oil pump retaining screw, more audible on the timing cover side cover bolts. I have to question what gets hot enough to go from quiet to rapping in ten minutes. I will check the distributer shafts and check valves again
Thanks
Ken
 
First step often is to shoot some MMO directly in carb to see if it has any effect. Model As are famous for sluggish valves and MMO should rule that out.
 
If you have a spare, or can borrow a different distributor try swapping. Then you can be absolutely positive. You already had the fan belt off, so can not be generator or water pump. You done the cam gear check with a dowel rod.


Seems next is to pull the valve cover again, check your clearances. Check valve operation - drain oil so oil does not spray out of valve access, use starter with ignition off to see if you have sticky/perhaps bent valves.


Sometimes things do not make sense until after you find the issue.


Good luck, stay calm, hope it is something minor.
 
Sounds like a valve that was not ground flat when setting the clearance. When the oil heats up you have no oil cushion between lifter and valve. Seems like I remember an issue about a radius between lifter head and block. Look in service manual.
 
I shot some penetrating oil into each open valve via a flexible tube through the plug hole today. Might free up a sticking valve. I will let it soak overnight and start the car tomorrow.
 
Ken
I had a similar noise/problem. After much checking and tear downs I found the valve seat was loose. We had thought maybe it was the spring on the oil pump drive gear. We took the engine out and found the spring in fact was broken. Since we had the engine out I wanted to do a valve job. We removed all the valves and turned the engine over on the engine stand. When the engine was inverted the valve seat bounced across the floor. We replaced the valve seat and the noise went away. I hope this helps. The noises are frustrating to say the least. Good Luck Bill
 
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