Mystery flathead tapping noise, suggestions?

[Randy]

My 59AB has a tapping noise that sounds like a bad hydraulic lifter but obviously they're not hydraulic. It started out just doing it every now and then on cold startup, but has progressed to doing it more often than not. It only taps at idle, anything above idle and it goes away. Sitting at idle, the noise comes and goes, doesn't seem to matter if the engine is hot or cold.

It sounds to me like a definite mechanical tap, but I would think any unwanted clearance somewhere would get worse as the rpm's get higher.

It sounds like it's on the RH side, I pulled each plug wire off one at a time and it didn't make any difference. I heard that was a way to check for a bad wrist pin.

Any ideas?

Thanks, Randy

[Dee]

Perhaps a valve is sticking slightly?

[Bruce Compton, Canada]

Randy : Is there a pattern or cycle the " comes and goes" noise , or is it random? I had a similar cycling noise in a "Y" block and it was an out of round wrist pin rotating in the piston. If its a random occuring noise, I'd suspect a sticking valve, or posibly too much end play in the camshaft if the engine was assembled with the wrong set of timing gears ( 8BA type) that thrust the cam to the front of the engine. You may want to run the engine for a few minutes with the belts off as the noise that the generator, fan, belts and pumps are creating will mask the noise you are trying to find, especially at higher RPMs. By doing this you will also eliminate any noise sources from these components. Good luck : Bruce

[Randy]

Originally Posted by Bruce Compton, Canada

Randy : Is there a pattern or cycle the " comes and goes" noise , or is it random? I had a similar cycling noise in a "Y" block and it was an out of round wrist pin rotating in the piston. If its a random occuring noise, I'd suspect a sticking valve, or posibly too much end play in the camshaft if the engine was assembled with the wrong set of timing gears ( 8BA type) that thrust the cam to the front of the engine. You may want to run the engine for a few minutes with the belts off as the noise that the generator, fan, belts and pumps are creating will mask the noise you are trying to find, especially at higher RPMs. By doing this you will also eliminate any noise sources from these components. Good luck : Bruce

It does kind of cycle, but it's not a consistent rhythm. I'm kind of suspecting a sticking valve, since flatheads are known for that. I pulled the plug wires off each cylinder and no change, so don't think it's a wristpin although I guess it still could be. I don't think it's incorrect timing gears as this engine has quite a few miles on it and it only just started recently, but seems to be getting worse. Thanks for the advice, I will run it with the belt off and see if that makes a difference. I think I'm going to add some Marvel Mystery Oil to the crankcase. It only occurs at idle and goes away as soon as it's off idle. Thanks!

[B-O-B]

Also run some/a lot MMO through the engine, heavy smoking is good. Use a long piece of steel rod like a long screwdriver/socket extension or stethoscope & listen for where the noise is loudest BECAREFUL WITH THE ENGINE RUNING fan blades don't for give & spark doesn't care who it bites.

[FlatheadTed]

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The bush in the push Rod can make a noise and often a cam follower rotating gets noisy then quiets down

[Bruce Compton, Canada]

Randy : BOB has a good suggestion with the MMO, but pour it down the carb after the engine has reached operating temp. Make sure you do this OUTSIDE, and pour it in while opening the throttle enough to keep the motor running till all the MMO is in. Let it stall the engine then leave it sit for a few hours before starting it again ( don't forget to turn off the ignition). I also would not eliminate the timing gears as a potential cause as even many parts suppliers still don't know the reason for the tooth pitch angle difference between the early and late gear sets, as they totally interchange. If this is the problem, it would take quite a few miles for the wear on the inside of the timing cover to increase to the point that it would allow any noise. However, now I'm guessing that you will find your noise when you run the engine with the belts off. One last guess though, is the tube over the fuel pump push rod. I've had these come out of the fuel pump stand ( press fit) and fall down so that the umbrella on the push rod hits the bottom of the tube causing a noise that sounds remarkably like a loose valve. Again, Good luck : Bruce.

[Mike51Merc]

Sounds like it could be too much lifter clearance. If you have Johnson style adjustable lifters, sometimes the adjustment bolts loose their grip and turn, leaving too much valve clearance.

[swedishsteel]

A worn piston pin bushing can make a light "knock" that you can't hear at higher rpms. When I rebuilt my '36 LB the machinist was supposed to put new pin bushings in the rods, well, he only did 7. Sounded like a rod bearing starting to go, but it never got any worse. Finally pulled the motor and found the cause. Good luck.

[Dave72dt]

I'd take a good look at the fuel pump.

[34billct]

put a hose to your ear and check the fuel pump!!

[fordscript]

Afew years ago I had a similiar problem....turned out to be the bendix drive on the starter motor. The little spring that holds the bendix back from engaging the ring gear had 'disappeared', and every now and then with the engine running, the bendix drive would move forward and touch the ring gear, and made a very convincing knock/tap.

[Ted52]

I'm having the exact same experience with my my '48 coupe. I haven't had time to really investigate the source of the tap. I'll follow your post to see if you find the source. Thanks for posting.

[George/Maine]

My guess would be a broken piston ring,and maybe some piston slap.

[Kurt in NJ]

Another possibility is a lifter that has a groove, if it stopped rotating for a while and got a groove worn in it, then is now rotating every time it rotates to the groove you will have a noise , it will come and go at random intervals.

Piston slap usually gets quieter as the engine warms up.
Wristpin noises usually get louder as the engine warms up and the oil thins.

There is a KRW tool that would raise up the intake manifold so you could run the engine and look in the valve chamber for noises ---perhaps you could ask around to find one to use.

[Ol' Ron]

I built an engine for a fellow many years ago and when I started it it had a faint tapping sound. I spent weeks looking for it, actually took the engine apart. When I started it again the noise was still there. I used my new stethoscope and found the noise coming from the front timing cover. Removing the cover I inspected the gears and found a small chip out of one of them. Using a file and a magnet I dressed the chip and the noise wen away. Happy customer. See how we learn.

[Don]

My 35 with a 37 engine does the same thing for several years now. Have been thru the valves a couple times.it doesnt seem to cause a problem , so far, might ck the fuel pump this summer..while playing with some distributors this winter i found that if there is to much end play they will interminyally tap a little until i put another washer in front of the rotor to take out slop. Don p

[cdan34]

Randy, I likewise had a tapping noise in a 276 ci flathead a few years ago. When I first installed the engine I didn't hear the noise, than after a few thousand miles I started hearing this tapping. Off with manifold and readjust valves. The noise was still there and was becoming more noticeable. I knew something wasn't right so I located the cylinder, it was #6, head off, couldn't see a problem. So jack the '34 up and pull the pan, rods, pistons, bearings out. Everything mics OK, I look more closely at the #6 piston and there was too much clearance in the top ring. Everytime the piston reversed direction it would click. I don't think it was a machining error but the ring actually wore on the section that went in the groove. The groove in the piston was over, maybe .002. If you were to look at the ring cross section it was worn like a T the part that was in the groove was .075 thick and the very thin side that was between the piston and the cylinder wall was .093. They were 50s, 60s racing pistons never used with Grant rings. After cleaning engine up, in with new Ross pistons with thinner rings, problem solved. I've talked with other people and nobodies heard of this problem. How about anyone here ?

Chuck

[Randy]

Thanks for all the replies and input. I'll follow up on the suggestions and post any results. Randy