Engine tap tap tap

[Mister Moose]

I just noticed a tap tap noise at idle. It isn't very loud, but noticeable. It goes away at higher RPM.

Likely a valve?

The engine has 2,000 miles since the rebuild, it seems early for routine valve adjustment... or is it?

[CWPASADENA]

Once a model A engine is assembled and the valve clearances set, the valves should not need to be adjusted again, at least for a very long time.

However, it adjustable lifters were used, occasionally, one may back off and the valve clearance will open up and there will be a noise.

If an adjustable lifter changes its position, the adjusting screw may be loose in the lifter.

Chris W.

[700rpm]

I spent a year and a lot of money trying to find a ticking/tapping noise. Rebuilt the engine. Pulled and disassembled the engine three times. Finally discovered it was the oversized timing gear I had used. Put a new standard one in and it went away. These are hard things to track down.

[Werner]

Originally Posted by 700rpm

... Finally discovered it was the oversized timing gear ...

Ray,
can you please explain that to me in more details? Was the gear in the bore hole too big and was it sitting loosely on the krankshaft stub? Or did the tooth flanks have too much leeway?

[Patrick L.]

Could it be coming from the starter area ? Maybe a problem like Fred's.

[BRENT in 10-uh-C]

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Originally Posted by Mister Moose

I just noticed a tap tap noise at idle. It isn't very loud, but noticeable. It goes away at higher RPM.

Likely a valve?

The engine has 2,000 miles since the rebuild, it seems early for routine valve adjustment... or is it?

Does it really go away, -or is the sound just masked by the higher RPM noise??


If I were in your shoes, if possible I would first contact your engine rebuilder and let them know.

If contacting your rebuilder is not an option, then there is a whole procedure that you may need to go thru. To begin with, a valve that has excessive clearance to make a ticking noise at idle will still have the same clearance at 3,000 RPMs. A weak/missing cam plunger spring can cause a ticking noise. A bent connecting rod can cause a ticking noise, as can a loose piston pin. A loose Valve Push Rod (tappet) in its bore can cause a ticking noise, or a worn Oil Pump Drive Bearing. And this list is just the beginning. Maybe start by canceling each spark plug while idling the engine to see if the sound of the ticking is affected??

[nkaminar]

The book Model A Ford Mechanics Handbook, Vol. I has a Troubleshooting Chart 4.6, Engine Noises on page 4-8. Number 1 is Piston Slap which "Makes a sharp metallic noise." "The noise will will disappear when plug with bad piston is shorted. Noise will also disappear at acceleration."

Number 2 is Valve Noise. The chart does not say so but the valve noise will not go away at engine speeds above idle unless other noises drown out the valve noise.

Other noises are described including Timing Gear Knock and Wrist Pin Slap which may be what you are hearing.

[700rpm]

Originally Posted by Werner

Ray,
can you please explain that to me in more details? Was the gear in the bore hole too big and was it sitting loosely on the krankshaft stub? Or did the tooth flanks have too much leeway?

Werner, I’m not sure I am qualified to explain it, except to say it was .005 oversized and my problem had to do with the lash in the gears. I’m not a professional machinist or mechanic, so I am unclear just how the oversized gears work. I was just advised by a man who knew and I took his advice and changed out the gear. Probably someone here can explain the mechanics of it.

[katy]

Originally Posted by 700rpm

it was the oversized timing gear I had used.

I'm assuming you mean the camshaft gear.

The spec for the clearance between the crankshaft and the camshaft gears is from .003" to .005". An oversize camshaft gear is used to take up the clearance when the crankshaft gear is worn. It is better to replace both gears at once, but easier to just replace the camshaft gear w/an oversize one.

[nkaminar]

One other thing that is mentioned in the book Model A Ford Mechanics Handbook, Vol. I but in another location is that a tight distributor shaft can cause an engine knock. The screw that secures the distributor can cause a knock if it is too tight as it binds the distributor shaft. The list goes on.

I don't know if they are still available but years ago you could buy an engine stethoscope to help pinpoint the source of knocks. It had a steel rod that you placed at different locations on the engine.

[700rpm]

Originally Posted by katy

I'm assuming you mean the camshaft gear.

The spec for the clearance between the crankshaft and the camshaft gears is from .003" to .005". An oversize camshaft gear is used to take up the clearance when the crankshaft gear is worn. It is better to replace both gears at once, but easier to just replace the camshaft gear w/an oversize one.

Yes, it is/was the cam gear, and the crank gear is new. Thanks for the clarification.

[Chuck Sea/Tac]

A weak cam spring will do that. You need a listening device to pin point the area the noise is coming from.

[Mister Moose]

I hadn't thought of the stethoscope idea until after I wrote the post, and I have one in the tool box. So I drove the car for 5 miles to bring it up to temp and opened the hood.

OMG, there sure are a lot of noises in there!

The ticking noise is quiet enough that it isn't really noticeable until you open the hood. Probing around, I noticed it is loudest at the #2 or #3 cylinder. I also noticed I could hear it through the intake manifold, and almost not at all through the exhaust manifold. There is a different squirrel cage noise by the timing gear. As I said, there's noises all over. The block by the distributor is quiet by comparison.

So it seems it's valve related. How loud is loud enough to worry about?

[nkaminar]

I would say to just turn your hearing aids off, like I do, and drive the car. Much less noise that way.