Odd knock

ModAfan

ModAfan

Senior Member
My ’28 Tudor developed a knock of some kind recently. There is no knock on startup or until I am into a ride for five or ten minutes. The knock starts slowly, then it gets worse as the engine gets hotter. The knock happens only on acceleration. If I retard the spark (until the lever is about 1/4” from the retard stop) the knock goes completely away. If I advance the lever, the knock get’s really pronounced. There is no knock at idle, either on startup or when the engine is hot after a trip.

Any ideas? Thanks.
 
Can you get this knock while sitting still with the hood open ? I'm wondering if you could try to locate it.
 
ModAfan said:
My ’28 Tudor developed a knock of some kind recently. There is no knock on startup or until I am into a ride for five or ten minutes. The knock starts slowly, then it gets worse as the engine gets hotter. The knock happens only on acceleration. If I retard the spark (until the lever is about 1/4” from the retard stop) the knock goes completely away. If I advance the lever, the knock get’s really pronounced. There is no knock at idle, either on startup or when the engine is hot after a trip.

Any ideas? Thanks.
Click to expand...

My guise loose center main. You should be able to get the knock, by speeding up the engine with the spark lever down. Short out number 2,3 cylinder and see if that changes the sound.
 
What George said. Center main getting loose. Do the tests. Adjust it early and all will be well.
 
Center main was also my first guess.
If you need to take the engine apart it would be wise to add a counterweighted crankshaft, or have weights added to your crankshaft.
 
Many thanks for all of your comments.

Patrick L., The noise seemed to come from everywhere when I idled the engine with the spark advanced.

I am going to try to drop the oil pan this week to see what I can see.
 
ModAfan said:
Many thanks for all of your comments.

Patrick L., The noise seemed to come from everywhere when I idled the engine with the spark advanced.

I am going to try to drop the oil pan this week to see what I can see.
Click to expand...

Just try shorting out 2,3 plugs then you will know for sure.
 
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