I recently had my model A engine rebuilt. The first time it starts each day, there is a knock that sounds like a piston slab. Very noticeable. It only last for a few seconds then goes away. Sound like the front part of the engine. I thought it might be from chocking the carb. too much but decided that is not it. Seems once it starts the first time, it does not appear again that day. The engine runs smooth and quite. Sounds like cars used to when timing was off and had low octane gas. Any ideas what this might be?
Engine Knock
- Thread starter Shoat
- Start date
Patrick L.
Well-known member
Kinda sounds as if you're not getting oil somewhere that you should be getting it. Can you pinpoint the source of the noise ? Like maybe determining whether its a timing gear or a bearing. If it seems like a bearing I'm wondering if there is a pin-hole in one of the dip pans that is allowing the oil to drain out over night.
1931 flamingo
Well-known member
Methinks I'd be asking the re-builder..........................
paul
paul
hotmodelaford
Junior Member
Sometimes it is the timing gear. Other times it can be the cam tension spring and foot. Run it.
George Miller
Well-known member
Better talk to the builder. Sounds like a main is just a little loose. Have it checked before it is to late. Could be some thing else, but the odds say main.
H. L. Chauvin
Well-known member
Hi shoat,
Humble opinion:
Because the noise only happens for a "short" period of time at "only" the beginning of the day, & because of what you hear, there appears to be a possibility of it being a "piston slap" noise, here is a very simple engine test that can be conducted on four (4) separate days:
1. Morning one (1):
A. Remove spark plug no. 1.
B. Look inside to find location of position no one (1) piston.
C. Provide about two (2) tablespoons of engine oil on "top" of piston no. 1.
D. Replace spark plug no. 1.
E. Rotate spark plug connector no. 1, 180 degrees away from spark plug no. 1.
F. Start engine on three (3) cylinders & listen for engine knock "without" spark plug no. one (1) firing.
G. "If" no knock is heard, "piston slap" was formerly occurring at piston no. one (1).
H. "If" knock is heard, re-install spark plug connector no. one (1) & proceed to Morning Two (2) & piston no. two (2).
2. Morning Two (2):
A. Repeat same test, A. through G. as that for Morning One (1), except remove all phrases mentioning "spark plug no. one (1)" & "piston no. one (1)" & substitute in their places "spark plug no. two (2)" & "piston no. two (2)".
B. "If" knock is still heard, re-install spark plug no. 2 & proceed to Morning Three (3), piston no. three (3); & likewise later to Morning Four (4), piston no. four (4).
3. "If' after Morning four (4), after all four(4) pistons were checked whereby the noise did not disappear or "greatly" subside, let us know "if' there were no "piston slap" noises.
4. With similar symptoms not long ago, i.e., knocking on cold starts, & after conducting the above "piston slap" tests, it was found "not" to be a "piston slap".
5. Changed a fiber/metal center timing gear to a new Dan McEachern's solid aluminum timing gear & experienced no more knocking on cold starts.
Many Model A owners would rather perform test differently, or do nothing; & some may just want to live with the knock rather than take time to perform any test -- each to his own.
Hope this helps.
Humble opinion:
Because the noise only happens for a "short" period of time at "only" the beginning of the day, & because of what you hear, there appears to be a possibility of it being a "piston slap" noise, here is a very simple engine test that can be conducted on four (4) separate days:
1. Morning one (1):
A. Remove spark plug no. 1.
B. Look inside to find location of position no one (1) piston.
C. Provide about two (2) tablespoons of engine oil on "top" of piston no. 1.
D. Replace spark plug no. 1.
E. Rotate spark plug connector no. 1, 180 degrees away from spark plug no. 1.
F. Start engine on three (3) cylinders & listen for engine knock "without" spark plug no. one (1) firing.
G. "If" no knock is heard, "piston slap" was formerly occurring at piston no. one (1).
H. "If" knock is heard, re-install spark plug connector no. one (1) & proceed to Morning Two (2) & piston no. two (2).
2. Morning Two (2):
A. Repeat same test, A. through G. as that for Morning One (1), except remove all phrases mentioning "spark plug no. one (1)" & "piston no. one (1)" & substitute in their places "spark plug no. two (2)" & "piston no. two (2)".
B. "If" knock is still heard, re-install spark plug no. 2 & proceed to Morning Three (3), piston no. three (3); & likewise later to Morning Four (4), piston no. four (4).
3. "If' after Morning four (4), after all four(4) pistons were checked whereby the noise did not disappear or "greatly" subside, let us know "if' there were no "piston slap" noises.
4. With similar symptoms not long ago, i.e., knocking on cold starts, & after conducting the above "piston slap" tests, it was found "not" to be a "piston slap".
5. Changed a fiber/metal center timing gear to a new Dan McEachern's solid aluminum timing gear & experienced no more knocking on cold starts.
Many Model A owners would rather perform test differently, or do nothing; & some may just want to live with the knock rather than take time to perform any test -- each to his own.
Hope this helps.
Last edited:
Napa Skip
Senior Member
[This is a re-post of a reply I made a couple of days ago to another - but related - thread.]
An 'easy' way to check if the noise is being caused by a lose timing gear is to reverse the timing pin and apply hand pressure (push the timing pin against the timing gear) while the engine idles. Noise caused by a loose timing gear should diminish or cease while the timing pin is being pushed in and return when not. This is the way I isolated a "knocking sound" to a loose 2-piece aluminum-hub-and-fiber timing gear.
As an aside, stay away from two-piece timing gears.
And stay away from the fan blades while diagnosing a loose timing gear with this method.
An 'easy' way to check if the noise is being caused by a lose timing gear is to reverse the timing pin and apply hand pressure (push the timing pin against the timing gear) while the engine idles. Noise caused by a loose timing gear should diminish or cease while the timing pin is being pushed in and return when not. This is the way I isolated a "knocking sound" to a loose 2-piece aluminum-hub-and-fiber timing gear.
As an aside, stay away from two-piece timing gears.
And stay away from the fan blades while diagnosing a loose timing gear with this method.