Motor knock

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Topic author
Haroldc30
Posts: 13
Joined: Sun Jan 06, 2019 12:52 pm
First Name: Harold
Last Name: Chambers
Location: Winfield tn.
MTFCA Number: 50278

Motor knock

Post by Haroldc30 » Wed Sep 18, 2019 7:42 pm

I have a 25 t about 35 mph when the motor is running free I have a clapping sound when I give it gas the noises goes away when motor is holding back no noise. I have plastic gauge rods and mains they r within spec. Could it possible be a pistol slap? it has .040 over I put new pistons and rings in it.I have drove it several thousand miles sense then it's no worse or better. that noise is driving me nuts. Thanks in advance Harold.


philip
Posts: 80
Joined: Sun Jan 06, 2019 12:09 pm
First Name: Philip
Last Name: Thompson
Location: Graham nc

Re: Motor knock

Post by philip » Wed Sep 18, 2019 8:39 pm

Mind tends to make that sound when I have the spark too advanced. My chapter
Bought one of the solid-state coil testers we put new capps. And points in the coils and set them.
Now I don't need as much advance. Philip


FrankHarris
Posts: 9
Joined: Wed Jan 09, 2019 9:48 am
First Name: Frank
Last Name: Harris
Location: Long Beach, CA

Re: Motor knock

Post by FrankHarris » Thu Sep 19, 2019 4:19 am

Some times the connecting rods can get twisted and will cause a knock. We had a 1913 that had that issue. Straightened the rods and the knock went away.


John Dow
Posts: 60
Joined: Tue Jan 29, 2019 10:21 am
First Name: John
Last Name: Dow
Location: Leawood, Ks
MTFCA Number: 32344
MTFCI Number: 24459

Re: Motor knock

Post by John Dow » Thu Sep 19, 2019 11:26 am

Harold, Do you by chance have an aluminum high compression head? I do and I had a very similar loud knock as you described. It drove me crazy trying to find the cause. It turned out to be pre-ignition engine knock. I found by running 91 octane and using a little less advance the noise went away.


Topic author
Haroldc30
Posts: 13
Joined: Sun Jan 06, 2019 12:52 pm
First Name: Harold
Last Name: Chambers
Location: Winfield tn.
MTFCA Number: 50278

Re: Motor knock

Post by Haroldc30 » Thu Sep 19, 2019 1:25 pm

Don't have high compression head but have high compression pistons.I will try what you did.Thanks


John Dow
Posts: 60
Joined: Tue Jan 29, 2019 10:21 am
First Name: John
Last Name: Dow
Location: Leawood, Ks
MTFCA Number: 32344
MTFCI Number: 24459

Re: Motor knock

Post by John Dow » Thu Sep 19, 2019 1:52 pm

Harold, I bet you have the same problem! Hopefully, you can solve it as I did. Please follow up and let us know the result.

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