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Motor knock
Posted: Wed Sep 18, 2019 7:42 pm
by Haroldc30
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.
Re: Motor knock
Posted: Wed Sep 18, 2019 8:39 pm
by Philip
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
Re: Motor knock
Posted: Thu Sep 19, 2019 4:19 am
by FrankHarris
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.
Re: Motor knock
Posted: Thu Sep 19, 2019 11:26 am
by John Dow
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.
Re: Motor knock
Posted: Thu Sep 19, 2019 1:25 pm
by Haroldc30
Don't have high compression head but have high compression pistons.I will try what you did.Thanks
Re: Motor knock
Posted: Thu Sep 19, 2019 1:52 pm
by John Dow
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.