841 Backfire at high rpm

pops1948 · Feb 5, 2019

Measuring distance valves move up and down on a 841 to determine camshaft wear. Does anyone know what that would be? I am trying to determine if I have a bad camshaft. Problem I am having is back fire through exhaust at high rpm. Idles and runs sweet up to about 1800 rpms. Acts like crossfire when you have a bad distributor cap. Distributor completely rebuilt with all new parts and tried several caps and rotors points and condensers. Replaced valve springs today but did not have time to crank and check. Any help greatly appreciated. Thanks, Larry :?: :?:

Sean in PA · Feb 6, 2019

If it only does it at high rpm's I would suspect the springs being weak so that the valves aren't closing when they should. If the cam lobes were worn down then the valves wouldn't be opening as far as they should and I don't think that would cause backfiring.

Bob · Feb 6, 2019

Check the "lift" of all the intake valves, and note each measurement, and do the same with the exhaust, there souldn't be much variance within each.

WayneIA · Feb 6, 2019

Perhaps the advance in the distributor is at fault. You have said it was rebuilt. Is it all correct?? I happen to know mistakes can be made.

pops1948 · May 20, 2019

The advance and other parts were new. Found my problem. Checked shaft bearing and did not check it very good first time. Dial indicator show's over .015 play. This throws dwell way off which affects timing. New distributor corrected problem. Also replaced valve springs and seals but they were ok. Thanks and sorry it took so long to reply. No hurry on my end. Larry.
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841 Backfire at high rpm

pops1948

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Sean in PA

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Bob

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WayneIA

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pops1948

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