426 engine knock

2 replies to this topic

Posted March 29, 2009 - 11:33 AM


I went riding last week and noticed that the valve train was a little bit loud. Came home and checked the valve clearance and sure enough they were off. Adjusted the clearance, but being short on cash, I decided to sand down some older shims that were one size bigger than what I needed. I only did this for two shims. I checked the shims with a caliper to make sure they were flat. I put everything back together and fired her up. As soon as it started, there was a terrible knocking sound coming from what sounds like the valve train. It ran for about 2 seconds and then I killed it after hearing the knock. I took everything apart again and double checked my work. There was no scoring on the cam bearings or on the lobes, but I noticed the timing was off by one tooth on the intake cam. :thumbsup: so I re adjusted the timing and put everything back together again. Fired it up and it did the same thing. I ran it long enough to try and figure out where the knocking is coming from and it sounded like it was coming from the right side of engine near the header. Any ideas to what the problem may be?

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  • RJacks

Posted March 29, 2009 - 02:20 PM


I've seen some of these motors crack wrist pins. If you've checked the valves and their respective components, and are sure all is good there, it's time to look elsewhere.


Posted March 29, 2009 - 03:43 PM


The frequency of the knock is not fast enough to be piston/crank assembly. I can clearly hear the exhaust pluse and a knock that is about half of frequent which lead me to believe something with the valve train. I'll take off the cams again and see is I missed something.

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