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Just bought an 86 VN750. It ran, but barely and only at high RPM. I got it home and cleaned the carbs, and now except for a little backfiring due to a broken exhaust stud, it runs fantastic. BUT! And isnt there always a BUT... There is a hellatious knock in the top of the front cylinder that I didnt hear b4 I bought it due to how loud the pipes were just to keep it running. Also, I happened to be on the right side when I heard it run and the knock is predominately heard on the left. The knock seems like a solid enuff knock to be a rod bearing, but I'm not sure. It comes and goes like flipping a switch on and off at random. But only when the bike's cold. After it warms up good, no knock whatsoever. Matter of fact, everybody that hears me roll up hot thinks I'm nuts for saying its knockin. Then they hear it cold, and they're like HOLY $#!^, is that even the same engine? And I've put almost a couple hundred miles on it so far and it's not getting better or worse.

I know I'm asking for troubleshooting from afar, but has anyone seen or heard of this in these engines? Maybe a pattern failure? How about a wild guess??
 

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I think that you can pretty much rule out rod knock.
By your symptoms, two things come to mind as possibilities:

1. Collapsed/sticky lifter (HLA)
2. Piston slap.

These 2 seem to fit your description a little better.

How many miles on the bike?

Post back.
 

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Are we related

I have a 93' VN750 with the exact same, dead on, johnny on the spot, nailed it problem. Someone posted a reply to me saying it was not normal. Piston slapping sounds nice:D. And yes when she warms up, you'd never know it was ever doing it in the first place.
Thank you
Ray
[email protected]
 
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