knocking.... at random times

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Rolling_Thunder

Rolling_Thunder

Rolling Thunder
Joined
Jun 27, 2005
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Location
Los Angeles, CA
started up my freshly rebuilt engine and it will run but then knock once and then miss... then run fine and knock again at random times.... checked the top end and it is fine. spun thwe crank by hand and listened for a loose rod and heard nothing... pulled the plugs and spun it with the starter and heard nothing.... any ideas ?
 
A "knocking" sound and a mis sounds more like pre-ignition. What compression, cam, heads, and fuel does this engine have?
 
it is a 9.0:1 compression engine. Purple shaft 284/284* camshaft with ported 906 heads... running on 91 octane ---- i am almost positive it is not pre-ignition..... maybe a valve hanging open
 
I think I had the same sort of problem with my engine after I installed the new manifold. I left off a cap for one of the vacuum inlets or something on the manifold. As soon as I capped it, it idled much smoother and the knocking disappeared. I'm just throwing in my two cents, but odds are I have no idea what I'm talking about.
 
I would think it would not be preignition either, with those specs, but, if it's really a knocking noise, it will do it constantly, not intermittent. You can use a mechanic's stethoscope to try and isolate it, or you can use a long screwdriver, or socket extension (a long, solid steel bar) to listen to various areas and try to eliminate things as possibilities. Try it, you look silly, but it works..Mechanical noises repeat consistently. Spark/preignition noises will be more random, and can be heard clearly when the listening device is placed on the head casting, above the header flanges.
 
well figure this one out guys---- i put in a new set of lifters then i ran the engine again yesterday and it did the same thing... i did a compression check

1= 150psi
2= 150psi
3= 145psi
4= 150psi
5= 150psi
6= 145psi
7= 150psi
8= 0psi

dead cylinder - we turned the motor over and we heard the knock and then hole#8 had 150psi.... we started the engine and it ran great then after about 45 seconds it knocked and then started to sputter and die... it seems to be while running, it is dropping the #8 hole.... it seems to be a valve is sticking and knocking the piston top... thus also making no compression and killing the motor.
 
ouch..glad you found it tho..I thought it was running decent..I overlooked that. Make sure the cam is ok on that sticky valve..
 
It sounds like your hanging a valve alright, how does this happen doesn't anyone ever HONE guides anymore?

This is the 3rd time this week......
 
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