Mid thorttle Knock
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Mid thorttle Knock
I got a knock about mid thorttle at low rpms eveything is fine the motor is smoking so I think the rings are bad but at about mid thorttle I got a knock sounds like around bellhousing or bottom end dont really hear it when I just rev it up but when cuising down the highway about 60 then all of a sudden it will start knocking and doesnt stop untill I slow down, any clues on this?
Post Fiend
Joined: Mar 2004
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From: Union, Washington
This is almost always cause by the vacuum advance holding the timing to far advanced. Pull the hose off the vacuum unit and if it stops doing it, try changing the unit or if it an adjustable one back down the advance. The spring gets weak and allows the unit to over advance the timing.
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With the engine on, pull on spark plug wire on the distributor at one time, rev the engine to half throttle, listen for engine knock, and put spark plug wire back on distributor. Do this with every spark plug wire on the distributor and note which cylinder or spark plug wires removes or eliminates the knock. Post your results.
Post Fiend
Joined: Mar 2004
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From: Union, Washington
Originally Posted by 1975Ford
With the engine on, pull on spark plug wire on the distributor at one time, rev the engine to half throttle, listen for engine knock, and put spark plug wire back on distributor. Do this with every spark plug wire on the distributor and note which cylinder or spark plug wires removes or eliminates the knock. Post your results.
Postmaster
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Originally Posted by Bear 45/70
How is he suppose to do this a 60 mph going down the highway, which is when the engine knocks? This is not a mechanical engine problem, but an ignition problem causing a high speed knock, or in reality a to far advanced ignition timing.
Last edited by 1975Ford; Feb 20, 2006 at 02:39 PM.
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The truck has a 4 speed in it and its 2wd. the motor has race heads dont know the specs for them and the block is bored 60 over no stroker though. It has points and the vacum advance is hooked to the timed port of the carb. everything else is stock that I know of the knock has did it ever since I had but it just a steady knock at a certain rpm if I rev past it it seems to go away and it doesnt seem to matter if it has a load or not. just as long as it is in gear I dont know if it is because a little load from eveything moving or what also the motor shakes pretty good at idle but smoothes out if it revs up a little thought it was a miss but every things seem to be firing. runs good driving lots of power no miss just that knock. Sorry this was alot I know
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Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Originally Posted by 1975Ford
With the engine on, pull on spark plug wire on the distributor at one time, rev the engine to half throttle, listen for engine knock, and put spark plug wire back on distributor. Do this with every spark plug wire on the distributor and note which cylinder or spark plug wires removes or eliminates the knock. Post your results.
Posting Guru
Joined: Jul 2003
Posts: 2,232
Likes: 1
From: Colville, Washington
I was thinking of a flexplate problem(crack, loose bolt), but good point about the steady speed.
Besides I wanted to know!
Could it be the mechanical advance sticking after advancing, then in addition to vacuum advance causing the knock??
Besides I wanted to know!
Could it be the mechanical advance sticking after advancing, then in addition to vacuum advance causing the knock??
