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50 A knock

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brian N.

01-07-2002 07:49:47




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when I start the A it has a knock and goes away in
couple minutes oil preasure on med. any ideas thanks!1




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Marcus Haberichter

01-09-2002 17:52:44




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 Re: 50 A knock in reply to brian N., 01-07-2002 07:49:47  
My two cents... I had a similar knock. Turned out one of the main rod bolts had come loose, when it let go it bent to rod cap and rod end. Got lucky. Not much else was wrong, but turned a simple tightening job into about a $150 job by the time I bought a rod cap, then a rod and cap assy, gasket set to R&R the head, etc.



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easydoesit

01-08-2002 15:30:40




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 Re: 50 A knock in reply to brian N., 01-07-2002 07:49:47  
Something not loose in starter is it?



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Pete

01-07-2002 16:01:01




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 Re: 50 A knock in reply to brian N., 01-07-2002 07:49:47  
Brian, like they said, hard to diagnose without more info, and if Clooney can't I certainly won't attempt to. Just tell ya that when the fly wheel loosened up on our 70, that is the way it started, began to do it longer, and more often. The other thing to look at is are you in a winter zone? When it gets cold here in Upstate, NY, we sometimes get a start up knock or 2 if we didn't switch to thinner oil in time for winter. Pete

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Clooney

01-07-2002 14:55:14




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 Re: 50 A knock in reply to brian N., 01-07-2002 07:49:47  
~Brian, we will need a little more info to help you. The more info you furnish the closer the answer will be.
~For instance; once or twice per revolution? clutch in/out or no difference? Choke in/out make a difference? Hot or cold engine/ any difference? Pulling a load or no load change the noise? Pulling one plug wire then the other change the noise? Does a miss accompany the knock? Can you tell where the knock is coming from (use a piece of hose or long screw driver to your ear & probe around)? Can you feel the noise anywhere on the engine trans? Can you hear a similar noise by turning the flywheel with the engine off? Can you feel the knock by holding on to the clutch pulley (clutch dis-engaged & engine running)? Hydraulic pump engaged or not make a difference? How heavy of a knock & is it a sharp or muffled knock? ..... .Do I sound like your doctor yet?
~Anything else that will help us to pin the noise down will help.

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brian N

01-08-2002 13:23:49




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 Re: Re: 50 A knock in reply to Clooney, 01-07-2002 14:55:14  
it only does it when the motor is cold sounds like its around the flywheel, doesnt make difference with clutch in or out, no miss no difference with hydro. pump on or off !



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Clooney

01-08-2002 14:25:14




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 Re: Re: Re: 50 A knock in reply to brian N, 01-08-2002 13:23:49  
~Brian, you might want to check the crankshaft end play .005-.010", make sure the flywheel spacer is centered & isn't hitting the housing it runs in, make sure the flywheel isn't loose, make sure the flywheel isn't hitting the cover, if nothing found there pull the crankcase cover & make sure the L/H crank throw isn't hitting the cam gear or an oil line.
~Try retarding the ignition timing & see if that makes a difference, if so suspect loose flywheel or piston to bore clearance, if no difference suspect crank contact or oil flow problem. ~It probably wouldn't hurt to check the main & rod bearing clearance, but a loose main or rod usually doesn't knock cold & get better with a little run time, they usually get worse hot.
~You could also have a cam related problem like a lose cam gear or worn cam bearings that quiets down after oil pressure puts a load on the cam after starting due to oil pump resistance.
~When you isolate & find the noise let us know what you find.

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Phil

01-07-2002 12:46:29




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 Re: 50 A knock in reply to brian N., 01-07-2002 07:49:47  
Hard to diagnose over the wire - Where does the sound come from? Does the engine use any oil or puff combustion gases from the clutch / oil filler area? Could be piston slap that dissipates as the piston heats up & expands, reducing the skirt clearance in the bore. Had that problem with an '50 "G" that spent most of its life turning a large generator, running nearly non-stop for 10 hrs./day.



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David Sanford

01-07-2002 19:57:14




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 Re: Re: 50 A knock in reply to Phil, 01-07-2002 12:46:29  
sounds like you have loose mains,my jd b has same problem.check by lifting flywheel up.



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