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Discussion Starter · #1 ·
My buddies '90 750 recently developed a nasty metel-metel clanking noise thats about 1/2 that of the RPM...so I am assuming it's somthing to do with the cams, but the sound is comming from (I think) mid-block area. Any thoughts as to what it could be? ...hopefully somthing cheap.

...Also, after we heard it, I said, "when did you last check your oil?" Well, he was about 1qt low.
 

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piston to rod bearing maybe or crankshaft bearing. its hard to tell got a stethoscope.? is it a tap tap or a knock knock.??
knock knocks are expensive.!!
 

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Discussion Starter · #3 ·
Ouch. Def sounds more like a 'knock knock' as it is of a deeper pitch than say, hitting a piece of metel with another.

Could the piston/rod be at 1/2 the speed of crank? Thats what didnt make sense to me. It's def slower than the RPM, hence why I thought 'cam related.'
 

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Does it only happen under load? If so it could be detonation, it sounds a lot like a mechanical noise even though it isnt
Edmonds
 

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Discussion Starter · #6 ·
Nah. I know det...all too well...this happens at all times when the motor is running, and it fairly well pronounced. (aka loud)
 

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you need to isolate the noise and firuge out exactly what cylinder its coming from. and if its on the bottm ot top of the engine
 

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Discussion Starter · #9 ·
I went to his house just now with my stethiscope to try and figure some more out and we came up with this...

start the motor...you get the tapping noise...pull in the clutch, still tapping, drop it into 1st gear, NOISE IS GONE, but then ease out the clutch to roll away and it resumes at a speed relative to the RPM.

???
 

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Discussion Starter · #10 ·
Bump again. (I wouldn't be doing this if my buddy wasn't asking me "what did they say?" all the time. I told him you guys would know)
 

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so now u know the noise is associated w/ the crank/rods/pistons....

almost sounds like some form of 'crank walk'.. which would the crank comin' loose in it's journal.. if not that... a loose rod bearing

either way it doesn't sound minor... and it sounds like splitting the crankcase and preparin' for a freshen up is in the books
 

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something in the transmission? clutch? the transmission keeps spinning with the clutch in until you put it in gear due to oil drag.
 
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