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Method to determine where a knock is coming from?


Browning

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91 s10 just hit 195,050 miles. I have had some small problems with it in the past and overall it's a good running truck, until now.

 

Went to town a little bit ago and on my way back I noticed a knocking sound coming from under the hood. Blocked the tires, started it up and attempted to find where it was coming from but only having one good hear it's hard for me to find the source of the noise. I hjave heard main bearing knock before and this isn't as loud and doesn't sound like it has the same tone. It does seem to get a little louder when the rpm's are increased but what I found odd is when I was checking for it, it went completely away a few times.

 

What is a good method to finding out exactly where the knock is coming from? Really can't afford for this truck to be down nor can I afford to put another engine in it at the moment. I can't tell if it's in the bottom end or top. You can't hear it driving down the road unless you're in first or second. If it was a main bearing wouldn't it be very loud? Same with cam bearings?

 

edit-just had the neighbor who is a diesel mechanic listen to it and he put his hands on the valve covers and said he can feel it in the passenger side and told me he thinks it's a collapsed lifter. Now, if this were the case would I be able to tell for sure by pulling that side valve cover off and checking for a really loose rocker arm?

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Pull spark plug wires one at a time. The knock will quiet down or disappear at the affected cylinder. This works sometimes, don't rely on it! I do not think it will work for finding main bearing noise though....

 

Just saw your edit: Funny you say that, because a friend I work with has a similar year s-10 with the 4-cyl, and he has a collapsed lifter. It comes and goes. It is hard to tell just by looking at your valve clearance for a collapsed lifter, because even though they are "collapsed" they still may have enough pressure to give the illusion that the clearance is good. Just gotta get your stethoscope out and trust your instincts at that point :)

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p.s. its not a knock, its morse code for replace the pos.
lol it has needed to be replaced for a while now, just not in the budget.

 

Does seafoam in the crankcase still smoke like a son of a bitch? I'm hoping it is something stupid like a collapsed lifter of bent pushrod but wouldn't I also head the rocker arms chattering?

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It does not smoke when you put it in the crankcase as it is not actually being burnt (unless of you are burning oil then it may smoke a little bit more then usual however it will be diluted in 5 quarts of a smoke generating liquid anyways).
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