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Old 06-04-2019, 07:14   #1
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What could have been the knocking? High revs Perkins

What could have been the knocking? Perkins

After a short period of high revs the engine started knocking.
Turned engine off. Restarted and knocking Sound hasnít come back. But would like to be sure of no damage or hazard.
Perkins 4.108 50cv 1986

What could have been the knocking? Any thoughts?
Thanks!
Su
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Old 06-04-2019, 10:44   #2
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Re: What could have been the knocking? High revs Perkins

There are all kinds of things it could be.

Oil level (while running), oil filter getting plugged, high engine temps, low engine temps, mice in the alternator belt...

Get a knowledgeable local to listen/help.
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Old 06-04-2019, 15:12   #3
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Re: What could have been the knocking? High revs Perkins

Knocking is often nothing more than injectors that are dirty and instead of have a fine spray of fuel, they have a stream of fuel, this messes with the timing, and you have a knocking sound.

Of course your noise could have been most anything even a flex plate.
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Old 06-04-2019, 16:30   #4
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Re: What could have been the knocking? High revs Perkins

I've run into several 4 cylinder diesels with a bad injector that sounded just like a rod knock. Usually it's from contaminated fuel reaching the injector and partially plugging the nozzle. Often they clear themselves out, but I'd look at how well the fuel is filtered. You can buy just the nozzle for a 4108 injector.
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Old 06-04-2019, 17:32   #5
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Re: What could have been the knocking? High revs Perkins

I wouldn't even worry. Those 4-108 engines sound like putting your silverware drawer in the dryer all the time. If it went away, all good.
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Old 06-04-2019, 18:19   #6
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Re: What could have been the knocking? High revs Perkins

Try sending an oil sample to Blackstone or some other place that does oil analysis. They will tell you if you have metals you should not.
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Old 07-04-2019, 09:15   #7
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Re: What could have been the knocking? High revs Perkins

Quote:
Originally Posted by evm1024 View Post
Try sending an oil sample to Blackstone or some other place that does oil analysis. They will tell you if you have metals you should not.
An oil sample is certainly one tool and will identify fine particles.
A second easy check to complement above is to cut open/inspect the oil filter. Just be carefull of sharp edges and orient it to prevent metal shavings from entering during the operation.
1) drain oil from the filter
2) cut canister open
3) remove cartridge, then remove about 1/3 of the paper element
4) with removed section folded up along the pleats (itíll be like a block of oily paper) squeeze oil out of the paper. A vice is best for this.
5) unfold the paper element and inspect it for debris, metal etc. If present is it magnetic, what is the colour etc will help to narrow down where in the engine itís from.
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Old 07-04-2019, 10:02   #8
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Re: What could have been the knocking? High revs Perkins

If it "went away", it sounds like it is a momentarily clogged injector, causing one cylinder to misfire or not fire at all and then fire again. Diesels knock! That is what they do. So you have to analyze what was BEFORE and then AFTER, and eliminate until you figure it out.
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Old 07-04-2019, 19:19   #9
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Re: What could have been the knocking? High revs Perkins

Really, now it the time to send in an oil sample. It will establish a baseline (the before) for future samples.

Plus if there are excessive metals in the results you will be aware.

The folks who do oil analysis do have a feel for what level to expect and can offer an opinion.
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Old 09-04-2019, 10:58   #10
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Re: What could have been the knocking? High revs Perkins

Thanks for all your feedback and thoughts! I'll look into all of it.
So far, I haven't discovered anything unusual yet and also the knocking has not come back
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