1995 Chevy Silverado Quick Engine Knock at start up.

DUNAMIS

MEMBER
1995 CHEVROLET SILVERADO
V8
4WD
AUTOMATIC
203,000 MILES

This is an intermittent problem. Sometimes when I go to start my truck, I will turn the engine over and when it fires up there are a series of 4 knocks and then it goes away. Each and every time it does it, it's four knocks. It usually happens after the engine has been sitting for the night. I took my truck to a mechanic concerning this "knock". I explained to him that it sounded like a lifter to me. I started up the truck to see if it would actually knock for him and did. He got this puzzled look on his face. He said that it didn't sound like a lifter to him. He said it sounded like front/rear main bearings or possibly the crank shaft, but he could tell which area it came from. What puzzled him is that it only "knocked" four times and then went away. After that, everything sounded perfect. Absolutely NO ENGINE NOISE WHAT SO EVER. He commented that the truck ran remarkably well.

4 Replies

MASTERTECHTIM

MECHANIC
4,749 POSTS

This is most likely a problem with the crankshaft main bearings. General motors had a bulletin on this when these engines were new and the fix was to measure the main bearings and install oversized bearings on the mains. They also note that this will not affect the longevity of the engine. Bottom line is leave it alone.

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Sunday, May 4th, 2008 AT 2:35 PM

THE FACTORY MAN

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50 POSTS

IF I AM RECALLING THIS CORRECTLY, I think the TSB from GM brought into question the clearance of the front main bearing. I THINK part of the diagnosis was to remove the serpentine belt and if the noise then was less or went away that confirmed the main bearing issue. I can not access the bulletin right now but I think the fix was to install a.0005" larger bottom main bearing shell. I also think the bulletin stated that the noise would not affect the long term durability of the engine but was mainly a customer concern issue. If this is what you are dealing with I would leave it alone as MASTERTECH TIM says.

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Saturday, May 10th, 2008 AT 12:06 PM

DUNAMIS

MEMBER
2 POSTS

Someone told me to removed the serpentine belt and turn the engine over toy listen for the knock. The only problem with that is that my engine doesn't knock all the time.

I am eventually going to build an engine to put in my truck. I think I may buy one from a junk yard or something and put it I the garage to tiner with. The only thing I need to know is what spec's the engine has to be in order for it to fit in my truck.

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Saturday, May 10th, 2008 AT 12:17 PM

THE FACTORY MAN

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50 POSTS

Remove the belt and start the engine and listen for a knock. I assume this happens on a cold start after the engine sits over night. Don't run the engine very long with the belt off. I'm not sure what you are asking about as far as specs for a replacement engine. Keep it simple and get the same engine from a wrecking yard.

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Saturday, May 10th, 2008 AT 12:29 PM