Vortec knocks when cold

[Snowman]

GM has a TSB for Cold Knock from the Vortec engines. Noise is due to excessive bearing clearance.

File In Section: 06 - Engine/Propulsion System

Bulletin No.: 99-06-01-003

Date: April, 1999

TECHNICAL

Subject:
Engine Bearing Knock Noise,
(Re-support Crankshaft, Select-fit Undersize Connecting Rod Bearings)

Models:
1999 Cadillac Escalade
1996-99 Chevrolet and GMC C/K, G, P Models
with 5.0L or 5.7L Engine (VINs M, R - RPOs L30, L31)

Important :GM Canada Dealers require prior DSM authorization to apply this bulletin.

Condition

Some customers may comment about an engine "knocking" noise.

Cause

A condition may exist in some engines where, the crankshaft is NOT being evenly supported by all five crankshaft bearing inserts. In these engines, the number 1, 2, 3, and 4 crankshaft bearing inserts are supporting the crankshaft, and the number 5 crankshaft journal (rear) has excessive clearance relative to the number 5 crankshaft (main) bearing cap insert. In this condition, the crankshaft flexes under load, and pounds on the lower number 5 crankshaft (main) bearing insert creating the knocking sound. The engines were originally built with 0.0006 in. undersize crankshaft (main) bearing inserts in the number 2, 3, and 4 crankshaft (main) bearing locations and 0.001 in. undersize insert in the number 5 crankshaft (main) bearing location. The service procedure listed below addresses the above condition by lowering the crankshaft at the number 2, 3, and 4 crankshaft (main) bearing positions (increased crankshaft (main) bearing size of the lower crankshaft (main) bearing inserts) and raising the number 5 lower crankshaft (main) bearing insert (undersized insert) in order to properly contact the number 5 crankshaft journal surface. These engines may also exhibit a connecting rod knocking sound. In these engines, the connecting rod knocking sound is caused by excessive connecting rod bearing clearance.

A customer concern vehicle may exhibit one or both of the above stated conditions.

Correction

Follow strategy-based diagnostics for engine noise listed in the front of Section 6 of the Service Manual.

Some additional key points:

Rod Bearing Knock - Occurs on initial engine start-up, and can also be heard as high as 1,500-1,800 RPM. Rod bearing knock typically diminishes or completely goes away when the engine reaches normal operating temperature.

Crankshaft Bearing Knock - Crankshaft (main) bearing knock sounds deeper in the engine and also sounds more muffled. There are two different types of crankshaft bearing knock.

^ Short duration cold knock typically occurs for 1-5 seconds on engine cold start-up only, and almost always occurs on vehicles equipped with an engine oil cooler.

^ Hot knock occurs less frequently, typically occurring in very hot ambient temperatures, and can be heard up to 2,000 RPM.


Technicians can increase the likelihood of reproducing bearing induced knock sounds by slightly depressing the accelerator pedal while starting the engine.

 

[gmfan454]

I had an 01 Tahoe with the 5.3 and when it had just over 100,000 miles, I started getting cold start piston slap as well. Just delt with it till about 150,000 miles I got a tick in one of my heads. I brought it down to the local mechanic who is a retired GM mechanic (he is about 68) and he said "did you put that synthetic sh*t in it) and I said yes. He told me to drain the oil, get some sae 5w-30 regular oil and one quart of transmission fluid and add it to oil and only add 4 quarts of oil. I was reluctant but my uncle who had used this guy for years told me he would pure sugar in his gas tank if this mechanic told him too. Anyway, I did it... about two weeks later, piston slap and tick was gone forever. Sold the truck with 182,000 on it and it never slapped again. he said it is carbon build up and the transmission fluid has higher detergant levels and it cleaned out a big piece of stuck carbon for the tick and cleaned the heads for the piston slap. I never had an issue after that. Just telling you what happened with me.

 

[deadbeat]

I had an 01 Tahoe with the 5.3 and when it had just over 100,000 miles, I started getting cold start piston slap as well. Just delt with it till about 150,000 miles I got a tick in one of my heads. I brought it down to the local mechanic who is a retired GM mechanic (he is about 68) and he said "did you put that synthetic sh*t in it) and I said yes. He told me to drain the oil, get some sae 5w-30 regular oil and one quart of transmission fluid and add it to oil and only add 4 quarts of oil. I was reluctant but my uncle who had used this guy for years told me he would pure sugar in his gas tank if this mechanic told him too. Anyway, I did it... about two weeks later, piston slap and tick was gone forever. Sold the truck with 182,000 on it and it never slapped again. he said it is carbon build up and the transmission fluid has higher detergant levels and it cleaned out a big piece of stuck carbon for the tick and cleaned the heads for the piston slap. I never had an issue after that. Just telling you what happened with me.

Has anyone else tried this?

 

[twomanymontes]

Has anyone else tried this?

I have done this on old gunked up motors that haven't been started in years. And it has flushed the motors pretty good, but never tried it to fix a ticking or a knock.

 

[Constantine]

Mine does this and it has become far worse than just a start up knock.
A good firm clacking noise.
It always has had the start up knock for a few seconds when cold.
One thing to look at is the hydraulic roller lifter itself.
When there isn't any oil pressure it collapses, so to speak, on which ever valve is pushed open.
years of perhaps carbon build, maybe some other type of build up or just wear on the lifter body will allow the lifter to stick in a collapsed position for a prolonged period of time until the oil pressure and heat work together to allow the lifter to extend to normal operating position.

I'm in the air on wether or not to rebuild my engine with some hi Performance goodies or replace the lifters and keep rolling it until I find a nice 2007-2014 tahoe.
If I replace my lifters and it fixes the issue with mine, I will share the results.

 

[deadbeat]

Make sure to let me know, I am in the same boat. I am looking for a low mileage motor but would rather throw in a set of lifters if that is all I need to do.

 

[Constantine]

I changed my oil recently.
Except this time I replaced a quart of motor oil with a quart of ATF (yes, automatic transmission fluid).
The first two days of daily commute after the oil change I couldn't decide if there were a difference upon start up or not.
The 3rd, there was definitely a difference.
A couple days of a little start up knock.
I'm now on my 3rd day of a start up knock free engine.

Just giving you something to try since it did work.for my engine.

I was hesitant to try that but it was time for either to take vacation from work or try something to buy a little time.
I'll still put a set of lifters in mine since i now know they are worn or have some kind of build up on them or the pushrods or something.