I recently purchased a 94 Silverado with low miles and was told from previous owner the motor needed replacement. I wanted to keep the original motor so I decided to go through it and find out what the problem was. All cylinders had good compression, 180psi, except one cylinder (dead). More on that issue later.. A
nyway I got the truck running as it was sitting for 2 plus years. It clearly had what seemed to be a lifter noise..and just above idle it was loud. So I stripped the motor down to inspect what could be the problem. After removing intake..I could grab balance shaft and twist it from right to left creating the noise. After removing the timing cover.. the balance shaft drive gear bolt holes and dowel pin holes were hollowed out so the gear had excessive play making the balance shaft rock back and forth. If the bolts broke off this motor would be history! I installed new balance shaft gears..timing chain and many other parts. Discontinued balance shaft so couldn't buy a new one..so I replaced the front bearing (dealer only item/or bearing shop). It didn't need it but did it anyway.. rear bearing was still tight, (no play). Apparently the previous owner took the truck to a repair shop and someone most of figured it had carbon build up and revved the crap out of it trying to clean it out and spun a rod bearing and broke a push rod in half!. After new rod bearings and push rods it was a lot quieter but still had the rattle!. This isn't a lifter or rod bearing noise (experience over years).. I never heard the spun bearing noise, and I took it a step further and checked oil clearance on the spun rod big end and it was perfect! and inspected the lifters as well.
So there is a recall on 96 and up models but nothing on the older years! The fix is a timing chain tensioner but some blocks don't have the provisions for the tensioner to bolt to. So basically the engine needs to be replaced...they could of put out a recall for ones that don't have the provisions and put a double roller chain in or offered it to consumers. I am not sure if a double roller chain would fit either..so I ended up putting a cloyes single chain in. Even then I am not sure if it would take the noise away completely. Now I want to be clear on this noise.. if the noise is loud at idle (middle of engine) the chain is stretched or bolt holes in balance shaft drive gear are enlarged. A new chain and gear will make the noise quiet at idle..when it warms up it does get louder ( but not really noticeable while driving)..and no matter if cold or warm the noise is clearly present around 2K rpms and will go away higher then 2K rpms in park or neutral. I can't hear anything while driving..unless I am up against a wall or curb and noise is bouncing off of it. But it's tolerable now, but not completely.
Update from Jan 1, 2020: I wanted to update this complaint of mine..after doing all this work to this engine. It still had this knocking noise and I was down to a wrist pin that has excessive play or what is called piston slap. Basically one or more pistons is smaller in size then the cylinder size (rocking in the cylinder bore). I ended up yanking the motor and junking it. I had a non-balance shaft motor rebuild (1991) and put on the original heads and its on 20K miles with no issues. In conclusion the pistons are the issue and Ive seen others up to late 90s with this piston slap problem. Eventually the piston will crack and motor is done.Bad machine work or crappy parts!! I went as far as disabling the balance shaft by removing the gear and it still made the noise and believe it or not i didnt notice any difference in the smoothness of the engine!
A D V E R T I S E M E N T S
I recently purchased a 94 Silverado with low miles and was told from previous owner the motor needed replacement. I wanted to keep the original motor so I decided to go through it and find out what the problem was. All cylinders had good compression, 180psi, except one cylinder (dead). More on that issue later.. A
nyway I got the truck running as it was sitting for 2 plus years. It clearly had what seemed to be a lifter noise..and just above idle it was loud. So I stripped the motor down to inspect what could be the problem. After removing intake..I could grab balance shaft and twist it from right to left creating the noise. After removing the timing cover.. the balance shaft drive gear bolt holes and dowel pin holes were hollowed out so the gear had excessive play making the balance shaft rock back and forth. If the bolts broke off this motor would be history! I installed new balance shaft gears..timing chain and many other parts. Discontinued balance shaft so couldn't buy a new one..so I replaced the front bearing (dealer only item/or bearing shop). It didn't need it but did it anyway.. rear bearing was still tight, (no play). Apparently the previous owner took the truck to a repair shop and someone most of figured it had carbon build up and revved the crap out of it trying to clean it out and spun a rod bearing and broke a push rod in half!. After new rod bearings and push rods it was a lot quieter but still had the rattle!. This isn't a lifter or rod bearing noise (experience over years).. I never heard the spun bearing noise, and I took it a step further and checked oil clearance on the spun rod big end and it was perfect! and inspected the lifters as well.
So there is a recall on 96 and up models but nothing on the older years! The fix is a timing chain tensioner but some blocks don't have the provisions for the tensioner to bolt to. So basically the engine needs to be replaced...they could of put out a recall for ones that don't have the provisions and put a double roller chain in or offered it to consumers. I am not sure if a double roller chain would fit either..so I ended up putting a cloyes single chain in. Even then I am not sure if it would take the noise away completely. Now I want to be clear on this noise.. if the noise is loud at idle (middle of engine) the chain is stretched or bolt holes in balance shaft drive gear are enlarged. A new chain and gear will make the noise quiet at idle..when it warms up it does get louder ( but not really noticeable while driving)..and no matter if cold or warm the noise is clearly present around 2K rpms and will go away higher then 2K rpms in park or neutral. I can't hear anything while driving..unless I am up against a wall or curb and noise is bouncing off of it. But it's tolerable now, but not completely.
Update from Jan 1, 2020: I wanted to update this complaint of mine..after doing all this work to this engine. It still had this knocking noise and I was down to a wrist pin that has excessive play or what is called piston slap. Basically one or more pistons is smaller in size then the cylinder size (rocking in the cylinder bore). I ended up yanking the motor and junking it. I had a non-balance shaft motor rebuild (1991) and put on the original heads and its on 20K miles with no issues. In conclusion the pistons are the issue and Ive seen others up to late 90s with this piston slap problem. Eventually the piston will crack and motor is done.Bad machine work or crappy parts!! I went as far as disabling the balance shaft by removing the gear and it still made the noise and believe it or not i didnt notice any difference in the smoothness of the engine!
- Bruce M., Tucson, AZ, US