I have a 1999 C 3500 with a 7.4 Liter and it knocks GM tells me this is normal?

Question

It knocks in the mornings and after it has sat for a while or has sat at idle for a long period of time. I am almost certain the am knock is mains, it goes away after a min or two, but then if you leave it at idle it starts to knock again and it changes tone more like a rod. I have taken it a GM dealer and they say it is normal for this motor to have bearing noise, they even printed me a TSB on this. Well I dont know of any motor I have built to have a knock that was suposed to be there. Anyone else know of a simular situation?

Answer 1

GM motors are know for having wrist pin noise, and that is what it seems that you have. With a 1999, you are surely out of warranty, so any repair would be at your own cost. You could have the engine rebuilt, which would solve the noise problem (at a cost of several thousand dollars, or you could continue to drive and live with the noise.

I have a Chevy truck with the same noise problem, and have driven it over 100,000 miles since the noise started!

Answer 2

Yes,this may be normal.I have a 350 tbi in my truck and it does the same.This motor is brand new.I have the same problems when its cold.The engine starts knockin when started and then goes away after its warmed up.This is called piston slap.It is where the piston rattles against the cylinder wall of the motor until the motor heats and the piston expands to the size of the cylinder.I have known many people to have this annoying problem with Gm motors.It is normal and it will not hurt anything.There isnt much you can do about it.The fix isnt cost effective.You may just have to get used to it.I did.Sorry.

Answer 3

I had this problem with a Chevrolet Caprice. I read somewhere in a Chilton's guide or something like that that knocks were sometimes, sometimes caused by low grade fuel. I used to put in 87 octane, now I put in 91. It hasn't knocked since I upgraded octanes and this was six months ago.