knocking

I hate to be the one to tell you this but what you are describing sounds a whole lot like a connecting rod bearing that has worn out. Has your oil pressure dropped any? When you pulled the plug wire you took the load off that rod and the knock stopped.
Does the knock seem to come from the lower part of the motor? Try using a piece of hose as a stethoscope and see if you can zero in on just where the knock is coming from. But it really sounds like a rod bearing to me. Sorry :cry:

the oil presure has never drop,and the knock seems to come from the top of the cylinder. and when it exhaust

[quote:d72e9d9902="76 gmc"]i have a 76 gmc c10 pickup with edelbrock heads and a Holley carb. it has 147145 on a rebuilt 350 motor that was rebuilt about 3 years ago. this problem just started about a week ago. it started knocking. the only cylinder knocking is #7. so i changed the lifters. but that didn't solve the problem. I pulled the wire off the #7 and te noise stooped. need help trying to figure out what the problem is[/quote:d72e9d9902]

Sounds like a piston slap or a wrist pin

[quote:77615adc4f="rasmataz"][quote:77615adc4f="76 gmc"]i have a 76 gmc c10 pickup with edelbrock heads and a Holley carb. it has 147145 on a rebuilt 350 motor that was rebuilt about 3 years ago. this problem just started about a week ago. it started knocking. the only cylinder knocking is #7. so i changed the lifters. but that didn't solve the problem. I pulled the wire off the #7 and te noise stooped. need help trying to figure out what the problem is[/quote:77615adc4f]

Sounds like a piston slap or a wrist pin[/quote:77615adc4f]


how do you fix piston slap