rkellerjr
03-19-2009, 08:47 PM
OK, I know I don't post here much but I do visit the site and I know some of you guys are whiz bang engine guys. I just rebuilt my '76 400 (car is a '75) from the ground up, spared no expense, all new parts, block bored .040, heads done, etc.
When cold you don't really hear it, once she warms a bit you only really hear it when it runs around 2,000rpm's, doesn't matter if the car is under load or not however, it is consistent when under load, not so when not under load. It is a deep knock, not unlike a rod knocking. When it starts knocking, one of the rockers start rapping loudly too. My suggestion was maybe one of the lifters is collapsing or getting stuck for some reason but, then becomes "unstuck". It is hard to explain via the forum. The engine runs solid and strong, even during the knocking, AND when you unplug the plug wires, one at a time, it will still do it. Oil pressure is fine as well.
We've thought about the flex plate maybe being cracked however, Mike (a whiz bang Pontiac engine builder) is fairly confident it is coming from the front drivers side of the motor. We just replaced the fuel pump thinking that might have been the cause but it wasn't and he "checked" the concentric while we had the pump off and it "seemed" fine.
Thoughts?
When cold you don't really hear it, once she warms a bit you only really hear it when it runs around 2,000rpm's, doesn't matter if the car is under load or not however, it is consistent when under load, not so when not under load. It is a deep knock, not unlike a rod knocking. When it starts knocking, one of the rockers start rapping loudly too. My suggestion was maybe one of the lifters is collapsing or getting stuck for some reason but, then becomes "unstuck". It is hard to explain via the forum. The engine runs solid and strong, even during the knocking, AND when you unplug the plug wires, one at a time, it will still do it. Oil pressure is fine as well.
We've thought about the flex plate maybe being cracked however, Mike (a whiz bang Pontiac engine builder) is fairly confident it is coming from the front drivers side of the motor. We just replaced the fuel pump thinking that might have been the cause but it wasn't and he "checked" the concentric while we had the pump off and it "seemed" fine.
Thoughts?