I did a heads/cam/intake swap and no knocking or sewing machine noise. After I got my tune I was coming back from the tune shop and there was a "machine gun" sound coming from the engine. I drove it about 8-9 miles in this condition. I got it to a friends house and took off the valve covers and had 2 snapped valve springs. Replaced all the springs with Patriot Duals and changed the oil and fished my pan with a magnet...no metal. Now my car is making a knocking sound that when you have the hood up sounds like its coming from the vicinity of the intake. It stays at the same volume and is RPM repetitive. I can hear it with the windows up and slightly over my Loudmouth exhaust. There is no loss of oil pressure and no loss of power. Could it be a bent pushrod, not the right size pushrod or bent valve? I ordered a PR length checker and will check to see if they are the correct length. Could the snapped valve springs bent one of the pushrods (I have 7.4 PRs with stock milled .015 LS6 heads)? Whats the best way to check to see if there is a bent pushrod?

 

could be anyone of those.... or possibly a lifter maybe?

 

to check for bent pushrod, just pull them out, the rockers can all come off as one whole shaft, then take them out one at a time and roll them on a really flat surface, see if you notice one rolling out of order. i would talk to an engine shop and find out if they are the right length. was it running funny at all or just making the noise? maybe a rocker was overtightened. it does kinda sound like a pushrod issue though.

 

check the pushrods but if they are hardened ones probalby a valve I would locate the cylinders where the springs broke and pull the spark plugs out and put air in the cylinders. then listen for a excessive hissing or air noise

 

you probably didnt bend a pushrod if they are hardened ones. but if they are milled at all I would think that it would throw your valvetrain geometry off even if only a little bit could cause bad things to happen. I say start with the easiest (i/e rockers, then pushrods and springs,then if all else fails pull heads and check the lifters and vavles) you should find it.

 

Well, when I put compressed air up into the cylinders to change the springs, it didnt look like i was losing any compression due to the fact that the valves stayed up the whole time while i was changing the springs.

What makes me think its not the pushrods is that the knocking didnt start until after i snapped the valve springs. I'll chime back in when i get my PR length checker.

 

oops forgot you used air to change the springs

 

Hmmm I'm having the same problem aside from the broken springs. I have that same noise. Let me know how your push rod checker test turns out. I tried mine today and not much luck.

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