charv13

I'm hoping someone can help me decipher some noise I'm hearing when accelerating. It sounds like valve train noise, but not sure. I've included a link here to a video, but it's hard to hear the noise above the exhaust. It's almost like it's there all the time, but get's louder when you get into it. I assume it's always been there, but my exhaust had more leaks than the titanic. I've only noticed it now after redoing the exhaust.
'72 Olds 350, completely stock with the exception of hooker competition headers, Magnaflow mufflers, an Edelbrock 1406, and Hei. It does have 7a heads. Replaced the timing chain not too long ago. (That was fun. I asked a question about it here as well). The car says it has 45,000 on it, but I'm sure it has more than that, but the timing gears were in really good shape when I replaced them.

Has 50 to 60 lbs of oil pressure when it first starts up, goes down to about 35 to 40 when it's hot at idle. Timed at 12 degree's base timing, with mechanical, at 3k, it's all in at about 30 degree's. The vacuum advance is about 16 degrees, so all together around 46 or so. (Using manifold vacuum, on the edelbrock. I've also tried using ported, and there was no change in the sound). I did remove the vacuum advance and plugged it, capped the carb, and ran it down the road. and there's no change in the sound. Vacuum is right around 18/19, but moves up and down about a degree or two very slowly. Idles great when warm, and has power while accelerating, no bog or hesitation. There's no surging while cruising, and the sound is only when you put a load on the motor, like going up a hill, or from a stop. I've read a lot on here about spark knock, but this doesn't sound like that. I do hear some ticking from the valve train at idle, and in park, revving the motor up doesn't produce the sound that it does under load. I have compression of 135 to 140 in all cylinders with the exception of no. 6, which is 125. Motor doesn't seem to be using any oil, and no blue smoke out of the exhaust. I pulled the valve covers, and all the rockers are solid, with the exception of no. 6, both of which are very slightly loose side to side. All rocker bolts are tight.

1, 2, 3, and 4 plugs look fouled, but 5, 6, 7 and 8 plugs look great.

Pic is #4 plug and #6 plug.




I do have plans to rebuild the motor, but it's not in the budget right now and would like to put some more miles on it. Am I hurting anything by driving it like this? Any idea's to mitigate this noise?

olds 307 and 403

Maybe do the valve cover gaskets, if not already done and check valve train play without it running. It could be a sticky lifter or it could be worn rocker arms. Easy to pull a set of rocker arms and inspect for wear, especially if you find the cylinder. You could try an engine oil flush as well. The GM oil flush used to be really good. What brand of oil and what weight of oil are you running?

charv13

I'm running 10W-40, Farm and Fleet brand. I did find that I can wiggle #6 intake and exhaust rockers ever so slightly side to side. Would that cause that noise to get louder under throttle? Anyway to unstick a sticky lifter?

olds 307 and 403

Undo the bolts on those rocker arms and inspect them. If worn, replace them and check again. You could shoot some carb cleaner or similar solvent down the push rods. You could lightly tap the push rods. It may do nothing or really seize the plunger in the lifter, making it worse.

charv13

Thanks, I'll try that.

BillK

Header gasket leaking ? Sound like it has a missfire to me but hard to tell for sure. Not smooth.