Help with a knock in my 68

[68lemanspunisher]

I have a 68 pontiac lemans with a 69 code 350 in it. I was recently hit by a girl that blew a stop sign and now my engine has developed a knock under acceleration. It is only under acceleration when it is in gear and at light throttle it is not there but any moderate throttle makes the noise. I have true dual exhaust and the driver-side bank seems to sound just a little different like it is missing. can anybody help me diagnose the problem?

 

[melsg5]

You need to pinpoint the source of the noise.Is it a clatter like valves or something harder. If it's accident related the things that come to mind are broken engine or transmission mount or exhaust pipe hitting something. If not accident related do you hear the noise when in park and you raise RPM to say 2,000 to 2,500? You can use a rubber hose and hold it near you ear and move it around the engine to determine the source. Have you checked if the distributor hold down bolt is loose and your timing got knocked off?

 

[68lemanspunisher]

When i rev it up it does make the noise. it seems to be a valve problem or something because the tick is very fast. I now noticed what seems to be unburned fuel coming out of my exhaust. The distributor is fine and the motor mounts and tranny mount are good. I appreciate any help you can give me.

 

[melsg5]

determine whether it's from the right or left valve cover and remove it. Look for a broken valve spring, worn rocker arm, or some other valve/rocker arm abnormality.

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[68lemanspunisher]

It ended up being the driver-side and i took it to an engine guy and he said my valve retainers are old non-hardened ones so the unleaded gas made them deteriorate. no bueno

 

[melsg5]

That sounds like a load of ____! A valve retainer is made of hardened steel and is not exposed to gasoline. Valve seats under extreme load, towing, high speed driving, etc. in theory can deteriorate from the use of unleaded but I believe most machine shops that rebuild heads will tell you they have never run across one. Is this engine guy familar with older cars? This link shows you what a valve retainer looks like.

http://www.pontiacengines.net/Valve-retainers-locks.html

 

[68lemanspunisher]

my bad man. that was a typo on my part. its the valve seats.

 

[melsg5]

He determined this without taking the cylinder heads off? I'd put my money on worn camshaft/lifters due to most of the current oils having insufficient levels of zinc and phosphorus for cars with flat tappet camshafts. So what are you going to do?

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[68lemanspunisher]

He used a camera and went through the plug hole after there was no compression. Im either going to rebuild the motor myself or sell the car. not sure yet.