I have recently rebuilt my 350 engine - 9.1 compression, heads improved, comp cams camshaft (hydraulic) and adjustable valvetrain and line bored ... all gone through. I am getting pinging when engine is cold but when block is heat soaked (after a reasonable drive) the pinging is gone at all speeds from standing start to kickdown. Tried different timing settings but no luck. Distributor is mechanical.

When it pings its' when under load just to confirm.

Yes, I have adjusted the valves again and they seem fine, 1/2 turn from when pushrod stops as adjuster is tightened. I referred to this website for details : https://centuryperformance.com/tech-...v=6cc98ba2045f

I am getting annoyed with this sound and possible engine damage - maybe redo the valve adjustment and check lifts on each valve. Could I have a bad COMP CAMs hydraulic lifter?

 

You need to describe what you are calling "pinging" ?? When most people think of that term they are referring to detonation or pre-ignition which has nothing to do with valve adjustment. Does the engine make the noise just sitting there at idle ?

 

Hi Bill,

thanks for the reply. I use the term pinging when engine under load - there is no pinging at idle or at cruise.

Pinging to me sounds like valve float, a tinny metal on metal rattle. I see what you mean, it could be detonation but why does it stop when engine has well and truly warmed up.

Timing set to 10 degrees then 16 but still doing it.

Graeme

 

Thats exactly what detonation sounds like. I would start off by putting a vacuum advance distributor in the car and see what happens. It could also be something fuel related. What carburetor ?

 

Thank you Bill - I have the old distributor which still works so will drop that in on weekend.

The carb is a newly rebuilt Quadrajet unit using Cliffs parts to suit my engine. Should I drop in the old carb as well if the distributor change makes no difference?

I will post back my findings over the weekend.

Appreciate your feedback
Graeme

 

I would only try one thing at a time. That way if you fix it you will know what it was.

 

Got it ;-)

 

I was just thinking about another possibility since you said it got better as the car warmed up. Is it possible you have an exhaust manifold gasket leaking ? Guys have been fooled by them more than once thinking it was a mechanical noise. They will get quieter as the manifolds get hot and expand.

 

Or the convertor bolts maybe

 

Another thought too Bill - should be able to check that. Heads were rebuilt and planed so should be good and used Thornton Jr. manifolds with a smidge of yellow/orange permatex.

That would be a cheap fix.

Graeme

 

Converter bolts - can check those too, thanks.

Graeme

 

Hi All,

I posted my question back in April and finally have a solution. Thank you all for your feedback.

Turns out that a single Comp Cams rocker arm and/or the pivot ball in the rocker arm was galled up or faulty - not sure.

I only noticed when I pulled the engine out and turned it over, the rocker arm was stuck, flapping in the wind while the pushrod was nowhere close to rocker socket. The only reason it did not get bent/damaged I guess was to to with the guide plates I installed? I am also guessing that as more oil fed the rocker arm and heated up that it became unstuck and worked again?

Anyway, I have just put on standard rocker arms and replaced lifters along with shorter pushrods so see how that goes.

This is similar to the rocker arm I mentioned - https://www.summitracing.com/parts/s...ake/oldsmobile

Feedback or thoughts appreciated.

Graeme

 

Did you lube the rocker arm and pivot ***** during assembly? You should never leave a potential friction point dry during engine assembly.

 

Sure did, used the Comp Cams assembly lube everywhere when I put it together. Have not dug deeper yet but I will check for any damage on that rocker arm and the pivot although there is obvious wear on the arm.


Cheers
Graeme