That old knocking feeling

[Dellb]

Hi All
This must be one of the most publicised threads ever, but hugely frustrating.

My 1980 C3, with a completely rebuilt 400 inch engine has that single annoying 1/2 engine speed knock.
The cam is a new lunati voodoo, driving hydraulic roller lifters to comp cam roller rockers, on new edelbrock performer heads.

on cold starting there is a single 1/2 engine speed knock. This slowly fades away as the engine warms, but never quite disappears . When sitting at the lights, whilst all around are benefiting from that wonderful V8 burble, I am straining to hear the knock, but it is just there.
Performance as unaffected, and wonderful.

I have tried various methods of setting valve lash, and the best by far was the system Ross sent me. However my simple view is that a knock is caused by a bit of metal bashing another piece of metal and must be eliminated.

So my question is this; Can you set valve lash with the engine running on engines fitted with hydraulic roller cam lifters?
I have a spare set of valve covers and a very keen angle grinder.

Am I missing something?

Delb

 

[Roscobbc]

When I initially installed my brand newly built 489 stroker engine, perhaps 10 years ago or more I had several situations like this relating to unexplained noises. One was the flywheel inspection cover rubbing the flywheel. Another was the fixing bolts securing the viscous fan unit to the water pump drive hub were for some strange reason rubbing on the water pump casting.......yet another one was a rather large mechanical bang from the engine on the way home one evening after a 'blast' immediately followed by a loss of power and seemingly only firing on 7 cylinders. Next day I ran the car up and it was 100% fine........several months later after removing the inlet manifold to do something or other I found a favourite 1/2" open ended spanner that I had lost a year or so before lying innocently in the lifter gallery........was that the reason for 'loosing' a cylinder before?.......then there was the failure of no.1 big end bearing that shattered in to about 10 different bits.......there have been other issues and sounds in the distant past.......but my memory is very 'kind' to me and letting me forget so as not to cause a self inflicted mental explosion........

 

[Dellb]

The thing is Ross, you found them. That is 90% of the battle. Once you know what it is, you can fix it.

 

[Roscobbc]

Adjusting the preload on hydraulic flat tappet or roller rockers.......best way forward if you don't mind a RSI rated vibro massage to your fingers and hands whilst wiping oil Smuts off your face....

 

[Roscobbc]

The thing is Ross, you found them. That is 90% of the battle. Once you know what it is, you can fix it.

Eventually Dell.....but tappet noise for me on my engine has always been an irritation.....I usually need to do it (using 'that' method) two or three times to get it as I like.......but alloy heads, rocker covers are very good transmitters of sound.....couple that with cam spec's that would normally be seen on a hydraulic roller cam perhaps answers a number of questions.....

 

[Roscobbc]

I'm afraid the answer is to go through everything from the top down.......inc. lifters, lifter bores etc. Doing valve pre loads without valve covers may give you a better idea of things.....

 

[langlj00]

Couple of thoughts,
To diagnose where the knock is located - old school, get a short piece of wooden dowel / broom stick. Place one end against your ear whilst putting the other at various points on the engine - to locate the noise. (bit like a stethoscope). This will tell you whether the knock is high in the engine (or lower down).

Also, how stable is your idle vacuum? Incorrectly set valve lash is easily seen as variable / wobbly vacuum.

Jeremy.

 

[Dellb]

Engine vacuum at idle is 17 inches, and as steady as a rock. The question I asking now is can you use the hot method (engine running) with hydraulic roller lifters.