Nigel....I am leaning toward chain noise, but have you ever in your life heard of low feed to the chain tensioner? And regarding adjustment of chain guides.......what would cause noise on the slack side. There are basically two adjustment holes, and with a new chain etc. I have always opted for the right hand (bottom hole) adjustment. The chain is tight as can be. Also when I disassembled it, there was no signs of wear on the guides or tensioner boot. Guy

Nigel....I asked Z Doc about possible low oil to tensioner. He said no since the chain is oiled by the pinhole in the tensioner that sprays the chain. He said if there was no pressure, the chain wouldn't get oil and the guides and chain would self destruct. He also said and I quote "no oil in the tensioner would result in loud knocking of the tensioner foot like on an old tired Z engine when bumping the starter to set the valves_____knock knock."

Nigel....I asked Z Doc about possible low oil to tensioner. He said no since the chain is oiled by the pinhole in the tensioner that sprays the chain. He said if there was no pressure, the chain wouldn't get oil and the guides and chain would self destruct. He also said and I quote "no oil in the tensioner would result in loud knocking of the tensioner foot like on an old tired Z engine when bumping the starter to set the valves_____knock knock."

Maybe so, but I would be looking in this area first. Stranger things have happened,

You're absolutely right....I'll put that on my list of possibilties.

Hey Guy, have you had any luck diagnosing this noise?

correct length bolts holding the t-stat housing on?

I had already checked that......the thermostat bolt was not the problem. I pulled the front cover and put in another new tensioner and readjusted the chain......not the problem. It's the damnest thing I've ever dealt with ........the noise comes on at 1400 rpm and disappears at 3,000 rpm. There was no sign of wear or stress anywhere. The cam and rockers are perfect. The only other rotating items I haven't eliminated is the cam and the distributor drive shaft. Ron Isky said he had never heard of a harmonic problem with the L-series stage III cams. The engine runs perfect......I'm baffled!!! Guy

Might want to add the fan clutch to the list...from my research its designed to stay engaged until 2500rpm or so when it disengages. Upon deceleration it will reengage at approx 1600rpm where you seem to be hearing the noises. Heres a link with more detail:

http://www.hammondsplains.com/newtechtips/cooling/index.htm

The fact that you can hear the noise at the fuel pump, and its location near the water pump, leads me to the fan....hope this helps! Beautiful Z's by the way, I've spent many hours (maybe too many) looking at them!

Casey

Thanks Casey, but I disconnected the fan belt and still had the noise......that eliminates the fan. I'm going to check the cam sprocket bolt to make sure if it didn't bottom out before locking in the fuel pump eccentric cam......just thought about that as a possibility. Something is making the noise and that's a potential noise source. I'll let you know if that's it. Guy

Edited December 3, 200915 yr by Diseazd

Have you eliminated the PCV valve as a source, I have heard them rattle like this before and when you change the camshaft the manifold vacuum changes to a different RPM range .Worth a try.

Thanks I'll check the PCV, but it seems to be coming from the top and front.

Problem solved! The aftermarket crank bolt sold by MSA has a drop down on the washer that sets in the stock damper far enough to bottom out on the crank nose before the worm gear, crank sprocket, and slinger snug-up. This allows everything to be slightly loose! This eventually will wallow out the woodruff and could ruin your crank. It makes a noise that transmits up through the chain and sounds like a valve train noise. A $2.00 washer has ruined my life for the last 6 months. The washer needs to milled to work on that combo. Hope this prevents this from happening to anyone else! Guy