Strange noise in my modified L28

[Diseazd]

I built an L28 with standard flat tops,a P79 head shaved .080 shimmed cam towers and a Stage III Isky reground cam. Everything in the engine is new (rockers, springs, mains, inserts, chain, oil pump, guides, crank pulley,cam pulley, etc. etc. etc.) The engine runs great! However, when you rev the engine to 4,000 and let off, it makes a ball bearing type of noise at 2,200 rpm on the letdown.When you run it up the noise comes on at 2,200 and disappears at 3,000 rpm. I've eliminated the oil pump, the distributor, alternator, fuel pump and water pump as possible noise sources. This is driving me and everyone that tries to figure it out crazy. I've contacted Ron Isky to see if he's run into this before and he said no, but would check with some of his Stage III buyers to see if they've run into this problem. Any ideas ? Thanks Guy

[70 Cam Guy]

You can replicate the sound free revving it? I would grab the stethoscope (or equivalent vacuum hose/long screw driver) and start searching. If you have narrowed it to the top-end, pull the valve cover and check for complete oiling on your cam. I have never tried it on our L engines but when my friends were trying to chase down a noise on the dyno on a KA turbo, we removed the oil filler to find it got louder.

I know you have experience with these cars but you're sure it's not a heat shield resonating at those frequencies/engine speeds?

[Diseazd]

Yes we can replicate the sound free revving. The sound is definitely coming from the top end. The sound is almost liked loose ball bearings.....all valve train is getting sufficient oil. We put a stethescope and screwdriver on all sections of the engine. The loudest noise seems to emit when you put the screwdriver on the fuel pump......it almost sounds like it could be chain noise, but the chain is new and tight as can be. Called the Z doc in Roanoke and he said after eliminating all that I've done, it could be the cam profile, but Ron Isky had never encountered this problem....he's calling some customers to see if they've had problems. I've taken the engine completely apart and back together with no evidence of a problem on any parts. This is absolutely got us stumped! Any ideas?

[Zs-ondabrain]

sounds like the tensioner or valve wobble. When's the last time you readjusted the valves? I had a for V6 and could NEVER get the valves to quiet down. On deceleration, my chair and valve make noise. maybe it's common? maybe just a resinance at a certain RPM? Let us know if you figure it out.

Dave

[Diseazd]

Isky calls for .010" intake......012" exhaust. I went to .008" intake and .010" exhaust........that didn't change anything!

[Zs-ondabrain]

Maybe a stronger spring on the tensioner? Or try a different fuel pump just for experimental purposes? Kinda lost but at least you've narrowed it down to an area.

[Diseazd]

It's a brand new Nissan tensioner......and I've completely removed the fuel pump...taped up the hole and ran it off of the bowls. The noise was still there!

[70 Cam Guy]

It can't be the fuel pump cam spinning on the camshaft can it? I've only looked at it in the FSM so I don't know if that is even possible. Nothing is rubbing or interfering on covers? All more shots in the dark...

[ChrisZ]

Guy, you should really post a video of it, it would make things a bit easier.

Chris

[Diseazd]

Chris.......I'll get Brandon to do a video this weekend. Andy....none of the above....nothing rubbing and I've run it on the bowls w/o a fuel pump.

Edited October 28, 2009 by Diseazd

[70 Cam Guy]

I'm also curious how it sounds. I wasn't sure if the fuel pump concentric could still spin on the cam with the pump out. When I think of bearing noise, I think of a squeal like an alternator bearing. Just thinking out loud here, you've already taken it apart and re assembled so it can't be a cam bearing spinning or a journal not seeing oil. When everything was assembled (either the 1st or 2nd time), did you plastigage the bearings? Did the cam spin easily when it was installed? I'm at a loss to be honest but too darn stubborn to give up

Edited October 29, 2009 by 70 Cam Guy

[Nigel1943]

My guess is it's the timing chain rattling caused by either incorrect adjustment or low or nil oil feed to the tensioner.