Good news and bad news. tach fixed...

[Dynomite]

Originally Posted by Pete

Just wondering do you think maybe it's piston slap.
Some of our Z's have piston slap which is nothing to worry about,some are more pronounced/louder then others.

Pete

Yabut.......does not piston slap usually go away after the engine gets to operating temperature......
Or even faster within a minute or so (sometimes within a few seconds) when the cylinder walls/pistons warm up (and otherwise dry cylinder walls get splashed with oil)?

[Torchred96]

It is nothing that goes away I assure you. It is a rapid knock seemingly to correspond with half revs (up and down) motion and is constant from start up to shut down. It is not something I would even think about running for any length of time as you can almost palpate the damage being done.

I don't have a scanner but wouldn't it pull timing for the various noises that they tend to make like the flywheel/clutch when missing?

I have a medical stethescope and back when it happened (over a year) I remember hearing noises the loudest acrosss the plenum and over the drivers side cam cover toward #1

Also, I have pulled each plug wire (i know this isn't recommended) but it seems to make no difference in the sound of the any eight cylinders

What is the possibility of a valve being bent and hitting a piston. Though I didn't notice anything unusual when I put the lifters in, I couldn't press them down by hand.

I haven't done a compression test, but since I am going to go to the store to get one I could buy/rent a vacuuum gauge too if you think it will tell me anything.

[Torchred96]

Just put a stethescope on the cam covers and they are relatively quiet...I mean you can hear some ticking but it is minimial compared to what I hear on the top of the plenum.

Okay so I put the stethescope on the bell of the plenum and it was loudest there and interestingly the scope sounded far different at each set of runners..couldn't hear anything much ON the runners, but with the scope sliding across the plenum I hear lots of bad and loud constant low freq rubbing (described below) noises that you can't hear without the scope. ..no accessories hooked up.

Next got under the car and put the stethescope across the oil pan..sounded worse at the rear and also sounded different sliding it up toward the front.. Aside from the very pronounced tick (when heard from a stethescope (knock when hearing it without the scope)) there is another disturbing sound..constant:

The best sound I can liken it to is a rocket engine..low frequency noise that would seem to indicate two surfaces rubbing constantly...like sandpaper against sandpaper rubbed very slowly or maybe a wooden pallet being dragged across the asphalt very slowly. Or better, a large heavy steel drum rolling slowly on concrete or the sound the coasters(wheels) make from a vaccuum cleaner being pulled across the driveway

Those are only heard with the stethescope from the top of the plenum in which it is most prounounced or on the oil pan. ON the girdle below with the scope the noise wasn't as prounounced as it was from the plenum or from the oil pan. doesnt sound good guys

The ticking noise (more of a knock) I could describe as being about as fast as an injector tick, but it is defininitely not an injector though as I remember clearly the sound of the lt1's injectors

OH, I just thought of another analogy > It's the sound of brake pads worn out against a rotor..the metal to metal grind you hear when you are almost stopped and the rotors are being grinded into. that's probably the best one.

[Pete]

Originally Posted by Torchred96

OH, I just thought of another analogy > It's the sound of brake pads worn out against a rotor..the metal to metal grind you hear when you are almost stopped and the rotors are being grinded into. that's probably the best one.

If it sounds like brakes grinding I'd start looking for a short block/motor.

My old motor had piston noise even after warm up it was a bit less but people would always ask me what the noise was at cold start up it sounded like a diesel.

Pete

[Torchred96]

Pete, At least that does simplify things I've never had much luck replacing rods and having them last.. And finding a good machine shop around here is not easy. Hopefully I can find a good engine or shortblock for a reasonable price. Time to start saving my nickels and working some OT

[GOLDCYLON]

Originally Posted by Torchred96

While I had my engine down to replace the lifters I sent my tach cluster to be repaired. Total cost 50 bucks..maybe a little more with shipping. Turned out to be some kind of resistor that is calibrated at the factory which starts to break down after a while.

And, I replaced the pcv hoses, and my idle is back to normal..OH, and I finished powdercoating the cam covers and got the new ss bolts all over....Man does it look great sitting in my garage.

But unfortunately, there's bad news:
I started the motor up after getting it back together (probably over a year) but unfortunately, the 16 lifters on the driver's side didn't solve my knocking problem. I let it run a couple minutes to be sure. The ticking went away maybe 30 seconds as the lifters filled with oil after startup (i had primed the engine with oil) but the knock remains as before. Major Bummer.

Looks like it has to come down again. I just hope my crankshaft is okay and it turns out to be a piston end.

It was a calculated risk. I was hoping that the lifters were going to solve the issue. Hopefully I can get the exhaust off to pull the motor. I'm pretty sure the exhaust bolts will be snapping off (aft the cat) as I tried to turn them when I was under there to see what I was in for, then decided to stop and just put the lifters in.. sorry , just venting.

Boy I wish I would have bought that short block with 27k miles on it....but unfortunately, I had convinced myself it was only lifters. Oh well. wish me luck

Talk to Kurt White he has a motor exchange program or used too and he's in Florida his handle is Limey here on the forum. GC