how's the memory? ever notice a slight change to the noise, in neutral, idle, when clutch depressed?

there is/was a vid on u tube, "identical" sounds and symptoms. I thought it was the same, but the other was an 88. never heard the conclusion, but some thought it was dual mass issue, since it had been worked on just as the noise appeared...

joe

 

All bearings looked basically the same. I pulled one main and it looks pretty good.

 

I wish I would have paid more attention to that, but I did not. Right now I am thinking I am going to put some bearings in it and put it back together - it's worth the day and under $100 to see if I can stave off a new engine.

--Calvin

 

I hear you. I am just a visitor here, trying to learn new stuff. But bearing wear is not new. In theory, if there is always a film of oil on a bearing surface, the wear is uneventful.

It may have been your camera microphone, but the noise was more of a rattle than bearing noise. Rod noise only at idle -sometimes? Didn't stick together. Your bearings should have been blue from heat, ragged on edges, for the noise they made

I will be the first to say I am greatly surprised if it is gone.

saludos, joe

 

I agree with you. Put a fresh set of bearings in it, and see if the sound is still there. If it immediately is back, look for other problems. You seem capable, so check the flywheel and all other things before pulling it. If the sound goes away, then you have still diagnosed the problem and can run it for a short while before (at least untill) the problems return.

Sound like a plan? It's already apart, and at least you will know for sure as soon as you fire it up.

Once you know you can set up a budget and plan for your rebuild if needed.

Good luck to you.

 

Well I went to the machine shop today (Madcap Racing in Lakewood, CO that builds monster engines of over 600 cubic inches) with the bearings and both guys there thought that for 100k miles the wear pattern looked excellent. It seemed like they were even hesitant on me putting new bearings in there because it might mess up some pretty good clearances just because there is no way to resize the rods, etc.

I only pulled one main bearing so I will finish pulling those, but it seems like it is now onto other ideas.....

--Calvin

 

I read on another forum months ago that the guy, boomdriver, I believe, checked all bearings on a C4 at over 100K and was amazed that they had no wear, other than the "burnish" mark. (My words, not his.) Haven't been into an engine that far for 40 years, but they looked good to me.
I'm still confident the noise will still be there. All that rattling sounded like an old thrashing machine we once had.

joe

 

I wish I had listened to the vid the other day. That doesn't sound like Rod knock to me, and those bearings don't look bad to me. The plastigauge confirms that the bearins are ok, and so are the rods.

Noise is too "high pitched" to be rod knock, in my experience w/rod knocks. I'd put it back together and keep looking.

This just happened on another forum; people were prophesying doom for this guys' motor from a vid. The noise was CLEARLY "tin", not "rod knock" or crank. I said so, and it turned out the guy's crank was hitting his windage tray. Tin. I say you're "Knock" is something else. Not "Deep" enough sound to be rod knock, IMO. Get a piece of vacuum hose and a solid rod to use as "noise finders"...and spend some intimate time with your car.

 

The big question now is do I replace the rod bearings with new ones or just put the old ones back in. Normally I would say replace with new, but there is the possibility that the rod ends and existing bearings have kind of "ovalized" over the years together and it may be better to put the old ones back in, what do you guys think?
--Calvin

 

two days ago, the bearings had another 100k life. but they are not an advantage over new, at this point, opinion.

also, depends on how long you are going to run the engine.

get several educated opinions. some guys do this for a living.

joe

 

Its a real long shot diagnosing your engine knock noise from here & its a hunch I am going on from an experience of my own back in 1994.........

I read all posts.

I once had an input shaft ball bearing fail in a Muncie 4- speed,
also called a front bearing or "Clutch bearing" at times.

The transmission still shifted OK but in neutral sounding like a garbage can full of marbles & metal rolling around along with funny sounding metallic knocks.

I could not pinpoint the noise(s) for several days till I removed the transmission & seen that the input shaft was very wobbly & loose.

I removed the front bearing retainer & all the individaul ball bearings fell out & rolled onto the garage floor.

It might be worthwhile removing the ZF 6-speed transmission and checking like I did in the past.

Won't cost you anything but an another 1 hours worth of your time.

You can also leave the clutch assembly & bellhousing intact without the trans attached & start your Vettes engine.

See if the same noise ( knocking) is present or not.

Brian

 

Here's the deal. Unless you can put all the bearings in the engine exactly the way they came out, I'd replace them.

If the engine guy said to put them back in, I would....he's the expert.

Do NOT put them back in randomly.

I'd get the stethescope out. Does a cam lobe/Lifter sound out of the question?

 

can't elimiminate anything with certainty, I reckon. the symptoms he described in limited detail was noise at idle, after some hard running, so I eliminated valve train -although I might have jumped to that until I heard the noise.
In all fairness, the noise is from an amplified listening device and is not as accurate as our senses are used to, agree?

also, with pan off, you should see evidence, I would guess. Noitce that my words are "guess" and "reckon?"

 

I was sondering about that too. Here at work (ski are maintenance shop) we had a Chevy truck come in w/a noisy engine. It was a real stumper, but we finally diagnosed a bad lifter and cam; chunks were missing out of one cam lobe, and that damaged the lifter roller. Noise was "too heavy" to be a regular "lifter noise", and too "light" to be rod knock.

As for bearings and whether or not to replace them, it's probably "6's", but *I* would replace them. They're cheap and you're in there. At least the ones that I had taken apart. The rest I probably wouldn't touch.

 

So I did replace the rod bearings with Clevite "P" series. The clearances were all very uniform with the plastigauge - all about 0.0015 +/- 0.0003. I pulled all main bearing caps except the front and back and they looked very good. I checked end play on all journals and it was within spec (almost all were 0.014). I checked the crankshaft thrust bearing clearance and it was also within spec (0.004). Bottom line is everything looked beautiful for 100k miles. When I got it started back up it had a slight bump in oil pressure, but that could just be because I put in a different oil than the previous owner. At any rate it runs around 50-60 psi warm at anything above about 1600 rpm and only gets down to about 30 at idle when it is warm - very good numbers in my experience.

Unfortunately the knocking sound is still there. My most likely culprit at the moment is the flywheel. The clues I have are as follows:

1. Bill Boudreau from ZF Doc said the sound in the video is consistent with what a bad flywheel sounds like.
2. The previous owner just replaced the clutch about 5k miles ago and was advised to replace the flywheel and did not - but it seemed to just be because of tracks in the flywheel due to a clutch being changed entirely too late in its life.
3. Pushing the clutch in definitely lessens the sound - doesn't make it go away but certainly lessens it.
4. There is a noise that happens when I shut the car down that is like a few rattles in a row.
5. The noise started just after some spirited clutch action running 0-60 and 0-100 tests to check out my miniram install.

The noise is just at idle - it does not seem to be there when I rev the engine up just a little bit.

 

Unless your balancer is giving up the ghost sounds like a flywheel, esp if it goes away when the clutch is in.

 

There is an amount of play between the dual masses of the flywheel that is supposed the within specification.....I think it is approx. a quarter of an inch. I'm sure someone else can say with more experience than I, but I put a Spec one piece flywheel behind my l98, and have almost zero rattle, and it works great. Got it from Tom at Carolina Clutch, with a kit. Haven't heard the best about the aftermarket throwout bearings though.

Doubt you will be able to remove the inspection cover to check it for play, has anybody been able to do this?

 

Had the same noise happen to me on my 79 trans am i built a 750hp motor for the day before a track rental.
Turned out to be 2 of the flexplate bolts lossened up cause i didnt take the powdercoating off the sfi flexplate behind the bolt heads before bolting it on.
Its weird but could be as simple as a bolt or 2 loosened up on ur flywheel!

Was cluth recently done or tranny out for any reason?
Give it a look!

 

I don't know if anyone has mention this or if anyone has any thoughts but that sound from your video sounds just like Piston Slap from the rings wearing out and the piston have room to moving around inside the cylinder...?

My two cents.