Help! Bottom End Knocking, only @ idle, only after car warms up.

[EttevroC]

I have a very unusual issue with my 89, it has a pronounced knock at idle only after it has warmed up and has been driven, other wise it is running great.

Here's a video of the knocking...

http://www.youtube.com/watch?v=HldQq0Bpcng


I've googled the problem and since it doesn't knock when it is cold and when the engine is above 1000 RPM it doesn't seem to be bearings or rods since every article stated that the noise occurs at start and through the RPM range.

I've come across other articles that hint that it may be header or exhaust system being loose and knocking on something. I've also came across other articles saying that a cracked flywheel may cause the same issue.

Here's what has recently been repaired and replaced...

Prior Work:

1. Replaced Clutch, Fork Clutch and resurfaced Flywheel

2. New Exhaust from Headers to new single
Catalytic Converter

3. New fuel filter and injectors cleaned

Stats:
Oil level and pressure OK
Oil and Coolant temp within norms
Just over 70,000 miles on it...
Babied and never mistreated.

I keep seeing that if there is real trouble with the engine I should be hearing the knocking at first start and through warmup, and since isn't the case, I'm coming back to you all to see if you've seen (heard) this before. Thanks bigtime!!!

 

[boomdriver]

I have a very unusual issue with my 89, it has a pronounced knock at idle only after it has warmed up and has been driven, other wise it is running great.

Here's a video of the knocking...

YouTube - ‪VID_20110521_170140.3gp‬‏


I've googled the problem and since it doesn't knock when it is cold and when the engine is above 1000 RPM it doesn't seem to be bearings or rods since every article stated that the noise occurs at start and through the RPM range.

I've come across other articles that hint that it may be header or exhaust system being loose and knocking on something. I've also came across other articles saying that a cracked flywheel may cause the same issue.

Here's what has recently been repaired and replaced...

Prior Work:

1. Replaced Clutch, Fork Clutch and resurfaced Flywheel

2. New Exhaust from Headers to new single
Catalytic Converter

3. New fuel filter and injectors cleaned

Stats:
Oil level and pressure OK
Oil and Coolant temp within norms
Just over 70,000 miles on it...
Babied and never mistreated.

I keep seeing that if there is real trouble with the engine I should be hearing the knocking at first start and through warmup, and since isn't the case, I'm coming back to you all to see if you've seen (heard) this before. Thanks bigtime!!!

I feel your pain...
I have a similar issue, not anywhere nearly as obvious as yours, but there. Mine however is very very imtermittent. Its there one day...then vanishes for a week. I am almost 100% sure mine is related to the torque converter, or flywheel.

That sound you;re hearing is exactly what a rod small end sounds like when its failing. A rattling or rapping sound. The "knock" sound is a bit different because of where it originates in the rods big end on the crank. Either way,. if it were a rod it should rap as the rpm increase, or during decelleration from reciprocating forces. It's not...

One of the lessons that I learned working with big complicated machines for most of my life, was that when a series of failures appear, most of the time you can go BACK to the last work performed and find the cause...in this case the clutch work.
I've been told that flywheel bolts can back out or a crack thru the hole can make a knocking noise, a loose flywheel, torque converter, or even the TC shield being hit or rubbed can be the source. Mine is more of a rubbing or bumping, thats how I know that its not in the engine rotary group...that and the fact that I used a stetiscope to listen to the block...
You might try that trick yourself...use a length of small tubing, hold the end in various places and listen as the other end is held to your ear canal...you can hear everything, and you can pin down the location of that rapping...

One more thing...if you can hear it in the cabin better than when standing outside when the hood is down, thats a good sign thats its flywheel/trans related.
Good luck !

 

[EttevroC]

Thanks Boomdriver for the home made stetiscope suggestion I'm heading out today to pickup some tubing.

 

[ex-x-fire]

I'd first remove the drive belt to make sure its not a alternator, p/s pump, ect.
I'd remove the valve covers to make sure its not a loose rocker arm.
Its fairly easy to remove the oil pan, grab the rods & wiggle them. If you find one that moves, pull the cap so you can look at the bearing.

 

[EttevroC]

Thanks ex-x-fire, I never thought about the accessory belt. I just just joking with a friend that the next thing to go is the water pump. I'll check that out as well.

 

[boomdriver]

Thanks ex-x-fire, I never thought about the accessory belt. I just just joking with a friend that the next thing to go is the water pump. I'll check that out as well.

Yes...

Just take the belt off and start the engine and listen. You can run it for a minute or 2 safely when its cold. If the sound is exactly the same, its not related to an accessory but after hearing it, I feel safe in saying that is wishful thinking...

While the belt is off, take a close look at the balancer & pulley. A balancer thats coming apart makes a different dinging noise as it slips around and bangs itself, but it'll drive you crazy trying to find it...I had one come apart that kept spinning for 5-10 seconds AFTER shut down...made me nutty hearing something spinning after I had exited the car. Finally got the chance to see it spinning when I had someone else turn the key off so I could keep my face under the hood and look for the sound....
Look at the tensioner too. When the belt stretches as far as it possibly can, the tensioner pulley can contact the a/c pulley and make a knocking or chattering sound. I don;t think this is the case here but its worth looking at.

Even an air pump thats seizing won;t make a solid rapping noise like that. Its definately rythmic, indicating rotation at about the speed of the crankshaft.

You might have to reach under the car while its on jack stands to get a good listen to the bellhousing or around the pan as it idles. If you know someone with a lift...thats a bonus !

 

[G Winter]

Push in the clutch pedal and see if it changes . Put it in gear and slowly release the pedal and see what the sound does.
You said you surfaced the flywheel. If it is OEM it has the dual mass flywheel. You may have a flywheel about to come apart. ZF doc told me the early flywheels had no cover over the seal in the flywheel crap can get in and take out the seal.Then things start to go wrong.
If it appears to be flywheel related you might want to contact him, he is very good about sharing information.

Scav.

BTW Before I replaced my clutch and flywheel I had a similar rhythm but more of a click when it was warmed up. That is gone. Did you notice a click before the knock started ?
I located this after I posted.

ZF dual mass flywheel

 

[EttevroC]

You might have to reach under the car while its on jack stands to get a good listen to the bellhousing or around the pan as it idles. If you know someone with a lift...thats a bonus !

I checked all of the accessories on the top of the engine and while doing so I noticed that the knocking is definitely towards the back of the engine.

We've had to much rain for me to get the car up on jacks, but that's the first place I'm going to when things dry out.

Thanks for the suggestions, BoomDriver!

 

[EttevroC]

Push in the clutch pedal and see if it changes . Put it in gear and slowly release the pedal and see what the sound does.
You said you surfaced the flywheel. If it is OEM it has the dual mass flywheel. You may have a flywheel about to come apart. ZF doc told me the early flywheels had no cover over the seal in the flywheel crap can get in and take out the seal.Then things start to go wrong.
If it appears to be flywheel related you might want to contact him, he is very good about sharing information.

Scav.

BTW Before I replaced my clutch and flywheel I had a similar rhythm but more of a click when it was warmed up. That is gone. Did you notice a click before the knock started ?
I located this after I posted.

ZF dual mass flywheel

Thanks Scav. I'll check to see if the sound changes if I push in the clutch and when it's in gear and slowly letting it out.

The sound started out sort of like a softer clicking/knock sound, and then it went away. This time it came back and it was in full knocking sound.

I just watched that video, thanks bigtime for finding it!!! If that's a true representation of how my car's flywheel works, it makes more sense why it makes a noise at first and goes away as the RPMs increase.

Here are pictures that the repair-shop made of my flywheel before and after resurfacing...

 

[boomdriver]

I checked all of the accessories on the top of the engine and while doing so I noticed that the knocking is definitely towards the back of the engine.

We've had to much rain for me to get the car up on jacks, but that's the first place I'm going to when things dry out.

Thanks for the suggestions, BoomDriver!

YW !

I use the tube every so often just to ck for odd noises and lifters...when bored I'll listen to injectors tic...or the distributer clicks as it fires past the 8 post...all sounds so different when its crystal clear thru the tube.. for one thing....LOUD !

 

[gmjunkie]

Here are pictures that the repair-shop made of my flywheel before and after resurfacing...

View attachment 3897

So what did they use to resurface it,a 2 1/2 inch body grinder with a 16 grit rolock disc???My guess is THATS your Noise!~!! Buy a NEW DM Flywheel,I'll bet your noise will be gone!~!!

A properly re-machined flywheel will have a surface that looks more like the photo below!~!

 

[Hib Halverson]

Well...I've listened to that youtube footage twice.

It doesn't sound like a dual-mass flywheel. It doesn't sound like any accessory. It's coming from the back of the engine or the sides of the engine.

The knock is coming at the same frequency as the valve train noise, so I'm going to guess the engine has a valve train problem.

An automotive stethoscope will help a lot. The best on the market is the Lislie 52750.

 

[boomdriver]

So what did they use to resurface it,a 2 1/2 inch body grinder with a 16 grit rolock disc???My guess is THATS your Noise!~!! Buy a NEW DM Flywheel,I'll bet your noise will be gone!~!!

A properly re-machined flywheel will have a surface that looks more like the photo below!~!

I was thinkin 4" paint stripper wheel is what they used....or the edge of the 4" cut off wheel !

Looks to be a little rough....chatter chatter chatter clack clack....




knock knock?



Who's there?


Hadya.




Hadya who?





Had ya gone to a good trans shop they would have replaced the flywheel.....

 

[joe paco]

I listened to it. no flywheel finish would contribute to this, if that were the case, 90% of clutch autos would have it.

wasn't there before, and the finish was "most definitely" rougher than now, like a corncob.

sounds like clearance in valvetrain, lifter collapsed, tappet loose. with increased oil pressure, lifter pumps up enough to close valve gap. or, intake valve slapping onto seat due to clearance.
definitely not VATS or ECM!

 

[G Winter]

Well...I've listened to that youtube footage twice.

It doesn't sound like a dual-mass flywheel. It doesn't sound like any accessory. It's coming from the back of the engine or the sides of the engine.

The knock is coming at the same frequency as the valve train noise, so I'm going to guess the engine has a valve train problem.

An automotive stethoscope will help a lot. The best on the market is the Lislie 52750.

Hib, I thought valve train at first too, but the strange rhythm changed my mind. Has the same rhythm as the dual mass click. Pulsing with the idle. I really think he has a very bad flywheel. Another thing the noise goes away the instant the engine eccelerates that is not time for oil pressure to pump up a lifter. The noise also comes back when the engine is done deccelerating.



Glenn

 

[joe paco]

Hib, I thought valve train at first too, but the strange rhythm changed my mind. Has the same rhythm as the dual mass click. Pulsing with the idle. I really think he has a very bad flywheel.

Glenn

after re-reading your previous msg and looking at the video, I can see a lot of opportunities for the clicking noise! Wow! I am confident it is not surface finish -and too smooth is not ideal, either, but had never understood the dual wheel.
A short cut would be to push the clutch in at idle, which should alter the frequency. You suggested the guy do that, not sure if he did.

Thanks for the video. Have not worked on clutches since 1967. I learned something.

 

[EttevroC]

So what did they use to resurface it,a 2 1/2 inch body grinder with a 16 grit rolock disc???My guess is THATS your Noise!~!! Buy a NEW DM Flywheel,I'll bet your noise will be gone!~!!

A properly re-machined flywheel will have a surface that looks more like the photo below!~!

Holy Crap, that's worlds away from the picture I posted. :ugh When they said that they refinished the flywheel I never second guessed them.

As soon as I'm able to get under the car with the tube assisted audio enhancer that's where I'm going to check first.

Thanks bigtime for the photo!

 

[gmjunkie]

after re-reading your previous msg and looking at the video, I can see a lot of opportunities for the clicking noise! Wow! I am confident it is not surface finish -and too smooth is not ideal, either, but had never understood the dual wheel.
A short cut would be to push the clutch in at idle, which should alter the frequency. You suggested the guy do that, not sure if he did.

Thanks for the video. Have not worked on clutches since 1967. I learned something.

I don't think it's the surface either,I think the fly wheel has some broken springs in it!~!! I was pointing out the Butcher Resurface job,It's plainly been ground unevenly by hand!(blow the 1st 2 potos up 150% and take a good look!)At best it has to be somewhat out of balance now!! That will amplify any other noises from broken springs or worn bushings in the duel mass that not necessarily were audible before!~!! I've been on a couple Duel Mass rodeos before,even changed out a cam and lifters over a noise very similar!~!!

I may be WRONG,
I have been before!! :L

 

[EttevroC]

An automotive stethoscope will help a lot. The best on the market is the Lislie 52750.

Thanks Hib for the stethoscope suggestion, I popped into Loews this afternoon to see if they sold any, nope. But I do have the tubing now.

 

[EttevroC]

Had ya gone to a good trans shop they would have replaced the flywheel.....

:duh I thought I was dropping it off to a good shop, it's one of the highest rated Corvette Only shops in the DC area, but maybe I got a short timer for a mechanic that day. :cry