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post #1 of (permalink) Old 06-10-2009, 09:04 PM Thread Starter
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Rattling noise when running

Got the jeep running and most everything is going well, except...

When I first start it (i.e. cold start) there is a rattling noise that is RPM related. It almost sounds like a loose rocker arm hitting the valve cover (pulled the valve cover and no signs of that and retorqued the rocker studs bolts plush checked all push rods and no slop in those). After about a minute of running or so (plus some revving) the sounds gets noticeably quieter and will disappear when the clutch is pushed in. Let the clutch out fully and the noise is back (although quieter than when cold).

I need to try one more time, but I believe that on a cold start the clutch position did not affect the noise.

The guy that did the exhaust said he thought piston slap. However, this noise is a new development (since exhaust) and prior to that although it wasn't run much, I know it wasn't making this same sound. I'm still firmly in the break-in period on a rebuild (.030 over with new pistons, bearings, cam, 4.0L head). I don't think that piston slap would be a developed issue (if due to undersized pistons).

The only thing I can think of now is a bad throw-out bearing, but I wouldn't think engine temp would have an effect on that (making it go from uncomfortably loud rattling/knocking to just a minor annoyance). If anyone has had one that acted like that, please let me know. It doesn't make sense to me, but could be. It also idles smoothly, no apparent missing and the rattle appears to be coming from near the firewall (not sure top/bottom or bellhousing/engine).

P.S. Thanks for the starting help, ended up being an incorrect gasket between metering block and airhorn.

Mark
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post #2 of (permalink) Old 06-10-2009, 11:45 PM
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Clutch answers your question,

It's the throwout bearing on the clutch,
OR,
It's the thrust face on the crank wiped out and when things heat up, the crank expands enough to keep the clanking to a minimum.

I really think it's probably the throwout bearing from the way you describe it...

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post #3 of (permalink) Old 06-11-2009, 10:41 AM Thread Starter
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Any chance that a low lubricant level would be the same result. Loud noise until lubricant gets tossed up to the top of the tranny. Then quiets down?
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post #4 of (permalink) Old 06-11-2009, 11:07 AM
 
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I'll throw my two cents in -

Throwout usually seems to squeal or rumble *when the clutch is depressed*. So betting against that.

One think that could make sense - the input shaft bearing on the tranny. It's spinning when the clutch is engaged, and after the tranny fluid and bearing heated up it might quiet down. Have you checked the fluid level in the tranny? And changed it regularly?

Not sure why you would not have heard it before the exhaust work... unless you had an exhaust leak that was drowning it out.


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post #5 of (permalink) Old 06-11-2009, 12:10 PM
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It does sound like clutch or throwout bearing, particularly if pressing the clutch pedal quiets it regardless of engine temperature. Also check the bellhousing-to-block and transmission-to-bellhousing bolts.

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post #6 of (permalink) Old 06-11-2009, 12:25 PM Thread Starter
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Thanks for the thoughts. Started this morning (idles well) but when cold (w/in about 1-2 minutes of starting) clutching isn't as effective at totally removing the sounds as once it is warmed up. I haven't checked the fluid level in quite a while (expecting pretty low). I'm thinking my tranny input shaft might be able to just catch some lubricant and very slowly gets the gears covered while idling. Maybe revving while out of gear speeds up the coverage of the drive gears, while putting it in gear and driving it does even better at reducing the sound. From the feel of it my synchros into 2nd is almost shot and if there was one in 1st it is completely gone.

The sound never totally goes away. After idling for a while or being driven the noise gets noticably less and disappears almost entirely when the clutch pedal is depressed. Once released and underway you can just barely hear the rattle.

Never have figured out whether I have a T-4 or T-176 (86 CJ w/ Dana 300 and Dana 44 rear end).

We'll see if a good shot of tranny fluid takes care of the really loud sound. I'm guessing the throwout bearing may be bad too. I didn't replace the clutch during the rebuild so my wife could learn manual without destroying a new one.
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post #7 of (permalink) Old 06-11-2009, 12:28 PM Thread Starter
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For tapenick

I didn't hear the sound before the exhaust because I am pretty sure it wasn't there. It is a developed problem since sometime around the exhaust going on (not thinking the two are related).
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post #8 of (permalink) Old 06-12-2009, 12:51 AM
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Quote:
Originally Posted by mdn86cj7 View Post
I didn't hear the sound before the exhaust because I am pretty sure it wasn't there. It is a developed problem since sometime around the exhaust going on (not thinking the two are related).
You didn't say there was exhaust work done...

Check to see if your new exhaust is anywhere near the clutch linkage...

Exhaust pipes get CONSIDERABLY longer and move around like crazy when they Cool/get hot (Expand/Contract like crazy)....

Exhaust WILL make a 'Ringing' or 'Rattling' sound where loose inspection covers and stuff make a 'tinny' vibration sounds...

Also, dry throw out bearings make a 'Rattling' sound when you let them sit there DISENGAGED riding on the transmission, and STOP making noise, or reduce the noise when you push the clutch in and put them to work...

The throw out bearing won't make 'Squealing' noises when you push the clutch in until it's COMPLETELY SHOT and/or locked solid...

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post #9 of (permalink) Old 06-13-2009, 07:06 AM
 
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Quote:
Originally Posted by mdn86cj7 View Post
I didn't hear the sound before the exhaust because I am pretty sure it wasn't there. It is a developed problem since sometime around the exhaust going on (not thinking the two are related).
Does your vehicle have a catalytic converter?

When my "90" YJ's cat started making weird noises, it wasn't more than a month before the last little pieces of the ceramic honeycomb core came out the tailpipe.

That noise drove me nuts trying to find it'd cause!
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post #10 of (permalink) Old 06-22-2009, 09:21 PM Thread Starter
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Okay, after pulling the tranny and transfer case I found that without loctite the flywheel bolts had loosened and the flywheel was the rattling noise. (this after pulling valve cover and oil pan). Glad I caught this before the flywheel came off.

Now I have a new clutch plate, pressure plate, surfaced flywheel, and throwout bearing. Runs great, but now I am getting an intermittent squeal that is really annoying. Can't tie it to one thing, but is it normal for a entire new clutch to take a while breaking in? Possibility of a bad throwout bearing? Initially I would just get it occasionally when letting out on the clutch using the engine to slow down in 2nd when I had been in 3rd. Now it is mostly not there, but occasionally when going into gear is starts and gets really loud as I accelerate.

The old throwout bearing had a grease zerc but was completely shot while the new one seemed to have nothing of the kind. Do you need to pack the throwout bearing like wheel bearings? The guys at the shop I was working at said you didn't, it was already taken set out of the box. But if this squeal isn't normal and I have to cut down my exhaust and drop the tranny again I'll be a bit upset with Autozone (and the advice I got).

Thanks in advance.
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