Engine back in, new noise #$%^&*!!!.

emcon5 · emcon5's Garage

Well, I finished up the reinstall from my clutch job this evening. I pulled the engine to replace the clutch, and while I was there I did most of the stuff Wayne recommends in his 101 projects book, oil seals and stuff, plus the CIS injector boots. I also pulled the injectors out and had them cleaned and tested. Tonight, everything seemed to go OK, I connected and adjusted the clutch linkage and put in new oil, I cranked it with no fuel pump relay until I got oil pressure, then started it up. I let it warm a couple minutes, then did a nice slow drive around the neighborhood to get it up to operating temp so I could add the last bit of oil.

Here is the problem: There is a loud vibration/rattle, starting about 2000 rpm. It seems worse at 2200 or so, and gets quieter above 2400 or so. I did the old "put one end of a broom handle on the engine and the other in your ear" trick on both timing chain covers, as well as different spots on the case, and it doesn't SEEM like it is coming from anything internal. My father in law thinks it is coming from the engine fan, or just behind it. I have my doubts about there being a problem with either the fan or alternator, as they worked fine before, and I didn't do anything in that area. It sounds like metal vibrating against metal. It does not vary with engine speed, other than starting at 2000rpm as mentioned above. It sounds normal at idle.

Does anyone have any ideas, other than "you forgot to tighten something dumbass, and that is the frequency it resonates at"?

Any ideas at all of where to start looking would be greatly appreciated.

Tom

john walker's workshop · 12-04-2001, 07:04 AM

the heat shield on the cat is the usual culprit. push on it, and the rear tin above the muffler while it's making the noise. a piece of fuel hose on your ear can be used as a stethoscope.

911pcars · 12-04-2001, 08:28 AM

If John's suggestion doesn't solve the problem, you can try isolating the noise by disconnecting the fan belt, then run the engine briefly to see if the noise goes away. If it doesn't it's not the fan/alternator.

Is the nature of the vibration like sheet metal or heavier, like metal? Does this happen with the car at a standstill and/or just at speed?

Sherwood Lee

emcon5 · emcon5's Garage

Thanks for the replies.

It sounds to me like sheet metal. There is a crack in the cat heat shield at the front end, near where the cat bolts to the exchangers, I will try that first. I think I have an exhaust leak at that joint anyway.

The only other thing I can think of is maybe the tin is rubbing against the oil line for the passenger side tensioner. I added the pressure fed chain tensioners while I had it apart. I notched the tin, but maybe I didn't do a good enough job.

I will try again this evening.

Tom

jlr69s · jlr69s's Garage

Like John said earlier, it could be the heat shield covering the muffler at the back. Had simmilar noise on our '84 and it turned out to be that.

davis911s · davis911s's Garage

Does this sound go away when the engine is warm? I am asking because I also added the tensioners to my car last year, then there was a new noise, but it goes away when the engine is warm. I have been told it is the tensioners -nothing to worry about.

Shawn

emcon5 · emcon5's Garage

It didn't go away when the car was warm. It got up to 210F or so with no change in the noise.

I am thinking happy thoughts about it being the heat shield.

Tom
(full of happy thoughts about non-terminal sources of the ugly noise)

Jamie79SC · 12-04-2001, 03:42 PM

I have almost exactly the same symptom after a clutch replacement on the 79 SC and I can't locate the source either. (I'm CAT free, so that's not it).

You know that kind or rattle/chirp/whirr sound the 915 makes on a light throttle at low RPM? That's it, but louder. It's worst at 2200 rpm to 2800 rpm. I would have guessed chain tensioner too - but they sound fine when I put a screwdriver to my ear.

Here's the weird part. You can here it clear as a bell when you are in the car. My wife even comments on it. Stand by the engine compartment - nothing. Roll under the car on jack stands and run the engine- nothing. Now I'm starting to imagine all kinds of terrible sounds every time I start the engine.

John, I'm on the East Side. You open on Saturdays? javascript:smilie('

')

Jamie 79SC

john walker's workshop · 12-04-2001, 04:48 PM

mon-fri 8-6. sat i'm around but it's my hobby day.

emcon5 · emcon5's Garage

Well, I was in a good mood for a few minutes. Not any more.

I removed the heat shield from the cat, and bent the engine tin away from the right side tensioner oil line, and started it up. No rattle. Blipped it up to 3K or so, no problem. I figured it was good, so I let it idle while I did some clean up where I was working for the past week. While driving home, it started again. I don't think it is tranny related, it happens in neutral and every gear, clutch in or out.

I drove it home, and will see if I can take it over to my mechanic tomorrow and let him have a listen. I really think it is something stupid.

Can an exhaust leak cause a rattle like that?

Thanks again for the advice,

Tom

don911 · don911's Garage

My 87 makes a similar "whirr" noise around 3K. It only does it when driving. I've assumed it's the clutch. I'm hoping it goes away on a clutch change and it's nothing serious.

KTL · 12-05-2001, 08:53 AM

My 87 has that same odd rattle noise between mid-2k and 3k. Don't know what it is either. Very bothersome. Replaced clutch assy. with spring-centered disc last winter so I have to hope it's not a clutch-related issue. Sorry Don!

Superman · 12-05-2001, 10:47 AM

Tom, it sound like you are inclined to the noise as a nuisance rather than a big problem, and I hope you can hold that thought and resist the temptation to be scared by it. If you have listened to the engine and tranny cases and determined that the noise is not coming from inside them, then you must realize that this is just some external component that is rattling. I'd keep investigating of course, but I think you will find the source is truly no more than a nuisance.

emcon5 · emcon5's Garage

Update: I dropped it off at my mechanic's yesterday, for his opinion on the source of the noise. He went over the engine with a stechoscope, and found a rattle coming from the timing chain covers, with it loudest at the the left side. I gave him the OK to open it up, and when I went by today, he showed me that one of my new tensioners was bad, and he suspected the other was bad as well, based on a similar (but not as bad) noise from that side.

With the piston extended, I could push it down with my finger fairly easily. He had a used good one for comparison, that wouldn't budge when I tried it. He also used an compressor to pressurize the the piston and with very little pressure it would vent out the relief valve. He did the same to his good one and it didn't vent at all.

I gave him the OK to take apart the other side, and I will take the tensioners back to where I bought them next week. I got them locally. Hopefully the replacements aren't bad too.

Dammit.

Tom

Doug Zielke · 12-07-2001, 06:57 PM

Tom...I appreciate this useful information.
There is always some discussion on the mystery of (new) tensioner failure. There have been reports of some noise on new installations when first starting, then, it goes away after a few moments never to return. Luckily, that was the case in my motor. It really is a nasty noise, definitely *not* one you want to ignore.

emcon5 · emcon5's Garage

I just did a search of the archives, and found a couple threads on bad new tensioners. Nothing recent though.

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=38024

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=51734

Tom