Engine Grinding Noise
 

New guy here. I have a ’77 911S that I got about 5 yrs ago. I am in process of getting it cleaned up for winter and have a question. The engine is a Brumos Rebuild 2.7 with aprox. 50K on it. I have heard rumors Brumos does poor work so am curious about the following. The engine runs strong but just recently the oil pressure dropped to zero and fluctuates within the RPM range. 0 @ idle as high as 180 at 3k when warmed up. I have a suspicion it is the sensor and is soon to be done. What concerns me is the fact the engine makes a mechanical scraping noise when shut off. It can only be heard outside the vehicle. The scraping is not heard while the engine is running. But, I get pre-detonation (marbles in a jar) from a load. (Light to Go) My mechanic told me this is normal but have not run the car since. The pre-det could be from the 91 pump gas and blistering heat here in phx.(have not tried since) Roy @ motor meisters believes the engine may need rebuilt but cannot confirm unless he sees the car which I’ll have to trailer from phx to CA. My next step is to remove the belts to the accessories to see if one is the cause of the noise. .Has anyone experienced this? Mainly the mechanical scrape noise. Suggestions?

0 lbs at idle is normal. That used to scare the hell out of me too. It's OK. As long as you have pressure at higher RPM it is fine. (At least on my 70 2.2) Do you have pressure fed tensioners on this engine? If not it sounds like it could be time to upgrade. That scraping sound could be foreplay to disaster, as in tensioner failure. Bad ..very bad. Are you hearing this sound at idle? I don't quite get it that you only hear it when you shut down.

I only hear the scrape when standing outside the car, turn the key off and the engine rolls down. The sound is not evident when idling. The tensioners were upgraded to carrera oil feds when the engine was rebuilt.

Check your alternator/fan bearings/fan shroud for the source of the scraping noise. Could also be sometime awry in timing chains. Jim

I would find another local wrench to discuss your issues if your current guy is no help.

As far as your rebuild, personally, I would never have my engine rebuilt at a place that I would be unable to "drop in" and perform periodic progress inspections.

Re: Engine Grinding Noise
 

Please, please, please do a search on Motor Meister or "MM" using the search button (in the upper right corner of this page).
-Chris

I'm not surprized that Roy at MM believe a rebuild is in order. If you take it to MM, the real question will be whether your engine is effectively newer after the rebuild, or older. FWIW, I am not nearly as convinced as Roy.

I too would guess fan/housing contact. Scraping is a noise I have never heard coming from the inside of an engine. I expect it to be exterior. Look for scraped surfaces. Replace the oil pressure sender, or attach a mechanical pressure gauge.

Before you send your engine to MM, do at least two things. First, investigate. I think your engine problem is external, and the last thing you want to do is engage a rebuilder without even knowing whether there is something wrong with your engine.

And second, do a "search" on Motor Meister.

Superman,
I hate to disagree with you but..
I would so a "search" on Motor Meister first. ;)
(Way more entertaining.)

Seriously though, do you suppose a failing alternator bearing could be letting the fan touch the fan housing?
-Chris

MM = YIKES! Thanks. Sounds a lot like what I got on Brumos. I definitely want to find the source of the noise myself (I’m one of those freaks who can’t stand a squeak in the dash). That’s why I sought out a BB to ask opinions. I’m planning on checking all the accessories (fan, alt, a/c). Just been too hot here. By the time it cools down I have no light. I just need to bite the bullet. Thanks all of you for your input and help. I’ll keep you posted. Mission First, People Always.

Get a mechanic's stethoscope (Sears sells them) to check location of noises. Take care you don't get tangled up in the exposed rotating parts of the engine; watch out for your hair, clothing and external body members! Cheers, Jim

Mine makes a kinda amplified rumbling noise thats worse when its cold. Its not metallic sounding, & the period is irregular. Could this be coming from the alternator bearings? At 1 point the fan scraped the shroud because I can see marks in the shroud (but its not doing it now). I listened to the valve covers & chain covers & the noise is not coming from these regions.
Thankyou.

Harbor Frieght has them on sale for next to nothing.

I have the HF model, but a long screwdriver or dowel works just as well. Put one end of the stick against a component and the other end against your ear. And I mean AGAINST your ear. So that the stick is vibrating your head bone. You'll hear things just fine.

Yes, failed alternator bearings can sag and allow the fan to contact the housing. Yes, a failing alternator bearing will rattle.

The noise I hear is less of a rattle & more of a "rumble". Other than the bearings I can't see what it could be though.

Is "head bone" the correct medical terminology? :)

take off the belt and then run it for a few minutes to see if the noise is gone.

Good call John- thanks. I think I'll take the opportunity to put in a new belt this weekend.

I had the same problem with my 2.2 after putting it back in the car and I know exactly the sound you are hearing. The car wasn't really running before I got it so I don't know if was preexisting. Interestly, it stopped shortly after reinstall.
The sound happened during the final couple of rotations of the engine after the ignition was turned off . It scared the cr#p out of me the first time it happened. I think my problem was the exhaust was loose at the mufflers and the engine vibration/torque at the end was causing a metal rub. I tighted things up and haven't heard it in a while. It was definetly an external rub.

Have someone depress and release the clutch while the motor is running while you stand outside and listen. Sometimes these kind of noises can be a throw out bearing starting to go.

That's a good suggestion,come to think of it I originally started to car in neutral and have worked the clutch quite a bit since then. I'm sure the sound from the throw out bearing would resonate.

Brainwave- the rumbling began after my SC was off the road for a few months. Amongst other stuff I took out the AC compressor in that time. Maybe this changed the strains on the alternator bearings somehow??? (I noticed the sound the very first time I started it up)