You can ...

2001 boxster S
this afternoon started to hear a rattling noise from the front of the motor when i drive. it is not there at idle but begins to resonate a fast clattering, rattling sound when i reach 2800 rpm and gets louder to about 3500 rpm. if i rev the motor i can hear it right behind me, always at the same rpm. what the hell can that be? I parked it until i can work on it. tried to insert a mp3 recording of the sound but i can't figure out how

If you haven't already, it's probably worth taking off the front engine cover (the one parallel to the seat-backs) and having a look around. You may be able to isolate the sound this way.

i was going to do that on friday. was wondering if i can rev the motor without the serpentine belt on to see if it is from the inside of the motor or the outside? i am not sure if there is anything that might get damaged if i rev it to 4000rpm a couple times with no belt?

... run the engine without the Poly-Ribbed Belt for a few minutes.
Without the belt you will not have A/C, Power Steering, Alternator or Water Pump.
After you remove the belt but before you star the engine, manually check the idler and tension pulleys for play.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Once you have removed the inspection cover, I would inspect all the idler pulleys (3 off), ancilliaries (A/C, alternator / water pump / power steering pump) and belt to see if there is anything obvious. If all looks OK, run the engine with the belt still attached to see if you can identify where the noise is coming from.
If that proves fruitless, remove the belt (24mm spanner) and spin each pulley to see if they have rough / noisy bearings.
You can run the engine without the belt, BUT for not more than a minute or so with a cold engine. The last thing you need is an overheating problem !!.
Sounds like it could possibly be a broken water pump... Try gripping the W/P pulley and see if it moves up & down (wobbles) or see if you have a water leak from the shaft area.
If the clatter is still present with the belt off, there is another problem.

The A/C compressor has an electric clutch so that it doesn't drain power from the engine when it is not needed. As the compressor gets older, the clutch starts to get a little wonky and makes noise when turned off (my car does this). If you have the A/C turned off because it's winter, try setting A/C to "low" and give the A/C system a few minutes to warm up and then see if you can still hear the noise. Then turn the A/C button off and wait a minute and see if it sounds different.

1998 986 Turbo-Look Cab
172,000 Miles
Dilithium Crystal Supercharger

The alternator on manual Boxsters has a clutch system mounted inside the pulley. Tip Boxsters have a direct mounted pulley.
Last year I was experiencing a low rumbling noise at idle rpm. After removing the belt and replacing the bearings in the idler and tensioner pulleys the noise was still there - so I removed the alternator and discovered the "clutch" was seized. My local Bosch service agent replaced the clutch (~$180) and all was well. He said they usually are noisy when the seize - mine was not so I might have caught it early.
The alternator pulley has a black plastic cover over the clutch which is easily prized off to locate the clutch assembly, but the clutch itself has a special tool for its removal - which I didn't have.
It can be removed with the alternator in position but the belt has to be removed obviously....
As Marc suggested, I would still check your water pump and idler / tensioner rollers as well.

out of the ordinary when I checked for play at the various accessory drive pulleys and when I spun them and I'm sure I spun the alternator pulley along with the others. I do remember for instance feeling of pulsing when I spun the power steering pump which is what I expected.

But beyond that, I can't recall anything out of the ordinary and I think had there been I would be able to.

Darn near tempted to remove the cabin engine access panel and remove the belt and give it another check just to refamiliarize myself with my Boxster's accessory drives. If I had the car at the office today I think I would.

But I'm due to visit a Porsche dealership service department tomorrow on some other business and if I have the time I'll touch base with the tech on this alternator subject and see if he can shed any light it. I'm a bit curious to know more.

Sincerely,

MarcW.

took off the belt and ran the motor first to make sure that the noise is not from inside the block, that way i will not cause any more damage if it was. and the verdict is that the motor sounded fine other than a small tick tick tick from the passenger side. now i will put belt back on and try to isolate which of the outside troublemakers it is.

and after I verified the noise was coming from one of the accessory drives (by starting and running the engine (cold) sans the belt) id'ing the offending accessory drive (water pump) was not difficult.

I did it with the belt off and giving all the accessory drive pulleys a good shake/wiggle/feel looking for any play. Check the idler/tensioner rollers too. That noisy one has to be loose/wiggly.

All but one will be tight so the one that is not tight, that exhibits any play when you give its pulley the shake/wiggle treatment willl stand out.

If you put the belt back on you're right back where you started from. There's noise coming from the front of the engine, an accessory drive (or idler/tensioner roller), but which one?

Also, check the belt edges. If one -- with my car's water pump just the inside edge of the belt was sharp -- or both edges sharp the belt's rubbing against one of the accessory drive pulley sides. These belts are not supposed to contact the sides of the pulleys, ever. If there's enough to wear a sharp edge on the belt then the odds are very high the bad accessory drive's corresponding side is going to be shiny.

If none are shiny if the belt doesn't have a sharp edge then idler/tensioner roller has got to be suspect. There are less common reasons for the noise (as I think someone pointed out the A/C compressor clutch can generate some noise if it goes bad) but I think you'll find it is something more common.

Sincerely,

MarcW.

question is the alternator pulley supposed to engage when spun one way and disengage when spun the other way?

in such a way and the serpentine belt routed in such a way that it only gets spun in one direction.

I've never encountered an alternator that I could not rotate the pulley by hand in either direction with the same amount of effort. Nor have I encountered an alternator with a directional clutch. Are you sure you're not looking at the A/C compressor pulley?

Anyhow, even though the alternator can (or should be able to) turn in either direction, the alternator may not work as well or even at all when spun the other way. (The fan blade angle or the wiring or the electronics may be optimized for the direction of rotation.)

Sincerely,

MarcW.

when i spin the alternator pulley clockwise it feels tight and i can not stop the fan inside but when i turn it counterclockwise it feels loose and i can stop the fan inside and still spin the pulley

from an accessory drive on my 02 Boxster I just grabbed each drive pulley and gave it a healthy shake/wiggle test looking for obvious play and when I didn't find any then I went around again looking for a bit more play at one drive than the others. The second go round had me stopped at the water pump. It didn't have much play but more than the other accessory drives.

I spun the various drive pulleys around by hand and don't recall having any difficulty or noticing any real difference in trying to turn them one way vs. the other. I'm pretty sure I would have remembered because encountering this would have been contrary to my experience and expectations.

Now I might have say at the power steering pump or the A/C noticed a bit of a difference in spinning the pulley one direction or the other but I would have expected this, since these might be more directional than the water pump (though of course the water pump is intended to spin one direction cause its impeller is directional but this difference should not make itself known at the very low speed one can spin it by hand).

As best I can remember the alternator didn't have a clutch on its fan either. There's no reason I can think of it would need this. And I don't think the alternator has a viscous clutch that allows the fan to freewheel until the viscous fluid coupling heats up and then causes the fan to spin. Some radiator fans have this feature but I've never come across it at the alternator.

I'm looking at a pic of my Boxster's alternator (with the belt in place) and I don't see any evidence of any directional clutch mechanism in the pulley -- the pulley is quite small in diameter. The fan behind the opening of the outer housing does look directional, at least at first glance. The fins at their outer end are angled counter-clockwise. This does suggest the alternator is intended to spin counter-clockwise at least because this results in the better air flow from the fan. (But one may not be able to depend upon the fan fin angle entirely. Designers are pretty clever at coming up with a fin shape/orientation that works equally well when turned in either direction.)

You're going to have to find a way to check out another alternator and see if you spot the same behavior, characteristics to (possibly) determine if what you found is normal (and beyond my experience) or abnormal. Perhaps a friendly local Porsche dealer parts manager would let you look at an alternator? (Though I doubt it stocks any but it might have one sitting about.)

Or maybe you can visit a large autoparts supply store and see if it has a Porsche alternator in stock that you can examine? The alternator may be the same one used on a VW or Audi model, too. It may be my imagination but I seem to recall the Passat uses the same alternator as the Boxster. However, I'd not buy a new alternator based on this vague memory of mine without more confirmation. But right now you're not looking to buy but to get your hands on a known good alternator and see if there's any obvious differences. Or maybe even visit a Porsche wrecking yard and look over any alternators it might have handy.

Sincerely,

MarcW.

1998 986 Turbo-Look Cab
172,000 Miles
Dilithium Crystal Supercharger

and unless the alternator is tuned to generate power more efficiently when spun in one direction vs. the other or if there are alternator fan/air flow requrements, or the rectifying circuitry is in some way directionally sensitive it should make no difference.

I would not be surprised if one or more alternators were bi-directional to reduce the number of different alternators that need to be stocked.

But as I started out with, I don't know for sure.

Sincerely,

MarcW.

No way it is directional (electrically). You are correct that an alternator generates A/C voltage and current which is rectified (diode bridge) and regulated (voltage regulator).

dghii
2000 Boxster S 6speed 112k miles

1998 986 Turbo-Look Cab
172,000 Miles
Dilithium Crystal Supercharger

directional on an electrical basis can be directional on a mechanical basis and one area I was not aware of is the slip rings. These can be optimized to provide long life, long service for one direction at the expense of shorter life, shorter service in the other direction.

Sincerely,

MarcW.

There are alternators that can work in either direction. As a matter of fact one of our automotive parts supplier clients makes a micro-hybrid reversible starter-alternator. It is used on some of the OEM cars with start-stop technology (automatically shuts off the engine at the traffic light and then instantly restarts as soon as the accelerator pedal is stepped on). [The really nice feature of the combined starter-alternator is that it saves weight, space and in newer applications, horsepower.]

[www.986forum.com]

is harmful. Do you know if this is the case? I can of course believe that routing the belt wrong and running the alternator in the 'wrong' direction against the one way clutch would harm the pulley/clutch and right now.

Sincerely,

MarcW.

well i couldn't work on it today much due to work, but late last night i couldn't sleep so i spent about an hour spinning pulleys every which way and trying to twist them to feel for any play or sound of a bad bearing but they all sound fine spin freely and no play to speak of except for the AC pulley. when i spin it, it spins freely sounds ok but when i grab it and pull down on it there is slight movement, don't know if movement is normal. i have bought a mechanics stethescope and will tomorrow put the belt back on and try to hear while motor running. if it is the ac pulley, is it rebuilable or changeable?

manual. It did *not* have the alternator clutch. The tech assured me the alternator was OEM. BTW, the alternator failed in a rather unique and rare way. It was noisy but the noise was found to be coming from inside the alternator housing from electrical arcing. Some wiring or winding problem. There was no bearing or shaft play.

Also, on a semi-related note I was told that it is ok for there to be some coolant stain around the water pump. Even a healthy one can seep a bit of coolant. But Porsche calls out the size of the stain. And if any liquid coolant collects under the car that's it. Pump bad.

Sincerely,

MarcW.

not good news, i spent almost an hour and a half trying to single out a pulley by spraying WD 40 and listening with a stethoscope but couldn't single out a pulley. i finally pulled off the belt to try one last time with no belt and i heard it. at 3000 rpm you hear a clattering sound at 3000 rpm. the other night with the belt off i didn't hear it but today heard plain as day with the belt off wondering if it can be a collapsed lifter or a chain tensioner or a chain guide broken. I already changed the ims bearing about 2000 miles ago to the LN Engineering ims bearing. at that time the rear main seal sprung a big leak so while changing that i decided to change the intermediate shaft bearing, glad i did because it had already lost all its grease and the balls looked scored and it didn't spin smoothly at all. the motor has 42000 miles on it. now what?

You don't run it a single rev more.

You decide what you are willing to spend if necessary...in either time or money or a combination.

You start looking for an engine internals expert.

You ask their advice based on your investigation.

You ponder your options (some worst case options are listed here https://sites.google.com/site/mikefocke2/what-can-you-do-if-your-engine-is-blown)

And you decide how you are going to approach this problem...because it is your car and your money. Do you want to just rebuild the engine, just replace it, investigate the cause in case it is an easily fixed problem, ??? Do you have the time and experience to do any or all of the job you decide on yourself?

Good luck.

another post you indicate you have some experience so if you think the noise is a concern I can't do anything but agree.

I guess I'd start by removing the oil filter housing and carefully pouring the oil out into a clean drain pan then looking at the oil very careful, feeling it between my fingers, looking for any metal debris, gritty stuff.

Run a magnet through the oil. If it comes away with any metal shavings (actually very fine metal almost dust)... However, you state you've replaced the IMS bearing with an LN bearing which uses ceramic components and I don't think that stuff is magnetic so if you find ferrous metal in the oil I would have to think some about where it could be coming from.

If you find any soft seal or gasket like material, that could be a chain tensioner o-ring (if green). If dark colored it might just be a bit of some of the engine assembly sealant that has been washed/knocked loose and ended up in the oil filter oil.

If you find any signs of 'color' -- a fine metallic sheen -- that is not made of ferrous metal that's aluminum (most likely). A bit might be normal. The engine over time gets pieces of alum. flashing knocked loose and these go through the scavage pumps and get pulverized into tiny flakes. More than a bit, bigger pieces, could be a chain rubbing against chain guide. But this would require the chain guide loose its protective wear layer of composite plastic. These come in two colors: dark brown, almost black and caramel colored. And there'd be alot of this in the oil filter housing. If you find scary amounts of debris in the oil filter oil the sump might want to be dropped to see what is laying on the top of the sump cover and what didn't get pulled into the oil pump pickup.

If you find some debris that is not ferrous, but is light colored but not alum. it might be -- WAG -- the LN bearing. I don't know what the bearing produces when (if) it fails. I'd hate to advise you to pull the LN bearing to check it and probably replace it (unless it is reusable) again. You might want to touch base with LN engineering before doing this to see what it advises, what cautions there are pulling the bearing to check it out.

Risky, but you can put the belt back on and run the engine and use a stethescope and try to pinpoint more accurately where the noise is coming from. If under a camshaft cover it might be a collapsed zero lash lifter or a broken valve spring. But knowing which camshaft cover to remove comes first.

If the noise is not under a camshaft cover, but 'deeper' in the engine, then a chain tensioner becomes suspect. And the engine should be run as little as possible until the problem is found and fixed. A skipped timing chain (or a broken one) is possible and either case almost certainly destroys the engine if it hap;pens.

To get at both of these tranny has to come out. One head has it chain drive at the front of the engine, the other at the rear of the engine. The one at the rear of the engine has a bolt that that tranny covers a bolt that you need to get to to remove the chain tensioner stuff.

Then there is the crank to IMS chain drive guide/tensioner too. Not sure what's required to get at this and check it out and replace the tensioner is it proves to be bad. But it is at the back of the engine at least the transmission would have to come out.

Sincerely,

MarcW.

thanks marc
you are right i couldn't get the mic on my phone to pick up the sound as i hear it and my brother in law was there and also noted that he had not heard the noise prior. i really don't want to keep on reving the motor to try to record the sound as that might be doing more harm to whatever is causing the sound
this next week i am swamped at work so probably won't be working much on her, but if i get a chance i ill post what i find out. thanks for your time and thoughts i will go step by step and check.
take care

well i have always done my own work on my cars until i get stumped. but that is a rare case. have a 73- 914 2.0 that i have rebuilt the motor on and upgraded it to racing specs and a few Chevy v8's that i built, one of which sits in the 914 now. a rotary engine i souped up so i am not afraid to tackle a tough job. i know that the m96 motor is a completely different animal than a Chevy v8 or a 2.0 Porsche air cooled motor. but to a certain degree a motor is a motor. i just suck at diagnosing sounds. can it be a chain tensioner? it's not a really loud clatter it kinda sounds like chain clattering on the block. how can i test the tensioners to see if one is bad? is there any way that the chain guides could break? what else could give a clattering sound i am going to figure out how to upload a small video clip i made of the sound onto you tube to link to it. you can barely hear the noise on the .

figured out how to upload to you tube the link is [video]http://www.youtube.com/watch?v=em4MYUQ57wI[/video] you can barely hear the clattering towards the end. e didn't want to run it longer mainly because i heard the sound without the belt and because it had been idling for about 10 minutes prior while i as listening to bearings and pulleys and the motor was warm.

update on this issue. no more clattering at 2800 solved that issue created another. i have not had much time to work on the boxster for a while, but i had taken the apart the valve cover on bank 1,2,3 a couple of months ago and found what i took to be 4 collapsed lifters (tappets), 3 exhausts and 1 intake. I purchased a new set for that whole side, last week i had time to dedicate to reassembly, put it all back together it started once in the beginning and for two days after couldn't get that thing to start for nothing. it would shake and sputter and pop but would not start. by that time spark plugs were fouled, changed plugs tried again a few more times, nothing. next day checked plugs, they were fine, tried again until it started but it would backfire and pop for about a minute then it leveled off and sounded good but when i take my foot off the gas it would die. drained fuel put new fuel in (fuel had been in since February) checked timing again, timing is on on both sides, removed MAF cleaned it put it back in it starts, sounds good at 1000 rpm and above, take foot off gas and rpms dive and motor shakes and sputters, if i slowly give it gas it will pop or backfire and then levels off above 1000 rpm. code reader keeps giving me P0300 P0306,305,304, cleared them a few times but the reader pick them back up a minute or so after i start. swapped the coils to other side, re cleaned MAF still get the same P0300 for bank 4,5,6, and the check engine light comes on and starts to flash
anybody have any thoughts as to what it might be? the misfires are from the side i did not work on