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Old 07-16-2017, 09:09 PM   #1
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Noticed Some Wobble on Crankshaft Serpentine Belt Pulley

Hey folks,

In trying to diagnose some metallic rattling sounds of my 2001 Boxster base/2.7, I noticed my crankshaft serpentine belt pulley has some noticeable axial runout to it! The following video is on cold-start-up:
trim.262D9F95-2809-46F9-ADB5-1734EEA01D45.MOV - Video - VideoSprout

This next video is after it has been warmed up:
trim.A3E7C7EE-9CCB-4EEB-A065-AC4A1F58314E.MOV - Video - VideoSprout

There seems to be a metallic noise coming from behind the crankshaft pulley, but it's much easier to hear when driving the car, so I'm not sure this is the origin of this noise or not. I'm thinking because pulley bolt seems to be not wobbling, perhaps this is a bent pulley, or a somewhat loose pulley mounting bolt? (If it were loose, it would explain the metallic rattling sound.)

I found a YouTube video that shows someone else with a remarkably similar symptom, shown at 0:09. It seems when replacing the pulley, he found the key way was damaged. Seems like evidence it seems to me of an inadequately tightened pulley bolt!

Have anyone else experienced this? Cheers!
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Old 07-17-2017, 04:45 AM   #2
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Seems like a good opportunity to switch to an under drive pulley. It doesn't take but five minutes to remove the old pulley to take a look but I'm betting your pulley is in the beginning stages of what happen to the guy in the video.
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Old 07-17-2017, 06:40 AM   #3
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And check all the idler+tension pulley bearings for noise/wear
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Old 07-17-2017, 11:50 PM   #4
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Thanks for the comments and suggestions. I wonder if anyone else has experienced this experienced this problem, or have any good theories on its cause?

Woody - An underdrive pulley is not for this car, as I have thoughts of one day autocrossing it in SCCA stock/street class. I've now got a new (used) stock crank pulley on the way. (I tried texting you for it first! )

Gelbster - On the accessory pulleys, yes, At 100k+ miles, it's time to preventively replace these sorts of things! And a long time ago, I have some new 5202-2RS bearings for those (same specification as dual-row IMS bearing calls for, I hear!) I read that pressing them in/out of the stamped sheetmetal idler/tensioner pulleys may be a pain, but maybe I can figure it out. I noticed at 3000 rpm, the tensioner pulley had a noticeable resonance. Maybe it's related to the wobbly crank pulley.

Water pump seems fine as far as I can tell, but I'll inspect all the pulleys much more closely when I get the serpentine belt off. I have a new serpentine belt sourced for whenever I need it, but haven't noticed a single crack or other damage on the current belt, so haven't been quick to replace it.

When I got the car, there was evidence of a careless previous mechanic's work in this area. A forgotten large pry tool was retrieved from underneath. (Maybe previous mechanic carelessly pried against the crank pulley, and bent it?) A remnant of a nitrile glove was retrieved from under a bolt head, things in the knock sensor area weren't routed quite right. Maybe a previous mechanic thought this noise was engine knock? Previous owner thought the metallic rattling was exhaust noise, but I think I've mostly ruled that out. Maybe this noise is why he sold me the car.

It's been a good, reliable driver for the last 3 or so years! If I can solve this metallic rattling noise, it's going to be awesome/icing on the cake. Kind of excited to find this wobbling crank pulley!
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Old 07-18-2017, 01:22 AM   #5
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Check your crank shaft for end play.
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Old 07-18-2017, 07:23 AM   #6
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Thanks for the suggestion, JFP. I read in another thread your comment that it's possible the thrust bearing can fall out, so good idea to double check things are OK here, especially if it's convenient to do so.

Do you think I could get a good measurement on the axial crank play if I just removed the serpentine belt and gave the pulley a good push/pull? Will the timing chains being installed invalidate the reading? How about the clutch assembly? I'm pretty sure the rods and pistons being installed shouldn't invalidate it; probably a good amount of clearance at the piston pins.

This is a 5-speed / manual transmission car, FWIW. If the noise may be influenced by the axial/thrust crank motion, I think I may try as an experiment simply applying a bit of pressure to the clutch pedal under a condition where the noise is audible, and see if that affects the noise.

On another car I had which was known for thrust bearing issues, I recall a very wise mechanic suggested that a good preventive measure was to get in the habit of always starting the engine without depressing the clutch pedal! If you think about it, it makes perfect sense - loading the thrust bearing with full pressure plate force when you go to crank the engine over, when there is zero oil pressure, must be hard (to say the least!) on the thrust bearing. On that car, (it was a volkswagen) the factory crescent moon style thrust bearings were the best / most reliable. The ones that were most problematic were the integrated thrust/main bearing, especially if the top and bottom halves weren't properly "set" so there was no skew on the thrust surface. It's a bit dangerous to get in the habit of not pressing the clutch pedal, however, if you forget to put it in neutral! (And in the 986, the starter-clutch interlock would need to be "defeated", anyway, so it's definitely not Porsche's intention to start the engine this way). Aftermarket high spring force pressure plates are another factor which can also exhasorbate crankshaft thrust bearing problems...
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Old 07-18-2017, 07:40 AM   #7
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You are only worried about forward and reward motion; while the cam and IMS chains will inhibit the movement somewhat, what you are looking for is substantial movement with everything in place. Normal range for this is 0.05-0.24 mm, if you exceed 28mm, the engine needs to come apart.
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Old 07-23-2017, 09:00 AM   #8
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No apparent effect on metallic rattle noise when applying pressure on clutch pedal. When the replacement pulley has arrived and I have the serpentine belt removed to replace the pulley, I can certainly try pushing/pulling on the crank pulley to see if I can make the thing move more than the thrust bearing wear limit.
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Old 08-25-2017, 10:10 AM   #9
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I've got some time to work on the Boxster today! Removed the old serpentine belt, and found some looseness/play in the power steering pump when rotated back and forth (exactly like described and video'ed in this thread: Rattly power steering pump. ). Also, two of the three idler pulleys have small but noticeable rocking and bearing lash noise when rotated back and forth.

I'm actually not sure if that power steering pump rattling is problematic or not. Perhaps with the wobbling crank pulley, it "excites" this stuff which if the crank pulley were straight, isn't a problem? Worth a shot anyway, I think, (to just replace the wobbling crank pulley), before potentially tearing into the power steering system like contributor did here (he reported threadlocking the splined shaft to the vane pump was required to eliminate the spline play, and another used PS pump he picked up exhibited the exact same condition!)

The crankshaft pulley (when pressed both with hands and a prybar) exhibit no discernible axial (thrust) play. Not that I hooked up up a dial indicator to it to get a precise reading or anything, but nothing with crank play there subjectively seems amiss.

Although there is some evidence of some small oil leaking probably at the front crankshaft seal (behind the crank pulley), I'm but not sure how important that is (maybe this oil film has built-up over a very long time running without ever being cleaned.)

I'm in the middle of pressing bearings on the idler pulleys, and intend to put back together with a replacement, good used crankshaft pulley. Hopefully when that's done, it will take the wobble out and if I'm lucky, the metallic rattling noise!

If it doesn't take the metallic rattling noise away, I think I'll try "exercising" the power steering system while the rattling noise is happening to see if there's any effect.

Alternator seems tight, and water pump external appearance and pulley bearing also seem good - a bit of axial play, but (likely sleeve-bushing style) bearing feels tight! I think I see a 07/07/2011 date code, which is good to know it's probably not original water pump.
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Old 08-25-2017, 11:05 AM   #10
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Can anyone confirm this "070711" (hard to see in this photo, but readily apparent printed numbers on top of water pump in person) means a 2011 water pump manufacture date code?
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Old 08-26-2017, 08:44 AM   #11
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Update - I got the Boxster put back together with "new used" substitute crankshaft pulley, 3 new bearings pressed into the idler and tensioner pulleys, and with things cleaned up in the area. It was getting dark and late so I didn't get any videos afterwards, but the outer and inner faces of the new pulley still wobble to some degree, bit at least now the ribbed surfaces that guide the belt appear to be perfectly straight and true, so it's definitely an improvement!

There was no damaged keyway on the old pulley, like I was suspecting. It was either just manufactured poorly, or got bent (perhaps by a careless previous mechanic) somewhere along the way. I'm pretty sure my metallic rattle noise is still there (did one test drive so far and I still noticed it at one point), so perhaps I'll need to further explore the power steering pump "play" here at some point.

By the way, the substitute crank pulley I installed has an updated part number ending in .63, and the difference with the old pulley (ending in .62) is it's a little bit beefier. There is significantly thicker material near the middle, where the mounting bolt goes.

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Old 08-26-2017, 09:47 AM   #12
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You may have found the cause of the IMS failure, yay man!

That was quite a bit of unwanted vibration, geez :/ Good thing you got that done. No hope for that part though, seems formed then stamped. Meaning not a single pulley is the same. Lucky if you can find one that is concentric to the shaft loll. Slight offset on such thin material will wack out the shape of that part in less than 10k miles at revs... wouldn't surprised anyway.

If you are concerned about the shaft runout (TIR) just get an harbor freight mag base and a cheap dial indicator, no need for Japanese metrology there. My guess is if the shaft would be in such a bad shape it wouldn't sound like metallic rattling but more or less like metal crunching. Could be wrong

Some late advice I guess; I wouldn't use a hex wrench as locking tool, as per one of your video. You need the special tool for that part indeed, the rod shape one that fit snug in the pilot hole. Anything slightly unfit for this hole "could" bend the pulley easily when manual/uneven pressure is added to it (I mean look at this poor pulley)

hrrr Porsche sometimes lollllll

Nice write up btw (I'll chk mine also). Keep us informed
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Old 08-26-2017, 04:49 PM   #13
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Try a straightedge across the face of adjacent pullies -as many as you can span. I was surprised that the A/C pulley was significantly out of line with the rest of the pullies. This tended to put a lot of distorting force on the adjacent pullies.
If you replaced just the bearings in any pulley - you may not have seated the bearing fully or you cracked it on the press. Better to use a new combo pulley+bearing in my limited experience.
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Old 08-28-2017, 07:03 PM   #14
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Unhappy

Quote:
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You may have found the cause of the IMS failure, yay man!

That was quite a bit of unwanted vibration, geez :/ Good thing you got that done.
Indeed, it was really horrible! Now that I'm driving on a true-running serpentine belt setup, it seems like such smoother feeling reduced engine vibrations. Where before it kind of "hurt" to press down on the gas pedal, now it just feels good. Also, the engine just sounds better - that exhaust note sounds more "pure", and generally sounds good, although that might not make sense. As these are subjective observations, it's possible they can be discounted. But I'm really happy to have to his fixed! (And yes, even with the metallic rattle noise still going on, but perhaps that's another topic.)

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Originally Posted by Nine8Six View Post
No hope for that part though, seems formed then stamped. Meaning not a single pulley is the same. Lucky if you can find one that is concentric to the shaft loll. Slight offset on such thin material will wack out the shape of that part in less than 10k miles at revs... wouldn't surprised anyway.
I value your insights about manufacturing process, and am fascinated how uneven these parts were made! The uneven thickness and waviness of the outer faces was perplexing to me. At first I was wondering if they were ground that way for balancing (instead of drilling holes.). But the surface finish didn't really look ground. Your suggestion it's an artifact of an imperfect manufacturing process seems like a more plausible explanation.

It makes me wonder if one of these pulleys, brand new, were tested for balance, how far off would it be? And if they are out of balance, would the crankshaft be balanced together with this part as a unit?

The piece is extremely lightweight, however, so maybe even if the material is uneven, the amount of imbalance isn't going to be significant. If it can't support it's own weight and bends out of shape further in just normal operation, well then after the pulley "auto-bends" in normal service, the imbalance could become a much bigger problem!

Then again, I can't say for certain it wasn't just a careless previous mechanic who pried on this part when, let's say, trying to remove an alternator. I actually found a big pry tool lodged below this area after I picked the car up... no kidding. It's a nice tool also, snap-on type pro quality. A good addition to my tool box!

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Originally Posted by Nine8Six View Post
If you are concerned about the shaft runout (TIR) just get an harbor freight mag base and a cheap dial indicator, no need for Japanese metrology there. My guess is if the shaft would be in such a bad shape it wouldn't sound like metallic rattling but more or less like metal crunching. Could be wrong
I do have a magnetic base and dial indicator, but find very few flat magnetic surfaces on which to mount it, plus the quarters are very tight/cramped to do it with the engine in the car.

I did, however, place both pulleys on a flat surface plate and use a set of feeler gauges to measure surface waviness. Neither face of either pulley had even close a straight (planar) face! Depending which pulley (new vs old), which face (front vs back), and which direction I "rocked" the pulley on the surface plate before getting the measurements, I got surprisingly high waviness measurements:
Old pulley: .018", .012" (back face); .010", .022" (front face)
New pulley: .008", .010" (back face); .012", .018" (front face)

At least the new pulley is a little less wavy than the old, but nowhere near close to being flat. What I'm pleased by is at the least the belt now seems to run perfectly true on the new pulley.

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Originally Posted by Nine8Six View Post
Some late advice I guess; I wouldn't use a hex wrench as locking tool, as per one of your video. You need the special tool for that part indeed, the rod shape one that fit snug in the pilot hole. Anything slightly unfit for this hole "could" bend the pulley easily when manual/uneven pressure is added to it (I mean look at this poor pulley)
You make a good point, Fred. I used an Allen wrench to pin the pulley against rotation, and unlike they guy in the video who said he used a 6mm, I found a 7mm fit much better and seemed nice and snug. However, you are totally right, and using round profile pin would be even better. i suppose I could have thought to use one of my drill bit of the proper diameter - I have a rather complete set and am sure a I have many options to pick from in this size. You were too late in telling me this - lol!

The pulley actually wasn't under as much torque as I was expecting it to be, especially after watching that video and hearing the guy talk so much about the massive torque wrench he ordered to get the job done. Maybe only ~100 ft-lbs after the 3x ft-lbs + 90 degree turn? Threads were very clean. It didn't feel like the bolt yielded at all.

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Originally Posted by Gelbster View Post
Try a straightedge across the face of adjacent pullies -as many as you can span."
With the front face of these crank pulleys being as wavy as they are, and not really having anything to do with the surfaces that belt rides on, you'd get different/inconsistent readings. (At least if you used the crank pulley's face to guide the straightedge - other pulleys might work!)

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Originally Posted by Gelbster View Post
I was surprised that the A/C pulley was significantly out of line with the rest of the pullies. This tended to put a lot of distorting force on the adjacent pullies.
Thanks for suggestion, that's a good thought.

It seems my serpentine belt is now running totally straight and smooth. Well, the pulleys may be misaligned a small amount, but at least there is no more belt vibration, like there was before! Before, the tensioner pulley would get "excited" right at about 3000 rpm.

I may do some more tests and capture an "after" video when I have more time to probe around before that access panel.

Quote:
Originally Posted by Gelbster View Post
If you replaced just the bearings in any pulley - you may not have seated the bearing fully or you cracked it on the press. Better to use a new combo pulley+bearing in my limited experience.
I think I read this comment in some other thread, which prepared me for these pulleys putting up a fight. And while they did indeed put up a fight, I'm quite confident the repair was good one, and it saved me hundreds of dollars over replacing the complete pulleys.

It's hard to imagine the malleable sheetmetal these pulleys were stamped out of cracking if over-stressed. Bending, I think, would be the more likely failure mode if supporting the pulley well enough, or pressing in a "cocked" bearing.

On pressing the new bearing in, I also don't think it's critical how deeply they are pressed. The pulleys have flat cylindrical surfaces where the belt rides, and no grooves, so they don't axially guide the belt.

I took some pictures of how I replaced the idler and tensioner pulley bearings, so especially if there is interest, I could make a DIY thread about it.
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Old 08-30-2017, 12:01 AM   #15
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One thought: if not still done, check the pulley tensioner. If you have wobbling in the system these tends to get fatigue very fast.

A bent main pulley may affect the harmonic balancing. But a worn dual mass flywheel is much worse to the system.

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Old 08-30-2017, 08:44 AM   #16
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Thanks, Markus! It's all put back together now (and driving SMOOTH, I might add!), but I recall the tensioner seemed to have good and strong spring pressure/resistance when I was re-installing the belt. (I had to switch from a combination wrench to a longer-handled breaker bar to hold against the strong spring resistance while installing the belt.) As mentioned above, I also replaced the tensioner and idler pulley bearings, so I have no concerns there. I do have a feeling I'll be back in this area to deal with the apparently rattling power steering pump at some point here, and maybe I'll do some more visual observations of the belt vibrations at different engine rpms at that time.
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