IMS bearing QnA

[TrevMcRev]

 

 

the slip/stick cycle means that the balls are constantly tapping away at the cage.

 

Oh dear....that doesn't sound good!

[Peter M]

A quick discussion on the importance of bearing preloading to ensure long life:

http://www.bardenbearings.co.uk/index.cfm_articleid_717

 

http://www.nmbtc.com/bearings/engineering/preload/

 

As stated earlier, the axial preloading is something missing from the 996 IMS bearing.

[SteamWolf]

Something else to note, and probably why low kilometer cars get more IMS issues than high kilometer ones...

 

I did a bearing study a while back on one of my asset management business improvement reviews.  Sealed bearings that are in warm or hot environments can draw in moisture past the seals (and seals are generaly designed to be more effective in one direction - usually to keep the lubricant in).  So once the moisture is drawn in, and the bearing then sits for a period of time, it causes pitting on the running face from corrosion.  When the bearing begins to rotate again it rumbles across the pit and quickly takes the surface hardening off.  Then it's just a matter of time.  A bearing that is poorly chosen for the application will of course fail faster.

 

Observe:

http://www.skf.com/binary/86-62751/RTB-1-06-Bearing-investigation.pdf

 

So to my mind where the IMS bearing is replaced with a pressure fed friction bearing (plain bearing), or taking the inner seal out of the stock bearing and feeding it with a spray bar, I'd expect to be effective solutions - more effective than replacing it with some other type of sealed bearing!!

[firstone]

Agreed

Appreciate the insight.

[HowardMoon]

 

So to my mind where the IMS bearing is replaced with a pressure fed friction bearing (plain bearing), or taking the inner seal out of the stock bearing and feeding it with a spray bar, I'd expect to be effective solutions - more effective than replacing it with some other type of sealed bearing!!

 

Good god what a load of crap. The bearing would be subjected to the same amount of corrosives as the rest of the engine internals, so if you're going to direct a spray onto the bearing to save its life you'd better give everything else a squirt too.

 

It's not rocket science, it's a simple failure mode that occurs periodically and is usually easily addressed. Corrosive failure looks completely different and is even more easily recognisable. Hopefully though you're just trolling with the drivel above and don't really have your head up your arse.

[SteamWolf]

It's true, I haven't cut up any IMS bearings to determine what failure modes they are experiencing or where any given sample sits on the P-F curve. 

 

It's a shame that roller bearings used in other automotive applications such as intermediate gears and injector pumps, motorcycles and mini minor gearboxes all fail in similar spectacular circumstances - oh, wait. They don't.

 

The difference is the IMS is a sealed bearing, and sealed bearings allow moisture to sit in place once it has ingressed by the aforementioned thermal differences.  Back to the first sentence, I HAVE seen it in train wagon axle bearings and it's a known common failure mode, due to the sealed bearing design.  Wagons that are in use daily have bearings that have lasted far longer than the MTBF from the manufaturer.  Some of the bearings in service are over 40 years old.  Wagons that sat on the docks waiting for maintenance or parked for extended periods of time and then put back into service experience higher numbers of beairng failures.

 

So, yes, your points may be more valid than my suggestion because you have cut up IMS bearings and have direct knowledge.  That's not to discount the suggestion I have put forward as a possible cause until you are able to defend your failure mode with empirical evidence.  I'm not suggesting you go to that effort because arguing on the internet is for people with flat brim hats and pants too low.

 

So let me concude with summary and suggestion:

 

• You are probably right, as you have done actual investigation into it.
• I believe I may probably be right but haven't done any conclusive study specifically on IMS bearings (though I have on industrial ones) to take it from belief into fact.
• Your input into this forum is both interesting and valuable, please don't stop contributing.
• Up yours, and get off your high horse. 

[Peter M]

Steamwolf,

If corrosion was a contributing factor to failure, wouldn't the other un-plated ferrous based components of the engine show evidence of corrosion well before it would be an issue in the IMS bearing races?

Of the photos I've seen of disassembled 996 engines with IMS issues, they always seem like new on the insides, unlike many old disassembled air cooled motors that seem to have rust discolouration over many components.

Cheers

Peter

[tazzieman]

IMS autopsy pics

 

Moons and all  Another type of race pitting!

[Peter M]

....suggestion of a wave washer is interesting and I was wondering if this is something that should be considered when doing the bearing replacement and where and how should the wave washer be installed? Would it require any other modifications such as extra clearanceing or could it simply be used with the standard replacement bearing?                                    

Cheers, Jeff

Jeff,

Not Howard, nor do I profess to respond on his behalf but my understanding is that this engine relies on the IMS ball bearing to locate the shaft axially.

It is for this reason that the outer race of the bearing is located inside the shaft by a circlip and the inner race is firmly clamped to the IMS endplate by a centre bolt and the whole plate bolts externally to the crankcase behind the flywheel.

The other end of the IMS drives the oil pump and it appears it is the oil pump coupling itself that supports this end of the IMS. The oil pump uses plain bearings just like every other engine oil pump I’ve ever seen.

Since the IMS only carries chain sprockets and drives the oil pump via a hexagonal cross section floating shaft, there is essentially no axial loading on the shaft and no other means to locate the shaft and therefore no means of developing axial preloading on the standard bearing.

Consequently the only way I could see that the IMS bearing could be preloaded is to replace it with two separate ball bearings that would allow each bearing to be preloaded against each other.

I’m thinking now that no matter how much I dislike LN Engineering and all their hype, their $1700 USD IMS Solution kit that replaces the ball bearing with a plain bearing is the most sensible and easiest permanent solution.

[tazzieman]

Maybe the following has been discussed and I missed it. Anyway , if an IMS bearing is replaced prophylactically , is the mechanic in any way obliged to note the condition of the removed bearing ? The next owner might just like to know 

 

Obviously the current owner wouldn't want any inconvenient truths in the history file.

[SteamWolf]

IMS autopsy pics

 

Moons and all  Another type of race pitting!

Interesting!! That certainly does look like an overloaded bearing to me.  No signs of etching that I'd expect to see from corrosion.

No chattering marks like you'd see if the race was floating due to lack of preload.

[SteamWolf]

Steamwolf,

If corrosion was a contributing factor to failure, wouldn't the other un-plated ferrous based components of the engine show evidence of corrosion well before it would be an issue in the IMS bearing races?

Of the photos I've seen of disassembled 996 engines with IMS issues, they always seem like new on the insides, unlike many old disassembled air cooled motors that seem to have rust discolouration over many components.

Cheers

Peter

 

Once a bearing fails, it goes everywhere.  A sealed bearing will contain much of the debris until it gets bad enough to wreck the seal.

 

The type of corrosion I'm talking about is from moisture getting slurped in past the seal due to the pressure difference inside a cooling sealed bearing and the outside atmosphere. Moisture from atmosphere that gets into engines is usually boiled off next time the car is driven.  In terms of the IMS bearing, the bearing and the engine crankcase are completely separate environments.

 

 

 

 

OK everyone, I want to make very clear that I am not trying to be argumentive, or suggest that I know the answer to the IMS debacle.  Nor am I trying to discredit anything Howard has put up - it's as good a suggestion as any I have seen.

 

All I want to do is learn more about it for my own interests, and share any new learning that I find.

[tazzieman]

 Moisture from atmosphere that gets into engines is usually boiled off next time the car is driven. 

How hot does the engine have to get to "boil" this all off? Or just warmish enough , as with removing condensation from a windscreen?

Are cars from tropics/subtropics more "moisture prone"?

 

P.S. the day after a spirited long drive (air cooled) , if I look in my oil filler neck there is not infrequently new moisture. No surprise. Next pootle or six (commuting)  it doesn't really get hot enough to "boil off" IMO , but I certainly don't let tainted oil sit there for any length of time. And yes Mr Garage Queen,  I am looking at you! Sit up!

[SteamWolf]

How hot does the engine have to get to "boil" this all off? Or just warmish enough , as with removing condensation from a windscreen?

Are cars from tropics/subtropics more "moisture prone"?

 

P.S. the day after a spirited long drive (air cooled) , if I look in my oil filler neck there is not infrequently new moisture. No surprise. Next pootle or six (commuting)  it doesn't really get hot enough to "boil off" IMO , but I certainly don't let tainted oil sit there for any length of time. And yes Mr Garage Queen,  I am looking at you! Sit up!

not hot, and not hot for long.  But a good example of moisture condensation happening in engine systems is pensioner's exhaust systems.  I mean their car's exhaust systems.  lol 

temperature changes draw in moisture, then it's boiled off again as the car is used.  Short trip cars end up with condensation in the exhaust and combined with the sulphurs from combustion cause it to corrode out.  Used to have to change a LOT of rear mufflers on pensioner cars back in the day because of this.

 

I don't think it happens much with engines as they warm up even on short trips - but short trip damage manifests in other ways such as oil sludge.

 

What can happen, however, is oil sitting in the crankcase with moisture in it from short trips can cause the oil to become acidic, and lead to bearing corrosion.  Better to do lots of oil changes on short trip engines because of this.  It's exaserbated in race engines that use methanol - it's hydroscopic and unburnt fuel that sit in the crankcase mixes with sulphurs and can do some real bearing damage.  Moisture seems to coalesce in tight spaces such as between bearing and crank.  Have heard of a few race bearing failures due to them being started briefly, run rich because cold, doddled around workshop carparks for months then raced.  Because most people change the oil before events and not after, it makes the problem worse.

 

 

This is mostly anecdotal based off my own experiences. 

[tazzieman]

Not trying to turn this into an oil thread , but it would be interesting to test the pH of new and used oils in our own cars. (how???) This is a good summary of the corrosion potential. Of course "engine" covers a broad range of vehicles/years. (The word in 928 circles , backed up by personal obs , is that it takes a good 30 mins driving to "properly heat" the oil. A liittle less in my 911)

 

As I suspected , seaside cars may be at increased risk (here , HK etc). I guess also "salted road" cars (UK , Europe , USA).

 

 

 

Why are there low mileage sports cars that have ruined engines? Why do they have electrical problems?

Ferrari automobiles are perhaps the most problematic. But Why? It seems that most of those who purchase a Ferrari do not often drive them, and when they do they abuse them. Let me explain.

Each morning the lawn is wet with dew. This is because as the temperature drops the dew point is reached and the moisture in the air condenses. This happens in your engine as well. There is air and moisture in the engine. As it sits over night the moisture condenses. It is a repeating cycle. It is actually worse than the outside air. After driving the engine is very hot so as it cools it sucks in a lot of moist outside air. 

Remember the products of combustion are water and CO2. The water condenses in the engine during start up and even steam blows by the piston rings for another source of water.

There are additives that help the oil absorb water but if the engine is not started then the water that condensed in all parts of the motor keep it wet. If the car lives near water or worse, salty water, then the situation is compounded. Another thing that makes things worse is mildew and fungal growth, yes it can even grow in oil!

Water is bad but there is another source of corrosion, acids. These result from byproducts of combustion that slip past the piston rings and from fuel dilution of the oil. Again, the oil has additives to neutralize these acids but work only when the oil is splashed around the inside of the engine.

Corrosive products and water in the atmosphere also take their toll on electrical components. Electrical switches are problematic. These are helped by using the switches. When you get in the car and role down the windows and click all the switches they scrape some of the thin corrosion off the contacts. Again, use of the car helps whereas sitting around is detrimental.

Fan and timing belts age at accelerated rates when static and in cold climates. Cold is also bad for plastic, leather and all rubber like parts. Winters are tough on cars. Up north it is cold and the cars get little use. And down south it is moist all the time. Moisture is an independent factor increasing engine wear. Engine tests are usually performed in controlled humidity environments.

People think that taking the car out for a 10 or 15 minute spin will keep it in good shape. Well that is better than nothing because at least everything is splashed down with oil in the engine and some switches are activated that helps remove corrosion. But to burn off excess fuel and water from the oil it must be brought up to full operating temperature. This takes 20 or 30 minutes. Your coolant heats up in as little as 2 – 3 minutes but oil takes up to half an hour to get up to full operating temperature. You should drive the car for another half hour or more after the oil is up to temperature.

People do not realize that “severe” driving conditions that require more frequent oil changes include stop and go city driving of only 20 minute drives or less. This is a severe condition because the oil never gets hot and never burns off the extra fuel or water. For this reason the oil must be changed more often.

[SteamWolf]

Yeah I think the oil discussion should be put in the other thread so we don't muddy this up too much.

[Peter M]

Interesting!! That certainly does look like an overloaded bearing to me.

 

SW,

 

Surely if the bearing failure was due to overloading there would be many more reported failures and there would be a greater correlation between failure rate and kilometres travelled?

 

The bearing is only directly loaded by one cam chain and one crank drive chain and I wouldn't think the bearing is undersize for this loading.

 

The failure rate appears to be between 1 and 4% depending on the source and whether you are trying to sue Porsche or not and doesn't seem to have any correlation at all with kilometres travelled.

 

Hopefully your appeal for some used IMS bearings will locate some that have the first stages of deterioration but not so far gone that all the usefully information have been flogged out in the explosion of balls and races. 

 

I appreciate the approach you are taking to getting to the root cause.

 

Not trying to turn this into an oil thread , but it would be interesting to test the pH of new and used oils in our own cars. (how???) This is a good summary of the corrosion potential. Of course "engine" covers a broad range of vehicles/years. (

 

Tazzie,

The oil change intervals set by manufactures are deliberately very conservative to ensure the engine oil has sufficient base capacity to neutralise acid formation and to keep corrosion at bay.  None of the photos of disassembled engines I've seen have any evidence of corrosion on the un-plated components which are normally the first to discolour if the environment is unfavourable.

I don't think the failures are correlated to engine oil at all although changes to how the IMS bearing is lubricated may improve life depending on what the root cause is found to be.  My money's still on skidding balls!

[tazzieman]

SW could soak his balls in old +/- watery oil for a few months and see if there is any corrosion.

[SteamWolf]

SW,

 

Surely if the bearing failure was due to overloading there would be many more reported failures and there would be a greater correlation between failure rate and kilometres travelled?

 

The bearing is only directly loaded by one cam chain and one crank drive chain and I wouldn't think the bearing is undersize for this loading.

 

The failure rate appears to be between 1 and 4% depending on the source and whether you are trying to sue Porsche or not and doesn't seem to have any correlation at all with kilometres travelled at all.

 

Hopefully your appeal for some used IMS bearings will locate some that have the first stages of deterioration but not so far gone that all the usefully information have been flogged out in the explosion of balls and races. 

 

I appreciate the approach you are taking to getting to the root cause.

 

Thanks!  And I think you are right. 

That example appears to be an overloaded bearing, but it's not to say it actually WAS overloaded.  Just looks that way in the poor and tiny image shown.

[Peter M]

Nice photo of an unravelling race:

http://cimg4.ibsrv.net/gimg/rennlist.com-vbulletin/600x441/80-picture_php_pictureid_15417_fa42af7ffbb915b8a8494f82805eb61c7e1c529c.jpg

[SteamWolf]

There's no fretting, nor is there false brunelling.

It's not chattering

it's not over sped or overheated

It's not contaminant damage

It's not due to lack of lubrication.

 

Basically it's either massively overloaded or it has had an inclusion that has taken the case hardening off and has spread the damage over time.  It actually looks like a classic overloaded bearing, which is very interesting!

 

 

 

[symsy]

Great thread , maybe a real silly question , but there is a lot of talk of load , my question , how is it that 996 turbo doesnt seems to have any greater level of issues over other 996 yet the design remains the same or very similar? People are working these motors with tremendous load are they not ?

[Peter M]

Symsy,

The 996 and 997 Turbo engines use a different engine to the 996 and 997.1 normally aspirated engines.  The Turbo engines are based on the old air cooled engines with a plain bearing on the IMS - just with a water cooled set of cylinders and heads added.

 

Cheers

Peter

[JV911]

http://autohaushamilton.com.au/news/ims-bearing-the-facts-made-simple

[Peter M]

A few blunders and questionable reasoning that I wouldn't expect from Autohaus:

......IMS stands for ‘Intermediate Shaft Bearing’......

.......due to high load and lack of lubrication to the IMS bearing, eventuating in the continuos over heating. This eventually will cook the metals in the bearing and cause large amounts of friction......

 

I wonder why they don't recommend the IMS Solution over the Retrofit?