Looking for tips on S52 engine post-failure analysis

[mda185]

Long post here and thanks in advance for those of you who take time to read it and respond. I recently swapped an S52 into my 95 E34 Touring. This forum has a lot more S52 swap expertise than any of the E34 forums so I thought I would try looking for info here. I purchased the engine from a fairly well respected salvage yard a couple of years ago and it sat in my garage when health problems forced me to delay the swap. It supposedly only had 90K miles on it at time of sale. There is no warranty coverage now but I accept that it is my problem because I waited too long to install it and am not complaining about the seller. I got the engine running well in April but had repeated difficulty getting it to pass emissions for HC at idle in NJ. That was with new plugs, good coils, cleaned injectors, all new intake gaskets and hoses. I don't know if the emissions failures were any kind of precursor to what happened.

At my last try to pass emissions, the engine failed while waiting in line on a very hot day. I shut it down as I pulled into the state inspection garage because that is the procedure. I think they make you sit long enough for the cats to cool before testing. When I restarted, the engine immediately started misfiring and running very rough. It had been running and idling beautifully prior to this. I pulled it out of the building on something like 3-4 cylinders and parked it to wait for a tow. I noticed loud crunching noises and knew there was metal on metal contact but had to get the car out of there. No one was going to help me push it out on a 90 degree, humid day. Here is what I know so far:

Zero compression in cylinder 1 and I can see the piston is clearly cracked with a fiber optic inspection camera. Cylinder #1 seems coated with wet paste-like layer of aluminum and I assume this is because something was getting smashed repeatedly before I could shut down. The piston still goes up and down with the connecting rod when I turn the engine over by hand. It turns over freely by hand. I did not see any obvious foreign object in the cylinder with the inspection camera and was not able to get a good image of the valves. Something was smashed in there but I don't know what yet.

180-195 psi in the other cylinders but it was definitely misfiring on more than just #1. I know what this feels like with only one cylinder out and this was worse.

A/C compressor belt was new and is worn severely on both outer edges almost like the crankshaft was moving in and out. When A/C was on, there was always noticeable shaking from the engine that stopped as soon as I turned A/C off. I used it as little as possible because of that but had run it for about 10 minutes while waiting in line to cool the car interior down. I figured it was a bad compressor and did not imagine the problem was more than that until the failure. I can't detect any axial movement of A/C compressor from a quick inspection and the crankshaft does not move axially with engine off when I push and pull on the harmonic damper/pulley assembly. I didn't expect it to but tried anyway. The main serpentine belt does not show any unusual wear.

I am going to pull the engine, put it on a stand and tear it down to try to understand what happened and why. My questions are for experts out there that have dealt with S52 failures before:

1. Does this engine have any known problems with dropping valves due to valve keeper failure? I thought only some of the early S50 engines had this problem.
2. Are there any known S52 issues with the crankshaft developing axial play that could have caused this? (Crank 'walk')
3. Are there any known issues with bad A/C compressor contributing to engine failure due to vibration?
4. I searched for information on crankshaft 'walk' but did not find much useful. Are there any web pages or threads that have useful information that I may have missed in my search?
5. When I tear down the engine, are there any tips or suggestions of what to look for? I will document what I find with pictures and post here if there is sufficient interest.

[328ijunkie]

You running a lightweight flyhweel? They like to jump ship on the S52s sometimes (esp *blue* ones) and wreak havoc on the rest of the motor. They can also kick the crank pulley bolt. check and make sure both are still tight/attached.

[mda185]

You running a lightweight flyhweel? They like to jump ship on the S52s sometimes (esp *blue* ones) and wreak havoc on the rest of the motor. They can also kick the crank pulley bolt. check and make sure both are still tight/attached.

I am running the blue flywheel. What exactly is problem with them? I searched for info on blue flywheel of death and found very little specific information about what the failure mode of the engine is with this flywheel. I personally installed it and am sure it was done correctly.

I certainly will not use it again if I can find specific information on what is wrong with this flywheel on the S52.

[LJ851]

^ Not much a flywheel can do except fall off. Or explode, but it doesn't sound like that happened.

[Beej '86 325es]

I'm not sure if it's of any help, but I recently heard about Blackstone Labs in Indiana. http://www.blackstone-labs.com/

I have a modified engine that had some initial issues that I remember Dave here helping me out with some troubleshooting a bit. After I had the car fixed down at Technica, it came time for an oil change. Blackstone will send you a container for an oil sample and they'll ask for some basic information on the engine. A week or so later they'll send you a full report on how things are wearing internally...it's all very scientific, but they dumb it down for you. It's really pretty interesting for a mere $25. It showed my engine of 2,000 miles was wearing as if it had 5-6,000 miles possibly due to poor air filtering or track use.

[318isbmw]

The flywheel doesnt always break loose or anything like that, its just too light for the factory balancing setup and will throw the rotating assembly out of balance and thus rattling the motor to death from the crank.

[LJ851]

The flywheel doesnt always break loose or anything like that, its just too light for the factory balancing setup and will throw the rotating assembly out of balance and thus rattling the motor to death from the crank.

You cant "throw the rotating assembly out of balance" on an inline 6.

All the rotating and reciprocating parts are balanced to themselves only, there is no balance factor in the crank to affect.

A lighter flywheel could let harmonic vibrations increase in the crank assembly, but it's balance is still the same as it was.

[matthugie]

You cant "throw the rotating assembly out of balance" on an inline 6.

All the rotating and reciprocating parts are balanced to themselves only, there is no balance factor in the crank to affect.

A lighter flywheel could let harmonic vibrations increase in the crank assembly, but it's balance is still the same as it was.

Along the same lines, I have heard underdrive pulleys with a lightweight flywheel can amplify the harmonic vibrations and cause some issues. I'll let the more knowledgeable people chime in on that one though.

[mda185]

I have been searching furiously for information about harmonic vibration and S52 engine failures but still nothing that seems to apply to my situation. What I did find indicates that harmonic vibration in the axial direction (along the axis of the crankshaft from front to back) can be a problem in S52 engines that are consistently revved close to or higher than stock redline. All inline six engines have this problem to some degree. Rod length and piston design seem to be related to degree of harmonic vibration possible. This has nothing to do with balancing an engine rotating assembly. It is an inherent property of a long crankshaft on inline 6 engines. The failure modes seem to be oil pump nut or shaft failure, crankshaft nut backing off, and possible crankshaft walk from degraded thrust bearings. Some of the info indicated that lighweight aluminum flywheels can make the problem worse because the dual mass flywheel provides some dampening. My situation:

1. Engine failed on warm restart after sitting for 5 minutes. It was running well prior to failure and I had been in line idling while waiting for inspection for about 45 minutes.
2. I am running UUC lightweight flywheel and M5 clutch kit but I don't see any correlation between that and the failure I experienced yet.
3. I had noticeable vibration when running the A/C compressor but but no vibration under any other condition.

[wazzu70]

You cant "throw the rotating assembly out of balance" on an inline 6.

All the rotating and reciprocating parts are balanced to themselves only, there is no balance factor in the crank to affect.

A lighter flywheel could let harmonic vibrations increase in the crank assembly, but it's balance is still the same as it was.

This is not correct in the slightest. At very low RPMs an inline 6 is balanced. As the RPMs increase an I6 becomes pretty horrible with "harmonics" or more properly torsional vibration due to the long length of the crank. The S52 is about the worst crank BMW makes in respect to this because of its long stroke reducing the overlap of main journals and rod journals.

Also a lightweight flywheel most definitely impacts the rotating assembly negatively. The torsional damper is not tuned around the resulting frequencies that happen when you remove mass from the flywheel!

You will find lots of stuff on the interwebs saying an I6 is inherently perfectly balanced, but that only applies to a small part of the rev range. It took me many years to find the proper academic documentation for me to stop beloeving the I6 is perfectly balanced nonsense. There is a good white paper at BHJ dynamics that covers TV if you are curious.

To the OP, my first guess is to check your torsional damper (harmonic balancer). See if the damper has delaminated or worked itself loose. The damper is a wear item most people overlook. They can overheat and delaminate which will cause all kinds of bad issues. This is also more common on the S52/M54b30 than any other motor. Crank vibrations can also damage the CPS because the crank actually wiggles enough to smash the toothed wheel into the sensor! Without a crank position reference, or a dirty signal you can have all sorts of running issues.

This is where I would look first since its easy to diagnose from the outside. If thats not the case we can keep digging :)

[golde30]

i had a woodruf key shear in half on my s50 crank, which in turn threw off timing and made engine run like shit.

[golde30]

also many many people are running the UUC "blue" flywheel setup without issues. the M5 clutch and pressure plate are quite heavy and are supposed to make up some of the difference in weight. I have been running my UUC flywheel for about 5K miles of hard driving, i love it. Just make sure you torque it to 85ft/lbs WITH red locktite.

[AndrewBird]

Guess guess was a valve hit a piston for some reason. Possibly timing chain problems caused the timing to jump?

[mda185]

also many many people are running the UUC "blue" flywheel setup without issues. the M5 clutch and pressure plate are quite heavy and are supposed to make up some of the difference in weight. I have been running my UUC flywheel for about 5K miles of hard driving, i love it. Just make sure you torque it to 85ft/lbs WITH red locktite.

I like how my UUC 'blue' setup with M5 clutch feels but I am very worried about continuing to use it until I understand what failed and why. I am concerned that a failing A/C compressor may have excited torsional vibration that was not damped by the UUC flywheel and this led to whatever trashed this engine. Can't blame that 100% on the UUC design but if true, it will be enough for me to use something else. I notice that Turner and VAC only sell the JB racing flywheels with Sachs or Clutchmasters kits. The cost is much higher than UUC but if they are better in terms of harmonic damping, I would gladly shell out more money to avoid what just happened.

I am gaining a deeper appreciation that BMW designs these engines, harmonic dampers, and flywheels as a system intended for specific operating conditions. With a stock S52 engine operated within stock DME rpm limits, the factory parts are good enough with some margin for safety. The axial harmonic vibration is not a big problem. As soon as we start to modify them and/or operate in non-stock rpm zones, the factory design is compromised. The Euro M3 engine is a very different animal, has better controlled harmonics and can rev much higher safely. We got an engine that was good enough for its intended market but apparently does not have a large tolerance for higher performance modifications that alter its rotational dynamics. I could reliably modify the 3SGTE turbo inline 4 in my Celica All Trac with fewer concerns than I am discovering with the S52. Even if only a small percentage of S52's suffer from damaging harmonic vibration when used with lightweight flywheels, that is too many for an engine that is supposed to be designed for high performance. The LSx swaps are starting to make more and more sense to me. I have already lost about $3000 in this swap if I can't use the UUC setup and the engine is not rebuildable.

I am getting ahead of myself. I need to tear down the engine and look for signs of what happened but hearing that there is cause for concern with a lightweight flywheel is very disturbing.

[LJ851]

This is not correct in the slightest.

^ I agree with your whole post except this part.

The light flywheel does not change the balance of the rotating assembly, which is all i said in my post. If you balanced the rotating assembly with a stock flywheel and a light flywheel it would balance the same. Perhaps you could have worded your first post better...

It certainly affects the harmonics and torsional vibration and i even said that in my post that is "not correct in the slightest"