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R & R of cam chain tensioner

BMW's V-12 hydraulic camshaft chain tensioner contains an O-ring that hardens over time and allows oil to seep past the O-ring and out through the tension adjustment screw threads. This results in small puddles of oil on the garage floor and an oil-soaked A/C compressor and drive belt. This slow leakage does not affect the operating performance of the tensioner.

The tensioner is located on the right front of the engine, directly above the A/C compressor. Most tensioners still have their "anti-tampering" cap in place, a black cylindrical plastic cap to protect the adjustment screw from damage. Oil typically weeps along the adjustment screw and exits the tensioner at the end of this cap, which is open. Some tensioners have their protection cap missing, exposing the adjustment screw and lock nut.
Here's a schematic of the entire assembly:

drawing of tensioner parts
Tension set screw
Set screw lock nut (17mm)
Screw plug (19 mm)
Aluminum crush sealing ring (07 11 9 963 355)
Dowell sleeve O-ring (11 31 1 702 953)
Dowell sleeve
Spring
Piston
You also need 17mm and 19mm deep sockets and a torque wrench calibrated up to 50 NM.
To gain access, remove the intake mass airflow sensor and rubber ducting between the air cleaner housing and the DK motor assembly. Also, disconnect the high tension lead from the coil and carefully put aside. You'll need to remove the protection cap by vigorously wiggling from side to side. It can't be reused, so don't worry about damaging it.
Next, take your 17mm socket and release the tensioner set screw locknut. Leave it loose on the set screw and give the set screw precisely 1 counterclockwise turn to release a tiny bit of pressure off the tensioner piston. Don't disturb the set screw any further, and gently snug the lock nut back down onto the screw plug.
Next, get your 19mm deep socket, fit over the screw plug, and giving a mighty heave, unscrew the plug. Do not release the plug entirely from the cylinder block. The piston inside is under considerable pressure and will definitely damage hands if you're not prepared to press against it when the screw threads release. Slowly unscrew the plug. When it releases, a capful of oil will drain from the tensioner piston all over the floor, so be prepared to catch it. Once free, you might have to extract the piston from the bore by fishing around with your little finger.
Now, using an Exacto knife, carefully nick and pry at the O-ring on the dowell sleeve. Do not scratch or otherwise damage the dowell sleeve. The O-ring will be very hard and sealed in its groove. Once free, clean the groove, replace the O-ring, and replace the crush ring on the screw plug.

Now, time to assemble everything. Insert the piston into the bore with the end of your little finger, and press and rotate until you feel the end of the piston "key" into the tensioner ramp.

Now comes the hard part. Seat the narrow end of the spring into the dowell sleeve, and seat the sleeve into the screw plug. I then put the screw plug into my 19mm socket, guided the spring into the back of the piston, and tried repeatedly to compress the spring enough to allow the screw plug to engage a thread on the cylinder block. It's really tough, so take your time. You'll get the hang of it after about 10 minutes. Once you've got it threaded, torque the screw plug down with 40 NM.


Next, turn the set screw 1 turn clockwise to restore the original tension setting, and tighten the 17 mm set screw down with 20 NM torque (my guess - it's not in the specs). Place the protection cap on the set screw and wiggle it snug onto the screw plug.


Because you've drained a small catch reservoir the tensioner uses to feed oil to the piston, the tensioner will need to be primed. If the right camshaft cover is off, you can pour a small amount of oil down the right side of the camshaft front cover, where it will fill the reservoir. Then insert a long screwdriver (I used a wood paint mixing blade) and depress and release the tensioner ramp repeatedly until it becomes resistant to movement.

If you don't have the covers off and the tensioner ramp accessible, I've been told the following works pretty well. Set the OBC antitheft CODE feature of your car to disable the ignition, crank the engine three times for 10 seconds each time, and then disable the CODE feature to allow the engine to fire. You'll probably hear a lot of chain slap for the next 30 seconds while the reservoir fills and the tensioner piston primes.

Degree of difficulty: 5 on a scale of 10.

Your humble servant, Mark in NBA (E31 850 owner)

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Replace Starter Motor

check this photo to get an idea of the problems you have -- the exhausts and the  heat shields!!


1. Don't read Bentley, then tell your wife that "it looks pretty straightforward, maybe 4 hours."
2. Make sure you have all the tools known to man, especially mirror, flashlights, 1/4, 3/8, 1/2 socket sets with extensions.
3. Just because you see the nut/bolt, doesn't mean you can get to it.
4. Just because you CAN'T see the nut/bolt, doesn't mean that you CAN'T get to it.
5. Read the Bentley manual, then use it to prop up your beer; it IS good for that at this point.
6. Brown Jersey gloves. Perhaps my admission of this will absolve some of the razzing/chiding I gave my father all those years!!
(now I understand why he always used them, and now I do myself! Thanks Dad.)
7. This job would be much easier / quicker with TWO people. One above, one below. Otherwise you'll wear yourself out
getting up/down, scooting under the car, etcetcetc......(even if its a 10 year old kid,)
8. Remove: washer tank, right airbox, carbon canister, (disconnect only the larger hose on aft end, move forward)
9. Disconnect muffler from BOTH sides of exhaust. (this one is VERY important when reassembling)
10.Remove right side catalytic converter, (not necessary to remove O2 sensor, although if car is up high, then you must remove it
(I left my cat lying on the garage floor! )) remove heatshield below exhaust downpipes.
11. Remove both exhaust downpipes, front one will come out the lower/back first, then the back one, out same place.
12. Remove heatshield from starter; then remove positive lead and solenoid control lead.
13. Now the fun starts: remove the two starter mounting bolts. A thin wall 16mm socket is needed.
A 5/8 sparkplug socket ground down will work, if you don't want to sacrifice a good 16 mm socket for the job.
14. Installation is reverse of removal. with these following notes:

15. When installing the exhaust, leave the downpipes loose until the catalytic converter is in and tight.
 This is imperative, as the pipe-to-pipe flange connection is tight, and there is NO ROOM for error.
Then the downpipe connections to the exhaust manifold can be tightened. Bentley says to compress spring, back off 1 1/2 turns.

16.The tops of the two inner boltheads for the downpipes can be seen with a mirror,
between the manifold and the plugwire - heatshield. Mirrors are a must for this job.

One other note: the use of Beryllium copper nuts (or whatever they are) for the exhaust is wonderful.
Can you imagine being able to remove (and reuse!!) 15 year old exhaust nuts on a Detroit-built car??

I hope this helps to simplify the process for somebody else. It was a tortuous job, especially since
I was doing it lying on my back on a cold garage floor. If a creeper is available, make sure you use it;
 jack the car up high enough for access. Make sure the car is supported extremely well on jackstands.
And note that you'll still need access to the top side of the engine.

The new starter has a much different sound than the original....it is more 'turbine' sounding than the original.
 The original really sounded like the old Chrysler starters, this one is much smoother. It is a rebuilt Bosch from
Advance Auto Parts, $140. The problem with the original one was that the outer shaft that the 'Bendix' slides on
was rusty and corroded, and must have been preventing the full / quick retraction from the flywheel, which resulted
in the unusual sound of the starter being driven BY the engine, once it started, and until the Bendix disengaged.

Any questions, let me know. If anybody wants to copy and paste this to their site, please do so.
Sorry I don't have pix of the process.....

Author: Mark750iL on 2004-04-12



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Starter Motor Disassembly


This is from the old 1988 parts 750
The plastic carrier has failed - -all the plastic parts are cracked to some extent
Bosch # 0001218027, produced 08/1988
Planetary gear up to date number 12411736763 , old one 12411736760,
Part use:  E30 , E28 , E32 Modell (Motor) 750iL (M70), 7' E38, 750iL (M73) 750iL (M73N) E31
























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