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Discussion Starter · #1 · (Edited)
Surely i must be the luckiest e34 M5 owner ever!!
I had my harmonic balancer out on the s38b36 to check if the key might have sheared since i found out that my car’s timing is slow which i will discuss in another thread.
Anyway, when reinstalling everything after i found no issues, i unknowingly did not torque the bolt on the damper flange to the right specouich. After driving the car like only 10km i revved it to 7300rpm in first and selected 2<SUP>nd</SUP>. All of a sudden it made a terrible knocking noise. I switched it off the moment i heard it and towed the car home.
After inspection i saw that the timing chain jumped a tooth on the lower sprocket (since it was 2 teeth out @ the cam). What i don’t understand is why the cams advanced:confused2. Wouldn’t they normally ****** when skipping a tooth while running?
When turning the engine, i found the big bolt on the damper flange to be completely loose. It wasn’t even finger tight, and i remember that i surely fastened it with my short T handle (which was obviously not enough).
I took a wild chance and rectified the cam timing and am very very VERY lucky to report that after 2 days of work the car is running perfectly with no bent valves:eek:oohhh::biggrinbounce:. The compression is 1100 KPA on all cylinders and that the shim clearance is between 0.3mm and 0.38mm which i believe to be in spec. I have to add on a side note that we had this motor out previously whereupon we installed bigger stainless steel valves and that we also made the pockets in the pistons slightly bigger since there was not enough clearance.
I searched all over this forum to try and find out what torque the specification equalled to with no success. The specified procedure is:
1. Torque the bolt(30mm socket; M20 x 1.5) to 60nm. (45lbft)
2. Then turn it 60deg.
3. Then turn it another 90deg after it sat for a short while.
What i found was that i picked 400nm (298 lb-ft) just as a random number on my (actually borrowed) torque wrench when i went through the procedure. When i did the final 90deg, the torque wrench clicked +/- 10 deg before i reached the final 90 deg. I therefore assume, that if i torqued it 420nm (313 lb-ft) from the beginning, it would have been just right.
Any comment would be welcome, since this was my experience but would not like to proclaim this as the gospel truth.
I assume this is the exact reason that some b36 owners report damper flange key failure. Since the key is only there for alignment and not securing. The friction of the force applied by the bolt is what is supposed to keep everything together, and i also assume that most mechanics would never think of fastening that bolt so much. If the friction is not enough, it will shear the key, since those resonant forces and harmonics are greater than most anticipate. I once read that on the M1 Procar’s M88, the damper would glow from the head generated as a result of constant 9000rpm limits:goldcup:.
Just hope this helps someone in the future, because i don’t think everyone would be as lucky as i was.
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