R56 Engine failure, all exhaust valves bent.

[Jake S]

Hoping someone can help me understand the “how on earth” this happened.
Picked up an 08 Cooper S for my daughter on the cheap…..maybe that is also part of the “how on earth” problem!!!!! As I’m going to be paying for it now.
Car is in great condition 170 kms, was suffering a really bad death rattle that was quite obviously the timing chain. Top guide had snapped off and was laying in between the two runs of vertical chain banging around.
Already had a lock tool set on hand from a strange deal for a welding cart. Ordered all my parts, guides, tensioner, chain, new sprockets except for VANOS, new sealing washer, new hdwe. From BMW and o rings. Had the crank oil seal given to me, went through the job and everything was set and torqued to the letter.
Fired up the car and it was hesitant to start, finally did and ran ok, had a little pop on run down that my son loved. Stopped it started it several times. Let it run for 5 mins then it started rattling, immediately shut it down. Came back to it a few days later, pulled the valve cover off, lock tools in and cams were out ever so slightly, thought maybe I over tensioned as the 0.4 nm was a tough one to replicate, re did timing and with lock tools, went a little less on the pre tension of the chain, reset everything to spec. new stretch bolts, re cleaned all mounting surfaces of sprockets, re torqued (all my torque wrenches have been calibrated recently and are within one to two pounds ft.). All back together, fired up immediately and ran beautifully. Let it run, several cycles of run and shut down as I moved it about in and out of my shop.
Decided lets road test it. Got on the road, started driving, put my foot in it, boost came on, stutter, back fire, off the throttle and it coasted to a dead stop. Had to call for the worlds shortest tow as it was late and I was solo and there were a couple of hills to deal with. Got it home, pulled the valve cover. Every exhaust valve is bent!!!!!! All the intakes are fine, exh-rockers all knocked out of positon and laying under the cam. Threw the lock tools on the cams as they were pointing almost straight up and they were perfect, locks dropped right on. Go to crank pin, no go, go to put a wrench on, look at crank bolt, its loose!!!! Sticking out by ½” or so. HOW??? This was torqued to spec. and given the 180 degrees of “crap something going to snap” stretch. I knew I should have loctited the damn thing. The hub/boss seated beautifully when it was re-assembled and wasn’t interfering with anything when I installed it. No tools were left on the bolt.
I work as an engineer and am by no means a stranger to in depth technical wrenching therefore I would love to meet the friction fit fool that came up with this assembly method instead of keyed shafts, likely the same one who decided the friction drive pulley was a great idea to solve a clearance issue. I understand the tradeoffs but from all the timing issues people have when doing this job with TTY the risk assessment on this design should have spoken loud and clear.
So now im going to stock up on parts to rebuild the head post inspection for damage that might bin it! If anyone has some insight how that crank bolt could be that loose and far out please chime in. Im going on very little sleep and cant see how there would have been that much energy in the rotational mass of the ancillaries to spin the bolt off once the crank locked up on the valve train. All exhaust valves bent open so there was no single lock effect from but as they all hit then there likely would have been a staccato effect to jerk the pulley but still!!!!!!
Somebody talk sense to me!

Am asking the question here as I came across the mini head repair performed by Eric where two valves had bent. Never did catch what the cause was. As stated all new hdwe used, torque was to spec and verified. Head rebuild to follow. Thanks for the content and any I sight that might be offered. Think I’m going to use loctite new time.

Topic