Hi, have a question I was hoping to get input on. I am doing my first timing chain replacement on my 08 Cooper S. When I installed the crankshaft bolt I couldn't get it to torque the +180 degree after the 50NM no matter how much I tired, best I got was about 90 degrees. Thinking I might have done something wrong, I backed the bolt out and tried it again. The second time I was able to get the full torque on the bolt. Did I ruin the single use bolt by doing that and is that bolt now compromised?

 

Yes, I would get a new bolt and get it torqued correctly the first time. I know it's a HUGE pain and it is a ton of torque. The first time I did it, I happened to get the original spec torque values and ended up spinning the bolt and bending all of my exhaust valves lol. I would 100% buy a new one and do it again for peace of mind

 

Since proper tension on the crankshaft hub bolt it the only method to keep the crankshaft timing sprocket in time relative to the camshaft sprockets, it would be wise to replace the bolt. Now considering this is a "torque to yield" fastener, and you didn't make it to 180 degrees on the first attempt, you didn't fully stretch the bolt. These are very robust fasteners. 50 NM is equal to 37 ft lbs. I have a torque angle meter, so when I finish the final 1980 degree rotation, the meter gives me what the final torque value. On my 2012 N12 engine, I torqued the bolt to 37 ft lbs and then rotated it 180 degrees; the final torque was 137 ft lbs, your results may vary, but make sure you have a nice long breaker bar on the socket so you can get the full 180 degrees. Remember, you don't have to rotate it the full 180 on the first turn, and in most cases you'll have to reposition the breaker bar to complete the full rotation. For example, in your original case, you could have just gotten a bigger breaker bar and rotated the bolt another 90 degrees without removing it. Worst case scenario, just torque it to 140 ft lbs. Mine hasn't slipped at 137. ;-)

 

Thank you. That's what I figured. Since I have the whole timing chain system replaced at this point. Can I just put the flywheel pin in and cam locks back into place and remove that bolt or do I need to release tension by removing the chain tensioner. Or do I need to undo everything and start over.

 

You'll need to backtrack a little; the crank hub bolt gets torqued before you install the cam sprockets. Considering where you are, I'd get the special tool that hold the crank hub bolt, torque the bolt, then check the timing. The special tool looks something like this. I would not rely on the timing chain, cam sprockets, and camshaft locks to hold the torque on that crank bolt, but I know there are some that do it that way.