Exhaust Cam Rotated During M62TU Timing Chain Guide Disassembly

[MattyL]

Currently in the midst of replacing timing chain guides on my m62tu. When I was removing the left-hand-threaded bolt holding in the intake sprocket to the camshaft on the p-side, the exhaust cam, which I had loosened the bolt/sprocket of earlier, snapped/rotated, I assume because of a release of tension in the chain, which may have not been squeezed tight enough with the zip ties I was using.

After a little thinking, I deduced (POSSIBLY correctly) that with the crank being pinned at TDC, and thus having NOT moved, and no other cams having rotated when this happened, there shouldn’t be any issues if I rotated the exhaust cam to a point where the German Auto Solutions Cam Locking Kit i'm using fits on as designed, and the valves will be allowed to move back (via spring tension) to whatever position they're supposed to be at TDC. I did this, as well as locked the intake cam with the G.A.S. blocks, and the now both front cam lobes are facing the correct ~45 degree (inward) angles towards each other.

This is my first time dealing with motor timing so I am a bit nervous about what happened, to say the least. Does anyone have any thoughts on whether I handled the situation correctly?

Thanks!

[MotorMouth93]

I deleted my first reply because it's been a while since I timed my motor and I forgot the order of some of the steps.

The exhaust cam should not have snapped, it sounds like it might have been a bit stuck to the sprocket even though the bolt was already loose or the bolt wasn't loosened enough, then messing with the intake side caused it to free up and move a bit.

Sounds like you're fine, but if you have access to leakdown gauges it can't hurt to use them.

[JimLev]

It probably turned cuz the intake cam vanos bolt was still tight.
Don't worry about this as you will be taking everything apart before your done.
The cam lock blocks will position the cams correctly. Make sure you use a 27mm wrench on the hex part of the cams when you loosen and tighten the center bolt on the vanos and exhaust cam sprocket.

If you need some reassurance watch this 2 part video.
https://www.bimmerforums.com/forum/s...a-540tu-engine

[MattyL]

I deleted my first reply because it's been a while since I timed my motor and I forgot the order of some of the steps.

The exhaust cam should not have snapped, it sounds like it might have been a bit stuck to the sprocket even though the bolt was already loose or the bolt wasn't loosened enough, then messing with the intake side caused it to free up and move a bit.

Sounds like you're fine, but if you have access to leakdown gauges it can't hurt to use them.

It probably turned cuz the intake cam vanos bolt was still tight.
Don't worry about this as you will be taking everything apart before your done.
The cam lock blocks will position the cams correctly. Make sure you use a 27mm wrench on the hex part of the cams when you loosen and tighten the center bolt on the vanos and exhaust cam sprocket.

If you need some reassurance watch this 2 part video.
https://www.bimmerforums.com/forum/s...a-540tu-engine

Thanks guys. Good to know this doesn't appear to be much of an issue. The rotation was so forceful that I was actually worried that a valve may have smashed and bent against one of the pistons lol! Don't think this is the case, however.

Forward we go, then!

[MoonX5]

Not a problem. A partially open pair of valves simply snapped closed. This will move valves AWAY from the pistons, not towards them. You're fine...