jumped time?
 

87 420 SEL - Think it may have jumped time. Will pull valve covers tomorrow. If chain is still intact, what is best way to determine if it jumped time. Also, will the upper guide rails be accessable with just the valve covers removed.

One of the easiest ways to tell is if you have a cracked cam cover (seriously, not being sarchastic). There isn't much room between the gear, the chain, and the cover!

There are more scientific ways to do this that will get you # of degrees (I think 1 tooth=12 degrees, very bad) but with the valve covers off, and assuming that you dare to turn the engine (clockwise only), use the crank hub nut (a PITA from under the engine, I admit) to get the engine to the zero timing mark on the balancer. There are alignment marks cast in or scratched (I can't rememember) on the cams and front cam bearings that should be very, very close to lined up with each other with #1 TDC (that is, neither lobe is pushing down on the valves on cyl #1, the passenger side towards the front of the car). If they are way, way off, check the #1 TDC.

The top guides can't be removed without pulling the P/S pump on the left, and the alternator and its mount on the right, and then pulling the pins is not fun. But you should be able to see them.

Good luck, hope this didn't happen.

if you pull the valve covers, worst case scenario look for loose rocker arms if the valves are bent they will not allow spring tension on the rockers, this will be the first indication of jumped timing, if it has not jumped enough to bend valves, you will need to put the crank on tdc and make sure all the timing marks correctly align.

Actually, one tooth on the cam gear is worth 18 degrees of timing - wow.

It jumped!
 

Chain still intact, but it jumped. Chain guide on driver's side head broke. Lots of loose rocker arms. Think I'll part the rest of it out.

Pardon my ignorance but what happens if you crank it over counter-clockwise?

risk
 

For example, loosing time between the crank and injection pump, maybe the camshaft too, but the injection pump timing is the big thing and you can't see that like you can the cam/crank timing.

I think that the way the tensioner and it's arm works is "one way", and if you turn it counter-clockwise, the tensioner arm might not keep tension properly or even catch on the chain. Any instructions I've seen have stated "clockwise only"; when I was doing my timing chain, I saw that the area of chain between the RH cam gear and the tensioner arm was going slack if I moved it backwards. Needless to say, not good, and I didn't go any further to find out what would happen!

Yes check for loose rocker arms on the left bank. If you find any loose ones, you're screwed.

The guides are not designed to have the chain move over them counter-clockwise. You risk having the chain catch on the plastic guides and cracking or chipping them. This will increase the risk of a piece of plastic getting caught in the chain and causing it to jump.