Is this normal behavior for a cam sensor?

[syclone98]

I'm still in the process of trying to diagnose the no-start problem with my 87 GN from last Monday and despite trying virtually everything suggested, I still can't get it to start.

I just pulled the cap from the cam sensor to verify that it was turning while the motor was cranking and noticed something that I thought was a little odd.

As the motor is cranked the cam sensor doesn't seem to be spinning at an equal rate. What it seems to do is spin slowly for about 1/3 of a complete revolution and then speeds up for the other 2/3. If I keep cranking the motor the pattern repeats itself - slow for the first 1/3 revolution and then fast for the remaining 2/3.

I'll be pulling the cam sensor off in a couple of hours when I get back home but was curious in the meantime whether it was supposed to do that.

Thanks,
Christopher

 

[83ttypecooled]

Hi,
I'm guessing it's time for a timing chain replacement.While you're at it, pull the oil pan and clean out all the nylon from the original cam gear.The motor will most likely be good as new when you finish these easy steps. Good luck!

 

[syclone98]

Is there any way of determining if the chain is bad without pulling the cover? Or is that pretty much the only way to know for sure?

 

[Slow91z]

I bet what you are seeing is the motor coming up on the compression stroke and then passing it while cranking.

I'm sure the RPM's of the motor slow when this happens, and as it pushes through to the power stroke speeds back up.

 

[83ttypecooled]

Hi,
I doubt that is the case. Try manually turning the crankshaft, back and forth. The feel of it should make it obvious. Buick motors use a tensioner on the timing chain, which prolongs the inevitable failure. but fail they do, eventually. Pull the cam sensor and have a look-see. With a pencil light, you can pretty well check it out. Pull your oil filter,cut it open,look for nylon and aluminum. Hell, check the dipstick. That should show something.
Im out of ideas. Anyone else have a plan for sure bet diagnosis? Good luck with your issue!