DeTomaso Mailing List: May 98, Message #200

Brent wrote:

>So this weekend I got around to putting a light on it and at cranking 
speeds it showed 25-30 deg ATDC.  I normally run it with 16 deg BTDC.  
Correct me if I'm wrong but this indicates 41-46 deg retarded from 
normal.  The car's odometer show's 78K.  If it is actually 178K, is it 
possible to stretch the timing chain enough to get it to slip a tooth or 
two?

>>>I'm told stock Cleveland timing chains are only good for about 30K 
miles.  If you've got 78K on the original chain, it's probably WASTED!  
I've heard of stock chains with so much slack that they were flopping 
around and started sawing into the side of the timing chain cover!  I've 
heard cars with loose timing chains, and you could hear the chain 
slapping around inside the motor.  Certainly possible that it could 
start jumping teeth on the gears, particularly since a worn chain will 
GREATLY increase wear on the gears as well.

Modern roller timing chains are supposed to offer greater durability; 
four years ago I switched to a Pete Jackson gear drive in my car, and 
it's worked great, although I must admit that I haven't actually DRIVEN 
the car anywhere since then! :<(  I've heard both good and bad things 
about gear drives; good thing is that they provide 100% accurate cam 
timing; bad thing is that they don't have any 'give' and thus can 
transmit 'shock' to the valvetrain that a timing chain would help 
absorb.  Whatever...I know I won't have to screw with it ever again 
(even AFTER I start driving the car!)

Sudden changes in timing are most often caused by the dreaded 
distributor roll pin, however.  While normally these pins simply shear 
completely, stopping the car dead, sometimes they can shear just enough 
to allow the gear to rotate slightly on the shaft and then become jammed 
in place.  Thus, when you pull the cap and crank the motor, the rotor 
turns which leads you to believe everything's hunky-dory down there and 
you waste time searching elsewhere for the problem.

I'd pull the distributor and check it out; since you've got it out 
anyway, even if the existing pin hasn't broken yet, you might as well 
put in a super heavy-duty pin (or perhaps one smaller roll pin jammed 
inside a larger one) before re-installing.

Mike

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