A Nice Drive on a Cool Morning, then . . .
 

Took the $print for a pleasure drive this morning. No troubleshooting, nothing to test, just a drive. The car ran beautifully after several weeks of carb tuning, fixed oil leaks, tranny shift adjustments, and other miscellaneous repairs. After about 15 miles and just two miles from home, she quit. I was able to coast downhill into a parking lot and a restart attempt revealed an obvious timing issue.

Got her home and into the garage. Removed the timing cover and rotated the crank to TDC. Cam gear correct, accessory gear off two teeth. Distributor short of the #1 position in sync with the accessory gear.

No explanation why this occurred. The accessory drive was recently re-sealed and belt properly installed. Tension was set just as when removed. The belt is still tight, no movement of the accessory housing. An easy fix, but why did this happen just cruising at 2000 rpm?

Easy fix as in how?
retiming the accessory drive?
please list all the steps you took after diagnosis.
Did you move the accessory housing?
Its possible it jumped time but never heard of that.
How do you know the timing was right and belt tension proper?

It definitely jumped time and when I said "easy fix," I meant I know how to fix it - but I don't know how to prevent a repeat.

I haven't yet made an effort to fix it because I clearly did something wrong when I reinstalled the accessory drive after replacing leaky gaskets. But I don't know where I erred. The only thing out of place after the stall was the accessory drive gear.

When I reassembled the accessory housing last week:

1. The gears were aligned perfectly when the belt was reinstalled. I applied tension that was equal to the belt tension prior to removal. After a few spins of the engine ((manually and with the starter) the marks remained aligned and the belt the same tension.

2. The engine fired up immediately, ran just as before, and two test drives (to check for oil leaks) revealed no issues. I re-checked belt tension and all seemed normal.

3. The belt had and has now about 1/2" of slack.

It seems obvious that the belt wasn't tight enough but it was as tight as when I started disassembly. My plan is to loosen the accessory housing, loosen the belt, re-align the gear and re-install the belt. Hopefully the accessory housing cooperates and slides without damaging the gasket (I used grease on the block side).

Any further suggestions are much appreciated - still learning the wonders of the OHC6!

Kent Moore made a fixture for adjusting belt tension.
My buddy bought one,supplied it to machine shop,but
it somehow came up missing when he picked up motor.
That car was cursed as it was stolen on way home from body shop.
We think it was an inside job.
Go to the part of belt that has the largest amount of span and in the middle turn 1/4 turn.
If its easy to turn past 1/4 turn its too loose.
It also should be hard but not impossible to slide belt off the cam sprocket.

Scotty

Did you use a new timing belt or re-use the old one? If new what brand is it and how old was it?

Once you have the belt off, try spinning the accessory housing gear by hand to see if it may be binding or if it has a rough spot in the rotation.

Even if the belt was loose, it seems odd that it would jump when running at a steady speed under light load. Seems like it would happen on acceleration or maybe when lifting off the throttle.

I would also mark the housing position before loosening it, and then compare that to where it ends up after you reinstall and tighten the belt.

Good luck and let us know what you find.

I always set my tension so I could just barely slide the belt off and on with the engine cold. This technique worked for me, never had any issues.

George

I loosened everything today and found no other issues. Reassembly went well, the housing still was able to slide without gasket damage. The belt tension seems the same as before, which I thought was tight enough. However, the accessory housing is definitely sitting lower on the block. In retrospect I think I was checking tension between the accessory gear and cam gear and paid less attention to the run between the cam gear and crank. I think that's where I screwed up.

The belt is 10 years old but only 300 miles. Brand is Avon. I was going to replace the belt due to age but Woodland Motorsports doesn't have any in stock, and Rob was pretty confident the belt wasn't the problem, with a pretty good track record of these belts.

After tightening it cranked right up. Ran it until the thermostat opened then re-torqued. Will take a few short drives with the top cover off and check for belt walk or loosening.

I found an odd thing while doing this. My cam gear has two timing marks, 180 degrees apart. Both appear to be identical factory marks. Any one seen that before?

Again, thanks for the suggestions, all very helpful.

Good to hear!
With the change in position of the Acc drive I bet you have the right tension on it now.

Changing the belt requires removal of balancer so the lower cover can come off.
Many years ago when my 67 Sprint was the only family transportation,on a cold morning,
the oil soaked belt stripped a couple of teeth off.
First and only belt failure,but it wasnt the belts fault,I couldnt stop the car long enough to put in a
crankshaft oil seal.
I destroyed the lower cover to change out the belt with a new one,wasnt proud of the hack job
but It got the car going again.

I had oil inside the cover although the belt was wearing only a trace. In addition to resealing the accessory housing, I changed the oil pump bottom plate gasket, the crank seal, and fuel pump gasket, all suspect of leaking. I was going to change the accessory drive shaft seal but that looked a little daunting (gear removal). If I still get oil inside the cover I would suspect that seal.