Timing Issues on BBC

This hasn't been the best season for us due to an endless string of problems. Long story short, our latest problem started when we had the driveshaft coupler come loose and the motor went to 11,600 rpm and bent every exhaust valve. Pulled the motor and checked everything over except did not touch the front. Didn't pull bottom pulley , timing gears or cam. Put it all together and when 3.95 1/8 mi first pass which is as fast as we had went before. Next pass started good but developed a miss midway in the run. Data recorder shows a jagged line for engine rpm. Still went 4.05. Checked everything, tighten this and that and tried a couple more passes and could not get rid of the miss and it got worse. It sounded like it was on a rev limiter. We were sure it was the MSD 10 plus coil. So we get a new coil and tried it today. Before it sounded great in the pits. On trying to start it today, it had the same miss. Nothing too violent, just not all cylinders were firing every time. Something we had not checked before was the distributor phasing. Pulled the cap, rolled the engine to line up the crank trigger to 32 degrees and the distributor was no where close to where we had it set with the rotor now in between #2 and #1. Our distributor in under the blower and is tight to the intake so we could NOT rotate it to the #1 position. Pulled the distributor and moved it a tooth, lined it up and engine fired and sounded perfect. SO, if you are following all that, what can cause an engine to advance timing? Distributor gear? Timing gears? Pulley/crank trigger wheel rotate on crank?

 

Pull the bottom pulley drive off. I bet the key ways are shifted. Also pull the mag drive out and make sure the shaft isn't twisted and the roll pin is still in its correct position.

 

I am with Mike on this, could be anything. I would pull everything down and check all the parts, be a real shame to find one part that changed the timing then run the car again and find out you missed another and take out an engine.

 

RLPRACING,
I am curious why the rev-limiter didn't prevent the motor from over revving?
Thanks, Joe

 

Had this problem

Check your bolts on your timing gear for the cam. When the loosen up there is enough tension to "move the cam back. The helical gear in the back rotates the distributer and now you're out of phase

 

bbc timing

had a very similar issue and it was the crank keys as mentioned in this thread. Had assumed the timing gear had jumped so went and brought a milodon unit only to find it was the keyways that had let go ( 2 x 1/4")

 

Finally taking things apart. Nothing wrong with distributor gear or pin. Cam gear bolts good. Crank gear key good and nothing wrong with idler gear that I can see. Blower pulley hub keys good. SO now what???? Could we have screwed up and had it out of phase all along but was close enough to run okay on one pass then went go bad after that? This crap will drive you crazy.

 

Camshaft thrust clearance set correctly ? .

 

It is entirely possible to jump a tooth on a Milodon gear drive when you tag the exhaust valves on an over-rev without any visible damage to gears, bearings or any other components. Don't ask me how I know....

 

Seems like this would retard it, but maybe not...

 

We've had everything from too much cam endplay, too much distributor shaft/gear endplay, hold down clamps come loose, spiral pins partially sheared, twisted shafts, timing belt (offset drives) pulleys slipping on shaft, mag clamps not holding and pins coming loose in the X driver area. But all of this RETARDS the timing.

 

If it was between #2 and #1 it did retard it. It would have to be between #8 and #1 to advance it.