What happened to my engine last night?

[Whaler]

Cleaned all the contacts. Reinstalled cap. Ran rough. Took timing light to motor. WEIRD. Timing is now a few degrees BTDC. I had originally had it timed alot closer to 15 degrees BTDC. Distributor bolt was TIGHT - no way the distributor twisted. Any thoughts on that circumstance?
Loosened bolt, turned distributor, and around 20 degrees BTDC the motor sounded a LOT better. Hard to say that it's back 100% - but certainly ten times smoother. Timing remained extremely stable - even at low RPM. No movement in the timing except on hard acceleration.
Removed the bolt, pulled the distributor, and NO damage to the distributor gear. YAHOO. So at least I know it's not a sheared pin or mis-matched gear on the distributor. I didn't look down at the cam gear (guess i should?) but there were NO filings or weird wear on the distributor gear. That, at least, was a relief.
So I'm going to wait until tomorrow when the engine's cool, and retime it.
QUESTION. How could the timing have moved as it has????
- Paul



Discovered an exhaust leak on passenger side - that's probably causing SOME of the backfiring.

[ryans88gt]

stock dampener?

Probably time for a new one. outer ring of the dampeners are known to separate from the inner.

timing will appear to change, but really it is the outer ring slipping. Causes the motor to run rough with a lot of vibration.

[FritoBandito]

I remember a post where someone had a dist gear pin shear and there were no visual indicators. From the outside of the gear the pin looked like it was in place. He just slowly lost timing until it sheared completely.

Your comment about it having a few degrees less timing without anything being loose made me think of it.

Hmm... Think before I install my dist I'll file or scratch an indicator groove in the end of the shaft to show how the pin should be aligned.

Mario

[Whaler]

Edited the first posting. Still have issues - any feedback is appreciated!
- Paul

[CraigS]

Frito makes an interesting point about the gear on the distr. Most are a tight fit w/ the pin as the final locator. So the pin could shear, or partially shear, and the gear could just slip slowly out of alignment.OTOH, timing being retared usually makes the engine run weakly and have a lower than normal idle. But it doesn't cause a misfire unless it's WAY off. And it wouldn't be way off and then be good the next morning. All your symptoms seem to be related to how long the car is driven.That usually equates to something getting warm and causing a problem, then being ok once cooled. The one thing that jumps out to me in all of this is...MSD. There have been SO many weird problems that are fixed by a new box or new coil that I would never buy an MSD for myself. Just my 2 cents from being on this forum for 7 yrs but no personal MSD experience.

[Cone Basher]

Just a thought here. Some Holly carbs come with a sintered brass filter where the fuel line attaches to the carb.,The way they are designed is to catch small particles before they enter the carb which allows the particles to settle but when you get on the gas they flush back to the filter and add restriction. If you have these you might remove them and take a look, some guys just remove them and rely on a good filter before the carb. I'm assuming you have a fuel filter between the pump and the carb. Sounds like a fuel delivery problem to me. Remote possibility but it also could be that you are creating a vaccum in the tank as the motor burns fuel. You can test this buy leaving the gas cap a little loose and taking your car for a ride.
Keep us posted, this one has me stumped.
HTH
CB

[Whaler]

Thanks Craig and ConeBasher. I do have a filter between the pump and the regulator. I've checked the brass screen on the carb - nothing there now, but stuff could be migrating on acceleration or heat...
Definitely NOT a sheared gear - I can see through the locating pin from one side to the other. Thanks for the suggestion though.
As to the MSD thoughts - I'm going to swap the rev limiter "plug" for a different value and see if for some reason that might be failing... It's a -6AL...
I'll be doing a vacuum test after I get the vacuum gauge on Thursday.

[Whaler]

OK. I don't know EXACTLY what the problem is, but I fixed the car and it's back to its original performance. Turns out there is a blockage somewhere in the carb. I took another carb I had lying around and swapped it in 20 minutes. Took it out for a spin and VOILA! NO ISSUES.
So now I need to go through the carb and find out what the cause is. nc1Mike and Bob Cowan get the prize for QUALITY REMOTE DIAGNOSIS!!!
THANKS TO EVERYONE.
- Paul

[bgbadaz]

paul, glad to hear things are better. i just read thru the thread and thought id offer my .02 as well (just incase). If by chance your problem re-occurs (and i hope it doesnt), it sounds EXACTLY like something that happened on my race car. I searched for almost a year trying to find the problem and it turned out to be a bad distributor. Once it got some heat from the engine in it the module would intermittantly short out. Anyway, glad to see you are up and running and your gremlins are gone. Enjoy some summer driving.

Bobby

[Whaler]

Thanks Bobby!!! So far so good!!! Now off to get an alignment, and really start using it!!!
WAHOO!
- Paul

[Cheapsnake]

Great news! I had a similar problem that turned out to be a tiny bit of silicone sealer blocking an idle air bleed, almost too small to notice. How it got there, I'll never know, but hope your fix is as simple.

Tom