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Discussion Starter #1
Hey fellas...I apparently just can't win. Today on the way home from work, I smelled gas and felt a reeeeeeal bad stutter, which I thought was a carb issue that showed up Friday but I hadn't dealt with yet. Well, driving to the gf's house last night, the Bronco seemed like it was on it's death bed...acting like it jumped time...again. Sure enough, I get a light on it, and it was advanced about 25-30* further than I set it. About a month ago, I replaced the timing set with a new Comp Cams double roller set...but wasn't thrilled with the quality. I doubt any teeth broke or the chain stretched over the course of a month, but I guess it's possible. So what are the other possibilities? Sheared dizzy gear? But I didn't figure I'd be able to get it restarted if that were the case? Cam bolt backed out? Didn't think it would hold a consistent time then? Any other ideas or suggestions for me? Thanks in advance.
 

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balancer has spun, verify tdc
 

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Discussion Starter #3
balancer has spun, verify tdc

Will do and a very good possibility, cuz it was pretty near crap, didn't even thing about that. If it is the balancer, how do I go about picking the proper replacement? Looking through a summit catalog, they have about 38 different weights/styles/etc. for a 351M/400 ranging from $90-450. The OEm replacement is $90 from Pioneer. Here's a pick of the damper:

 

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Discussion Starter #4
Got to thinking a little bit...I understand if the balancer spun, the timing marks would be off...but what about it spinning would cause it to run like crap...like it jumped time?
 

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it is extremely rare for the chain to jump especially if you just replaced it.
 

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Discussion Starter #6
it is extremely rare for the chain to jump especially if you just replaced it.

I get that...but what I'm questioning is...if the balancer spun, then wouldn't the marks just be off? It wouldn't cause the vehicle to run like crap, right?


Anybody have any other ideas? Only a few things it could be...but as much time as I've spent with that rig over the last month, I don't wanna go any further than I have to...hahahaha.
 

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I have had this happen to me. I had sheared the pin off the distributor gear and it twisted just enough to ad about 25* more.
 

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oscar espinoza
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check to see is ur oil pump got stuck....it happened to mine ..first timing whent a bit off then the pump completly got stuck and broke my distributor
 

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Not going to take long. Pull #1 spark plug, make sure you are on compression stroke, use small screwdriver sticking up out of SP hole (make sure it is straight up and down, or as close as possible, don't want it in sideways to hit a valve) to see exact TDC. See if that matches crank pulley and/or #1 on distr.

if after all that, you still think timing chain jumped, put compressed air in cyl (should not have heavy leak out either valve) and/or pull valve cover to look @ valves.

All of that should not take more than an hour.
 

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I get that...but what I'm questioning is...if the balancer spun, then wouldn't the marks just be off? It wouldn't cause the vehicle to run like crap, right?
You're on the right track. If the balancer spun & assuming the dist tie down is tight then the timing itself didn't move & something else is causing your engine to run rough.

Grab the dist with your hands & see if you can turn it.
 

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Discussion Starter #12
Didn't get any time to work on it yesterday, was busy with the fam and it was raining pretty good.


I have had this happen to me. I had sheared the pin off the distributor gear and it twisted just enough to ad about 25* more.
That's the route I'm leaning...so then you just got a new gear and called it good, right?

check to see is ur oil pump got stuck....it happened to mine ..first timing whent a bit off then the pump completly got stuck and broke my distributor
I thought I was playing Russian roulette with that oil pump...so I figure I'll just go ahead and replace it now anyway.

You're on the right track. If the balancer spun & assuming the dist tie down is tight then the timing itself didn't move & something else is causing your engine to run rough.

Grab the dist with your hands & see if you can turn it.
The dizzy is good...first thing I checked...got on it with a pipe wrench in it's current state and couldn't get it to turn. So I'm pretty sure it was good and clamped down.

Do you have an aftermarket carb? If so, which port do you have the vacuum advance hooked to? Just curious...
Yes...from the vac adv. on the dizzy to the port on the backside of the carb.
 

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I would just double check the vacuum line and it's connections at the carb and dizzy. I don't know which carb you have, and whether that port on the back is full vacuum or ported vacuum, but it's worth swapping just to check. I've read a bunch of info on ported/full vacuum, and I STILL don't fully understand the benefits/drawbacks of each. All I know is that I had been running full vacuum on my modified 400, and it was behaving really weirdly, and I couldn't get it above 1500 rpm at all. I switched to ported vacuum, and it now runs great. No idea why, but the other difference between the two was up to 15 degrees of timing at idle. That seems like a LOT of vacuum advance in the full vacuum setup (vs ported), and I can't really explain it....
 

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Discussion Starter #14
I have a 4150 series Holley, PN is 80783c. I guess there could be an issue with that line and I'll give it a look, but I have a feeling it's dizzy or oil pump related...although I never lost any psi.
 

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Yeah, look at the easy stuff first :) It would suck to rip out the oil pump just to find that the dizzy shaft was fine....

If nothing else, if your conditions improves or worsens by switching from ported to manifold vacuum, then you know it might not be the oil pump
 

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I too sheared a pin on the dizzy it made my timing over 30 degrees off
 

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Discussion Starter #17
I too sheared a pin on the dizzy it made my timing over 30 degrees off

If that's the case I just need to replace the pin and gear, drop the oil pan and oil pump and clean up any debris, right?


Can someone tell me what material distributor gear I would need? AFAIK it's just the stock cam.
 

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allI needed to do was replace the roll pin.
 

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Discussion Starter #19
TDC lined up just right and Here's the distributor...everything looks fine to me, unless I'm missing something:











So what's my next course of action? Pull the nose off and check to see if the cam bolt backed out or if something did happen to the cam gear?



.
 

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check to see is ur oil pump got stuck....it happened to mine ..first timing whent a bit off then the pump completly got stuck and broke my distributor
x2 for me, except it only sheared the roll pin in the gear. Made one hell of a backfire show until it died......
 
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