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Mine had similar symptoms a couple of years ago on the highway. Can you manually turn the rotor? My original distributor somehow locked up internally, and broke the shear pin to the cam gear. A new Autozone Duralast Gold distributor (hey, I was on the road) fixed it. I was afraid it was the timing chain but no, just the distributor.

Pat
 

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Discussion Starter #42
Thanks, Pat.
With the distributor still in the car, should I be able to turn the rotor?


It seems like the engine would need to turn.
If the rotor turns, the gear pin is sheared?
 

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Yeah, if you can turn the rotor freely (i.e. more just a few degrees back and forth), it means the pin is broken. Mine backfired/sputtered too, when cranking. Apparently there was enough friction between the shaft and gear that it would spin a little when trying to start it. Another tell-tale sign in my case was the distributor was also rotated in the manifold until the vacuum canister hit something. This must have been when the pin broke.

Pat
 

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It might be the timing chain then. Try turning the engine clockwise using the 15/16" nut (that size on a 390 at least) on the front of the crankshaft, with the cap off. The rotor should turn. If not, the timing chain is likely broken or stripped off the gear. If it does turn, rotate the engine until the rotor is pointing to the number one spark plug wire. Then look at the front pulley. Is the timing pointer close to 6 degrees BTDC (or whatever you had it set to)? If not, the chain could have jumped a tooth or two.

Pat
 

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It's definitely a bronze gear, and it looks fine. Might make sure the pin that holds it in place is not sheared.

Did you do a compression check before this failure occurred? If so, you might check it again. It it's significantly off, it could be an indicator the timing chain jumped.

If it's not fuel or electrical related, the timing chain might be the next thing to check. Just be careful with it, as if the cam timing is way off (jumped too many teeth) you risk the valves and pistons colliding... bending valves.

A 'roadside' limp home mode for an engine who's timing chain has jumped, is to advance the timing a lot to see if it will run in order to get home. Looking back, it's possible that it had already jumped a little, and recently jumped some more. (this is just a POTENTIAL diagnosis)

Good Luck
 

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Discussion Starter #50
Thanks, Mike.
You called it on the distributor. The pin was sheared.


The previous owner that replaced the gear did not drill a second hole through it and only used a pin that went through one side of the shaft, didn't even make it to the hole on the other side,which is wallowed out a bit.


A guy yesterday at a shop remounted the gear, running a new pin in the existing holes, making it through the holes in both sides of the shaft, but did not drill out the other side of the gear and run it all the way through.


Is this a high stress situation on the gear if it is already a tight clearance? He had to tap the gear on and off with a brass hammer and brass punch, took a few minutes.


Should I be ok with this setup?


Thanks.
 

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Thanks, Mike.
You called it on the distributor. The pin was sheared.


The previous owner that replaced the gear did not drill a second hole through it and only used a pin that went through one side of the shaft, didn't even make it to the hole on the other side,which is wallowed out a bit.


A guy yesterday at a shop remounted the gear, running a new pin in the existing holes, making it through the holes in both sides of the shaft, but did not drill out the other side of the gear and run it all the way through.


Is this a high stress situation on the gear if it is already a tight clearance? He had to tap the gear on and off with a brass hammer and brass punch, took a few minutes.


Should I be ok with this setup?


Thanks.
The 'proper' procedure, is to drill another hole perpendicular (90 degrees) to the original, but not inline with it. Two reasons...

1. It provides a brand new surface for the pin.
2. The gear needs installed at a specific distance from the mounting base of the distributor. (Google 'setting distributor height') Not all gears are drilled in the same spot for the pin... so you cannot blindly swap gears, or the height can be off. Setting the height, and THEN drilling the hole is technically, how it should be done.

However, if the last gear was installed correctly, and you measure it's height to the mounting base of the distributor, and the new gear looks identical, and measures the same... it can often be directly swapped, as long as the pit fits tightly. Last one I did, I was able to do a direct swap.

The main load on the distributor gear is the oil pump. The cam turns the distributor, and the distributor turns the oil pump. This puts a significant load on things, so the distributor gear attachment needs to be right. If the opposite hole in the gear is wallowed out to the point you only have one side of contact, I'd probably shop for a new gear.

Good Luck
 

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Discussion Starter #52
The gear only has the hole in one side. It's the shaft that has holes in both sides. The one that was on the distributor hole is fine. It is the holes on the opposite side of the shaft that is wallowed out.


We are using the same gear, so no change in height.


The sheared pin was only a short one, didn't even go across the shaft into the other shaft hole.


We drove a new hardened pin though both shaft holes, butting up against the inside of the gear opposite side.


Do you think this is ok to go with?


Looking at the bottom of the gear and the surface at the bottom of the hole, they both look good, no damage. You can see the gear has been touching the bottom due to oil marks, but no scoring.


The gear may have moved down a fraction of an inch, though (1/8 to 1/4" at most), so I am not sure if it was properly seated to rest on the bottom.


Not sure how to check this without taking the cam out from what I am reading.
 

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Discussion Starter #53
Hi all- I got back up there, got a second pin installed in the distributor gear, and got the balancer rebuilt by Damper Dudes, who were great. It is a Boss 302 balancer with the 28 oz. weight ground out and several relief holes drilled in both the hub and outer ring. The engine was built by Ernie Elliott back in the day, and he was apparently making it internally balanced with a lightweight rotating assembly.

I got it timed and fired up, but still grossly underpowered and no top end above 5-6k.
The 750 VS Holley had a screw installed in the secondary linkage to force them open. I removed it and found that the VS were not opening on their own.

I drove down to Ernie's shop in Dawsonville to try to catch him there and see if he recalls my motor. He wasn't there, but I spoke to his two engine builders and they also gave me a tour of his shop. They gave me some carb parts for mine, and are great guys!

They also had a bunch of boxes of NASCAR carbs from cars when NASCAR went to FI in 2012. Ernie had tricked out these carbs for racers.
They sold me an 830 and went through it, replaced gaskets and jetted it down from 110's to 90's, which they felt would be a good starting point based on my description of my engine.

I also got to meet Bill's wife , who was in Chase's office in another of the 5 buildings at their complex. She was very nice. As I was leaving, a black Learjet flew directly overhead, taking off from Bill's private airfield. Very cool.
That was a great experience going down there.

I installed the carb, and it started right up each time, unlike my pos 750. As I was ready to take it for a drive before I hade to leave, my clutch or linkage was screwed up, so no go. I will be back in August to address it.
I think that engine is finally going to scream.

The carb idled at about 1400 rpm. I turned down the idle adjustment screw quite a bit and was only able to get it down to 1200-1300. All 4 butterflies have a hole drilled in them, and are cracked open at idle. Will it be possible to get the idle down to about 1000 and should this be a good carb for this engine (400 block, Boss 351 SVO heads, solid roller, Torker, 12/1 or so compression, 4.11 gear, toploader)?

Thanks!
 

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The carb idled at about 1400 rpm. I turned down the idle adjustment screw quite a bit and was only able to get it down to 1200-1300. All 4 butterflies have a hole drilled in them, and are cracked open at idle. Will it be possible to get the idle down to about 1000 and should this be a good carb for this engine (400 block, Boss 351 SVO heads, solid roller, Torker, 12/1 or so compression, 4.11 gear, toploader)?

Thanks!
Both the front and rear throttle blades have an adjustment for idle. The rear is just small. If you look, you'll find it.

The edge of the blade covers up a slit in the baseplate. Start off with the blades covering up most of the slit. The exposed portion should be roughly equivalent to a square... not a long rectangle.

The holes in the blades are for extra airflow at idle. If too much of those slots are exposed, it overwhelms the idle circuit. The holes allow the blades to be closed further, and still flow enough air at idle.

Carb likely has a 4-corner idle. Adjust all four screws the same number of turns out. Turn them all in all the way in until they lightly seat... then with the engine fully warmed up, turn them all 1/2 turn out and see how it idles. You will then turn them in and out in 1/8 turn increments until you get the best idle. This can be determined with a vacuum gauge, idle speed, or just by ear. Adjust them all the same number of turns.

If you have a significant vacuum leak, they may be hard to adjust.

4-corner idle (carbs with four idle mixture screws) will usually end up around 3/4 turns out. 2-corner (just the front barrels having idle mixture screws) will usually end up around 1-1/2 turns. These adjust the fuel mixture for the idle circuit only. Out is more fuel, in is less. The carb jets take over when you are past 1/8 throttle.

This being said, lack of revving past 5-6k rpm is rarely the carb... but, hopefully it helps!

And... as for your particular case... I'd probably recommend you just turn the idle down a little on the rear baseplate, and call it 'good'. THIS being said, if it's got a solid roller, you don't want to go down below 1200 rpm, as solid roller lifters lube from oil being thrown off the crank... and the extra idle speed helps. A decent sized solid roller isn't going to idle very well much below 1200 rpm, anyway.

Good Luck
 

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Discussion Starter #56
Yes, it is a 4 corner idle. I'll try those adjustments.
The engine does run better than it did, and will rev, but just lacks power.


I shifted from 2nd to 3rd cleanly at 6400, but in third is started breaking up at 5500.


It seems like it may have been starving for gas.This new carb provides tons of that.


I will also be replacing the 5/16 fuel line with 3/8 next time I'm there.
 
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