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Diagnostic Now....Broke XJ shaft, melted rotor. Cause?

Im keeping all that in mind too. But first (im 1000 miles away, wtf do i have to do it?! anyway...) im curious to see what the fundamentals look like first. If everything in the book checks out, then all that questionable electronic stuff is what my mind would resort to.
 
I still had spark in my truck when my pickup coil went out, but like was already said when it warmed up is when it started acting up. When the pickup coil went out in my K5 it ran like crap cold and warm.
 
The rotor melted and spun! Richmond performance distributor with cap rotor lasted about 45 miles...

Ordered new msd distributor, wires.

Took a Stack of ****ty orileys stuff back for refund. Never again!

Any stuff outside the distributor I should be checking that would cause pickup coils/.distributors to heat up or fail?

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We all told you it was that darn dist.!!:haha:

As far as heat is concerned, unless you have routed an exhaust line up by the dist., the only think I could think of would be overvoltage from a bad voltage regulator.

But that would make the coil, module, or pickup coil hot, not the rotor.
All it should see is the high voltage of the spark.

Now, if there was some way hot engine gases were coming up around the shaft............
 
Well that was one of my guesses!!! I wonder if its possible that the shaft itself carried the heat from the upper bushing in the distributer up to the rotor and that was hot enough to melt it. You know like if the bushing failed or was too tight it would generate a ton of heat.
 
Fordum said:
But that would make the coil, module, or pickup coil hot, not the rotor.
All it should see is the high voltage of the spark.
Click to expand...

I recently lost 2 modules and 1 pickup coil....

How do i test the voltage regulator?
 
dhcomp said:
I recently lost 2 modules and 1 pickup coil....

How do i test the voltage regulator?
Click to expand...

Well, you don't exactly. If its letting the output of the alternator go above 14.5 volts, then you assume its bad or has a bad ground.
On most of these trucks, I think they are built into the alternator. Most of those are replaceable, but its easier to just replace the alternator.


If you have a voltmeter on the truck, get a good quality digital voltmeter from somewhere, and check the accuracy of the one on the dash.
Hook it to the battery wires, not the posts, or one leg to ground and the other to the output wire from the alt.

Run the truck at various RPMs, with different electrical loads switched on. Compare the voltage between the voltmeter and the dash unit.

If the dash unit is off, but by the same amount each time, just make the correction in your head for now.
If at any time you see more than 14.5 volts, you have a problem.
A couple of years back, I had the dash unit out of my truck for some work.
I had a precision variable power supply along with a good meter. I pulled the needle off the meter, put exactly 13 volts into the meter, and put the needle back on at that reading.
Then, checked it a different voltages, and it was dead on.

You really need either a scope or a meter with a maximum capture function for this one, but you might see it without it.
Run the engine at a good RPM, 1K or so. Watch the digital meter closely, and turn on a heavy load.
Fan on high is usually a good one. The voltage may dip and recover, or dip and not recover.
Either on is OK, but if it does not recover well, you may need a bigger alt.

Then, watch the voltage carefully and dump the load off quick. This is when a lazy regulator may let the voltage float too high for a brief time.

The battery will absorb some of the overvoltage, and it might not last long. But electronics can be damaged by brief spikes.

A bad battery can cause an overvoltage condition, but usually will not crank the engine afterward.

Also, if you have an AM radio, turn it on and tune it off a station. A faint high pitched whine, that usually is there even with the volume all the way down, is OK, a loud harsh whine usually means a blown diode in the alt.
 
Soudns good, i'll check it all when its up and running.

Scott - Clear you pm box!

Thanks!
 
dhcomp said:
The rotor melted and spun! Richmond performance distributor with cap rotor lasted about 45 miles...


Any stuff outside the distributor I should be checking that would cause pickup coils/.distributors to heat up or fail?
Click to expand...

Melted parts in the distributor usually means you have too much resistance or too much current. When I got my HEI up to 8A on the primary, it would melt everything around the little carbon button the rotor spins on. This is why MSD less a lower resistance button. If something makes bad contact it will arc and cause a lot of heat. There is usually evidence of this if it happens.

Now didn't you say that at #1TDC that rotor was still pointing at the #1 plug wire?
 
Blue85 said:
Melted parts in the distributor usually means you have too much resistance or too much current. When I got my HEI up to 8A on the primary, it would melt everything around the little carbon button the rotor spins on. This is why MSD less a lower resistance button. If something makes bad contact it will arc and cause a lot of heat. There is usually evidence of this if it happens.

Now didn't you say that at #1TDC that rotor was still pointing at the #1 plug wire?
Click to expand...


Yes, but based on the way the rotor was "reclocked", it was pointing at 1 and thought it was firing on 2 or 8...i forget which way it spun.

Regardless, it was probably close to 1 at TDC, but far enough off that it didnt' run. When it ran that test, i was looking to see if it was close, or if i had skipped a tooth on the timing chain....



What would cause high resistance?
 
High resistance is caused by bad contact or connection. Corrosion, or loose fittings. I don't think that is a factor in your case.
The only place a bad contact or high resistance would occur is where the tab on top of the rotor touches the center button under the cap.

There is not a lot of current there, but if it got hot, the tab would show signs or the melting would start where it goes into the rotor.

Yours looks like it came from below.
It looks like the shaft got hot and melted the bottom of the rotor. Unless hot gasses are leaking in from around the shaft, I like the idea y5mgisi had about the top bushing generating heat.

Those were really good pictures of the rotor, but is there any other sign of damage on the top?

It kinda looks like the end where the metal arm comes out is eroded or trying to come apart.
Unless the rotor its self was defective and the material had a too low melting point, then something got way hotter than it should.
And it looks like it came from inside the cap. Does the cap look like its been hot?

You also mentioned losing pickup coils and ignition modules. High voltage will kill them fast like I mentioned, but so will heat.

Is there any way hot exhaust is getting to the dizzy somehow?
Like a crack in the back side of the manifold, or something to do with the EGR?

Something is getting things too hot, and the exhaust is the hottest part around there.
 
Fordum said:
High resistance is caused by bad contact or connection. Corrosion, or loose fittings. I don't think that is a factor in your case.
The only place a bad contact or high resistance would occur is where the tab on top of the rotor touches the center button under the cap.

There is not a lot of current there, but if it got hot, the tab would show signs or the melting would start where it goes into the rotor.

Yours looks like it came from below.
It looks like the shaft got hot and melted the bottom of the rotor. Unless hot gasses are leaking in from around the shaft, I like the idea y5mgisi had about the top bushing generating heat.

Those were really good pictures of the rotor, but is there any other sign of damage on the top?

It kinda looks like the end where the metal arm comes out is eroded or trying to come apart.
Unless the rotor its self was defective and the material had a too low melting point, then something got way hotter than it should.
And it looks like it came from inside the cap. Does the cap look like its been hot?

You also mentioned losing pickup coils and ignition modules. High voltage will kill them fast like I mentioned, but so will heat.

Is there any way hot exhaust is getting to the dizzy somehow?
Like a crack in the back side of the manifold, or something to do with the EGR?

Something is getting things too hot, and the exhaust is the hottest part around there.
Click to expand...


No other signs of heat on the cap/rotor.

Don't think there is any other place exhaust is leaking out. I'm running headers with those killer graphite gaskets.

Recently changed intake manifold gasket, so it should be sealed up fine. Although, that may not be the case, as it runs crappy on cold start.

Haven't been running the EGR solenoid. Its caused me issues, so the vac line to the TBI is currently plugged.
 
To be honest, I've run out of ideas. Something got that rotor hot, but I'm not sure what.
The bushing friction is about the most likely suspect right now.

I think at this point, I would get a cheap rotor from where ever, put it on and make sure it runs OK.
If it does, then I would run if for a few minutes, shut it down and pop the cap.

Then carefully feel around for heat. See if the shaft is real hot. Anyplace else inside or outside the cap.
Just in general try to figure out where any heat is coming from.
 
If its bushing friction, a good, new distributor should solve the problem.

Going to check voltages carefully when i get it back running.

MSD Dist and Plug wires on their way.
 
I'm willing to bet that you get another 50k trouble free miles out of this thing after the new distributor! In my opinion, if the only thing that got hot enough to melt was the rotor, we aren't dealing with I high voltage situation. At least It's not high voltage that killed the rotor. The only voltage the rotor sees Is from the coil which is something like 50,000 volts. We may ALSO be dealing with high voltage killing your other components, but I'm pretty certain it didn't lead to the rotors death.

EDIT: I'm going to go remove those bottom end pictures cause you don't need them and they are too big.
 
I want to say the part is no good, as far as I know the good rotors are not plastic, but a heat resistant polymer, I wanna say Bakelite.
Are you sure it melted and twisted or it twisted and melted from the rotationnal friction.
At least you found the problem.:dunno:
 
y5mgisi said:
I'm willing to bet that you get another 50k trouble free miles out of this thing after the new distributor! In my opinion, if the only thing that got hot enough to melt was the rotor, we aren't dealing with I high voltage situation. At least It's not high voltage that killed the rotor. The only voltage the rotor sees Is from the coil which is something like 50,000 volts. We may ALSO be dealing with high voltage killing your other components, but I'm pretty certain it didn't lead to the rotors death.

EDIT: I'm going to go remove those bottom end pictures cause you don't need them and they are too big.
Click to expand...


Some sort of heat killed the rotor, but the 2 ign modules and pickup coil make me worried. Hopefully those were just 2 crappy distributors (1 jegs/summit? and one other), and the problem will be solved.
 
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