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Distributor cap and rotor

7K views 38 replies 20 participants last post by  madcarson 
#1 ·
Hi,

I have a 468 running a MSD system on it. The distributor is an MSD 8360. Yesterday while driving, the distributor cap flew apart. It came completely off and the rotor left the scene. I coasted to a stop and after I could not find a part store around in the area with that cap and rotor, I had to tow it home.

Anyone ever have a distributor cap and rotor fly apart like that? I haven't.

The only other symptom was previously during the drive, I noticed when I was driving up a very steep hill, I noticed if I accelerated with some authority up the hill my oil pressure actually started to fall off. It would only happen under a load. It acted normally when driving but would actually drop when putting a load on the motor.

Please help me diagnose this,

M
 
#2 ·
Re: distributor cap and rotor

Yes, I've blown a cap or two apart :yes:
The cause varied for most ...
Cap retainers not properly seated or vibrated loose - cap contacted the firewall or other area due to engine flex - cap had a crack and was weak to begin with (new cap installed just a few minutes before, you could see the old and fresk crack lines) - rotor tip came apart and took out cap when it wedged in - weight popped off at speed, took out rotor and cap - wires were pulling on cap during acceleration and caused it to ****-off to one side ...
Lots of different reasons for the failure.
Look over your install carefully to see if you can identify any interference and if not, install new cap and rotor making sure they are installed and setted properly.

Oh, and carry a 'spare' until you know for sure what caused it ;)
 
#8 ·
The gear could seldom cause a broken cap - unless the end play became (or was) so great from the load(s) of the gear and pump and somehow it pushed the shaft up into the cap.
Besides, the shaft is loaded downward during operation ... so I wouldn't suspect it to be the cause of a lost cap.
 
#14 ·
Besides, the shaft is loaded downward during operation ... so I wouldn't suspect it to be the cause of a lost cap.
I think if you look again, you'll note that the distributor mainshaft is loaded upward during operation; that's why there are hardened shims between the top of the gear and the bottom of the housing and why that's the only part of the mainshaft that gets engine oil. The Delco distributor assembly drawings clearly show that the thrust of the gear is upward, against the housing. :)
 
#10 ·
Yes, the shaft will move up & down some normally, but not enough to disengage from the pump drive tang - unless the tang or gear are really worn, the shaft was to short for the assembly stack-up or there's something really wrong with the distributor.
 
#13 ·
I should be able to check the motor mount problem by putting some wood under the oil pan and then a floor jack against that and lifting it a bit right?
Then it should let off tension from the front coil springs relatively evenly if all is good. If a motor mount is allowing the motor to move, the jack should lift the motor on one side right?

Or is there a better way?
 
#16 ·
Did I mention that the screws that hold the rotor cap in place were just completely gone? No trace?
If a rotor came in contact with the distributor cap at 5000+ rpm, would that necessarily remove those screws too?

I remember putting that rotor on there. 2 screws and I snugged them on with a screwdriver. I didn't reef on them but I didn't think I had to.

:(
 
#18 ·
Very funny this thread was here... My 1991 s10 needs motor mounts and i havent gotten around to changing them (and yes i work in a garage and go to diesel mechanic school too haha) but they are the original mounts and my drivers side mount is completely destroyed... well needless to say i was at a stop light 2 weeks ago and i hammered down on it to beat some cars that were in the wrong lane to begin with and my truck cut out after i passed them.. Got out and i guess my motor pushed the distributor cap in to the firewall and broke it in a ton of pieces... Luckily i was in walking distance to home to get a spare i had.
 
#21 ·
OK, guess I'm gonna have to check into motor mounts.


Whats the best way to do that?


One more question to the forum; Lets just say the motor is rising up on hard acceleration, could that maybe be why the oil pressure dipped? I went back and looked at some home video that was shot by me while driving the car and a couple times I got on it, the oil pressure dipped instead of rising with the rpm. Only on hard acceleration. Fortunately, it was only for brief periods of time. Like 1-3 seconds. (didn't want to exceed the speed limit, any longer at WOT and I would have)
So if the motor was rising up under hard acceleration, does that mean that the oil in the pan was running to the low side of the motor and away from the pickup causing the oil pressure dip?
Oil pressure acts completely normal when normally driving/idling. When the car is hot, the 20-50W oil comes down to about 25psi. Cold, its 50-60 psi at 1000 rpm.

Also; I looked at the car last night. Both the motor mount bolt and nuts are there. I could only see the front of the mount though.
 
#22 ·
If you have an automatic, it's pretty easy to check for a broken driver's side motor mount. Open the hood, start the motor. Put the trans in drive, left foot firmly on the brake. Slowly bring the RPM's up with your right foot (like power braking). If your driver's side mount is broken, you'll see the engine rise up like magic and then flop back down when you let off the gas. Be careful, esp if you have rod type throttle linkage. The rising engine can cause the linkage to stick and act like a Toyota.

A little trickier with a manual trans as you have to rely on the e-brake, unless you happen to have three feet.

The driver's side mount is usually the most likely to break.
 
#23 ·
First I would pull the distributor and check it thoroughly.
Make sure end play is within spec., the gear is in good shape, the oil drive slot in the gear is properly engaged, and look down into the engine to make sure the oil pump drive shaft is in good shape.

After checking and reassembling the distributor, reinstall it and check timing.
Then - WITH DRIVE AND FRONT WHEELS BLOCKED OR AGAINST A CURB, THE PARKING BRAKE SET AND YOUR FOOT ON THE BRAKES - open the hood so you can see the engine and watch for it to move in mounts - then (not sure if this an auto or manual) put the car in gear and press accelerator or release clutch to slightly start to load the drivetrain - the engine will 'strain' against the mounts if they are good and remain in place - if BAD the engine will begin to 'rise' on the left (drivers) side and raise up in the mount - STOP as soon as you see this movement to prevent damage again and replace the mount(s).
"Wash -Rinse - Repeat" the above, after replacing the mounts to be sure things are fixed ...

The oil pressure dropping can be a lot of things - very hard to tell without knowing and seeing the set-up.
If electrical gauge could just be a wire stressed when accelerating ( maybe from mount movement ;) ) cutting signal to gauge - or bad connection in ciruit somewhere else.
If mechanical it could be line getting kinked/pinched during engine movement (see mount ;) ) and cutting flow to gauge.
Or .. it could be something mechanical about the pump;
* Drive issue
* Pick-up issue
* Pump issue
 
#24 ·
Mike I had the same thing happen last year on the freeway. Was cruising along then two loud bangs and the motor died. Opened up the hood and found the cap off to the side and the rotor on the manifold. One screw was completely gone and the other was still in the rotor. Reinstalled the rotor with the remaining screw and put the cap back on and drove home. I found it hard to believe this happened too as the dizzy had been in the motor for 6 years and I never had an issue and the screws had locktite on them. I did find that a stock rotor will work in place of the MSD rotor, then have a couple of #8 I believe screws and a small screwdriver in the jockey box just in case.
 
#26 ·
MSD got back to me after I sent them some detailed pics of the destroyed cap and rotor.
They seem to think that I didn't install the included washers with the rotor correctly and the screws worked out and then everything went very badly when it finally came off inside the cap at rpm.

So I put a new cap and rotor on it.

But it won't start. It keeps acting like its too avanced. Its dragging down the starter (a relatively new MSD starter) and sometimes back fires through the carb.
I have it now very retarded and it acts the same.

(during the violence that destroyed the cap & rotor, the distributor somehow turned clockwise as you look down on it and jammed the vacuum advance diaphragm against the fire wall)

I returned it to about where it was(the vacuum advance diaphragm about 1" away from the firewall) before starting it and it was acting way too advanced.
I retarded it more and more until it seems way too retarded and it doesn't drag the starter as bad but about every 4th or 5th crank it bogs the starter and you hear and see it phhoosh!! through the carb. Not quite a back fire more of a valve allowing compression to go up through the carb.

Any ideas?
 
#27 ·
Maybe I missed it being mentioned so just wanted to make sure that you've already pulled the dist. out and looked down that hole with a flash light to make sure the oil pump rod is in good shape and not missing pieces. That is very strange about the screws being gone - seems to me as they got increasingly loose your car would start to run like crap prior to the cap flying off - I just find it hard to imagine that they'd gradually vibrate completely out w/o any signs of misses/stumbles prior to cap completely launching off. That means that one screw would have to be barely hanging on there sufficiently to hold the cap in place till the very end when it came apart and that seems unlikely. Strange....
 
#28 ·
Maybe I missed it being mentioned so just wanted to make sure that you've already pulled the dist. out and looked down that hole with a flash light to make sure the oil pump rod is in good shape and not missing pieces. That is very strange about the screws being gone - seems to me as they got increasingly loose your car would start to run like crap prior to the cap flying off - I just find it hard to imagine that they'd gradually vibrate completely out w/o any signs of misses/stumbles prior to cap completely launching off. That means that one screw would have to be barely hanging on there sufficiently to hold the cap in place till the very end when it came apart and that seems unlikely. Strange....

Well it was weird. So weird(and violent) that I checked for bullet holes. Because the other part of this incident was me on the side of a road in a rural area waiting for a tow truck. Sharks were circling if you know what I mean.
The same dudes over and over kept driving by and looking at me. I noticed them down the road about a half block sitting down there talking, all of them looking at me.
So one finally came forward and started asking me questions to feign an interest in hotrodding. I could tell he was casing me. I also saw immediately that he had a gun in his waste band. I've been around guns a fair bit and could tell from the sliver of the gun that I could see, that it was a Glock and a very worn one. The parkerization was coming off.
I kept up an act and pretended to not notice the gun. (what was I gonna do?)
He was asking me detailed questions about the car and I know he had dreams of a chop shop job that night. He looked very 'meth'.
I tried to make the car seem as unappealing as possible.
"That rear end? Oh that rear end is a 10 bolt open rear end"
"YUP!! This motor's blown, plum seized....just GONE"!
"Tranny? Oh I dunno, I think its out of a MOPAR"!!!!
Anyway, finally my wife showed up and I came up to her car and told her to get going, this guy's gotta gun. She reached over to her purse, pulled out my 9mm and gave it to me!!! She said, "thought you might want this"!!

WHAT A WOMAN!!!!! :thumbsup:

So the dudes finally went away but not far. They slipped into the woods as we waited for the tow truck.
From our left came gun fire from what I estimate was about 50' into the woods. I could feel the concussions of the reports. That's how close it was although I saw no muzzle flashes.
Had a target presented itself, I would have engaged it but none did.
I called 911. To which the operator said, call us back if anyone is injured. Great, thanks. Appreciate the concern. :mad:

Right after that, the tow truck arrived and I kept a vigil for the dudes as the driver put the car up on the flatbed.....but no dudes appeared.

I got to thinking about how odd this all is with the screws working out and all. Then I thought about the shots and wondered perhaps they'd been shooting earlier and a stray round took out my distributor?
No bullet holes though...

I'm pulling it tonight to send to MSD, they want to inspect it.

Word to the wise, when driving your classic hotrod that can be turned into 1000$ by a chop shop in a matter of hours;
Carry a gun.
:boxing:
 
#30 ·
Having a gun around has defused danagerous situations 3 times for me so am a believer. There's just too many people w/o care or remorse in the world who are influenced by addictions and don't follow rules. One time was when I was 12 and scared off 2 guys trying to break into our house in Chicago at 1:00a.m. This was with my c02 BB gun but it looked real and menacing to the burglars when I tapped it against the window to get their attention. Another time was when a classmate (female) invited me over to study for an exam and her X came into the house with his foot through the door first. I used her son's toy gun and pointed at his face with attitude and was enough to send him runnin. A third time I had a random meth-head trying to kick in the door at 3:00a.m. This time was a real gun but just had to fire a couple rounds into the floor and that was enough to make him go away. Bringin a gun along is not a bad idea - so long as follow the rules in the state.
Your wife rocks!!
 
#32 ·
Having a gun around has defused danagerous situations 3 times for me so am a believer. There's just too many people w/o care or remorse in the world who are influenced by addictions and don't follow rules. One time was when I was 12 and scared off 2 guys trying to break into our house in Chicago at 1:00a.m. This was with my c02 BB gun but it looked real and menacing to the burglars when I tapped it against the window to get their attention. Another time was when a classmate (female) invited me over to study for an exam and her X came into the house with his foot through the door first. I used her son's toy gun and pointed at his face with attitude and was enough to send him runnin. A third time I had a random meth-head trying to kick in the door at 3:00a.m. This time was a real gun but just had to fire a couple rounds into the floor and that was enough to make him go away. Bringin a gun along is not a bad idea - so long as follow the rules in the state.
Your wife rocks!!

Yes I am still in awe that she had the presence of mind to bring it. It made me feel SO much better because I was largely defenseless without it.

Better to have one and not need it than to need one and not have it.

I pulled the distributor and sent it to MSD this morning. They want to inspect it after what happened.
Gotta say, their customer service has been very damn good!
 
#33 ·
Mike - My dad owned a repair shop in my younger days, and I can remember one instance when I went to start a car and discovered the distribitor cap and rotor was blown apart. We eventually diagosed it as a bad vacuum advance can. Apparently the diapham was bad, and gasoline vapors got into the distributor while the car was sitting. When the owner tried to start the car - BOOM! It would be worth putting a vacuum pump on your vacuum advance and checking whether the diaphram is bad.
 
#35 ·
We pulled a buddy's accel distributor out of a bbc 427, pointed the vac can at the floor and gasoline ran out. That can't be safe, it prob sucked if from the carb, this could be the issue here?
 
#34 ·
I see this thread is a couple of weeks old but here a little piece of info that might help someone one of these days...If I remember correctly, a distributor cap from a chev points type distributor and the rotor should work with that MSD. The one issue now is that MSD just recently updated their dist caps to the HEI or Male posts so the wires won't work...very well anyways but in an emergency I'll bet you can make it work just to get you home or in your case, somewhere SAFE. I'm really not sure if MSD made changes to the housing on any new "Updated" distributors but it might be worth looking into.
 
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