Moparts

Distributor Cap Blow off

Posted By: Caparco

Distributor Cap Blow off - 05/01/11 01:43 PM

Having trouble with my Cap blowing off when I get up on the gas to pass or from a stop, Doesn't come right off just one side pops and cocks to the right, throws it way out of time.
Tried to adjust (bend back) the thin metal 'barbie pin' clip, worked a little but soon re-accured. I don't think drilling a vent hole in it is good as presure is good there. right?.. would some Twine burn up in the compatment? What are your thoughts

And yes I don't see anything in the way under the hood would be in the way when the engine lifts from exceleration, seems to be just Presure.
Marcus
Posted By: BDW

Re: Distributor Cap Blow off - 05/01/11 02:05 PM

How old is the cap? All the newer ones have a vent.
Posted By: FASTBACK340

Re: Distributor Cap Blow off - 05/01/11 02:06 PM

The only things that come to mind are either the rotor is rising and pushing the cap off, or maybe the shaft is bent or the shaft bushing is shot.

I'm curious on this one....
Posted By: RapidRobert

Re: Distributor Cap Blow off - 05/01/11 02:08 PM

Quote:

What are your thoughts

grab some clips from a junk dist & do check rotor fit/clearance on the inside
Posted By: Caparco

Re: Distributor Cap Blow off - 05/01/11 10:19 PM

Quote:

How old is the cap? All the newer ones have a vent.



its kinda new a few years, I took the Points out and put this electronic egnition conversion one everyone was highly recomending it, So there are vents?.. you or anyone have a pic of this?

not even sure where I can get a new clip for the cap, really no data plate or marking on it at all
Posted By: B5 Bee

Re: Distributor Cap Blow off - 05/01/11 11:42 PM

I've had a parts store rebuilt slant six dist that were poorly remaned. When it was blasted to clean it up, they erroded the caps seating surface and would not allow the cap to seat properly. Vibration from driving around would pop the cap off.
Posted By: Mopar_Country

Re: Distributor Cap Blow off - 05/01/11 11:42 PM

If it's a Chrysler distributor you can get clips here:

http://www.henryspartsdepot.com/chrysler-mopar-nos-parts/
Posted By: Golden-Arm

Re: Distributor Cap Blow off - 05/02/11 12:57 AM

caps have a vent, with a little cover over it. there shouldnt be anything making that much presure inside the cap, unless you are getting crankcase pressure leaking up the shaft, into the cap. i suspect you'd see a lot of oil coming up and into the housing, if this was true. snap the cap on and then try to lift or wiggle it off. it shouldnt really move. of it does, something isnt right. i've had junk caps, that just wouldnt mount properly, and could be moved off the dizzy, when clipped down. replacing with a quality cap fixed it for me.

you didnt mention engine size, but if you have a small block, make sure you dont have a broken motor mount. the engine twisting when torqued from a stop, could drive the dizzy into the firewall, and pop the cap. (depending on clearance in your particular car)
Posted By: BDW

Re: Distributor Cap Blow off - 05/02/11 02:14 AM

Black part is the vent

http://www.jegs.com/i/Mopar-Performance/312/P4529791/10002/-1?parentProductId=747038
Posted By: JohnRR

Re: Distributor Cap Blow off - 05/02/11 04:27 AM

Posted By: 62maxwgn

Re: Distributor Cap Blow off - 05/02/11 04:30 AM

John,ever see gas inside a distributor ?
Posted By: Evil Spirit

Re: Distributor Cap Blow off - 05/02/11 05:34 AM

Vacuum advance diaphram can fail, letting gasoline vapors get into distributor, ignite, and blow cap off. AMC's had this problem mid/late 70's.
Posted By: JohnRR

Re: Distributor Cap Blow off - 05/02/11 12:51 PM

Quote:

John,ever see gas inside a distributor ?




No I haven't but I knew as soon as I posted that there would be someone contradicting it .

Think I'll hang in the general section from now on , hippo and penguin talk is getting more interesting by he day
Posted By: Challenger 1

Re: Distributor Cap Blow off - 05/02/11 01:17 PM

Sounds to me that you have junky dist, where did you get it?
Posted By: Mopar_Country

Re: Distributor Cap Blow off - 05/02/11 05:03 PM

Take the cap off and try pulling up on the shaft. It's possible the clip is weak or broken and the shaft is riding up the gear.
Posted By: 62maxwgn

Re: Distributor Cap Blow off - 05/02/11 05:20 PM

Quote:

Quote:

John,ever see gas inside a distributor ?




No I haven't but I knew as soon as I posted that there would be someone contradicting it .





Boy John,never knew you were that easily offended. Why do you suppose they vent a cap ? !!!!!
Posted By: JohnRR

Re: Distributor Cap Blow off - 05/02/11 05:25 PM

Quote:

Quote:

Quote:

John,ever see gas inside a distributor ?




No I haven't but I knew as soon as I posted that there would be someone contradicting it .





Boy John,never knew you were that easily offended !!!!!



I'm not offended easily , my memory isn't as good as i thought it was I guess, I need to just sit back and and let others that have the answers do the talking, maybe I'll learn something. I have personally NEVER had a cap come off on any vehicle I have own that had a distributor cap.

I could have sworn I have seen an extra hole or 2 in the bottom of a distributor housing, the alum chrysler single point anyway ???
Posted By: scratchnfotraction

Re: Distributor Cap Blow off - 05/02/11 05:35 PM

caps have vents to let positive charged ions out,when they build up inside the cap it can cause carbon tracking and mis-fires.

used to see it on roundy round dirt track cars,mostly with the chebby HEI dizzys and big fat caps.

dont think it blows the cap off though

Posted By: JohnRR

Re: Distributor Cap Blow off - 05/02/11 05:48 PM

Quote:

caps have vents to let positive charged ions out,when they build up inside the cap it can cause carbon tracking and mis-fires.

used to see it on roundy round dirt track cars,mostly with the chebby HEI dizzys and big fat caps.

dont think it blows the cap of though





I can see that . Reason you don't see it blow the cap of an HEI I guess would be because it is bolted down ?
Posted By: scratchnfotraction

Re: Distributor Cap Blow off - 05/02/11 06:08 PM

Quote:

Quote:

caps have vents to let positive charged ions out,when they build up inside the cap it can cause carbon tracking and mis-fires.

used to see it on roundy round dirt track cars,mostly with the chebby HEI dizzys and big fat caps.

dont think it blows the cap of though





I can see that . Reason you don't see it blow the cap of an HEI I guess would be because it is bolted down ?



now I know why chebby used screws on the cap.

I had a 69 440 4-v 4-speed RR blow the cap off 1x.i was running in 4th at 4800-5000 rpms,let all the way off the throttle real fast and bang...blew out a muffler,had the coil wire out of the cap and cap cocked side ways with 1 clip still holding it.

never did it again,and I have no idea why it did it that time either,but it sure skeeerd me when it went bang!

dont think it had anything to do with the dizzy and cap.
Posted By: Mopar_Country

Re: Distributor Cap Blow off - 05/02/11 06:21 PM



Boy John,never knew you were that easily offended. Why do you suppose they vent a cap ? !!!!!



A lot of it has to do with moisture, the vent gives it somewhere to go instead of creating corrosion.
Posted By: Challenger 1

Re: Distributor Cap Blow off - 05/02/11 06:25 PM

Quote:



Boy John,never knew you were that easily offended. Why do you suppose they vent a cap ? !!!!!



A lot of it has to do with moisture, the vent gives it somewhere to go instead of creating corrosion.



Yea, it's not there to relieve pressure. The OP either has a cheaper dist cap, cheaper dist or it's not on right. imo Maybe he has wrong parts too.
Posted By: RemCharger

Re: Distributor Cap Blow off - 05/02/11 06:32 PM

I wd40'd my weights once, fired it up and,..POW! blew the sucker right off. Thats the closest I've seen.
Posted By: Challenger 1

Re: Distributor Cap Blow off - 05/02/11 06:36 PM

Quote:

I wd40'd my weights once, fired it up and,..POW! blew the sucker right off. Thats the closest I've seen.



Posted By: Mopar_Country

Re: Distributor Cap Blow off - 05/02/11 06:44 PM

Quote:

Vacuum advance diaphragm can fail, letting gasoline vapors get into distributor, ignite, and blow cap off. AMC's had this problem mid/late 70's.



Evil Spirit may have nailed it.

Because I am inquisitive in nature I had to ask. Spoke with an acquaintance of mine and he said the same thing, check your vac canister, after shut down gas vapors can come up the vac line and fill the cap with enough vapor to pop it of upon start.

That's not something I would have ever thought, and I have never seen it happen.
Posted By: Challenger 1

Re: Distributor Cap Blow off - 05/02/11 07:03 PM

Quote:

Quote:

Vacuum advance diaphragm can fail, letting gasoline vapors get into distributor, ignite, and blow cap off. AMC's had this problem mid/late 70's.



Evil Spirit may have nailed it.

Because I am inquisitive in nature I had to ask. Spoke with an acquaintance of mine and he said the same thing, check your vac canister, after shut down gas vapors can come up the vac line and fill the cap with enough vapor to pop it of upon start.

That's not something I would have ever thought, and I have never seen it happen.



If that was the case, it would blow off as soon as he starts the car, which is not happening.
Posted By: imfixinmopars426

Re: Distributor Cap Blow off - 05/02/11 08:13 PM

i would ck the end play of the dist,maybe the thrust washer is gone,and the rotor is pushing the cap up?
Posted By: StandOnIt

Re: Distributor Cap Blow off - 05/03/11 10:33 PM

I have a brand new cap in the top of my tool box that won't stay put on the dist. It rocks back and forth popping the clips loose. I went and bought an accel cap and it didn't rock. Been running it wide open for a few years now without an issue. I don't really know why I haven't thrown that other one away yet. I guess its the horder in me...haaaaa.

I did have a small block ford dist grenade on me one time driving down the road. I was on the gas pretty good too. Put another cap and sleeve (busted that too) on it and took off again. Never did it again....
Posted By: SixDRacing

Re: Distributor Cap Blow off - 05/04/11 04:54 AM

vacumn advance canister is bad. suck on it with a rubber hose. it will not hold vacumn.
Posted By: pushbutton

Re: Distributor Cap Blow off - 05/05/11 12:41 AM

Quote:

Vacuum advance diaphram can fail, letting gasoline vapors get into distributor, ignite, and blow cap off. AMC's had this problem mid/late 70's.




Posted By: Caparco

Re: Distributor Cap Blow off - 05/05/11 02:55 AM

Quote:

Quote:

Vacuum advance diaphragm can fail, letting gasoline vapors get into distributor, ignite, and blow cap off. AMC's had this problem mid/late 70's.



Evil Spirit may have nailed it.

check your vac canister, after shut down gas vapors can come up the vac line and fill the cap with enough vapor to pop it of upon start.



That sounds like a good cause, not sure where my vac canister is or even if im running one!
But this is more ... when I gun the gas, on the road passing or from a red light... more feels like the other gent said the engine lift from a bad mount.. But there new
The vent info is great guys thanks, but its a capped vent and the cap never comes off..??.. or is this optional only.. you can run your car with no vent cap?
More info for the others who asked.. Small block 360, got the electionic conversion kit off some speedshop years ago.. red cap, no real markings on it.. "generic"
Posted By: MY340

Re: Distributor Cap Blow off - 05/05/11 02:21 PM

Had a 79 Scout Terra with Chrysler electronic ignition and the cap kept coming off due to the clip issue on one side. I wired it down if I remember and no more problems with it coming loose.
Posted By: Evil Monkey

Re: Distributor Cap Blow off - 05/07/11 11:24 AM

Quote:

Quote:

Quote:

Vacuum advance diaphragm can fail, letting gasoline vapors get into distributor, ignite, and blow cap off. AMC's had this problem mid/late 70's.



Evil Spirit may have nailed it.

Because I am inquisitive in nature I had to ask. Spoke with an acquaintance of mine and he said the same thing, check your vac canister, after shut down gas vapors can come up the vac line and fill the cap with enough vapor to pop it of upon start.

That's not something I would have ever thought, and I have never seen it happen.



If that was the case, it would blow off as soon as he starts the car, which is not happening.



That's exactly what would happen on my 75 Jeep CJ7. It would only happen when starting the car - never happened driving down the road. As soon as I cranked the starter, there would be a big bang from the distributor cap hitting the hood - maybe happened 1 out of 5 times I started the car. Popped the hood, clipped the distributor cap back on, and it would fire right up. I thought someone was messing with me the first few times it happened. Eventually I found out about the vacuum canister problem, replaced it, and it never happened again.

I used to have one of the clips come loose on the cap of the 318 in my 5th Ave. I re-bent the clip a few times until I got it so that it wouldn't come off any more, but it took a few tries to get it right. It seemed to be twisted a little and I'm guessing that's what caused it to pop off.
Posted By: RapidRobert

Re: Distributor Cap Blow off - 05/07/11 01:43 PM

As said the clips need the same bend/tension on each side which is rarely a prob. I think the prob is the cap & I'd R&R it & maybe the clips from a junk dist & I'm assuming there is no rotor interference
Posted By: Supercuda

Re: Distributor Cap Blow off - 05/07/11 02:59 PM

The vacuum advance canister has no real direct path to the distributor internals in a stock Chrysler distributor. there are too many areas to vent any gas fumes out to atmosphere before it gets to the internals.

I doubt it's fumes.

It's possibly a worn distributor allow the shaft to move around knocking the cap loose or it's a bad cap.
Posted By: badblubeee

Re: Distributor Cap Blow off - 05/07/11 06:03 PM

The only time I seen caps pop was on ol' Fords that had been fed a steady diet of Penzoil for too long
Also I have tried rotors for later model apps on an older car and they don't fit right cap wouldn't clip down right.
Posted By: Caparco

Re: Distributor Cap Blow off - 06/01/11 12:22 AM

No this is not when I start.. starts fine.. its when you really give it the gas.. from a stop or passing on highway

and I can't make it pop off in park reving the engine or with my head under the hood , in fear of damaging something!

And blowing off isn't real correct.. the 2 clips stay on and it just cocks to one side.. throwing the timing way off.. popping and choking un- drivable

someone said tie it down... but I really don't like this at all!!..LOL may work, ill have to see when i get her running but isn't this a electrical hazard!!.. lol got to be a better answer!

Posted By: Sinitro

Re: Distributor Cap Blow off - 06/01/11 01:27 AM

The top shaft has play and the rotor hits the cap/contacts..

Just my $0.02...
Posted By: ph23vo

Re: Distributor Cap Blow off - 06/01/11 01:59 AM

broken motor mount... engine pops up and hits wiper motor knocking it off.. dan
Posted By: Caparco

Re: Distributor Cap Blow off - 06/01/11 02:31 AM

Quote:

broken motor mount... engine pops up and hits wiper motor knocking it off.. dan


Thought of This!.. New mounts though

Lose rotor?.. how to fix?.. test?
Posted By: RapidRobert

Re: Distributor Cap Blow off - 06/01/11 02:37 AM

Quote:

Lose rotor?.. how to fix?.. test?

up/down play in the dist shaft. Dist bottom side lower shaft/Drive out the roll pin/remove the plastic collar/add 1/2" ID flat metal washers till the end play is near zero/reinstall collar/roll pin
Posted By: ph23vo

Re: Distributor Cap Blow off - 06/01/11 02:39 AM

yeah ok.. plastic collar on dist could have broke allowing shaft to come up and pop it off too.. pull dist real quick if you havent allready dan
Posted By: mopar_man

Re: Distributor Cap Blow off - 06/01/11 02:47 AM

Quote:

No this is not when I start.. starts fine.. its when you really give it the gas.. from a stop or passing on highway

and I can't make it pop off in park reving the engine or with my head under the hood , in fear of damaging something!

And blowing off isn't real correct.. the 2 clips stay on and it just cocks to one side.. throwing the timing way off.. popping and choking un- drivable

someone said tie it down... but I really don't like this at all!!..LOL may work, ill have to see when i get her running but isn't this a electrical hazard!!.. lol got to be a better answer!





Looks to me that you have a wrong clip on the right side of the pic. i don't think it will seat in the groove correctly.
the left clip seems to be the correct one. as a matter of fact the cap doesn't look just right . are you sure the cap is fitting in the groove/notch of the dist ?
Also the vent in the cap is not to vent gases , its there to keep the cap free of moisture by equalizing the humidity outside to inside .
Bottom line ..........looks like a clip problem
Posted By: RapidRobert

Re: Distributor Cap Blow off - 06/01/11 03:48 AM

get a good cap and a pair of clips from a junk dist & I'll bet my next to last buck this prob will b behind you
Posted By: superwrench

Re: Distributor Cap Blow off - 06/01/11 04:50 AM

Quote:

Quote:

I wd40'd my weights once, fired it up and,..POW! blew the sucker right off. Thats the closest I've seen.









Even better when the shop "flunky" uses brake clean!!! You otta see the mess it makes!!!
Posted By: scratchnfotraction

Re: Distributor Cap Blow off - 06/01/11 12:59 PM

pull the cap,look and note which way your rotor is pointing.

pull the dist,go get a new reman one from autozone for around 30 bux.

install it with rotor faceing the same way.

should take care of the bent/wrong clips and worn shaft bushing in the one you have.

Posted By: Caparco

Re: Distributor Cap Blow off - 10/04/20 01:17 AM

Looking back at my old post. LOL

Hindsight is 20/20

Golden-Arm was right from the start.
It was spent motor mount. Engine lifted up and got pushed off
Posted By: BDW

Re: Distributor Cap Blow off - 10/04/20 01:45 AM

Better late than never, nice update 9 yrs later
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