Help needed please.

[BenzBoy]

Ok - it's not a Benz.
It's the PV. Cruising along comfortably and then a loss of power traced to the exploding distributor cap - see the picture below. A quick call to Paradise and the car is again mobile with new rotor button and cap. The old one had been checked in the last service a week ago and tested OK on the analyser and looked OK with a visual inspection.
The question is why did this happen? Yes, there is a vacuum advance and I have heard of older Holdens having this problem when petrol vapour is picked up by the vac advance line and causes an explosion inside the distributor. No, there are no centrifugal weights to come loose and do this as can happen in a Fiat - so please Brains Trust, what is the issue?



Regards,
Brian

 

[abl567]

The pic dont show...

 

[motec 6.9]

I have had this happen with a 186 HT Premier and it was as you said petrol vapour. So maybe that's were you should start looking for a leaking seal or gasket.

 

[Oversize]

Maybe it wasn't put back on properly??

 

[motec 6.9]

I think Brian is on the right path or WD40 was left wet under the cap after service. Causing explosion.

 

[BenzBoy]

Maybe it wasn't put back on properly??

I considered that but it's a lock fit so it's either on or not on and had done 500 ks since being checked - hmmmm.
Regards,
Brian

 

[BenzBoy]

I think Brian is on the right path or WD40 was left wet under the cap after service. Causing explosion.

500 kms since the last service so any WD40 should have evaporated ...
it has to be a petrol leak through the advance vacuum hose.
Regards,
Brian

 

[motec 6.9]

Yes I believe you are right there Brian as I said happened to me once with old 186 powered HT Premier. Just about needed clothing change afterwards .

 

[Helmet]

Maybe it wasn't put back on properly??

Looks like lots of scratches on the inside, I'd say you are correct.

 

[BenzBoy]

Looks like lots of scratches on the inside, I'd say you are correct.

The scratches are interesting but the cap is bolted down and the bolts were still in place. HM always insisted on new tyres, fresh oil and bolt-down distributor caps on any of her cars - remember she could strip and re-build a Lanchester engine (possibly a little known fact but I have seen the photos of her in action.)
As I mentioned earlier, the cap is either on or not on - there is no possible halfway position; rather like the Marelli distributors that use the same system.
The scratches might indicate that the rotor button simply left home - and that will be investigated.
However, Helmet, you could be correct - clearly something went wrong!
You can understand why I am mystified and concerned - we still need to drive the PV back from Tamworth tomorrow....
Regards,
Brian

 

[Oversize]

Maybe it was the rotor that was installed incorrectly?

 

[BenzBoy]

Maybe it was the rotor that was installed incorrectly?

If you rule out all that is impossible, then what you are left with is the answer, no matter how unlikely it seems. I have an engineer going over it on Thursday - the same engineer who delivered the car new in 1968...
Regards,
Brian

 

[BenzBoy]

OK - the Beast has been examined - no vacuum leak to draw in petrol vapour so we can rule that out. That leaves a distributor cap disintegrating with age - or maybe it was the rotor button. Which one came first will be impossible to tell. Since fitting the new cap/rotor the Beast has done just over 300 kms and no issues.
However, I can't help but feel I am still overlooking something ......
Regards,
Brian

 

[Styria]

OK - the Beast has been examined - no vacuum leak to draw in petrol vapour so we can rule that out. That leaves a distributor cap disintegrating with age - or maybe it was the rotor button. Which one came first will be impossible to tell. Since fitting the new cap/rotor the Beast has done just over 300 kms and no issues.
However, I can't help but feel I am still overlooking something ......
Regards,
Brian

BenzBoy, with that sort of scenario, you must be reluctant to drive any further from your base than Darlington - I mean, who can afford to become stuck any further away from home base. It is a real problem you are likely to have on your hands. . Regards. Styria

BTW, I thought that a vacuum advance draws just that - vacuum. Where does the petrol issue come from ?

 

[BenzBoy]

BenzBoy, with that sort of scenario, you must be reluctant to drive any further from your base than Darlington - I mean, who can afford to become stuck any further away from home base. It is a real problem you are likely to have on your hands. . Regards. Styria

BTW, I thought that a vacuum advance draws just that - vacuum. Where does the petrol issue come from ?

Oh dear - Styria - you just don't read ALL parts of the post do you? The issue is resolved as I have noted with a new rotor button and cap and the car has done over 300 kms since then without any issues.
Old Holdens like many other cars, drew the vacuum advance form a port in the base of the carburettor just like the old vacuum operated windscreen wipers. Thus, any petrol leaking from the chamber of the carburettor onto the port could allow the petrol vapour to be sucked in if the vacuum advance line was perished or leaking at the clamp. I can forgive you for not knowing this since you are really a youngster....
Regards,
Brian

 

[sean sherry]

Simple answer Brian ,
carry a spare Rotor and Button in your back pocket. Then you will never have the problem again !
I carry a spare ignition Module for my old Merc to insure that the original one never fails . Murphy's Law.

 

[Styria]

You have actually proceeded beyond Darlington ? . Seriously though, I still cannot understand how the distributor cap could have shattered ? Sure enough, at my age, being a youngster, I have not come across the situation of a vacuum unit drawing in petrol - the advance units are fully sealed, and are only connected to the working part of the base plate by the vacuum arm.

That applies to the rover 3 litre P5 I which, incidentally, has a thin copper tube being the medium of drawing air from the Carburettor. The P6 3500 - sure enough, it has a plastic tube that is connected to a small orifice on the bottom of one of the carburettors, but again you have a mechanical arm from the advance unit to the base plate. So It is no surprise that, on my part, I cannot understand how petrol could be sucked in by the Ignition Distributor. Regards. Styria

 

[BenzBoy]

Styria - we ran a vacuum test and ruled out the possibility of petrol vapour. In the absence of any other possibility we are left with either a disintegrating cap or rotor button. There is nothing else.
Yes - it's been to Tamworth and back and from Oak Flats and the City and back without dramas. All of that is in the preceding posts....
Regards,
Brian