HELP! Blew oil cap sky high...

[MitchaPaLoOza88]

14 minutes ago, TobyB said:

I'm in the 'so not a big deal' camp on this one.  If you want to be cautious, change the oil

in case fuel's leaked into it in storage and diluted it, but honestly, I let cars sit 6 months and don't even

think  about it besides making sure the battery's not flat.

 

On the K-Jetronic systems there's a test for this, its called...

 

?FLAMMABLE DIPSTICK? 

[Mike Self]

There's a safer way to prime a mechanical fuel pump fuel system that's been sitting for awhile so that gas in the float bowl has evaporated--that seems to happen within 4-5 days on a Weber 32/36 but a week-10 days on a 1 bbl Solex. 

 

Fill the carb's float chamber directly.  On a 1 bbl Solex it's easy.  Pop the top off the air cleaner and on the floor of the air cleaner you'll see a 8-9mm diameter brass pipe surrounded by a rubber grommet.  That's the float chamber vent.  Use a small funnel or a squeeze bulb and decant a few ounces of gas down the pipe.  On a 32/36 (and presumably on a 38/38) look just forward (toward's the car's front) of the two venturis, and you'll see a very small opening--the float chamber vent.  You'll need a very small funnel, or better still a squeeze bulb (I use an [otherwise retired] ear syringe) to fill the float chamber.  

 

Priming this way will allow gas flow normally into the intake manifold and cylinders, and the car will start with a few turns of the crankshaft--and run on that prime long enough for the mechanical fuel pump to start supplying gas to the carb.

 

mike

 

PS--FWIW I've never heard of the oil cap blowing off either--but it's gotta be gas fumes being sucked into the crankcase from the air cleaner vent pipe...really strange.

[John76]

7 hours ago, 02Anders said:

I gave her just a tiny amount of fuel straight into the carb to help her fire up

After the fuel shot, did you replace the air cleaner before hitting the ignition switch?

All those fumes had to go somewhere....the choke was closed, so the only path for the fumes was through the valve cover breather.

The valve cover atmosphere sucks as well as blows!

[Conserv]

3 hours ago, TobyB said:

... but honestly, I let cars sit 6 months and don't even

think  about it besides making sure the battery's not flat....

 

+1

And that’s why Toby and I are... simpatico ! ? Well, sort of... ?

 

Best regards,

 

Steve

 

[02Anders]

Gents, once again thank you for all your input.  ?

 

I'll try to answer the various questions - pardon if I miss one or two...

 

- Yes, I primed the 1 bbl Solex straight into the barrel.
- Yes, I did replace the lid on the air filter house before turning the ignition key.
- Yes, the vent pipe between valve cover and air filter house is entirely clear.  Admitted, I did not think of checking this before I turned the engine, but I checked afterwards and there's no restriction here.

- The oil filler cap which made a break for freedom only to be held back by the garage ceiling, now doesn't have the required tension to seal properly.  The two tabs are slightly bent.

- Much as I'm always very careful when priming the carb like this, in hindsight, there's probably no point in denying that on this occasion, I clearly overprimed...  ?
- That said, I'm still hugely surprised about the result!

 

Moving forward, I sadly won't have time to do anything about it during the week.
But hopefully next weekend, I'll treat her to an oil change and drop by my lock-up and fish out another oil filler cap.
At the very least, I'll at least check all four spark plugs.  Then I guess I'll try cranking her over again.

 

And @Mike Self thx for the tip on priming straight into the float chamber.  Top Tip...  ?
I'll definitely use this method from now on...

 

 

 

[KFunk]

Oh, so the breather tube is going straight back to the air filter housing, where you dumped too much gasoline.....

(myself and many others just have breater tubes just going into a catch can or filter, venting to atmosphere)

 

Soooo....... in an unhappy cold engine with a little backfire out the intake, through the breather tube, and boom!

[John76]

Shot of gas into the front opening should do it.

You will know when you have enough when the pump jet squirts when you blip the throttle.

 

 

[Vicleonardo1]

Instead of this being a volatile explosion, could this be due to high oil pressure at startup? (thick oil/cold temp) Someone  on this forum said that such a situation caused their oil filter to puff up....

[Hans]

1 hour ago, Vicleonardo1 said:

Instead of this being a volatile explosion, could this be due to high oil pressure at startup? (thick oil/cold temp) Someone  on this forum said that such a situation caused their oil filter to puff up....

 Oil pressure might puff out the filter but I don't see anyway it could cause this.

What I don't understand is why the pressure didn't blow either end of the breather hose off, or damage the air cleaner. That's a huge amount of pressure to go through that small tube.

[02Pilot]

Is it possible that the oil cap was in place but not fastened? If it weren't, it would certainly be the point of least resistance. Can the OP describe the condition of the cap, specifically the locking tangs? If it was locked in place, they would have to be severely bent at a minimum.

[tzei]

On 2/2/2021 at 11:13 AM, 02Anders said:

The oil filler cap which made a break for freedom only to be held back by the garage ceiling, now doesn't have the required tension to seal properly.  The two tabs are slightly bent.

I believe this is description. Makes me think it was (at least partially) locked close.

[M3M3]

What ein and toby said.

 

And lesson #1.... Don't ever pour any fuel down the carb to start a car.  That is what the carb jets and fuel pump do for you in a much more controlled manner.

[02Pilot]

3 hours ago, tzei said:

I believe this is description. Makes me think it was (at least partially) locked close.

Missed that somewhere along the way. Still, "slightly bent" seems less than would give necessary clearance to free a fully locked cap from the valve cover. A photo from the OP would help, if only to determine why that was the point of least resistance at the time of the earth-shattering kaboom.

[Hans]

My first thought was that the explosion took place in the sump. I'm having trouble with the idea that this pressure wave went through the carb, air filter, and  breather hose with enough power to blow the cap, what, eight feet in the air. Where is the dip stick in all this?

[tzei]

A true internal combustion engine to the letter.