Double stacking fuel cap washers

A optimus 80 I just received like this one, had two washers in the cap but held no pressure when first tested, so in removing them, saw there were two. I tried three different caps, each only having the single washer. In my testing, thought maybe a small crack in the fuel bung, so to get the edge of the cap far enough away from the fount to get a clearer view, added a second washer, that stopped the leak. Lucky? So if one washer can't make a seal because it can't screw onto the bung far enough, were threads not cut far enough on the cap or bung to allow the washer to make a tight seal? Thoughts.
Duane
Optimus No.80 from the early 1950's

 

I think I spotted the issue. The lowest thread on the fuel bung is too close to the next thread, maybe had been forced closer or buggered up, resulting in the cap not being able to go past a certain point. I verified with another 80 I have to see if the cap would screw on further. Now need to see how to fix the errant thread, I don't have a small file, not sure that is the best way to go, I don't have tools to chase the threads.
Duane

 

Pictures?

 

ah ha
you found it, good.
If i get this right, with trying other caps it is just the bottom of the male thread that is boogered, also good (cap threads are fine).
Small file sounds like a good step but,
now with damage identified, for this one stove there is also the temptation to be satisfied that a double washer seals that imperfect filler tube. ATB

 

Funny, when I dunk tested with the double washers, no leak, but on my bench it leaked bad. No luck messing with the bung threads, so will try for parts next time in town to check thread type.
Duane

 

Further looking(thinking), if the cap(s) only thread on less than 3/4 of a turn, can't be the bung threads closest to the fount. Contacted Gary for info and a part number to clean up the threads. Seems threads can vary from standard per a post of his.
Duane

 

Trickery I tell ya! With one of my pump caps, I can get pressure after placing in freezer then hot water, good stream of bubbles out of the jet when the valve is opened, but when preheating on my workbench, only a brief, pitiful flame. Stumped. No release from the SRV.
Duane

 

Small cracks?
Stress cracks?
I have had that show after stove got hot.
Preston loop leaked when hot.

 

My earlier starts, a little flame around the fuel cap, indicating a poor seal was all. Ordered a thread count tool and a hardened steel nut to work the threads over per Gary so I can use the original cap. Usually can figure things out by now, worse than a pesky NRV. Not a common model 80.
Duane

 

Good for you. Something often lacking here. Using original and using skills to make them work.

 

Duane, pardon my nudge here, i hope you don't mind i bring your comments back to your topic.

in discussion/thread i quoted you from
mirumir of Ukraine has a different thread request. that is still an open request (also unresolved).
=============

back to your topic,
you're stumped (for now), you'll get there.
did the nut successfully clean filler neck threads to allow the cap to thread further down and seal with single washer?

 

I think it only goes on a little bit further now, not much. Don't know why a dunk in hot water shows no bubbles if cap is tightened good and tight but a brief candle flame when preheating. I've even opened the valve when in hot water and get a good steam of bubbles.
Duane

 

not sure why "brief"? a brief candle flame when preheating.

filler tube threads cleaned some, not much difference and i guess you're saying it still does not seal w/single washer.
i'm hearing it has leaked from the same place since you've had it.
leak does not show up in dunk test.
no change with different filler caps.

that is sounding like filler tube/neck area is suspect.
may be worth another close look, not that i expect an ah ha moment.

do you recall another stove in the past w/leak that did not show up with dunk test?
good luck

 

Will try moving cap around, try it on a good stove and its cap on this one.
Duane

 

Sorta successful, plus found a second issue. The mesh wrapped wick was loose and not fully inserted into the vaporizer, good reason for the candle flame. Added another cotton strand to the wick and reinserted.
I still see the cap needs to be really hand tightened as while preheating you can see a lite flame around the bung, have wondered sometimes if that is priming fuel that has spilled over from the priming depression.
Been running 5 minutes since photos were taken, flame is still half power but nice blue. I think flame would be more robust if it wasn't for the initial loss of pressure.
Duane


After 10 minutes?

 

Was pointed out to me that the above linked stove was later than mine which has ribs top and bottom making mine a earlier version than the one linked. So I'll have to check out stoves in the SRG.
Duane
PS: Like this but in brass. Optimus № 80