Discussion in 'Stove Forum' started by Gunner, Jan 2, 2021.
Easy to judge when not there. Arm chair critics. I await John and his findings.
I back @Big Si on this one. We await John's verdict.
Got it working properly. Sad to say, it’s down to a manufacturing shortfall.
Little used as you say.
The fault, a poorly machined thread on the burner stem. It’s meant to be a tapered thread, which it is, but the thread’s been cut on too slender a stem. Result, it ‘disappears’ into the tank mount.
Comparison with older Svea 123R on the left, then individual photos below.
In this photo, the older 123R burner spindle is in the correct position relative to the tank. The spindle has to coincide with a windshield access port for the control key and the windshield is in a fixed location on the tank. The spindle of the newer example on the right is too far over and the threads are about to tighten up. Even another third of a turn couldn’t be done, so the ‘lining up’ procedure could only happen if the threads were backed off slightly, enough to create an air leak in fact.
Getting back to the machining issue, if the burner could be forced - without shearing off or corkscrewing - to get the spindle to line up with the next available windshield access port for the control key, a portion of the burner riser threads would by then be running out of thread form. Again, a likely air leak.
Solution was to use a smear of thread-lock paste. It shouldn’t be needed to seal tapered threads, but is certainly necessary in this case and in this application not getting hot enough to ‘burn off’ or degrade when priming or in use.
Incidentally, Gunner, you mentioned in your post swapping caps during your tests and the cap with the stove isn’t contemporary to the stove. The cork safety release valve ‘pip’ is one clue. The seal was also brittle with age.
Maybe that cap is for one of your Optimus 80’s? If so I guess you’ve got the one for this stove. Happy to swap if so.
After re-assembly, I test fired the stove and after the priming it occasionally flared and didn’t settle into its stride. Penny dropped from past experience with these little self-pressurising stoves, I’d not hand-tightened the burner bell on the burner sufficiently. They need to be tightened (without tools) as tightly as possible short of stripping the threads! Thermal conductivity is that critical to achieve and maintain vapourisation. In fact, I clean off any oxidation on the mating surfaces/threads to make sure.
Great analysis and fix, John. Disappointing to see a manufacturing defect on an Optimus stove....
Well done, John!
Well done John knew you'd bottom it mate.
Well done fantastic presentation
Never gave it a thought about thermal feedback except on my Governor. Good info about conductivity. One forgets about that. Nice fettle John.
Failure in manufacturing. Good eye.
Thermal conductivity. I will keep an eye out for that now.
This was a very interesting thread to follow. Learned a lot. Makes me want to unpack a few of my stoves and check them.
Well done @presscall
Again - I bow to the worthy here!
Good outcome John and thanks for the effort you put into your projects and presentations.
Well, John, I'm glad I passed it over to you. I did notice that if I fully tightened the burner, the squared-off end of the valve spindle went too far round - but, short of comparing it to another 123R, I never would have worked out the root cause of the problem for myself!
Re. the cap; I've just looked at my pair of Optimus 80s; the one I bought from twoberth has a cap with a hex nut on top, and a screw with a pentagonal hole fitted into it. My other one has a cap the same as fitted to the 123R in your photo - so my guess is that the one on your 123R should be on my Optimus. If so, I will pop it in the post to you in a Jiffy bag on Monday, and include the necessary stamps for you to send the Optimus cap back to me.
Re. the fit of the burner bell; again, that's something that I'd never have worked out for myself - though I've always snugged them up pretty tight when I've taken them off. Many years, and probably over 100,000 miles riding motor bikes, and being a bit paranoid about bits shaking loose has made a habit of that.
Though, contrary to widespread belief, I never had any bits fall off on any of my Brit bikes, no matter how hard I rode them, but my Kwak 550 regularly unscrewed the nut holding the rev counter cable in place when I did my regular trips from Hastings to Inverness, and Harley-Davidson Sportsters break the dip filaments in the rubbish headlamp they fitted in the 80s / 90s if you cruise for any distance at 80+ . . . at least, that's what I've been told . . .
Going back to the thermal conductivity between the vaporiser and the bell; it just confirms what @Harder D. Soerensen said, about these self-pressurising stoves being a bit fussy about having everything 'just so'.
I'm chuffed to bits that you've resurrected this 123R from the dead (or, at least, 'walking wounded') - and I'm pretty sure that if I hadn't accidentally stumbled across this forum some years ago, it would have been hurled into the 'Scrap Metal' skip at the local recycling centre long ago!
With best regards,
@presscall - I've just watched the video-clips you uploaded, John - and what a delight to hear that steady 'Doodlebug' roar!
Hey, no need to include the return postage for the ‘80’ cap.
Okay, so it wasn't the flux capacitor, can't a guy make at least one mistake in his life?
@presscall , nice work sir. I would have never noticed that.
How many of us would? At least this fast!
Not me, guv - and that's for sure!
You, sir, are a gentleman and a scholar!
Off on a bit of a tangent, but in the course of our correspondence, John pointed me at this thread:
Data on PTC Optimus 80s & Pimus 71Ls
It was started by the late kaw550red, which (assuming I've studied the info correctly) enabled me to roughly date my two Optimus 80s - one rather ratty one which I bought off Ebay, dating from the early 1960s, and the one in far better shape which I bought from Twoberth, which appears to be from the late 1970s onwards. Mind, those are youngsters compared to my ex-Army Burmos, which is dated 1955, and still going strong!
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