Sticking metering rod

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Vendo63 guy
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Sticking metering rod

#1

Post by Vendo63 guy »

I recently fettled a 220D and was suffering from a sticky metering rod despite a complete tear down and thorough cleaning. I did not expect the solution below and thought I’d post it here with hopes it may help another with similar troubles. Cheers :)

The ‘sticking’ was very predictable. Only air would pass through the valve until two full rotations of the valve wheel had been made at which point I’d get an audible clink and fuel would begin to supply. I pulled the valve again and ensured everything was meticulously cleaned and checked for burs and marring that could be hanging something up. The tapered end of the valve spindle showed no abnormal signs of wear, spring had good energy, everything seemed normal and behaved as it should in isolation. Reassembled and reinstalled the valve and checked the operation - same behavior…

I pulled the valve again and pulled the metering rod from the F/A tube. I manually held the metering rod to the valve with my hand keeping the spring under heavy tension. I began to open the valve and sure enough, felt the ‘click’ in my hand after two rotations of the valve wheel. This ruled out the F/A tube and spring as any source of the problem.

I had two hypotheses:
1) The tapered end of the valve spindle had perhaps mushroomed out the seat and was now advancing farther into that seat than originally machined.
2) The tapered end of the spindle was machined too steep and perhaps this lantern has always behaved this way (this seems less likely)

In either case, the metering rod was behaving as if it was riding along the spindle for two full rotations before hitting the tapered end where I would then get the ‘clink’ and the rod would begin to lift and allow fuel to advance.

Using fine sandpaper, I filed down the angle of the taper at the end of the spindle ever so slightly. Upon reassembly, the ‘sticking’ occurred after one full rotation where before it had been two. I repeated this filing two more times until the sticking was gone and I could observe a slight movement of the metering rod at the end of the F/A tube with the normal prescribed quarter turn of the valve wheel.

The lantern was then fully reassembled and is now behaving as it should. Because I can’t physically observe the metering rod’s interaction with the valve spindle, I can’t say for 100% this was the correct diagnosis/treatment, but it seems to have done the trick.
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Tgarner01
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Re: Sticking metering rod

#2

Post by Tgarner01 »

Jake you don't want your metering rod opening at a quarter turn.... You only want it to open when the valve is fully open or nearly fully open... That's when it allows straight fuel to enter the generator instead of an air/fuel mix.
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Re: Sticking metering rod

#3

Post by Ridge Runner »

Jake, when you rebuilt the lantern, did you take a toothpick and ream the orifice at the bottom of the F/A tube? How about buffing up the metering rod with steel wool?

It doesn’t take much for old fuel residue or corrosion to restrict fuel flow in that annular space.
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Re: Sticking metering rod

#4

Post by Rustytank »

I think you just reinvented the quicklite.
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Re: Sticking metering rod

#5

Post by Gavercronos »

There's a little bit of manufacturing jargon that might be informative: Tolerance. Some valves lift the rod right away, others after a bit of turning. That's why the instructions say to open fully once it's bright. Same with tip cleaner needles, some barely poke through the hole, others you can see sticking out with no visual aid. But as long as it does what it's supposed to, the little variation in how isn't really a problem. I actually like them when they click because then I know the mechanism worked.
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Re: Sticking metering rod

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Post by Vendo63 guy »

Tgarner01 wrote: Fri Jan 14, 2022 8:04 pm Jake you don't want your metering rod opening at a quarter turn.... You only want it to open when the valve is fully open or nearly fully open... That's when it allows straight fuel to enter the generator instead of an air/fuel mix.
Perhaps I have a misunderstanding of the mechanics of the F/A tube. Fuel is picked up from orifice at the bottom and air from the two on each side at the top of the tube, correct?

When the metering rod is fully ‘closed’ would you get straight air or is there some piece of the metering rod that is also ‘metering’ the top two orifices that would prevent you from getting anything at all? My understanding was that the rod is only metering the fuel and in order for you to get a light at a quarter turn wouldn’t some fuel have to pass?
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Re: Sticking metering rod

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Post by Vendo63 guy »

Ridge Runner wrote: Fri Jan 14, 2022 8:35 pm Jake, when you rebuilt the lantern, did you take a toothpick and ream the orifice at the bottom of the F/A tube? How about buffing up the metering rod with steel wool?

It doesn’t take much for old fuel residue or corrosion to restrict fuel flow in that annular space.
Yes, everything was sparkly clean and polished with 0000 steel wool. And depressing the metering rod with a finger would operate smooth as it should. As stated in the original write up, I could replicate the sticking without the F/A tube in place so I don’t believe this section of the assembly was the source of the problem.
Jake

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Re: Sticking metering rod

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Post by Tgarner01 »

Vendo63 guy wrote: Fri Jan 14, 2022 10:04 pm
Tgarner01 wrote: Fri Jan 14, 2022 8:04 pm Jake you don't want your metering rod opening at a quarter turn.... You only want it to open when the valve is fully open or nearly fully open... That's when it allows straight fuel to enter the generator instead of an air/fuel mix.
Perhaps I have a misunderstanding of the mechanics of the F/A tube. Fuel is picked up from orifice at the bottom and air from the two on each side at the top of the tube, correct?

When the metering rod is fully ‘closed’ would you get straight air or is there some piece of the metering rod that is also ‘metering’ the top two orifices that would prevent you from getting anything at all? My understanding was that the rod is only metering the fuel and in order for you to get a light at a quarter turn wouldn’t some fuel have to pass?
Correct. When the valve is opened a quarter turn the metering rod is still protruding through the pickup orifice. When everything is clean there is a little bit of fuel that can pass by that metering rod through the orifice with a mixture of air up through the generator. Once the lantern has warmed up in his generating correctly you open the valve fully which retracts the metering rod from the orifice allowing only fuel. Gary has a good illustration of this process. I will see if I can find it for you.
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Re: Sticking metering rod

#9

Post by zoomkat »

" Only air would pass through the valve until two full rotations of the valve wheel had been made at which point I’d get an audible clink and fuel would begin to supply."

I consider that within the normal operating bounds of the lantern. I have two lanterns that have a click at about half way open on the fuel control valve and they operate normally. Based on only just hearing a "click" being the issue, I would recommend people NOT do this mod/hack to their lanterns. Sounds like to me that the lantern was operating correctly to begin with. YMMV
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Re: Sticking metering rod

#10

Post by JimL »

Jake,

You are calling it a metering rod, but I wouldn't. It's not precision and it doesn't totally seal the bottom of the F/A tube, so no, you won't get straight air unless there's crud at the bottom which seals it when the rod is down. This is why the suggestion of reaming it with a toothpick.

Fuel will get into the F/A tube and since the air hole is allows less resistance, it'll mix with the fuel in the F/A tube.

At least the above is my take on it. :)
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Re: Sticking metering rod

#11

Post by Majicwrench »

When the metering rod is "Closed" as you call it, or pushed down through the opening, some fuel--enough to start the lantern--pass between the rod and the hole it is in. That hole and the rod need to be really clean. Can't clean the hole with steel wool, a pencil or skewer stick works good. Hope that helps.
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Re: Sticking metering rod

#12

Post by Tgarner01 »

This is Gary's (Grob) illustration.
fuel_valv_fa_diagxs-16399342.jpg
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Re: Sticking metering rod

#13

Post by Vendo63 guy »

Rustytank wrote: Fri Jan 14, 2022 9:32 pm I think you just reinvented the quicklite.
😂

That’s a real possibility. That said, the “filing” done in my drawing was completed with very fine sandpaper and was pretty minuscule in all relativity. The drawings provided more or less accentuate what I did for explanation purposes. Material removed was not as drastic as what the drawings make it out to be.
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Re: Sticking metering rod

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Post by Vendo63 guy »

Tgarner01 wrote: Fri Jan 14, 2022 10:14 pm This is Gary's (Grob) illustration.

fuel_valv_fa_diagxs-16399342.jpg
This is a great illustration. The “starting position” diagram is what I was trying to describe with my “normal” sketch above.

When fully closed, this particular metering rod would protrude through the orifice and would still be there at a quarter turn. However, it’d still be there at a full turn. It wouldn’t start to move until two full turns.

After filing, it still protrudes when fully closed, but is now flush with the outside of the orifice at a quarter turn and will continue to retract through the orifice as the valve is opened further.

I had assumed this tiny movement was enough to make all the difference, but thinking on it now, protruding or flush shouldn’t show a difference - there’s still a rod in the orifice…unless perhaps, my polishing with steel wool tapered the end of the rod.

Perhaps as Jim mentions, there was just enough crud remaining in the orifice to plug things up and all this fiddling around at the orifice was enough to wear it off and the assembly started functioning as it should 🤷‍♂️
Jake

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Re: Sticking metering rod

#15

Post by Vendo63 guy »

Perhaps this has been a lesson in ‘what not to do,’ although I don’t believe the light tapering at the end of the spindle has done enough to create a straight fuel pick up situation. It has created movement at a quarter turn vs two turns.

I had always assumed the metering rod effectively cut off fuel and didn’t really begin to feed the tube until a quarter turn, but it sounds like that is not the case. It never really cuts off the fuel and anywhere from closed to roughly a quarter turn is ‘restricting’ fuel.

Learned something new!!!
Jake

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Re: Sticking metering rod

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Post by Gunhippie »

Image

Image
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Re: Sticking metering rod

#17

Post by MYN927 »

The fuel-air pickup tube is really an ingenious design.
It was described in detail in the patent: US 2008882. That is most likely the patent for the Coleman 242. That's the only Coleman patent that I could find having a description of the fuel-air pickup.
If interested, you can download it from Google. Its in PDF format. I couldn't upload any files having the ".pdf" extension here.
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Re: Sticking metering rod

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Post by Gunhippie »

Oops. Here's the rest of the description:

Image

From:

Image
It's priceless until someone puts a price on it.
Walk a mile in a man's shoes before you criticize him--then you're a mile away, and he has no shoes.
Texan's last words: "Y'all--hold my beer--I wanta' try sumptin'."
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