Linkers throttle shaft leakage

[otis71]

Even with new bushings installed and reamed to .250 I get some leakage. What is the diameter of a new throttle shaft? I measured a couple old ones and at best they were not n the .2485-249 range. Seems like .0015 is excessive.

[T. Cotten]

Otis!

How are you measuring the 'leakage'?; A thou and a half is noticeable shake!

Even NOS OEM shafts vary slightly, but repops can be a bonus if they are really fat.

(Please believe me, even a 'perfect' fit is only for a while; That's why we obsess over leaks downstream.)

....Cotten

[otis71]

I initially tested with carb cleaner while running and it stalled. Then I bubble tested the manifold and carb with all valves closed using 15 psi air. Only place I got bubbles was around the shaft and they were excessive.

[T. Cotten]

You can't bubble-test with the carb installed, Otis...

(Even a sweet shaft and bushings has a gap that's orders of magnitude larger than what we are looking for.}

Please review http://virtualindian.org/11techleaktest.html
And please be certain to use a constant, regulated air supply. That way you only need to bump the motor through to where the intakes close, and adjust the pressure.

If carb cleaner killed it, its a BIG leak!
Did you grind the carb and manifold flanges 'flat'?

...Cotten

[otis71]

Yes I carefully flattened the flange. I know it’s a huge leak. My initial question is about what is the diameter of a new shaft? No sense buying a new one if it’s comparable to what I have though I suspect it’s undersized.
As far as the valves being closed, I put the front cylinder on the compression stroke and relaxed the the adjustment on the rear intake.

[T. Cotten]

A quality shaft would be .250", Otis,..

But you never know what you will get. Beware of some modern 'stainless' bushings that are already shot out to two thou over.

Messing with the valves is pointless: Even if they leak, the regulator keeps up with it.

Just set the regulator with your thumb over it, hook it up to the manifold, and kick the motor through till it shows pressure, and readjust.

....Cotten
PS: Chief intakes seem never to to be closed at the same time, but it doesn't matter!
PPS: With a Pan, always test the pan cover screws over the intake ports.

[otis71]

I think the shaft was the problem being about .2475. I line reamed the new bushings with a .250 reamer as shown. I think a new shaft is in order.
P.S. I’ve bought several of your floats through the years and you schooled me on the manifold bubble test long ago. Just for kicks I made a plate to fit the carburetor to check it also. Granted you need to keep a constant pressure but it still showed bubbles around the shaft. When you rebuild is there a way you test the shaft or you just go by feel?
Thanks for the help!

[otis71]

I also think my carburetor problem is being compounded by the compression is getting a little low. Time to tear her down.

[T. Cotten]

That's a tiny shaft, Otis!

Every carb is different, as sometimes the bushings are skewed because its been dropped or something. Over-torquing the flanges is the common issue (I had one customer crack the casting at the bushings, and wonder why the throttle stuck on him.)

Often I pressed flanges flat just to align the bushings, before a final grind.

So basically one 'finesses' it as sweet as possible. Its more art than science.

....Cotten
PS:

I also think my carburetor problem is being compounded by the compression is getting a little low. Time to tear her down.

Gosh Otis, how often did you have to measure it? Did it go down fast? Do the cylinders match?

[Steve Slocombe]

I had a memory of Harley saying 3 thou wear on the throttle shaft was OK before replacing it, but now I can't find the reference. TM9-1879 military maintenance manual for the WLA just says on page 94 'the monel metal throttle shaft bushings need not be replaced during the life of the carburetor'. I'm guessing your problem is elsewhere.

[otis71]

I get about 80 per cylinder. I did a test on a bike that runs and starts easy and got 85-90 range so I’m not sure if kick starter or inaccurate gauge is keeping me from getting 110 or so. The difference is the known good bike comes up by the second kick jumping considerably each kick. The bike in question only comes up over several kicks.

[T. Cotten]

What cam are you running, Otis?

Eighty is typical for some with a lot of over-lap and kick-only, and plenty to start and run.

Carbs are upstream from compression, not downstream. All they know is vacuum from displacement.

....Cotten
PS:

I had a memory of Harley saying 3 thou wear on the throttle shaft was OK before replacing it, but now I can't find the reference. TM9-1879 military maintenance manual for the WLA just says on page 94 'the monel metal throttle shaft bushings need not be replaced during the life of the carburetor'. I'm guessing your problem is elsewhere.

The "life" of a WLA wasn't much, Steve!

I read somewhere that JEEPs averaged a couple of weeks in combat; Reconnaissance machines not so much...
Nobody expected them to last eighty years, yet they produced literally tons of spares anyway.

If you fear your throttleshaft clearance, Otis, then repeat the running idle test with an un-lit propane torch around it, top and bottom.

[otis71]

The propane will increase idle I assume? How pronounced is the idle change? In other words are leaks very sensitive to the propane? In the past I had tried propane but never got results.

[T. Cotten]

The propane will increase idle I assume? How pronounced is the idle change? In other words are leaks very sensitive to the propane? In the past I had tried propane but never got results.

Propane is only a diagnostic, Otis!

Its nothing 'quantitative', and it may increase, or it may decrease the idle, with a zillion variables involved.

But if you are aiming it right at the throttleshaft and it does anything, that means something.


....Cotten

[otis71]

In a separate endeavor I’m trying to build a spare M35 front parts. I don’t have the 27218-36 air intake shaft and choke disc. Is there any reason it can’t be substituted for the 27218-48 shaft and corresponding choke disc? Also what is the most effective way to stake lock the friction ball in place for the choke?
Thanks in advance.