M61B Carb body

[billpedalino]

Does anyone have a Linkert M61 or M61B body for sale? I bought an M61 Linkert body for my '53 FLE at Oley and it turned out to be bad, most likely distorted in a fire. Therefore, I need another. If so, please send me a Personal Message or email me at WMP@soundindustries.us.
Thanks...

[T. Cotten]

Bill!

Are you certain it is beyond salvage?


....Cotten

[billpedalino]

Cotten,

No, I'm really not certain that it's beyond salvage, but this is what I noticed and how I plan to approach the problem:

The bore on the throttle side is slightly non-concentric by about 0.006" and the throttle disk binds when new bushings are installed. There is also a lot of light showing around the closed disk at odd and intermittant points arond the disk circumference. However, I 've observed that this out-of-round of the left side bore is only slightly more than the three other 1-1/2" M-series bodies that I have, so I've looked deeper.

After more careful observation, I believe that the slight binding and disk displacement is caused by what looks and feels like a very smooth 'bump' on the bottom of, and transverse to the bore just outboard (air cleaner side) of the throttle shaft hole. This bump is about 3/8" long and runs along the bore circumference perpendicular to the bore. There are absolutely no signs of impact to the outside of the body that may have causes this displacement and build-up of material. In fact, the body looks absolutely perfect in every other way, which is why I bought it.

My plan is to mount it onto a bridgeport with the throttle side up, locate the true center of the bore and try to clean up the 'bump' down to the original bore circumference as best I can by taking very shallow cuts in the area of the bump, and stopping above the elevation of the inside edge of the venturi.
Hopefully this 'bump' is what is causing the slight binding (it looks shiny from the disk passing over it) and the slight non-concentric bore can be cleaned up with a very shallow (say 0.001" or so) skim-cut to a point where the runout is similar to my other carb bodies. My hope is that even if the bore is say, 0.002" greater than stock, the throttle disk will correctly seal.

Mike at, 'Into the Wilderness' who has been very informative and helpful suggests hand-filing an oversized disk if necessary, but I hope that's not.
However, as a backup I am trying to locate another M61 or M61B body. If my machine work is sucessful, I'll have a backup carbutetor for the '53; if it doesn't work, I'll need the backup body.

I know that you're also an expert at these carburetors, so your evaluation would be greatly appreciated.

[T. Cotten]

Bill!

I encounter such things on a regular basis; Potmetal Scheblers are often far worse.

Since I must approach this as quickly and economically as possible, the first step is to rough off the bulge with a machinist scraper. This takes a fraction of the time of a machine set-up.

Then the bore is honed round again, including the common eyebrow of wear from the throttledisc (attached), which is normally deeper than distortions. Often this cleans up at .006-.011" over the original bore.

Since nearly all potmetal venturies have shrank and require swageing anyway, I just take it all the way to where ever the bore cleaned up.

The venturi must fit with no daylight around it, just like the throttledisc, and only a fresh bore allows a perfect fit.

And then a fresh oversize disc is cut on the lathe to match.
Hand dressing a 12° disc is quite a feat.

An overbore and fresh disc requires less than an hour of flat-rate.

If your flange is distorted to cause the shaft bind, I can go into that as well.

....Cotten

[billpedalino]

Cotten,
As always, your information is both informative and helpful. However, as I'm out of the professional Harley business for many years, I don't have the resources or the experience that you have, so please forgive my amaturish questions;

Swaging: I've been lucky of late, with four carbs that I've rebuilt over the last several years (all turning out extremely well). The venturis all slid into the cleaned bores with moderate finger pressure. However, the new venturi slides into this M61B body a little more loosely, so swaging looks necessary. I assume that you made a beveled fixture that you press into both sides of the venturi to slightly expand and center it, thus enabling it to 'squeeze' into the bore?

Also, concerning what I thought is excessive runout on the bore diameter, I've looked at two additional M-series bodies (one that I did last year and currently installed on my beautifully-running '47 FL) and the vertical and horizintal bore measurements of all five bodies seem consistant with the M61B body. I'm not saying that they shouldn't be round, but it seems that they all must experience, and will run properly with a certain amount of slight warping of the bore. Is this your experience as well?

Therefore, given the above I do believe that the 'bump' in at the bottom of the bore appears to be the sole culpret for the binding and misalignment of the throttle disk in the bore. As I don't have the tooling, experience and (I assume) custom-made fixtures at my disposal that you have, I will probably try to just remove the material buildup that exists inboard of the throttle shaft hole using the Bridgeport, and maybe a very light polishing on the Sunnen. If the disk seals all the way around and swings free with the factory 0.001" bushing clearance, I'm going to assemble the unit and see how it works. I'm just reluctant to open up the bore on the hone (which I know is the correct way to fix this condition), as I have no idea how to chuck an oversized disk in the lathe and correctly cut it. By the way, I noticed that new disks are non-concentric, measuring approx. 0.259" vertically and 0.281" across. I've never custom-fit an oversized disk and simply don't know how properly to cut this disk so that it lays correctly in the oversized bore.

Thanks again for your help!

[T. Cotten]

Bill!

You were quite lucky to have even one venturi to fit with zero daylight (attachment).
Even modern productions are often loose to the eye, but not the finger.
Sadly, even a snug-fit swaged and re-cut potmetal venturi will return to shrinking, and show dayight after a year or more on the shelf!
And yes, my swage is merely a collection of cones on a screw. Great care must take of course, as I still "lose" one occasionally. It is then trimmed upon the lathe to size between centers, or upon a rosewood/maple tapered mandrel, previously used for a pool cue.

And yes, forgiving Linkerts and Scheblers ran inspite of all kinds of bore problems.
(Nearly all M35TPs are dented in at the stamp).
The two spots that must be round are at the rear of the venturi, and at the idle bleeds.
At the front of the venturi, you just need it not to rattle!

Not all Linkerts require a borejob, of course, and the venturies are flexible to a degree.
And I have taken up daylight at the bleeds with an oversized disc alone.

Cutting a disc on a lathe only requires a mandrel slashed at the correct angle, with two screws to hold a punched disc blank.
The disc is oval because of the angle of the edge.

....Cotten

[fillibuster]

thx Bill and Tom!
I've had good carb luck on the Chief.. The John Deere's became a new challenge, but same price tags, tricks, etc, and more experts in close proximity.
I think the A John Deere was more common than all American motorcycles put together!

[T. Cotten]

Hokey Smokes Folks!

I ain't never seen nothin like this M61B...
You can put your fingernail between a throttledisc and the bore on the side opposite of the bleeds.

Graciously, the bleeds are pristine, for now.

The internal surface suggests rough burnishing with a wire wheel, however much of the bore is unmolested, sort of....

....Cotten
PS: For all I remember, this might be the first M61B body across my benches, so it is a learninglearning experience for me.

[T. Cotten]

Just to bring this to a conclusion, Folks,

I fixed it with "the up-and-down wrench".

....Cotten

[fillibuster]

Just to bring this to a conclusion, Folks,

I fixed it with "the up-and-down wrench".

....Cotten

Primitive club??

[T. Cotten]

Fillibuster!

The thumbnail is of the piece of Lyman ingot that cushioned against damaging the casting's lettering.

But otherwise, it was a chill in the freezer, and discipline with tool number one.

Then the bore cleaned up at .010", so fitting the venturi and a disc went as usual.

....Cotten