Linkert M31 carburetor

[T. Cotten]

Harley airbrushed out their history in the parts books to remove the early 1930s Scheblers, explaining why later books assign the Linkerts back to 1930. We see the same with the 1935 domed taillight glass retrospectively fitted back to 1920, and the 1934 full pan saddle retrospectively replacing the 1925-33 Mesinger.

On my Linkerts I have an M2 and M31 with the 2 stamped and two M41s with 3 stamped. Wartime Shop Dopes show all 1 1/4 inch Linkerts with the same sized idle holes (retrospectively). Only exception is early M2 and M21s, where Shop Dope 106 describes problems with a flat spot on early Linkerts cured by putting a number 55 drill through the larger idle hole. Dealers were supposed to punch a dot after the model number after this was done, and about half the M21s I've seen have this change marked.

The MOCO was (and still is) certainly 'revisionist', Steve!

Shop Dope 106 addresses 1933-early'34 VLD and RLD specifically;
I wonder what the dot means on M5s?

Shop Dope 229 from '42, but revised in '49, lists the M5 with a #53 large idle bleed, and all other 1¼" Models with #55.
I must check my un-dotted four-screw M5s, but I suspect the two-screw M5s are #55.

It would be great if someone with a two-screw M5 could contribute.

....Cotten
PS: Sorry I forgot who to credit, but apparently M5s had both 3(4)8 and 348 castings, at very least...

[Steve Slocombe]

Harley airbrushed out their history in the parts books to remove the early 1930s Scheblers, explaining why later books assign the Linkerts back to 1930. We see the same with the 1935 domed taillight glass retrospectively fitted back to 1920, and the 1934 full pan saddle retrospectively replacing the 1925-33 Mesinger.

On my Linkerts I have an M2 and M31 with the 2 stamped and two M41s with 3 stamped. Wartime Shop Dopes show all 1 1/4 inch Linkerts with the same sized idle holes (retrospectively). Only exception is early M2 and M21s, where Shop Dope 106 describes problems with a flat spot on early Linkerts cured by putting a number 55 drill through the larger idle hole. Dealers were supposed to punch a dot after the model number after this was done, and about half the M21s I've seen have this change marked.

[T. Cotten]

Remember the four line writing on the side of the body is pre-1940 and the three line later. The M31 was used quite a bit, starting with the 1935 VL with the early style you have. The machined flat on the bottom variant must be for the later float bowl mounted centrally rather that off to one side. The M31 was also used on the small twins I guess from around 1936-41 after which the M88 was used on the military models. Maybe it was also used as a Schebler replacement, as the M21 had been earlier. The four screw inlet flange started with the M41 on the 1936 VLs, making the M31 the last Big Twin carburettor with two air intake fixing screws.

Steve!

Some listings show the M31 for 1930-1933 Harley 74" (except Commercial), 1930-1936 Harley DLD, RLD, 1936 Harley RL.

The machined deck for a centered bowl, with dowel holes, was common on pre-War M51s as well, but they still used the side-bowl.
So far,.. I have found nearly all pre-War 1¼" Model Linkerts to use the 3(3)8 body, with the exception of M6 and M21, which used the 3(2)8 body (some with a 'sprue' on top), and the M5 with a four-screw 3(4)8 body.
(One listing suggests the difference is a larger idle bleed hole.)

(All had a 2- before them. The parenthesis indicate stamped numbers; Most post-War 1¼" Models had 348 cast numbers, including Indian models.)

So the mystery is why two dramatically different castings carried the 3(3)8 number.

I suspect the casting number for a two-screw M5 is 3(3)8; Can any '36 Knuck students confirm this, and guess when this change in production occurred?
(Thanks in advance..)

....Cotten
PS: My copy of the July '36 Service Parts catalog only lists two bodies, 1¼" and 1" Models!

[Steve Slocombe]

Remember the four line writing on the side of the body is pre-1940 and the three line later. The M31 was used quite a bit, starting with the 1935 VL with the early style you have. The machined flat on the bottom variant must be for the later float bowl mounted centrally rather that off to one side. The M31 was also used on the small twins I guess from around 1936-41 after which the M88 was used on the military models. Maybe it was also used as a Schebler replacement, as the M21 had been earlier. The four screw inlet flange started with the M41 on the 1936 VLs, making the M31 the last Big Twin carburettor with two air intake fixing screws.

[T. Cotten]

David!

It appears you have an early issue with a two-screw intake flange.
Somewhere by mid '36, they went to the four-screw intake flange, but none have crossed my benches.
....Cotten

[Rubone]

Linkert changed bodies often even with the same designations. The 3 was a later version than the 2 as is obvious with the body changes. You can tell that the later body was already in use or near so for the OHV models where the 2 had not been adapted yet. They often used a common casting for more than one model if it would suit them. How high is your engine number? I would guess a version "3" would be late season when OHV prototypes were being built or it was a replacement carb after OHV production had started in earnest and could also become an early M5 from the Linkert factory.

[David Uhl]

SDC16155.jpg SDC16158.jpg Both marked M31

[David Uhl]

Can anyone explain why there were more than one body style for the m31 carburetor? different numbers on side.