1939 knuckle tranny vented or not vented?

[knuckjunky]

Hello fellas, in my lifelong pursuit to drive myself nuts, I continue to build a “correct” 1939 knucklehead. I’m getting there but one of my biggest issues is the transmission. A while back you guys gave me some great input on the correct gear pattern for my “E” motor. Now I want to pick your brains on the proper transmission case.

Palmer’s book indicates that from 36’ to 39’ the transmission cases on big twins were not vented. Instead the kicker covers had the vent hole. However, I have recently seen a few cases for sale with December 1938 date bosses (L 8) which are vented. Now, my motor case is 39E3*** and the date boss on the motor case is L8.

I know that a lot of what went on back in 1939 was based on what was left over from the prior year and when the new years’ components were shipped. However, Palmer’s book, the cases I have seen lately, and the date boss on my motor have left me a bit confused. Palmer seems to say that vented transmissions didn't come out until 1940.

At this point, I am under the assumption that any transmission case made in a late 1938 (even if to be used in a 1939) should be vented. Please give me your thoughts on what case would be correct in my bike? Is there any particular month in 1938 when the venting switched? Should a L8 transmission be vented? Any help is greatly appreciated!

Eric Hitzel

[Sargehere]

Bruce Palmer, as much as we like him and rely on the vast amount of reliable information he collected, isn't a god. If you have an unmolested L8 transmission case to go with your L8 engine, I think that what the transmission case in your hand has or doesn't have trumps "theory."
It's highly unlikely that original L8 trans cases were built "vented" in 1938 and put away for use in late '39 or 1940.
Otherwise (OTOH), the vent could have been added as a modification on 'leftovers' that were installed in '39 or '40 bikes. There's just drilled hole, not a boss, under the vent, is there? There were instances of date codes not being changed for years at-a-time; later, like cases bearing "3-3" are found for about three years, running.
This might get interesting!

[Chris Haynes]

Bruce certainly isn't a god. Just a man who has done a lifetime of research. He has spent more time over factory photos, shop dopes, Enthusiast magazines, AMA Magazines, sales brochures, The National Archives, and anything else he can find to do his research than most of us have spent on their bikes.
Below is a photo entered into the Pohlman H-D archives on July 22. 1938. it shows a 1939 prototype. Actually serial number 38EL3072. You can clearly see the vent in the transmission kicker cover. Below that is a 1940 showing the breather in the tranny case.

[flat-happy]

the L8 case if it has the vent on it would be DEC 48 cast date and used on a 1949 bike. the proof of that is how the case is machined inside. the 1939 case with its one year only shift pattern of 12N34 is slightly different inside and if you contact carl olson he will verify this as he has on this forum in another thread. i have a kicker cover with a J8 date code that is correct for 1939 and has the vent on it that i will take a picture of and post later today.

[koanes]

The early Knuck case has a bronze insert for the bolt at outside mount. The Pan trans has steel. The 3-3 date code Pan trans case was used at least through 1958.

[knuckjunky]

Thanks for your help. I have seen a number of earlier 1938date bosses on transmission cases where there the case is not vented. I will continue my search for a late 1938 non vented case to go with my motor. However, if you have a second to go on ebay, take a look at item 160404273370. This is an example of what I am talking about. He's advertising the tranny as a 39' sliding gear transmission. It has an L8 boss but the case is vented. It this actually a 48-49 transmission that Flat Happy is talking about?

(Just want to make sure because a while back I bought an early non vented tranny for my 39 and it turned out to be a late 37/early 38. Very nice but not much use to me....live and learn the expensive way.)

[flat-happy]

that is a 48-49---even the kicker arm is not 39 as the bend is in the wrong place.
this is the 39 kicker cover i have with J8 code and vent

[koanes]

Flat Happy, Is your kick cover milled for throwout bearing clearance or as cast?

[Sargehere]

Flat Happy, Is your kick cover milled for throwout bearing clearance or as cast?

Now, THAT's an interesting thought! The first, 1936-38, I guess, throwout bearings were two little tin cups caging a handful of balls, with a hole through the middle. The throwout rod went alla way through it. The improvement, the cast "cone" throwout that takes up almost the whole kicker cover was PN 2448-39 (new PN37310-39). I know for a fact that if you have the original, early kicker cover (with a vent cast in) it won't fit the '39 throwout bearing. So, if the big -39 cone bearing fits without machining the inside of the cover, it's later than 1938.
Best fix in these days, BTW, if building a 36-38 Big Twin, with the little tin cup throwout bearing being "unobtainium", is to buy the dash-89 (I think it is) Big Twin clutch throwout set up: a clutch release lever finger, throwout rod, and tiny, starburst bearing that rides between what look like two quarters, on the end of it, with an oil-pickup tin star next to them. That's all you need. And shorten the throwout rod thru the mainshaft about three quarters-inch.

[flat-happy]

Flat Happy, Is your kick cover milled for throwout bearing clearance or as cast?

well offhand i would say it is as cast. when i compare it to two other covers i have one dated B6 and one dated J6 the J8 is different. it has two flat sides around the bottom of the top throwout arm hole and the two previously mentioned covers have a clean radius bevel at the same location. i also have a cover dated K5 that is identical to the J8 cover with two flats. all covers appear to be identical inside other than that and all have clearance for the large throwout bearing. when the covers have the usual cracks around the kicker arm hole i mill them out and press in a one piece stainless steel sleeve then bore it to accept stock size kicker bushings and o-ring. this repair doesn't show on either side and i have never had one fail again. i've been doing this for 20 years i guess. that way you still have the correct date code

[Robert Luland]

I just got done selling a tranny case dated J8 and it was vented. Matt Olsen told me that they had a ton of these to get rid of whating on the fouties to get there and started tapping the cases with out the boss. This was done mid way though the 39 season. I've already deleted the pictures but managed to find these on fleese-bay. Bob L

[t-bone]

39 gearbox

you guys got me wondering about the tranny that came with my 39 el i always thought was original to the bike[ wrong again.] it has the vented case with a bronze insert in the mounting hole under the kicker cover L3 date code on the tranny case and b6 on the cover. it is just gonna be a rider so no big deal.

[knuckjunky]

The tranny that Bob Luland posted is EXACTLY what I'm talking about. My motor being 39E30** with date boss L8, I still feel like I should be finding an unvented case. (And a J8 kicker cover...as posted by Flat Happy) However Bob makes me think that either vent setup could be "correct".

Bye the way, if anyone has a correct 39 tranny and is looking for a 37/38 for trade, I'm certainly interested. (It would make my expensive "learning experience" a little less painful)

Thanks again guys.

Eric

[flat-happy]

i would weld the vent hole shut and carefully blend the boss down to match surface with the rest of the case. if you have a kicker cover i can use i might trade you the j8 vented one---i don't need it and was going to but it on ebay anyway. i need to get money up for a set of gas tanks on caimag forum for 59-60 panhead

[flat-happy]

I just got done selling a tranny case dated J8 and it was vented. Matt Olsen told me that they had a ton of these to get rid of whating on the fouties to get there and started tapping the cases with out the boss. This was done mid way though the 39 season. I've already deleted the pictures but managed to find these on fleese-bay. Bob L

mr luland---does the trans case you posted look like this pic on top? it looks different to me like maybe the vent could have been added later as a dealer update or something? probably just my failing eyesight