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Trans possibilities for a knuckle in a Pan frame

3561 Views 15 Replies 7 Participants Last post by  hd74
So I'm about to finally build my first Knuckle bike and have a few questions on the trans to use. I have an FL motor going in and early 50s Pan rigid frame. I dont have any early transmissions on the shelf, but have a couple early to mid 70s shovelhead ratchet 4spds and a skinny belt drive for those transmissions. I know the knuckle takes the keyed shaft so at least a new front pulley is in order, but what about using the 4spds that where meant for a aluminum inner primary and E start? The belt drive has the gear for e start as well...not really planning on running a starter, and will have at least a partial outer steel primary. these E start trannies have a longer shaft that wont line up correctly with the motor? ....or should I just freshen up one of these trannies I have , sell it, and buy a pre-'65 trans?....I read tons of threads on trans ID and whatnot, but didnt really answer my questions.....
Thanks a ton in advance.
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The trans mainshaft was extended when the e-start alum. primary was added, 1965. It was extended again when the alternator was put under the engine sprocket in 1970, and gawd knows when else. You can find out by the dash-year numbers of the various trans mainshafts. There's a -41 that goes back to kickstart, a -65, a -70, each one a little longer than the last. That will determine where you end up, left-right.

What I want to advise you is that the front Knucklehead engine mount pad is 3/8" higher than the Panhead. Knuckles or UL Flathead motors mounted in Pan frames require a 3/8" spacer on top of the frame, under the motor mount, across the front. Ignore this, and once tightened down and run, vibrated, the front motor mount will snap off the Knuckle engine cases.
Like sarge confirmed for you, there's 3 diff length mainshafts for the ratchet tops, and they will not line up correctly when not coupled with the same era motor. For aesthetic reasons I'd run an early trans case (non-estart), but if you are inclined to use one of your transmissions, here's a few ways of which I can think:

1) swap the guts of one of your transmissions into an early case, but get a 36-64 mainshaft, then you still need a front pulley.
2) simply swap the mainshaft in one of your transmissions. you could cut the primary ears off if desired. still need a front pulley
3) or since you have to buy a pulley anyways, you should be able to get one with a removable insert and then you can get the correct offset, but it might be kinda goofy looking sticking too far out and that will definitely limit your ability to run a tin primary.
-i'll add that as I recall, the BDL e-start shovel primary kit had a weird pulley combination and as I recall, I wasn't able to find a replacement front pulley that accepted a removable insert. I ended up gutting a BDL pulley with cast insert and machining it to accept a primo insert.

-I also recall that the front pulley on the BDL kits (unless specified for a particular application) will not quite fit in a tin primary, at least the early ones.

also, if you have a BDL primary w/ a press on starter gear, and you are going to remove it, you are better off simply cutting it off, rather than trying to press it off. trust me on this one.

lastly, most would agree that if you stick w/ a later transmission and don't swap to a shorter mainshaft, your best off running some form of bearing support.
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Sarge,Scott, thanks for the good info. Sounds like the thing to do is just Finder a '64 or earlier trans....but...if I were to come across a good early case and short shaft, will my e start guts drop right in or is not worth the trouble?
I as well was earlier reading a thread on swapping drums/tops from ratchet/tank shift trannies and their compatibility but couldnt find the thread. I'm not dead set on either type shifter at the moment as I as well havent completely decided on the clutching type I want. I'm working on a couple different ideas at the moment but Wont clutter this thread with them
The gears will just drop in. They didn't change. Basically, the mainshaft just got longer, 1941 to 79. What you do is basically take the opportunity to build a fresh tranny using your later gears, new bushings and bearings and a shorter mainshaft. That's what belongs behind a Knuckle motor.
Of course, I do know a man who modified his Knuckle motor for electric start with the longer sprocket shaft, welding build-up and machine work on the left case, to create and electric-start Knuckle. He was kind of a puny little guy, and also disabled, but he ran the hell out of that Knuck.
If you are planning to use a belt primary drive it is simple to change the mainshaft in an ES case and use the assembly in the Knuck/Pan frame. Early cases cost two to three times what later ones do so you instantly save money. No issues with leaving the ears on the case and running tin primaries, (I have a '48 set up like that right now), and an aftermarket twin pull adjuster takes care of that aspect of it. And any 4 speed top, either hand or foot shift, fits any box from '36 up to the cow pie with the exception of 1939 with neutral between 2nd and 3rd.
Robbie, Thanks, I was just wondering my clutch drum with the ES gear on the outside fit inside a tin primary?..I'm assuming since the trans shaft changed lengths, the clutch assys will interchange. As far as finding a shaft, is it best to fond a good used original, or are there repops of decent quality? Any tips for fitting the tin primaries, I'm not versed in the various differences...I can fab whatever needed, but if there Are differences, would be Nice to know...thanks for all the info guys....Hans
Just for info if someone uses this thread in the future:


OEM # 35040-50*Fits 37-64 and is*11.73" lomg.

OEM # 35039-65 Fits 65-69 and is 11.985 long.

OEM # 35039-70B Fits 70-84 and is 12.47" long.
so...will my clutch drum with the ES gear on the outside fit inside a tin primary?..I'm assuming since the trans shaft changed lengths, the clutch assys will interchange.
The ring gear won't fit, it will have to be removed. All the clutch stuff will interchange. Original shafts are hard to find, Andrews stuff is usually fine.
no tricks on the primaries. Just pull the studs out of the tranny ears and the stock tins will lay right on there. You may need to do a little minor adjustment but that is the case with ALL aftermarket primaries anyway!
+1 for Rubone!
I ran a 1972 FX trannie with a 1957 pan motor in a 1957 frame. All I did was swap out the main shaft for the shorter and run all the same guts. Works fine. The ring gear has to go. 1.5" belt drive. I do run a copper tube from the crank case breather to keep the oil mist off the belt. Make sure when you put that trans sprocket on you rattle that good with an impact. The mainshaft seal is dependant on that being tight.
And Thankyou, HRC for posting the Info. Thats going to help someone out huge some day.
I see your above point here shovel/Pan belt setup has 41/61 tooth pulleys as most all do....whereas the Earlytapered shaft and up to '64 splined models take a 39/62 ratio....this larger 41 tooth might interfere with the tins. This seems to be the case with both BDL and Rivera/Primo. 41/61 gives a 1.49 ratio and the 39/62 gives a 1.59 pulley ratio....honestly I would really like the extra 6.2% reduction in rpm the 41/61 gives as I'm running a fairly built 80" Knuckle with dual carbs and Sifton 450 in a pretty stripped down bike...I dont need the gearing, but with a 4spd, could use the longer legs on the Rivera lists a 39 tooth with splines...and a tapered insert seperately.....Are all their pulleys made to accept a removable insert? it as simple as buying a 41 pulley and tapered insert and would it not line up with my BDL rear with the short trans shaft of course.....lots of questions, I know...
Thanks, Hans
This thread has hit the spot for me, you guys are covering everything I've been thinking about for the last six months. My plan is to run a belt drive in the tins with a six in a four speed case, but with a twist I want both kick and electic start. I'm still collecting parts, so the info will save some time and mola.
Great info guys. Just a simple eloquent solution to the OP if I may. Sell you current tranny and buy the correct one?? Just a thought....
Pete, I will likely try to find the earlier trans or at least the case parts and use my guts , mostly for aesthetic much as I hate *Bay..I dont mind it the last 24hrs I got the required short trans shaft for 20 bucks and a tapered front pulley for 47 bucks...I'm not quite ready for the trans yet, but at least now I have all the required parts(hopefully) to use my ES trans and belt drive. If I'm lucky I can come up with an early trans or case in the near future and just rebuild that one. The front belt pulley I got is a Primo..hopefully is has the same spacing as the BDL rear drum, but should be able to make it work...and hoping as well the smaller 39 tooth pulley(vs my 41 for splined) will work with my 132 tooth belt. I'll run at least partial tin primary covers, so I can move the trans back a hair to tighten the belt if needed...if anybody has early trans case/kicker parts that they can't STAND to look at any more drop me a line...;)
HRC, make sure you post some pictures of your progress, I'll do the same.
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