1972-74 Jackpiner tranny swap

[wildman]

I'm rebuilding a 74 Piner engine and the trans. has a lot of rusty bearing and shafts. I have a 72 piner lower end and wondered if its parts are all the same before I go to the trouble of splitting the cases. I know the early parts book would show part #s to match up but I don't want to buy one just for this. I suspect they are all the same but the 72 was an early model and frequently things change after the first year. Any help would be greatly appreciated. Thank you. Dan Pagel

1975 250 Cross Country, 1974 175 Jackpiner, 1975 125

[DKWRACER]

Wildman, having split many cases so far, you will never know until you split and then compare the parts. Some of the early JP's had their respective shift drums and shift forks reversed ie: male/female relationships, the drum had a raised surface (male) which captured the fork (female) wasn't so hot, but I've only seen one that way....
Adios for now....

[Auto5guy]

Hello Wildman

I don't see a problem with this swap as long as you retain the 74 clutch and shift drum.

I swapped a 74 Jackpiner transmission into my 73 harescrambler engine.  The gear sets and the shaft sizes were exactly the same. The difference was in the shift drum and the clutch.  The 73 250 had a clutch with copper plates instead of fiber clutch plates and had a welded shift drum.

Going with the copper clutch plates would be a step backwards in my opinion.  They expand a lot more than fiber plates.

I believe that all 73 and earlier KTM engines had a welded shift drum. (The repair manual refers to this part as a controller barrel but I have always known it as a shift drum.) Your 74 Jackpiner should have a milled shift drum.  The milled drum is a bit heavier but I believe that it must be an improvement as KTM switched to it and virtually every other bike manufacturer used a milled shift drum.

To keep the milled drum you will need to retain the milled drum, the three shift forks, and the center sleeve for the drum.  These pieces should fit with all the other transmission parts without issue.

Good Luck

Matthew


WARNING: The Surgeon General has determined that castor smoke can be hazardous to your health.  It is highly addictive and causes delusions of grandeur.

[rob w]

Could I please get more details on this 72 Piner to 74 Piner, shift drum conversion.

From what I gather, I only need a later model shift drum and forks - is this correct ? Are there any other parts required ?

Is there a big difference in doing this ? What is it about the shifting that improves ?
I remember back in the day, how clunky my friends 72 Piner trans felt. (I did'nt care for it)

Thanks very much for your help.
Bob

[G Ellis]

Here is what the different. 72 shift drum is a welded unit, the shifter forks have a slot in them to fit the 72 shifter drum. The 74 motor has a cast machined shifter drum. The shifter forks have a pin machined in them to fit in the machined grove in the shifter drum. This will make shifting smoother using the 74 drum and forks. Hope this will help Later Gary

[rob w]

Yeah that helps, thanks Gary. I later remembered I do have a 72 Jackpiner parts manual, to compare with '75 manual.
Looks like all later shift drums will work.
Also other than the three shift forks, will need the 3 shift rods, and the bushing for the shift drum.
Locating lever and shifting quandrant are the same.

[Doug Bridges]

Rob
I have a complete 74 lower end that is very rough. I bought it for the kickstart shaft and that is gone. I beleive that the parts you would need would all be in it and would probably be OK. You can have them if you want. Let me know.

Doug Bridges
73 Jackpiner
74 Rickman Zundapp
78 Suzuki PE175
82 XR200R

[Kip Kern]

You can swap either way just remember to change the drum, forks and drum retainer in the left case as a unit.  This is also a good time to check the shift forks to be true (90 degrees) and the actuator not to be spread more than 54.8mm

[Mike Lenz]

One thing to remember in general since we are talking about this.  if you are rebuilding a 250 and especially a 400, use the forged gears.  They are marked with a milled ring or groove in them.  I learned this the hard way on my 400! This is mentioned in the 78 and on parts books for some of the gears, but I have found more forged ones than are specified in the book. In all I have found 3/5,4 and 6th on the main shaft and 2 (lightening slot is machined on this one)and 5th on the countershaft. 6th gear on the countershaft also has two different part numbers for the one that goes with the 29 tooth mainshaft 6th gear as found on some 125 and 175's. Does anyone know the differance of this gear?  They are both 21 tooth.  Im wondering if one is just forged, but I cant tell any difference, or which one is which since all my gears were mixed together.

[Mike Lenz]

Another question.  Why do some of the shafts have lube holes in them for the needle bearings.  I have mainly seen these in older engines???  Did they find out they were not a good idea...or was it an economic issue?? Please! Answers!

[Kip Kern]

I vote for lube holes anyday under a tranny needle bearing!

[Mike Lenz]

I think I agree.  I guess I will see if I can get mine drilled.  Tried myself...too hard.
Thanks Kip