70's engine gear ratios

[Mike Lenz]

Am I right that the gap between first and second is tighter than the gap between second and third on the 70's KTM six speed engines?
Thanks!
Mike

[firstturn]

Mike,
  I do not think so, but being old I will have to count gears tomorrow.  I always felt that 1st to second was a real drop...so I geared it to come off in second gear.  Doug Wilford will square us up.

Ron Carbaugh

[Mike Lenz]

I was going by the ratios in the service book, but I want to make sure my understanding is correct.

[Doug Wilford]

I AM NOT SURE ABOUT THE "KTM" ENGINES but the Sachs engine for
sure has a bigger gap 1st to 2nd than 2nd to 3rd.   Have Fun!

[joe novak]

Hello,  We used a method with stock cars to determine the rear end gear ratio (without taking off the differential cover).  It was sort of like this:  mark the driveshaft and the rear wheel, spin the rear wheel, and count the revolutions of the rear wheel and the driveshaft.   Divide the two.  By spinning a greater number of times (ie.10 times), it lessens the error in calculating the ratio.   It seems likely that if you removed the spark plug to reduce compression, put the bike in each of the gears at a time, and spun the rear wheel while counting the number of revolutions of the engine (pull the ignition cover and mark the stator) rather than looking down the sparkplug hole, you could do the same thing.  OR you could kick the bike over slowly while in each specific gear, and count the rear wheel revolutions.   I sure would try this before splitting cases to count gear teeth.     Good luck,  let me know if this works.                     joe.   p.s.  maybe I think too much.

[firstturn]

Joe,
  Excellent point as I used to use this technique in the 1960's and 70's for race cars we used on the street(mostly Cheverolets).  In other words if you jacked a chevie up with positive track and rotated the engine one time and the rear wheels rotated a little over 4 times we knew it was a 4:11 rear end....and more we knew it was a 4:56 then next up was a 5:12.  With the motorcycles you must take into consideration the size(number of teeth) of the countershaft and rear sprocket.  Lot of variables.  But I like people who think too much[].

Ron Carbaugh

[Mike Lenz]

Well could someone who can think alot look at the service book and tell me (a real non thinker from way back) if I am right or wrong?

[joe novak]

Mike,  Please list the information (gear ratios, et.al.for each gear) from your manual, and we will try to help you out.  We need to know which gear is on which shaft, also.                            I want to inform everyone, that just because the manual says so, does not mean it is so.  I have heard about racers who change transmission gears, press gears off of shafts and reverse gear set-ups.   The ONLY way to know for sure is to count the teeth on the gears (or use the previously described method).                      I remember Dane Leimbach telling us one day in the pits, "A ratio is a ratio".   I also remember how tough it was to press the gears off the clutch shaft, too.   But it has been done.  joe

[Mike Lenz]

OK, here is what the manual states for gear ratios:
1st 14:36
2nd 18:32
3rd 21:28
4th 24:25
5ht 26:23
6th 28:21
Thanks
Mike

[linglewn]

Mike,
If you calculate the ratios (divide the right side number by the left side number) from the numbers that you provided, and subtract 2nd gear ratio from 1st gear, 3rd gear from 2nd gear, and so on, you will see that 1st to 2nd has a difference of .79, 2nd to 3rd is .45, 3rd to 4th is .29, 4th to 5th is .15, and 5th to 6th is .14. Therefore, yes, the lower gears do have greater spacings based on your numbers.

Nelson Lingle
73 Jackpiner
71 DKW 125

[john durrill]

Here are the ratios from a 77 manual . I think all the 175-400's first gen KTM engines  used the same gearbox. Primary ratios for the different sizes is on one of the pages.
 may help with selecting sprockets.




john d.