KTM transmission shims

[Auto5guy]

Okay I've had a few KTM engines apart now and I have a question that has been bugging me.  On one of the first engines that I split the cases on the transmission did not stay in one case half like it was supposed to.  Instead it dropped gears all over my bench.  At the time I did not have much experience with these engines and was quite worried that I'd never get that tranny back together.  I did get it reassembled but along with the gears that dropped on my bench were some paper-thin washer looking shims and I have no idea of where they went.  The manual that I used to figure out the transmission made no reference to shims so I didn't put them back in.  The engine has functioned fine without the shims.

Can anyone tell me more about these shims?  In the other KTM engines that I've had apart I haven't seen any more shims.  Is shimming a transmission common? Where do the shims go and what is the tolerance that is trying to be achieved?

Thanks

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.

[wildman]

Most KTM engines I've seen have only shims on the shift drum. Sachs engines have many on the gearshafts. IMHO, KTM was much better at holding tolerances  than fictel-sachs. Jap bikes almost never have adjustment shims, most european bikes have them. The shims make up for excessive clearance or endplay. I have read that  shimming the KTM shift drum for minimal endplay makes for better shifting. Whats necessary is to do a trial assemble of the engine with gasket, then using a dial indicator to check end float, then dissembling and adding shims to compensate. The motors I've seen with the most shims were Ossa's, like 6 or 8 per side. Back in the day as a bike wrench, we would play tricks on each other by throwing an extra washer or shim on the bench after someone built an engine, "Where'd that come from, scratching my head?" Dan

1975 250 Cross Country, 1974 175 Jackpiner, 1975 125

[Kip Kern]

Matthew  The shims that fell out, normally two or three thin ones, go on the right end of the shift shaft between the shift quadrant assembly and the right case.  The only other shims in the engine are on the crankshaft between the main bearing inner race and the crank journal.  In one instance though, I have seen one shim placed on the shift drum as mentioned earlier, but that was only one engine out of about 100 that I have torn down.  On that same engine, I found shims behind the clutch basket assembly so most likely placed there by a previous owner trying to reduce any axial play.  A lot of times, you will find no shims on the black cased early engines but on the later silver engines, you will start to find the shims on the shift shafts.  While the engine is apart, measure the distance of the shift quadrant, not to exceed 54.8mm between the fingers.  CIAO

[Auto5guy]

Thanks for the response guys.  The knowledge to be tapped here is impressive.

I think I'll spend some time fooling around shimming the shift shaft and drum on the 400 engine currently apart on my bench.

Smooth shifting seems to be the Achilles heel of the KTM engines that I have built.  Hopefully I will find a way to improve that performance.

Dan,  it's nice to know that the extra parts on the bench trick is used by more than just the demented people I call family and friends.

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

[tomale]

Matt, Last fall Mac and I torn into my 400. I was having shifting prooblems. What we found was easy to fix. The arm on the shift shaft had broken. on the one we replaced we made sure that the spacing on the arm was right before we put it back together. I have been told that having that right does help with shifting. My 400 does shift better now. The other thing I did was go to a more flexable boot. my old boots were so stiff that it made it hard to shift. I still miss a shift once in awhile. mostly if I am in an odd position on the bike. LIke that tight right hander that is followed by table top. It is just far enough away to need a shift but I am not quite in the best postion to do a good job. I am sure you know the one I am talking about. You and I sat and watch a bunch of guys take that same corner. I still have not got it locked down.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
78' 400 MC5

[TGTech]

Matthew,

   I have a piece of history to add to this thread. Most, if not all of the participants on this forum, are aware that the Sachs engines' shifting live and die on the back of the shimming job of the transmission and shift mechanism. When KTM came out with their engines, and it was found that some didn't shift the way that they should have. the Penton Imports technical staff, led by Ted Penton, began to look into doing some shimming of the KTM engines. Uncle Ted managed to find some shims made for the Detroit Diesel engines (I think they were diesel injector pump shims) that fit the KTM shafts, and we began to do the shimming process to the KTM engines as well. And in our humble opinion, the process worked. It made the engines shift better and helped make the gears last longer.

   The problem came from the tolerance of the circlips on the transmission shafts. Whenever the gears had too much play, when the transmission was shifted, sometimes the dog engagement was not sufficient to help the engine stay in the selected gear. Once the tolerance was tightened up by the shims, the shifting process would work the way it was designed to.

   I still have some of the shims, but none of them are still in the packages that the originally came in. There were a number of different thicknesses available, and as I remember, they were individually packaged, with each having a size on the package.

   My guess is that if you were to find an old time Detroit Diesel mechanic and give him the sizes of the shafts, he would probably be able to steer you in the direction you needed to go in order to find the shims.

   I hope this has been of some help.

Dane

[tomale]

Dane, that is very interesting. I quess that figuring out which one needed to be shimmed would depend on which gear was having trouble ingauging..
I use to race a Maico back in the day and I went through three transmission in three races. I cost me nearly a half weeks wages to fix it each time. not my idea of fun. What I found out was that the maico transmission lived or died... literally on proper shimming. When I took the KTM apart I was amazed at how few shims it really had.
Thanks for the history lesson

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
78' 400 MC5

[Auto5guy]

Thom

I definitely remember that corner.  It was a very difficult set up to the biggest jump on the track.  If you remember I went out to that corner to see how the big dogs were taking it.  It was giving me fits too.

I've actually gotten my transmission operating much better now than it was last year.  I switched to the shorter shift lever that Al Beuhner sells.  I added some footpeg extensions to raise my foot a bit.  Those two changes helped me get more positive engagement with each shift.  

The clutch pull on my bike was atrocious.  I would end up with Popeye arms after pulling that lever for a whole race.  At the farm this summer I ran into a vintage KTM rider from California named Dennis.  He gave me some good set up tips for my clutch and now I am able to use it much more effectively through a race.

I grew up riding Japanese bikes and maybe the way they shift spoiled me.  Even my 79 Elsinore shifts like its wired directly to my brain.  Maybe my KTM engines will never shift quite as good as a Japanese bike but I'll keep trying to make them work better.

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.

[Auto5guy]

Dane

Thanks for the inside historical scoop!  [8D]

I am determined to spend some time experimenting with some different setups as I keep trying to improve my current situation.  
Do you remember if you put the shims at the end of the transmission shafts to tighten the whole cluster or did you actually separate the gears and place the shims next to the circlips that were causing the problem?

Thanks

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.

[TGTech]

Matthew,

   I don't remember if we just shimmed the gear clusters or the shafts as well. Thinking about it, I would shim wherever necessary in order to make sure that the gear's dogs engaged fully with each other.

Dane

[Big Mac]

Matt - Hope your shoulder is mending up and you'll be back on a bike soon maybe... This thread and Dane's background is good info, since I've been perplexed by the to-shim or not-to-shim question ever since I merged two bad '73 KTM 250 black engine halves into one good one, and on disassembly of each, found one had a shim on the tranny shaft opposite the clutch while the other had none. The outcome was a motor that tended to jump out of gear at times for no apparent reason.

Larry Perkins suggested I search out the shifting drum from a later motor (with grooves cut in a barrel instead of plates welded on a shaft) and shift forks from same, and to check the engagement teeth in sides of the gears to be sure there was decent back-cut in them to hold engagement while being driven. I ended up pulling the entire tranny, shift mechanism and all from a throwaway '77 motor and put it in the 73 motor in place of the 73 internals. Looked to me like the 77 had much steeper back-cut on the side teeth of the tranny gears, while the 73 gears looked like the back-cut was almost nil.

When I put it back together, I wiggled all shafts to feel for play before cinching it all down. I used the same shim that came out of that original old 73 motor to remove excess side-to-side in the shaft that takes the clutch housing, putting the shim behind the furthest right side gear (6th I believe?) on the right engine side. Shifts beautifully and feels best of all my other old bikes now. (Thanks Larry!)

I got a '77 KTM engine repair manual and learned more than what the earlier books tell you. For example, I had no idea that the oil filler cap and two other caps in the top of the cases were for inspection of gear engagement after reassembly. And the manual talks about verifying that each shift fork has slight side-to-side free play after it moves it's respective gear into place, to be sure the drum or a bent fork isn't pressing the gear in/out of it's correct place after the shift. Good stuff in the later manual. Guaranteed all 3 of my Pen/KTMs motors shift better and more sure than my CZ or Huisky ever did.  Mac