KTM 495 “Works” engines

[ogm]

Hello

I have a question related to the crank bearings used on KTM 495 "Works" engines. Maybe some people in this forum have seen these engines and have more information. I will keep subject focused on the crank bearings.  

These engines did not use Steyr Magneto M30 bearings. Instead, they used regular 6306/C3 ball bearings with Rotax Teflon rings. To fit  the Teflon rings, they enlarged bearing housing or bearing bore from 72mm to approximate 76.2 mm. However, not all "Works" cases had bearing bore enlarged to accept these teflon rings.
BTW: The M30 and 6306/C3 have same OD of 72mm

The following are serial numbers of  "Works" cases I have seen. Maybe someone here knows meaning of these numbers. Notice last 2 letters on first CASES SET 1. The letters were stamped in different order. It is not a typo. It may not mean anything. Maybe they made a mistake when stamping cases

CASES SET 1 Serial #: VWK-5/L      
CASES SET 2 Serial #: VKW 53L      
CASES SET 3 Serial #: VKW 9      

My question is related to the last set of cases ending with VKW 9. These sets came with standard bearing bore at 72mm. You cannot install 6306/C3 with Teflon rings. You can only install M30 or 6306/C3 without Teflon rings. Only option is to enlarge bearing bore as they did on other two set of cases to fit teflon rings.  
 
I first felt, well,  maybe they used the smaller 6206/C3 (OD=62mm) with Teflon rings. But that is not possible either. Rotax Teflon rings for the 6206/C3 bearings have a thickness of 2.5mm. It is not enough to fill gap between outer race and bearing bore. Perhaps they used a different specification of thickness for the rings. This may be another possibility. But these were big bore engines. The modality was to use bearings with  OD=72mm

Then I thought, okay so maybe they used 6306/C3 and no Teflon rings. But that is difficult to swallow. Both, outer/inner, races are press fit into bearing housing and crankshaft. This was KTM preferred method. Just imagine how hard to split cases with this option.

I ran out of ideas and said to myself. Maybe these were some of the last batch of "Works" cases produced. After all, they end with #9.  Maybe they decided not to enlarge housing anymore to accept the 6306/C3 with Teflon rings. Instead they went with Magneto M30. But here is why I think this option do not make sense either.
 
When I got these cases, the only bearings missing were the crank bearings and the small 6205 bearing used next to the primary gear. The rest of the transmission bearings, including the crank seals were installed. Yes, both oil seals were there and untouched.  I doubt anyone went through the trouble of heating these cases with a torch in order to remove the M30 outer races.  Both oil seals look perfect. Plus they usually fall out if you heat bearing bore or the rubber can gets burn very easily. I also doubt they placed the cases in oven just to remove outer races. As I said, all other bearings were installed and would have fall out. I also looked at bearing bores and they looks as smooth as silk. Another sign Teflon rings were used. I saw no scratches of metal rubbing against metal. Usually, you see some scratches from outer races or oil marks on magnesium bearing bore after removing outer races.

I think they also used Teflon rings on these cases. But I do not understand, with a 72mm bearing bore, what bearing they used or how they were able to fit the 6306/C3 with the rings. Does anybody have any more ideas?


Thanks

[dirtbike]

Or does anyone here have a name, or a contact to a works mechanic or rider back in the days that perhaps could have a clue?

[ogm]

I just spoke with a former KTM tuner in Ohio and he doesn't know
I also sent three emails to Mr Josef Hattinger at [email protected] and no response. He may no longer be in business. The web site is down and all you get is a main page with his email address. But all 3 emails I sent did not bounce back. Weird

All these "Works" parts were made in Austria and sent to Ohio for factory riders only.  I hope to find a former factory tuner via this forum that know these engines and answer to my question.

[dirtbike]

I found Kees Van Der Ven at Facebook and sent him a friend request today. He was a factory rider in the 250 class back then. Even though he might not know, maybe he can help to locate a mechanic or someone with the answer.