KTM down shifting issue...

[skiracer]

I'm looking for some feedback on a shifting issue with a 76 250 motor.  When downshifting from 3rd to 2nd, many times it skips second gear, and goes into the neutral between 1st and 2nd. When it does this, I never "feel" second gear as I go by it.  Upshifts are always there without any issue.  No, it isn't my lack of knowing how much pressure to apply to the shifter.  I have been shifting this bike since it was new, and I also have a 175 that works perfectly.....Any thoughts?

1976 MC 5 Original Owner
1976 Penton 175 XC

[Larry Perkins]

Dogs on those gears need undercutting and or bent shift fork in my opinion.

Larry P

[skiracer]

On the second gear? So, what is "undercutting?"  If the fork was bent, wouldn't it effect all the shifts up and down?  Thanks for the input....

quote:Originally posted by Larry Perkins

Dogs on those gears need undercutting and or bent shift fork in my opinion.

Larry P

1976 MC 5 Original Owner
1976 Penton 175 XC

[Larry Perkins]

The gear gets worn engageing on each other and if you back cut them a bit they engage well again.  Of course new ones fix it also but not always an option.  I have seen a slightly bent shift fork effect a certain change and not others.  Gary Ellis could probably shed some knowledgeable light on this problem.

Larry P

[454MRW]

I have some in NOS gears I got from Donnie Smith, if you can determine which set of gears by either part number or description and teeth count once you get it apart and determine what you need. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Penton
1976 MC5 400
1978 KTM 78 GS6 250
L78-79 MX6 175-250 KTM's
1976-78 125-400 RM's
2007 CR125R Honda
1977 MC250 Maico
2017 KTM Freeride 250R

[Rocket]

I would remove the shift shaft and check the dimension on the part that rotates the shift drum, out of spec can cause problems shifting.  If the dogs on the gears are worn, that usually makes the bike pop out of gear when it is under load.  Just another thing to check plus you don't have to split the cases to check the shift shaft.
RCG

[skiracer]

Thanks Larry!

quote:Originally posted by Larry Perkins

The gear gets worn engageing on each other and if you back cut them a bit they engage well again.  Of course new ones fix it also but not always an option.  I have seen a slightly bent shift fork effect a certain change and not others.  Gary Ellis could probably shed some knowledgeable light on this problem.

Larry P

1976 MC 5 Original Owner
1976 Penton 175 XC

[skiracer]

Thanks Mike!  It might be a while before I take it apart.....

quote:Originally posted by 454MRW

I have some in NOS gears I got from Donnie Smith, if you can determine which set of gears by either part number or description and teeth count once you get it apart and determine what you need. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Penton
1976 MC5 400
1978 KTM 78 GS6 250
L78-79 MX6 175-250 KTM's
1976-78 125-400 RM's
2007 CR125R Honda
1977 MC250 Maico
2017 KTM Freeride 250R

1976 MC 5 Original Owner
1976 Penton 175 XC

[skiracer]

It never pops out of gear.  Where do you find the specs for this?

quote:Originally posted by Rocket

I would remove the shift shaft and check the dimension on the part that rotates the shift drum, out of spec can cause problems shifting.  If the dogs on the gears are worn, that usually makes the bike pop out of gear when it is under load.  Just another thing to check plus you don't have to split the cases to check the shift shaft.
RCG

1976 MC 5 Original Owner
1976 Penton 175 XC

[JP Morgen]

The spec is usually in the owners/shop manuals. By chance is your bike a six speed? Six speed engines are partially set up to facilitate another neutral between 2nd and 3rd, as when first is removed to make it a five speed, this makes shifts up or down from 2nd to 3rd, or the reverse tend to "miss", but what they are doing is going into the neutral detent valley on the shift drum between those two gears. the fix for that phenomenon is to weld up the valley. I have raced 175, 250, and 400 six speeds and they all had this tendency before being modified. Hope that helps. In my experience a bent shift fork and worn dogs tends to make the bike jump out of gear, especially under a hard load. Merry Christmas!

[Larry Perkins]

Listen to JP he is the master!  He is a very good, mechanic, engineer, all around great guy, and hauls the mail on the bike.  Very wise and I am sure he is correct.  Will not hurt to check the specs Rod refers to while you go that direction.

Larry P

[skiracer]

Hey JP, Merry Christmas to you too!  Thanks so much for your input.  Yes, it is a six speed. It is a MC 5, but arrived with all six gears working.  As stated earlier, I don't have any issues with the bike jumping out of gear under any conditions; only missing the gear on the downshift.  I really appreciate your help!

quote:Originally posted by JP Morgen

The spec is usually in the owners/shop manuals. By chance is your bike a six speed? Six speed engines are partially set up to facilitate another neutral between 2nd and 3rd, as when first is removed to make it a five speed, this makes shifts up or down from 2nd to 3rd, or the reverse tend to "miss", but what they are doing is going into the neutral detent valley on the shift drum between those two gears. the fix for that phenomenon is to weld up the valley. I have raced 175, 250, and 400 six speeds and they all had this tendency before being modified. Hope that helps. In my experience a bent shift fork and worn dogs tends to make the bike jump out of gear, especially under a hard load. Merry Christmas!

1976 MC 5 Original Owner
1976 Penton 175 XC

[skiracer]

Larry, that is an understatement......  

quote:Originally posted by Larry Perkins

Listen to JP he is the master!  He is a very good, mechanic, engineer, all around great guy, and hauls the mail on the bike.  Very wise and I am sure he is correct.  Will not hurt to check the specs Rod refers to while you go that direction.

Larry P

1976 MC 5 Original Owner
1976 Penton 175 XC

[skiracer]

JP, I sent you an email, did you get it?  James
[email protected]

quote:Originally posted by JP Morgen

The spec is usually in the owners/shop manuals. By chance is your bike a six speed? Six speed engines are partially set up to facilitate another neutral between 2nd and 3rd, as when first is removed to make it a five speed, this makes shifts up or down from 2nd to 3rd, or the reverse tend to "miss", but what they are doing is going into the neutral detent valley on the shift drum between those two gears. the fix for that phenomenon is to weld up the valley. I have raced 175, 250, and 400 six speeds and they all had this tendency before being modified. Hope that helps. In my experience a bent shift fork and worn dogs tends to make the bike jump out of gear, especially under a hard load. Merry Christmas!

1976 MC 5 Original Owner
1976 Penton 175 XC

[Big Mac]

Big kudos and thanks to Larry P for his advice on KTM transmission fixes over the years!  My first Penton re-birth project 15+ years ago was a '73 HS that I put a year into, only to find it missed shifts horribly, popped out of gear under power at times, other gremlins.

I posted here in despair and frustration...Larry steered me to a swap of trans gears from a '77 with the undercut dogs, and a right-dimension shifting "claw" (adjusted by a squeeze in a vice) with the tips filed nice square and sharp. Unbelievable improvement!!  Became the best shifting vintage bike I ever owned!

I'm eternally grateful for the great guidance from Larry and others here over the years. All the best health and happiness in 2019!

Jon McLean
Lake Grove, OR