73 vs. 74 Hare Scrambler frame

[rob w]

If I could get some help me with this, that would be great.
 
I have'nt got my 250 parts manual yet. I am wondering if a "73" frame and swingarm are the same as a "74" for the Hare Scrambler?

Are all displacements of KTM motors interchangable to each of their frames?

Up to what year would the motor mounting be the same for the 400?

I found a nice "73" 250 frame & swingarm, I'll probably decide I don't need it. Does anyone else need it more than me. He wants $100 + shipping.

Thanks very much for your help, Rob

 

[mosesnra]

rob if you got some pictures of the frame i can compare to mine and maybe measure the engine mounts across where the bolts go thru
also and ill post them here i dont have a digital camera yet. but thats in the works.
i got the 73 frame. i found a crack in the swingarm frame of mine but it can be welded.
 my idea was if somebody had the frame tabs for the pentons that could be bought and welded into place. if you dont take the frame i might be interested in it. i found a 74 engine running and i may want to build another bike for the kids to race.

dean    [email protected]

[mosesnra]

these are all outside measurements
 front motor mount is 5 and a half inches
 bottom middle mount 5 inches
 back motor mount 9 and a half inches
 swingarm front across hing point of attachment to frame 8 inches
 swingarm length 21 inches
 swingarm across the back axle moounts 9 and
  thre quarter inches. hope it helps i got a 73 manual if you need some pics or the whole thing let me know.

dean    [email protected]

[Larry Perkins]

Rob,

The 73 and early 74 250 Penton/KTM frames were the same.  They were high breather and there were three holes in swingarm for minor shock position changes.  In about April 74 the 250 frames went to the multi-position frame and swingarm.  You could have shocks in normal, forward mounted, or laydown positions.  All KTM motors from 1972 to 1978 will fit in all frames to the best of my knowledge.  Lightest weight set-up for a Vintage 250 Penton is to use a non hi-breather frame from a 72 or 73 175 and put the 250 motor in it.  You will save 3-5 pounds depending on if you are comparing against normal or multi-position frame and swingarm.  Of course most of us could skip a few meals and do the same but that is not as trick.

 

[rob w]

Thanks Larry, and Dean (you went through too much to help, thanks). These were my thoughts, I want to build a dirt track (1/2 mile) bike, starting with a 73-74 frame, and using the largest displacement KTM motor that will bolt up without changing the mounts too much.
So then in "78" was the big bore KTM a 420?
Was the 495 motor air cooled, no reed valve?
Thanks once again for any input on this matter.
Dean, what frame parts or brackets are you needing?
Rob.

 

[Larry Perkins]

Rob,

In 78 the 400 was still it.  The original 420 and 495 bikes were aircooled and no reed.  They are both a bit tough to find pistons for.  The 495 was scary fast.  You should get some pics of the flat track Pentons that were Kenny Roberts designed that would help.  I think kflash who has Penton stuff has one though I know that Kirk Sessions was trying to buy it.

 

[Mike Lenz]

If you wind up using the 400 moter you could port it along the lines of the Carl Cranke 250 porting. WE did this to a moter in 76 and it was VERY fast [and very pipey]. However it did blow to pieces after about six races. The rod let go and went through the bottom of the cases and smashed the piston into about 50 pieces! But it sure was fun while it lasted! If going this route you would have to check the rod play oftin to avoid a let go.