MC5 250 or 400?

[Tahitian_Red]

If I restore my 1976 MC5 could I build two motors (250 and 400) and basically have a bike that can run both 250 class and Open class by simply swapping engines?  Are there many diffrences in the frames and other items?

Racing the "FaltaNator" in 2010

[454MRW]

No differences that I am aware of, other than maybe needing a little stiffer suspension with the heavier engine and the 400 has a longer silencer attached slightly farther forward to the end of the pipe. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S

[tomale]

Yes, Michael is right, It would be possible to swap motors and pipe and of course different carb as well.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)74'
250 hare scrambler (project bike)

[joe novak]

I am not KTM familiar, but I was told that any KTM engine will fit in any 1972 through 1982 chassis.   Spacers may be needed.  Please confirm this info.

[454MRW]

72-73 KTM engines have a slight difference and were the first production KTM engines,(175 in 72 and 250 in 73), but may fit the chassis as well, and then up to early 1980 should also fit, but in mid 1980 the engines were redesigned with one rear engine mount bolt that shared the swingarm pivot and those require the correct designed frame to mount. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S

[garrettccovington]

GREAT question!  I often wondered about this. I have never seen 2 early KTM's at the same time to compare.  Now if I can only get my 250 motor in my 6-Day.

G

72 six-day

[brian kirby]

G, the '72 Jackpiner is in a modified Sachs frame, it is the hot setup for building a minimal weight KTM engine bike.

Brian

'72 Berkshire

[garrettccovington]

Dang it, My 250 is here with me in Chino Hills and 6-day is up in Barstow. otherwise, I'd be taking measurements right now.  Maybe I'll Call up Generation cycle and see if they have any old CMF frames laying around.

G

72 six-day

[Mike Lenz]

In an MC-5 with no bottom engine mount bolts I would not advise running anything with the old left engine strut mount.  Stick with 76-80 250's and 76-79 400's, although I feel the longer stroke 76/77 400 motors run a little better.

[tomale]

Mike, my 76 mc5 250 has a bottom motor mount....

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)74'
250 hare scrambler (project bike)

[Mike Lenz]

Might be ok then for the older engines but you never know about how a given frame flexes.