Engine for a '74 250GS/ Parts Interchange

[Daniel P. McEntee]

I'm in the planning stages for building up a 250GS from a frame and some parts I have for a '74 250, frame # 54-40775302. I've posted this frame number before incorrectly. The numbers are hard to read, and they used a different number 4 stamp for the two locations in the number. At first I thought it was just a forward slash, but I took a rubbing with a thick lead carpenter's pencil and a piece of paper and it comes through much more legible.So I'm sure of the frame number and model year now.
  I have been looking around the internet and see all sorts of different parts available individually. I'm thinking if i can get organized and be sure of what year parts I want/need I can piece together an engine. I've been researching my parts books for part numbers, and did a search on here a couple of times and picked up some information.
   So my question is, what is the range of model year 250 engine that I need to look for? Will late 70's KTM engine parts work with earlier 70's KTM Penton engine parts?? I have a '74 400 engine, #4-5501123 that I think the tranny is good on, but the top end may be toast. if I can find a good set of center cases, a crank rod assembly, and top end, can I use the tranny guts from the 400? I have a line on an almost complete '78 KTM 250GS top end. Would this work with earlier KTM engine parts? There does seem to be some stuff to be had out there, just want to spend my money in the right places with out accumulating more stuff I don't need or can't use. I'm running out of room!
   Thanks a lot in advance,
   Dan McEntee

[brian kirby]

250 engines up through '79 are basically all the same, and most of the engine is same as the 400.

Brian

[Daniel P. McEntee]

Hi Brian;
    And that would include kick start shafts and shift shafts? Pretty much everything but crank, rod and top end on the 400? Got to meet Mike Winters yesterday and talked to him again tonight and he mentioned making sure bypass port opening match up with later model cylinders. Doing this long distance with sellers and not being able to view stuff in person before handing over money is a lot less desirable than dealing in person, but there doesn't seem to be much available in the St. Louis area.
   Thanks a lot,
   Dan McEntee

[chicagojerry]

shift shaft and kicker shaft are the same.    chi jer

[G Ellis]

Dan give me a call I can help you. 217 260 0237 later Gary

[ALB]

The first 1973 black engine 250's are different. They used a shifting cam and the kick start shafts were 14mm. So, any 250 engine from 1974+ would be identical in the bottom end and would work for you. These bottom ends use a shifting drum and have a 17mm kick start shaft. All the 250 top ends are interchangeable. There could be some slight changes in porting between say a 1973 vs 1977.


Alan Buehner

[454MRW]

78-Early 1980 top ends are not directly interchangeable with the 73-77 bottom ends, due to the transfer port shape, which is drastically different than the 73-77 models. They are larger more squared off with a larger separation between the transfer ports. The bottom transfer area can be port matched to work with the later top end, but requires complete dissasembly of the bottom end to do the grinding necessary, otherwise a severe port mis-match would be detrimental to performance. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S
1975 Can Am 175 TNT & 77 250 Black Widow
1979 Husqvarna OR390
1976-78 RM & 77-79 PE Suzuki's
1974 CR250M 07 CR125R 79 CR250R