74 - 77 Engine/Frame Fit

[vmx1963]

G'day all, does anyone know the inter-changeability (how's that for some good Aussie english!) of engines & frames from 1974 through to 1978 (pre-MC80).  For example, would a 77 or 78 engine fit in a 1974 frame?  I'm still trying to build a Maico-beating 400

Cheers lads,

VMX1963
Western Australia
//www.vmxktm.net

[Larry Perkins]

Yes, the 1977 and 1978 motors will fit in the 1974 chassis.  In fact from 1972 to 1978 all KTM motors and chassis will interchange as far as bolting up.  There are other obstacles with some interchanges like swapping exhaust manifolds or a different style motor brace/strut but all can be done.  Hope this helps.  

If you want the best turning-lightest 400 Penton and don't mind some work here is the Hot set-up.  Start with a 1972 175 frame and swingarm.  Use a 35mm Ceriani frontend like the bigger Pentons had.  Have a gussett added to the lower head tube like a 75 frame has.  Use a 1976-1979 400cc KTM motor preferably the 76 or 77 they don't have the blunt transfer ports.  You will have to change out or make different motor brace/struts and change the exhaust manifold to the 74 or 75 one or change to a 76-77 MC5 pipe and change the mounting brackets.  The MC5 pipe is better.  You will also have to modify the brake mechanism on the chassis to be like the 74 or 75 style.  Then you can use the conical rear wheel which the 72 175 did not use.

That will give you a 7-8 pound lighter 400 than if it was the high breather frame and multi-shock position chassis.  If you really want it to bark match and polish the exhaust and trasnsfer ports, match and rough up the intake port, run a PVL ignition with only the rotor, find a GEM reed set-up, and run a 40mm Mikuni or a 38mm Bing.

Do that and you will eat Maicos for Breakfast.

Larry P

[vmx1963]

Thanks for the tips Larry, never stretched the thinking to using a 175 frame!  All I need to do now is hunt down a 400 engine.

VMX1963
Western Australia
//www.vmxktm.net

[Dennis Jones]

Wow! Larry that sounds like a cool bike. I hope somebody builds one just like it.A small alloy mx tank would really top it off.

Dennis Jones

[Mike Lenz]

Larry, Ive been thinking about building a 250 like that for a while. I somehow got ahold of a frame that takes the longer seat and conical rear wheel, but other than that is exactly the same as the 73 175 frame?? It has NO frame numbers and I thought it was an experimental frame or something but someone told me in 76 he thought they made a 125 enduro with that type of frame. It didnt have a swingarm so that makes it harder to figure out. I will prob use the 73 250 swingarm with the needle bearings. Have you seen anyone who did this?

 One other thing on engine swapping. If putting a pre mc-5 engine in a mc-5 or gs-6 frame dont forget to grind clearance on the engine for the swingarm on the left side! However dont grind one bit more than you have to. They were known to crack there on mc-5's.

[vmx1963]

G'day again fellas, I'm slowly sourcing bits for the 400 and wondering about exhaust pipe availability for fitting a 74 400 engine into a high-breather frame.  This will sound like a dumb question, but do the post 1975 MC 400 exhaust pipes fit the high-breather frames at all?  



VMX1963
Western Australia
//www.vmxktm.net

[James]

I had a 250 with the 72 175 frame and MC5 swingarm-I did not know what it was. It was light but I thought it handled much better in the high breather (74-75) heavier frame. James

7" and 4" travel? Hmm-that makes 11" Hey! I can live with that.

[Mike Lenz]

I run a 76/77 style mc-5 pipe on my 400 frame breather and boy does it ever make it run better than the oem pipe. It was an easy fit. Just made a bracket to come down from the frame gusset for the front mount. Had to redo the two rear mounts, and its a tighter fit (fatter), but very doable and worth it.  I've also seen the snake pipes on them, but I wanted to keep mine looking vintage.

[tlanders]

Hey guys,

I am currently building the above mentioned rocket. I am using a 1971 low breather frame, have welded a brake pedal support tube on the right side so I can use the conical rear hub. Also welded in a number of other braces and then powder coated the frame. Using sun rims, PVL ignition with flywheel weight to begin with, 38MM Mikuni bored to 39.5MM, J.P. Morgen ported and reed valved 400 engine, Renthal bars, extra high (1.5" higher than the tall seat) long seat, Ohlins shocks, Neeley fork bottles, heavier fork springs (28 #/in instead of 22#/in), Ferodo brake shoes, Magura 314 throttle, spring return foot pegs and a 420 snake pipe. The pipe may not be right for the engine but it's worth a try and I made it fit. I think this thing is going to be so fierce that I won't notice whether the pipe is right or not!!! I am also thinking about putting an MC80 aluminum swing arm on it. This would make the wheelbase about an inch longer to help with the wheelies, and it would be lighter and stiffer than stock. Spencer Ballentine is using an aluminum fabricated swing arm on the 250 Hare Scrambler that he races and he convinced me that it was worth the effort. He also is using the Neeley fork bottles. Now I just wish I knew how to race, this machine will be wasted on me. I am hoping that brute power will make up for my lack of riding skill. Hopefully I will have it finished in time for Diamond Don's.

Teddy

[Mike Lenz]

Glad to see your not going overboard on this project.

[tlanders]

Yeah, just your run of the mill Penton restoration project. It won't look half as good as Kip Kern's worst project. Oh, I forgot to mention.............

Teddy