250 engines

[metalkfab]

What is the difference between a '75 250 engine and a '76 250 MC-5 engine ?

[rob w]

Karl, Karl, Karl! You had one of the sweetest looking Pentons at the reunion. Along with Mike O'Reily's 73-250, and of course Paul, Doug, and Jack's bikes were so nice! We need to get some pics of those up on the site some day.

One difference between the motor's are the intake manifolds. The "75" is at 90 degrees, and the "76" angles to the right side.

I'm going to try to make it to the Dec. meeting, maybe I'll see you there for once.

Bob

 

[metalkfab]

Thanks Rob,As for these 250 motors I have,I was wondering about anything else.As in trans,power,anything.I'm thinking of going to Monster Mountain in Nov. and race a Post-Vintage 250 class and was thinking of putting in my MC-5 a '75 250 engine.See you soon.

[rob w]

And, you'll have to use a different motor to frame strut on the left side, the 76 had the mounting boss atop the center cases, where the 75 is a stud down abit lower.
 Not sure if the exhaust manifold angle is different also, could be?, can't say, maybe not?


 

[Big Mac]

The exhaust manifold is the same thru '76, with possible exception of 2 spring hooks on earlier vs. just one. I think '74 and on had just one. I just went through a '74 250 engine followed by a '76 engine and could find almost zero difference. The intake manifold angled and diameter at carb mount was different ('76 was same inside diameter, thicker wall for larger carb i.d?). Windows on porting looked like maybe very slight changes. The '76 has a conical housing w/ 6 tiny ball bearings on the actuator side of the clutch, while '74 still had raw shaft on either end. The '76 also had different size/spacing on teeth between pinion gear and clutch gear and heavier/better shift drum which seems to make better shifting. Not sure if '75 has the old or new shift drum. '76 also has the newfangled heavier clutch actuator arm mechanism with one-piece case protector from thrown chain. I'm using a pipe off a '73-'74 instead of the later '76 (engine is in a '73 frame) and so far not a lot of performance difference I can tell. Shifting definitely better and no clutch drag, although that might just be bad alignment on the older one.

 

[imported_n/a]

Karl,

I bought an NOS cylinder from Jake Fischer for a restoration on a '74 250 engine.  The early 250 cylinders did not have the cast-in provision for the compression release (or whatever it was) whereas I have a later '75 engine that has the 250 cylinder with the compression release design, like the 400 cylinders.

Glenn