75 to 78 engine swap

[Shovel Jockey]

The engine in my 78 went south big time and will require major surgery and I don't have the money. I have a 75 engine sitting in a frame in the shop; do you guys know if these two motors will interchange without too much trouble?

 

[nj1639]

Should be a piece of cake swap.

 

[Shovel Jockey]

Would there be any problem using the early 78 carbs with the 75 engine?

 

[nj1639]

No problem at all.
You could swap over everything, stator, rotor, carbs, points setup and all or just the basics to get her going and then see how she works.

 

[Shovel Jockey]

Thanks for the input; I'll keep ya posted

 

[5twins]

The late linked carb set may have clearance issues with the older, physically larger type C cam chain tensioner on the '75 motor. If so, just swap the type D assembly from the '78 motor onto it. If you haven't done so, it's a good idea to upgrade the D type tensioner to an E type w/ lock nut.

 

[Shovel Jockey]

Thanks 5T; did the D to E upgrade already on the 78 engine. Didn't know the C would interchange with the E as well

 

[5twins]

You'll need to swap the complete assembly, housing and all. Note the angle on the plunger/adjusting screw mount on the later D and E units. They are mounted lower on the housing but angle up most likely so they contact the tensioner in the same spot. The lower mounting point was probably also done for carb clearance.

 

[Shovel Jockey]

Followed my Clymer manual on engine removal and got it all the way down to the bottom engine bolt; They say nothing about removing the starter but it looks like the right thing to do; is that ya'lls experience?

 

[nj1639]

Is this just to get the engine out of the frame?

Leave the starter be, no need to remove it unless its broke or you're going starter less with some kind of a replacement plug, and even then it's easier to do that after the engine is out of the frame if you're going to remove the engine anyway.

Do unhook the power cable going to the starter....either at the starter or at the solenoid.

As far as top end work goes, the starter can still remain in situ.

 

[5twins]

No need to remove the starter. I put a small jack under the engine to support it and lift it slightly. Then that last long bottom bolt will slide right out.

 

[Shovel Jockey]

Got em swapped! Wasn't as much trouble as I thought. Using the early 78 carbs and starter and E type cam chain tensioner; (thanks5t you were right on the linked carb clearance) after I scrubbed her down the old 75 motor looks pretty good. Going to check timing chain,valves,points,timing and clutch free play then I'm going to oil her up and see if she'll run; it's been over three years.

 

[Shovel Jockey]

If anyone's interested, the swapped engine out of the 75 started on the first kick! Not bad for sitting for 3 years and having no history with it. Adjusted the cam chain, set the valves, gapped the points and set the timing first. none of that was off by much but I wanted to start off right. So far no oil leaks or obvious glitches except a light rattling on start up around the cam chain area. It actually seems to run a bit smoother than the original 78 engine. Plus the tranny shifts fine and the clutch feels smooth. Are there many internal differences between the 75 and early 78 engines? I noticed the valve settings are different.

 

[Shovel Jockey]

A leak has shown up on the tachometer drive, looked in the Clymer and only found the exploded view, not sure what the fix is. Any suggestions?

 

[TwoManyXS1Bs]

...Are there many internal differences between the 75 and early 78 engines?

I think the only things of significance are the starter gear dragclip and the changes to the splines of the tranny shafts and gears. Dig thru this for more detail:

http://www.xs650.com/forum/showthread.php?t=36766

 

[5twins]

There's a small oil seal (#3) and an o-ring (#2) on the tach drive assembly that seal it into the case. Try replacing the o-ring 1st .....