Mixing 78 top end with 82 bottom end

mjaw001

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Purchased a '78 xs650 with a bad bottom end.
was given a '82 donor motor with a bad top end.
I mated the good '78 top end with the '82 bottom end and did a back yard rebuild. After running the half assed rebuild for a couple weeks I decided to bite the bullet and take it in to get rebuilt properly. Spent $3000 for the full rebuild and have had to take it back 5 times because it just doesnt seem to want to run properly.

Long story short does anyone have any feedback about frankenstein motors? Is mating different year top and bottom ends ok to do, or will I be forever plagued with a cranky temperamental motor.

Would appreciate any feedback, thanks!
:banghead:
 
No those two motors shouldn't be a problem. Was it going ok before you spent the money on it and have you changed anything else, like mufflers/pipes/ jetting.
 
Sounds more like you are stuck with a cranky temperamental rebuilder....

Would you give us some more detail of the issues?


Skulls right 78head-82 lower should be bolt and go.
 
More details needed. I mix and match entire buckets of XS650 parts to create great running engines all the time... Something is amiss...
 
From 74 up all the engines used the same cases, heads, cranks, cams. Some of the Europen bikes had different rods and pistons. As long as you keep them straight you won't have any problems buillding engines out of many year parts.
The only thing to watch for is the cases, they are machined as matched sets. The heads and rocker boxes are sets too. THey have matching numbers stamped in them. Cases behind the clutch, heads between the exhaust ports.
Leo
 
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