Replace entire engine or just transmission?

Recently purchased 1981 KZ750 with 77,000 miles on it that leaks engine oil. At the same time I also bought another KZ750 same year model etc- but it was in poor cosmetic condition and was missing some parts (The missing parts are mostly on the bike that has 77k on it). The other KZ750 only has 8,500 miles on that engine.

At first I had the idea of replacing the compelte engine/motor on the 77k bike with the engine of the 8.5k bike. (I have to check the compression of the 8.5k bike first).

Now I am wondering if I should just replace the transmission of the 77k mi bike???

Obviously if I just replaced the transmission I would have to fix the oil leaks by replacing all seals and gaskets. I want to make the nicer looking bike last longer.

Thanks!

Just pick the best frame of the two and assemble all the best parts of the two bikes on that frame.

If I was going to open up a 77,000 mile 750 motor, I wouldn't put it back together again without a complete rebuild.

There's just not enough likely lifetime left on a 77k mile 750 four to justify doing anything less.

Cool Thanks! Then I will go woth my original plan. The 77k mi bike has most of the best parts on it already but it is the engine that is the killer there. So I will swap the two engines and go from there.

The only thing that I could really want off of the other bike is the 4 into 1 headers and muffler.

I like the look of the KZ750 and would like to have the finsihed project running for years and years to come. Any other advice or imput is always welcome!

replace the steering head, wheel and swingarm bearings/bushings, old bikes get worn out in other areas too, but these specific areas can KILL YOU, bad bushings and bearing may lead to speed wobble and these old kaws are known for it, at most you'll spend 120$ on all of them but is being cheap worth risking your life?

i ubgraded the steering head bearing and replaced the front wheel bearings on my 82 1000 and it only has 35k on it.

check your tires too, old flat style ones are known to wobble too.

Thanks machine

I dont mind spending a few extra bucks to make the biker safer to ride. Thanks for the suggestions