75 xs650b resto/mod

Tmills

XS650 Member
Messages
12
Reaction score
43
Points
13
Location
Mississippi
IMG_5122.jpeg
So, long story short my dad has been hauling around this 650 in parts for 30 years. Mostly it sat stagnant in his airplane hangars. We both recently moved to Mississippi and I have decide to bring it back to life. I mentioned in another post that I’m not new to bikes or wrenching on them (used to race them) but admittedly I have never done a full engine rebuild. I accept any advice/feedback/comments/whatever from the vast experience on this forum! And I am so excited to do this..

That being said, I got the frame powder coated and yanked the motor. Split everything down and now it’s time for reassembly. I’m trying to clean/replace parts as I go. I think I need new valves but what to y’all think? All 4 are still in spec as well as the springs. Maybe just some lapping? Thanks in advance and I’m glad I found this forum!!!
 

Attachments

  • IMG_5123.jpeg
    IMG_5123.jpeg
    548.6 KB · Views: 64
  • IMG_5125.jpeg
    IMG_5125.jpeg
    514.9 KB · Views: 53
  • IMG_5158.jpeg
    IMG_5158.jpeg
    501.9 KB · Views: 58
  • IMG_5383.jpeg
    IMG_5383.jpeg
    495.2 KB · Views: 60
  • IMG_5385.jpeg
    IMG_5385.jpeg
    487.6 KB · Views: 58
  • IMG_5382.jpeg
    IMG_5382.jpeg
    491.5 KB · Views: 63
  • IMG_5384.jpeg
    IMG_5384.jpeg
    464.9 KB · Views: 69
  • IMG_5791.jpeg
    IMG_5791.jpeg
    462.6 KB · Views: 65
  • IMG_5792.jpeg
    IMG_5792.jpeg
    602.9 KB · Views: 61
  • IMG_5795.jpeg
    IMG_5795.jpeg
    523.7 KB · Views: 60
View attachment 254886So, long story short my dad has been hauling around this 650 in parts for 30 years. Mostly it sat stagnant in his airplane hangars. We both recently moved to Mississippi and I have decide to bring it back to life. I mentioned in another post that I’m not new to bikes or wrenching on them (used to race them) but admittedly I have never done a full engine rebuild. I accept any advice/feedback/comments/whatever from the vast experience on this forum! And I am so excited to do this..

That being said, I got the frame powder coated and yanked the motor. Split everything down and now it’s time for reassembly. I’m trying to clean/replace parts as I go. I think I need new valves but what to y’all think? All 4 are still in spec as well as the springs. Maybe just some lapping? Thanks in advance and I’m glad I found this forum!!!
Following.
Get familiar with the Tech section. A lot of good info there.

https://www.xs650.com/pages/tech/
 
Yamaha Race mechanics were instructed to put a slot on the top of the barrel studs. This way the studs could be removed with a screw driver and top end maintenance and repairs could be performed with the engine in the frame.
 
The valves are probably fine. I test them for leaks, then disassemble and hand lap until the pits are gone. Reassemble and test for leaks again. Once disassembled, check each valve for a nice sliding fit in it's guide (no side-to-side wiggle). The valves are hardened steel so once out, you can safely wire wheel them to clean the carbon off. Here's a couple "before and after" shots .....

ExValveBacks.jpg


ExValveFronts.jpg
 
Last edited:
Man, that is exactly what I needed to know. Thank you 5twins!
Also, only has 13k original miles with 2 keys…
I’m debating on trying to figure out the old electronics (never been my strong suit) or buying all new and doing the pma so I don’t have a battery? Is that right? I’ve just hit the tech section and can’t wait to dive more into it
 

Attachments

  • IMG_5796.jpeg
    IMG_5796.jpeg
    404.2 KB · Views: 30
My tuppence worth. With an old bike, probably any old vehicle, most reliability issues are electrical so you're quite right to focus there. Could go down the PMA route as you're thinking. But there's probably no need to junk the original alternator/ignition and good reasons not to.

Why not buy a harness and fully rewire the bike? Or do what I've now done on three bikes (1970 Triumph, 1978 XS650, 2002 RE Bullet), rewire the bike yourself to a simplified bum-basics system - generator, ignition, lights, horn. That way, you end with a system that's as good as your own QC plus you know what goes where.

A few years ago, I knew next to nothing about bike electrics but getting stuck in has taught me enough to have reliable old motorbikes.
 
My tuppence worth. With an old bike, probably any old vehicle, most reliability issues are electrical so you're quite right to focus there. Could go down the PMA route as you're thinking. But there's probably no need to junk the original alternator/ignition and good reasons not to.

Why not buy a harness and fully rewire the bike? Or do what I've now done on three bikes (1970 Triumph, 1978 XS650, 2002 RE Bullet), rewire the bike yourself to a simplified bum-basics system - generator, ignition, lights, horn. That way, you end with a system that's as good as your own QC plus you know what goes where.

A few years ago, I knew next to nothing about bike electrics but getting stuck in has taught me enough to have reliable old motorbikes.
I’m in the stock alternator isn’t broken camp. I’m experienced and far more confident in the stock alternator than I could ever be with any aftermarket one. The rotor needs to be a rewind at this point and serviceable brushes. Good to the end of the Earth.
 
That’s great advice, thanks everyone! Thank you for the offer halftime but the one I have is in good condition.

So happy I didn’t have to buy new valves and just finished cleaning 3 of them. They look so much better to me and I’m looking forward to getting this engine back together.
 

Attachments

  • IMG_5809.jpeg
    IMG_5809.jpeg
    449.6 KB · Views: 37
  • IMG_5810.jpeg
    IMG_5810.jpeg
    253.3 KB · Views: 39
  • IMG_5811.jpeg
    IMG_5811.jpeg
    248.5 KB · Views: 43
You'll still want to hand lap them into the seats to insure they seal up. Your intakes look pretty good but there may be some pitting on the exhausts. That's where it happens 1st because they run hotter. Eventually the intakes do it as well and eventually you get so much pitting they start to leak. Here's a valve and valve seat lapped ......

IntValveLapped.jpg


IntSeatLapped.jpg
 
Nice..yea I plan to lap them tonight after the kids go to bed. Saw a few videos and it doesn’t look too bad…
Well, like 5twins pointed out, it looks like there's pits in the exhaust valve face. The easiest way I've found to make sure the pits are gone is to run a black or blue sharpie line across the pits. As you start lapping, you'll see the grey ring form... and little black dots where the pit are. When you get a solid grey ring with no black dots in it, you're golden.
Sometimes the lapping compound will wash out the sharpie. Just clean the face with some solvent and reapply it. I'll do that on the last few turns just to make sure.

Edit: Ideally you'd use prussian blue or some other machinist' dye. Most people don't have that on hand. A permanent sharpie makes a good cheap alternative for small jobs.
 
Last edited:
I've never needed to use any dye or a marker, the pits just seem to naturally show up as black dots or specs. Here's some seats compared. the intake is good, all gray, but the exhaust still shows black specs so is in need of some more lapping .....

LapsCompared.jpg
 
Well, after 6 laps? Is that right? Whatever…I had to do the intakes twice, I am happy to report no leaks. Time to move on!! Thank you gentlemen..
 

Attachments

  • IMG_5815.jpeg
    IMG_5815.jpeg
    339.9 KB · Views: 35
  • IMG_5816.jpeg
    IMG_5816.jpeg
    318.8 KB · Views: 38
  • IMG_5813.jpeg
    IMG_5813.jpeg
    411.1 KB · Views: 38
  • IMG_5817.jpeg
    IMG_5817.jpeg
    266 KB · Views: 34
  • IMG_5818.jpeg
    IMG_5818.jpeg
    475.8 KB · Views: 34
Back
Top