75 xs650b resto/mod

[Tmills]

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!!!

 

[Kevin Werner]

Good, you heeded the advice of "we like pics". I haven't done it myself but most here who have reassembled a 650 have steered clear of a particular base gasket that seem to creep out.

 

[Jim]

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/

 

[Jim]

most here who have reassembled a 650 have steered clear of a particular base gasket that seem to creep out.

The green Athena gaskets. They suck.

 

[Kevin Werner]

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.

 

[5twins]

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 .....

 

[Tmills]

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

 

[Raymond]

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.

 

[halfmile]

A week ago I bought a 1975 XS650 donor bike that I`m going to part out. It has a main wiring harness that has never been altered if you need one.

 

[jetmechmarty]

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.

 

[5twins]

Yes, the stock system is a very good one. It's a 3-phase alternator modeled after what most cars use, so it works very well and is quite reliable. And as a bonus, since it is an automotive style system, we can use low cost automotive regulators should we need a replacement.

 

[Tmills]

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.

 

[5twins]

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 ......

 

[Tmills]

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…

 

[Jim]

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.

 

[5twins]

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 .....

 

[Tmills]

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..

 

[Kevin Werner]

All valves bleed off pressure (leak?), it is just a question of how fast it happens...