Xs 650 engine serial number issue

WestonHeath02

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So I bought a 1979 Yamaha xs650 I was ordering parts for it and attempted to install them but the 1979 parts where not correct from what I read on here the frame serial and engine serial should start the same mine are different and I havnt been able to find anything related to this serial number 2fo-212558. Some help identifying the year would be greatly appreciated. Thank you.
 
These bikes are a lot like Lego's. Most parts fit most bikes. It's not surprising your engine and frame numbers don't match. Often if an engine goes bad, people just swap in a known good engine instead of rebuilding what they have.
There are lists on here in the TECH section that tells what years the numbers are from. The frame number is for the bike. The engine number is for the engine. Look on the list for your engine number and it will tell you what year bike your engine came out of.
79 still used the points and advancer. 80 up used the TCI. If your engine is from a later bike the PO may have used the TCI. If you bought ignition parts thinking you had points, they won't be needed with the TCI.
I don't recall other engine changes between the 79 and 80 up engines. About the only thing that comes to mind is the cam chain adjusters. They changed 4 or 5 times over the years just not sure if the changed for 80.
What parts did you buy that don't fit?
 
Engine # on front of crankcase?
1684618216702.png

Pics of the frame, especially the swingarm & passenger peg area, and wheels may help identify that too.
 
I just wrote a full description of the differences between 79 and 80.
Lost it so not redoing it as there are so many differences.

Have a look through the link JP posted.

Ned a full set of pics of the bike. Charging system, under both sides of the side overs, battery box.
 
The full engine number is the 2fo-212558. The frame has been chopped so I don’t have any pictures of the swing arm or the battery box. But I have these tell me if I need more or more specific ones.
 

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Engine # on front of crankcase?
View attachment 243296
Pics of the frame, especially the swingarm & passenger peg area, and wheels may help identify that too.
The full engine number is the 2fo-212558. The frame has been chopped so I don’t have any pictures of the swing arm or the battery box. But I have these tell me if I need more or more specific ones.
 
Ah, so it's the frame number that's missing. There's been a lot of modification done to the steering neck area in addition to the hardtail and I can't quite tell what it's origin may have been. There are for sure parts of an XS frame there, I suspect that the tubes have been changed enough that no stock motor mount (top) will fit - you'll have to fab one if you want to run one.

The motor # does jive with an '80 model Special, but someone has switched it back to points from an earlier model - no worries. The rear brake backing plate appears to be mid '70's standard XS, but it's mounted much differently than designed (brake pivot would normally be ~9:00 and the lever pointing downward).

Ya gots some fabrication in your future;)
 
Ah, so it's the frame number that's missing. There's been a lot of modification done to the steering neck area in addition to the hardtail and I can't quite tell what it's origin may have been. There are for sure parts of an XS frame there, I suspect that the tubes have been changed enough that no stock motor mount (top) will fit - you'll have to fab one if you want to run one.

The motor # does jive with an '80 model Special, but someone has switched it back to points from an earlier model - no worries. The rear brake backing plate appears to be mid '70's standard XS, but it's mounted much differently than designed (brake pivot would normally be ~9:00 and the lever pointing downward).

Ya gots some fabrication in your future;)
That you so much, that is very appreciated. That actually helps me a lot
 
That means the frame is (was) a '79SF....Special.
 
If I don’t run a top motor mount would that effect the way it runs/rides at all?
That steering head has no gusseting that I can see. It's gonna be a wobbly goblin with or without the top mount. :sneaky:
 
That's up to you. I would, but that's just me. Have a look at some pics of other front ends. Over 99% have gussets up there. There's a reason for that....
 
So I need add some extra support between the fuel tank and front of the frame?
Yep, something like this
1684642223432.png

I'll link a couple of popular suppliers for your parts & fabrication needs
https://tcbros.com/collections/metric-frames
https://www.hughshandbuilt.com/shop/page/3/

But, you're still gonna have fab work. For instance, your front downtubes have been "goosenecked" (they curve forward @ the neck) and the off the shelf gussets at the above suppliers are made for straight tubes. So, you're gonna have to trim and modify them to work
 
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