Is this a 78 or 72?

[spacejockey4]

Hello all,

Picked up an abandoned project to tear down and rebuild. Title and owner say its a 1978. Once i got home and started tearing it down I noticed the serial number on the engine starts with a GS (see attached). According to the ID chart on this site, it says 1972? Am I reading that right?

Also, anyone know what ignition this is? (see attached) The grey wire goes to a blue box with a washed out label.

 

[5twins]

Oh my, that may be one of the rare factory 750 motors (only 200 made) put out in '72 to qualify it for "production" racing. We'll need to see full engine shots to verify the year, things like the cam chain tensioner in particular.

 

[Mailman]

From our tech section,

https://www.xs650.com/threads/xs650...workshop-manuals-and-other-information.30569/

 

[spacejockey4]

I was reading that but im confused because the

Oh my, that may be one of the rare factory 750 motors (only 200 made) put out in '72 to qualify it for "production" racing. We'll need to see full engine shots to verify the year, things like the cam chain tensioner in particular.

See attached pics of the tensioner. I was reading that too but confused because the cylinder is stamped 653cc..?

 

[magoo66]

Hello all,

Picked up an abandoned project to tear down and rebuild. Title and owner say its a 1978. Once i got home and started tearing it down I noticed the serial number on the engine starts with a GS (see attached). According to the ID chart on this site, it says 1972? Am I reading that right?

Also, anyone know what ignition this is? (see attached) The grey wire goes to a blue box with a washed out label.

Oh WOW!You got the goods there my friend.

 

[magoo66]

I was reading that but im confused because the

See attached pics of the tensioner. I was reading that too but confused because the cylinder is stamped 653cc..?

Head must a been changed somewhere in its life but those numbers on lower,well——-Don’t look fake.What a score.

 

[GLJ]

Cylinders have been changed. Be interesting to see what it has for rods in it.

 

[Jim]

What's the VIN on the frame?

 

[5twins]

Yes, it appears the cylinders have been changed back to 650 ones. The cam chain adjuster may be mid '71 all the way up to '75, but it has the wrong cap nut on it .....

 

[spacejockey4]

Cylinders have been changed. Be interesting to see what it has for rods in it.

Yes, it appears the cylinders have been changed back to 650 ones. The cam chain adjuster may be mid '71 all the way up to '75, but it has the wrong cap nut on it .....

View attachment 261490

Damn that sucks, but thanks for info.

 

[Jan_P]

Damn that sucks, but thanks for info.

Not so fast here If a factory has a Tool setup and Die cast that says 653 and want to make a few hundred 750 .They are not interested in filing in that
Mold As a thumb rule -- Expensive tools and if it goes wrong ..Huge economic damage And how do you get it back

If You ask Me the Jury is still out Thinking it over May well be that a change has happened . But also as mentioned above
Big factories dont mess with production tools for a few hundred special motors and don't manufacture new tool for a few hundred

And changing a cam Tensioner is not strange either in these days for any motor

 

[Jim]

Not so fast here If a factory has a Tool setup and Die cast that says 653 and want to make a few hundred 750 .They are not interested in filing in that
Mold As a thumb rule -- Expensive tools and if it goes wrong ..Huge economic damage And how do you get it back

If I recall correctly, they ground the 650 off and stamped the 750 (753??)
And if that's the case, it could easily be done to another set of jugs.

 

[spacejockey4]

Not so fast here If a factory has a Tool setup and Die cast that says 653 and want to make a few hundred 750 .They are not interested in filing in that
Mold As a thumb rule -- Expensive tools and if it goes wrong ..Huge economic damage And how do you get it back

If You ask Me the Jury is still out Thinking it over May well be that a change has happened . But also as mentioned above
Big factories dont mess with production tools for a few hundred special motors and don't manufacture new tool for a few hundred

And changing a cam Tensioner is not strange either in these days for any motor

Nice! Whats the guaranteed way to tell, open it up and take measurements?

 

[spacejockey4]

If has been changed to a 650, I think id be a fool not to take it back to 750. That's a little out of my comfort zone, but nows a good time to learn apparently.

 

[GLJ]

The factory did grind off the numbers and hand stamped it 743. There is a thread here where a guy that has a GS750 posted a pic of the jugs.
Yes it can be done.

 

[GLJ]

If has been changed to a 650, I think id be a fool not to take it back to 750. That's a little out of my comfort zone, but nows a good time to learn apparently.

It can be done. You will need to pull it apart and find out what rods are in it so you can get the right pistons. 256 or 447.

 

[GLJ]

Post a pic of the vin numbers on the frame.

 

[Jan_P]

So the gentlemen here did come up with some answers.
If it was me I would investigate some more This being a rare machine Nothing wrong in thinking it over the Engine Casing numbers looks as solid it can be.
Sitting on the hands Inspecting the Ceiling asking around. for a while
Can be difficult .but at times previous owners can be found and more info and or Cylinders still be out there .
Perhaps a dealer knows more

 

[GLJ]

So the gentlemen here did come up with some answers.
If it was me I would investigate some more This being a rare machine Nothing wrong in thinking it over the Engine Casing numbers looks as solid it can be.
Sitting on the hands Inspecting the Ceiling asking around. for a while
Can be difficult .but at times previous owners can be found and more info and or Cylinders still be out there .
Perhaps a dealer knows more

Yamaha made and sold 200 of them to satisfy a AMA requirement so the XS650 could raced as 750s in the Grand National Series. They were sold as is with no warranty. There was not a parts book for them. The only difference between them and a XS2 was the cylinder liners and the pistons.
What he has is a piece of history. The engine cases are worth something. But without the matching frame not a whole lot.

 

[spacejockey4]

Post a pic of the vin numbers on the frame.

It doesn't match. See attached, it was a rusted forgotten hard-tailed bobber in the corner of a garage. ( I'm going to start from scratch) I bought it because the frame vin matched the title, and the engine turned over. Once i cleaned the carbs it fired on the 2nd kick. Didn't bother to look at the engine number till I tore it down.