What the heck are these forks from?

[NashGTI]

I bought an XS-2 a couple months ago and after getting it running decided to replace the fork seals. The guy I bought the bike from said that the guy he bought it from thought it had XS850 forks on it. I don't believe that is the case as the caliper brackets are on the leading edge of the forks I have. They also have the ear cast onto the lower tubes to hold the brake line clip above where the ears for the front fender are. The cap on the upper tubes takes a 17mm allen to take them off.

They sound exactly like 74-76 XS650 forks, except they are 36mm tubes. The seals I pulled out were 36mmx48mmx10.5mm and looking through the bikes that seal size is supposed to fit nothing looks anywhere close to what I have. Was it a common thing at any to machine the lower fork tubes out to fit larger upper tubes? I've spent the last week looking since the 34mm seals I assumed I needed obviously won't fit and haven't found anything that looks right.

Any ideas would be appreciated. I haven't taken any close up pictures of the lower fork tube, but if anyone thinks that it'll help it's easily done.

 

[MaxPete]

Those look pretty beefy to me - much bigger than 34 mm from where I sit.

 

[fredintoon]

Hi Nash and welcome,
OK, 36mm is stock diameter for XS750/850 fork tubes.
But the earliest XS750 was the '78 and Yamaha gave up those 2-pot calipers and 2-part brake disk in '76, for the XS650s anyway.
Although the XS series ain't the only bikes Yamaha made in those years.
I reckon it's far more likely that the fork came off some other kinda Yamaha than that someone re-machined an XS650's fork lowers and innards to accept fatter fork tubes.
But hey! Be Happy! Fatter fork tubes are an excellent upgrade. Go to your local Bearing & Seal store and buy two new 36 x 48 x 10.5 fork seals.

 

[weekendrider]

TX750 possibly.

 

[5twins]

Yes, that's my guess. They were 36mm and produced in '73 and '74. They used that old style caliper and had solid mounts for the bars that angled back, which I think I see on yours. Here's a drawing .....

http://www.boats.net/parts/search/Yamaha/Motorcycle/1973/TX750/STEERING/parts.html

 

[jonesey]

Yes Nash I'm pretty sure its a TX 750 front end, they had the deep Dust seal with multiple ribs like yours. You could check the front wheel rim as well. The TX used DID rims. Can't quite see the clocks, the TX had unique clocks similar looking to the XS650B but with an angled cable drive instead of straight. A good score.

 

[jonesey]

Back wheel may be TX too and if your real lucky also the swing arm. The TX had a bigger diameter rear drum.

 

[gggGary]

Pic of a 73 TX750, they had a "wobble catcher" under the lower triple. (steering damper disk and housing), about 3"diameter.
I think I can see that on your bike. THe TX front wheel used a disk that bolted to the hub and has a siffy cast aluminum cap covering a disk mount on the LH side. The XS2 had an oddball "floating disk that sat on it's own set of ball bearings and "connected" to the hub though a pair of tangs in rubber sockets. Jeez wonder why THAT was a one year only deal?

 

[5twins]

Yes, that could be a 750 rear wheel. The brake plate didn't have the bulge around the axle hole like the 650 did .....

And besides the alloy left disc mount cover, the 750 also had a nice natural alloy colored speedo drive. All this stuff polishes up real nice .....

 

[gggGary]

couple shots of Xs650 and TX750 hubs the 650 brake plate OD is 8" the TX750 is 9"
When I see a "non stock front end" on bike I assume; crash repairs. Hint take a close look at frame steering head alignment, the early frames are pretty flexy up there on a "good day". Doesn't take much of a hit to make them point in funny directions.

 

[NashGTI]

Thanks for all the info, the front end seems to definitely be from a TX750, which is something I hadn't even heard of till yesterday. The rear drum does seem to be 9 inches outer diameter, I had noticed that the wheels didn't seem to be XS-2 wheels as they have the extra lips on the rims but even when changing the tires never looked into brake drum diameter. Both wheels look to be TX750 according to pictures.The bars are solidly mounted to the upper triple clamp and there is a steering damper on the bottom of the tree, which, did the XS650 already have the provision for this on the frame? The gauges have the cable fittings coming straight out of the back of them so presumably the stock pieces. The tachometer itself is trash as the tach cable is too short and broke the spot weld on the tach body causing the drive cups to grind into each other inside the tach.

Looking at pictures it seems the front turn signals are TX750 pieces too. It was mentioned that the TX swingarm was a larger diameter (close to 1.5 inches?), mine looks more like 1.25 inches and the chain guard looks like the XS2 piece and bolts right up to the swingarm so I'm guessing it is the stock swingarm.

Nothing feels out of whack riding as compared to anything else I've been on, in fact it feels straighter than my CB650 did. Lots of stuff is just worn out on it and the front fork felt nearly solid riding it but when I drained it last weekend the fluid was as thick as gear oil.