35mm forks for a 72 frame.

[Quinn]

Hi I've been looking around the forums for info but haven't quite found what I'm looking for... My next project is a 72 (for my second street tracker) - it came with only the frame motor and tank. From what i understand it's a good idea to convert to 35mm forks. Good news is that i have the triple tree/steering head and forks from a 74. Mad news is that the stem is too long for the neck of the 72. Here's my question...
Do i find another steering head/triple tree that will fit the 72 frame and 35mm forks, or do i press out the stem shaft/stem (thing that goes into the neck) and have it shortened and then repressed/welded?

Or is there an entirely different option?

I hope that makes sense?

Thanks for the help!

 

[650Skull]

74 is 34mm same as the 72, 35mm didn't arrive on the scene till 77 and later models. Yes pressing out and swapping the stems is a way to do it

 

[XSLeo]

If you figure out how much too long your 74 stem is then put that much shim under the lower bearing.
This will get it to work but I don't know about the steering stops. This might get the lower tree to low to hit the stops.
I might figure out how much too long the stem is and have the upper end turned down and the threads extended to fit. I think a good machinist can do this with out cutting the weld and pressing out the stem.
If I had a 70-73 lower tree then I might just swap that stem into a later set of trees. And as 650Skull mentioned the 35 mm forks started in 77.
Leo

 

[nj1639]

I believe the '77 xs750 has the shorter neck stem.....comes in 36mm but will add about an inch plus in overall fork height, uses a smaller diameter disc rotor for the front brake. IF I had a '72 that's where I'd be looking.

 

[jay760]

It's only a tiny bit too long, take it to a machine shop and get the top bearing surface taken down the shaft a bit,

 

[Tim of DO THE TON]

I went through this exact issue with my '72 about 5-6 years ago, and found nothing online about it. All I could find online was that all front ends on XS650's could be swapped.

True, except for the early frames

Trial and error is how we did mine. First thought was to lower the stem. Ground out the bottom weld, pressed it down further (can't remember but seem to recall about 1/2") and welded it back up.

But, we didn't check the lower bearing surface. Turns out it ever so slightly tapers above the stock bearing location, so the lower bearing was loose.

Had to weld on material and turn it in a lathe to make it the right size for the bearing.

If you can make it such that you can lower the top bearing further on the stem, you'll have to add a spacer above it to cover the distance to the threaded area for the locknuts. Downside is you have a tall span from the steering tube to the upper tree.

Swapping the stem is likely the easiest thing to do. I would have except I had sold off my stock front end and didn't have the tree (and didn't know I was going to have all these issues).

So now there are these conversations online for Google to index for future generations to learn from

 

[Quinn]

Hey guys thanks for all the help. When I bought the 72 I also bought a 74 and a 79 (both complete bikes but non runners). Anyway someone must have swapped out the forks on the 74 somewhere down the line because both forks measure exactly 35mm.

As for the mod itself I measured the neck on the 72 and it's about 1" (15/16) shorter than the the 74 neck. With that being said I don't think an inch worth of spacers is feasible or aesthetically pleasing so I plan on grinding out the weld and having the stem shortened. Hopefully I won't have too much trouble with the bearings... I'll post my results when I find out.

Thanks again,
Quinn

 

[hard_y_rd]

I did it Quinn. 35mm front end on a '73 frame. Machine shop turned the old weld down on a lathe, shoved it down. For me it was only 5/16". Do your own measuring though because I read a post on chopcult and the guy said it was 1/2 inch or more.
Mine was dead nuts on.
You have to add some material on the lower stem like Tim said for the bearing to seat correctly.
As you can see in the first picture, I didn't weld it right away in case my measurement was off. It's better to be too long than short cause you can always cut some more off.
It's going to kill about $100 or more at a machine shop unless you have a buddy with the tools to do it for ya.
I should point out that the steering stops will have to be modified as well.

 

[gggGary]

I have done a stem swap, it's not too hard to do, probably easier/stronger/better than shortening a stem, Ebay for triples is your friend. As someone else stated the XS750 forks fit the early frames. I believe the stem length difference is near 1/2". I will assume you want to use the 72 frame because of title issues? If so simplest would be to restamp a later frame with the early numbers and destroy the early frame. I believe the later frames are stronger and less flexible with perhaps a bit more rake.

 

[gggGary]

A different approach is the forks from an SV650 they will fit with little work. With several internal mods available they can give much improved handling. Search the site for several threads about doing this mod.

 

[hard_y_rd]

I was wondering about the rake on the earlier frames, Gary. I was looking at the stance of mine last night with the fork tubes pushed up in the trees 3 inches cause i'm going with a 21 inch front and it looks just a bit off. Something else to ponder...

 

[XSLeo]

The rake of the neck was speced as camber and was 63 degrees in the factory manual for 70. The camber angle of 63 degrees subtracted from 90 degrees give the rake of 27 degrees.
This was used on all years. Never changed.
On using the XS750 forks having the shorter neck applied to the XS850 and XS1100. I have a set of XS1100 forks and they use a shorter tree. From the lower bearing seat to the top of the stem is about 8 1/8 inches, The stem on the 75 forks setting next to the them has a stem 8 7/8 inches long.
THe length of the forks from axle center to top of the tube is XS1100 31 1/4 inches, the 75 is 29 3/4. The XS1100 forks I have use 36 mm tubes and has the axle straight under the fork like our XS650's. It also uses a flat upper tree. The XS650 uses a upper tree that drops off from the center to where the tubes are. By about 3/4 inch. So using the XS1100 forks will actually hold the front end 1/4 lower than the 650 forks.
Leo

 

[hard_y_rd]

Does this apply to The TX 650's as well, Leo?

 

[XSLeo]

Yes, they used the TX prefix when they came out with the TX500 and TX750 counter balanced twins. They had a tremendously poor sales due to engine trouble. In 75 they went back to the XS prefix to distance the XS650 from that debacle.
Leo

 

[Quinn]

Hey hard-y-rd, thanks for the info - good to know. Btw: do you happen to have know the finished stem length? Reason I'm asking is that I measured the neck on the 74 and the neck on the 72 and there's about an inch different in length. You post suggests that there is only about 1/2" difference??? Maybe I'm missing a lower spacer? Do the bearings which I don't have right now take up some of the space?

Gary: good to know about the strength of the frame. I'm using the 72 for two reasons... 1st I have a matching motor, and 2nd its all good with the DMV, where as the 79 I have owes the state about $700 in fees.

 

[Quinn]

Gary, I was looking on eBay... I think you might be right; a lower stem swap from an xs750 might be the most cost effective way to go. Do you know which years I should be looking at?

 

[hard_y_rd]

I didn't necessarily go by the neck length. I had both stems and just compared the two. If you don't have the short stem there the amount I took it down was 7/16".
I said 5/16" earlier but that was a guess.
Btw, I have a 73 frame so that may be different than yours. What is the neck length on the frame your using?