Fitting a Yamaha XS750 Front End

BarrieC

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Hi Guys,
I did say I would do a brief write up once i had this sorted and now i finally have.
Bit of background as to why i fitted an XS750 front end:
My bike is a basket case, I believe intended to be made into yet another Cafe Racer. The front end that came with the bike was a set of R6 USD forks and a second XS650 Special Rear wheel intended for the front!

Well, that was not going to happen! I started off by coming across an XS750 front wheel with a brand new tyre, perfect discs (Brake Rotors) spindle, spacers, speedo drive and cable for £40. Seemed a good place to start.
I then found that XS650 forks in decent condition are very rare, so i came across a set of XS750 in perfect condition, again reasonably priced.
I knew the 650 forks are 35mm and the 750 are 36mm

Looking at an older post on the forum, it looked like the XS750 complete front end was a straight fit - Later posts and experience, I found out that the Stem is shorter and also the steering stops on the lower yoke only just touch the frame stop.

I then made a bad mistake! I had bought a set of XS650 yokes and Taper Bearings and it seemed reasonable at the time to get an engineering shop to machine 0.5mm off the yokes.
I wont go into detail, but this was a proper engineering business, with full workshop. After getting the forks home and only checking that the holes had been correctly machined out to 36mm. The stem was 5mm out from fitting in the top yoke - plan scrapped and decided to do it properly and swap stems.

Stage 1.
Measure the distance from the top of your existing stem to the base where the bottomm yoke bearing sits Pic 1

Stage 2.
Remove the good stem, now its been said you need to have this pressed out, thats not the case. If you remove all of the weld at the bottom of the yoke a smart tap with a lump hammer will move the stem. To ensure you have removed enough weld, you need to see a fine line, wher the stem joins the bottom of the yoke. This line has to be a complete circle otherwise you have not removed all the weld - Afraid i did not get a picture of this stage, but look at Pic 2 for an idea
But, do NOT strike the top of the stem - screw on 2 of the bearing lockrings at the top part of the thread and use an impact socket, of the right size, see Pic3
Always knock the stem in or out in this way from the top, if you hit the stem from below, you risk splaying the stem and then nothing will move

Stage3.
Repeat the same process on the XS750 bottom yoke, you will lose about 4mm of the bottom of this part of the yoke, but the yoke is a lot "beefier" than stock 650

Stage4.
Though this means knocking the stem back in, it is worth sizing everything up with bearings yokes and spacers as required. By putting the stem in the freezer, the fit is quite easy.
with stock XS650 and stock XS750 yokes, you need to raise the bearing by 4mm (excluding the bottom seal) to enable the bottom yoke to clear the frame
see pic4. Shims of 2mm thickness for M30 (31mm) are readily available on ebay.
so place 2 x 2mm shims, followed by the bearing seal, then the bearing onto the pre chilled stem and knock into the bottom yoke from above by the same method used to remove both stems. Tap in until you have a matching measurement to the original yokes - from the point where the bottom of the bearings sit.

Stage5.
Check the bottom yoke clears the frame, and sits in the lower bearing cup. Check that the top bearing shield and 2 x lockrings fit correctly, also that the top yoke fits ok.

Stage6.
Remove bottom yoke, The stem will be slightly recessed in the bottom yoke - see pic2 measure how deep the stem is in and make a note. Then using, the same method of stem removal, knock the stem and bearing down out of the yoke - this is only to remove the bearing, so it does not get subject to the welding heat (optional i guess)
Freeze and replace the stem to the correct depth and do a much neater job of welding than i did! I'm new to welding and only have a Gasless MIG, but I did check metal pentration and weld strength on my old yoke and the stock 750 stem - I really need to practice welding

Final part.
The steering stops on the lower yoke, only just make contact with the tab welded on the frame - i've seen it suggested before that the tabs on the lower yoke, should be ground of and bolts drilled in at the corect locations. I dont think this is a great idea and would suggest grinding out a piece of 5mm bar, i think its about 20mm X 25mm and welding this onto the frame in the correct location.

Parts:
you only need XS650 Taper bearing set, both stems are 30mm diameter.
Shims for spacing under the lower stem bearing are 2no. 2mm 30M x 42mm

Sorry post is a bit jumbled, any questions, please let me know

Now, I can start piecing together the engine, from many boxes, packets and bags!
 

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BarrieC

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Another way would be to bore the 650 yokes out to 36mm.
Hi, if you read the post, i had an engineering firm do that, with bad results. they must have been slightly off square, which ended up with the stem being out of allignment with the top yoke by 5mm.
Doesnt sound a lot and you could manipulate it into place by loosening up the yoke clamps, but the yokes would not be holding the forks straight and that seemed very wrong. They used proper milling equipment and swore blind they had just followed the original holes - wont be going there again.

when you compare the XS750 yokes to the XS650, there is a big difference, the 750's are a lot more robust
 

Signal

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I apologise I did not read your post thoroughly enough.

I have had that experience before where engineering firms take forever, charge the earth and the work is wrong. Looks like you have a good result now.
 

BarrieC

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I apologise I did not read your post thoroughly enough.

I have had that experience before where engineering firms take forever, charge the earth and the work is wrong. Looks like you have a good result now.
Hey no worries! The bad part, was i took everything back to them left it with them because the guy that had done the work was away. When i went back the next day they claimed evrything fitted and could see no problem, they had clearly opened up the bottom yoke clamps. But denied having done anything.
Lesson learned the hard way
 

BarrieC

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Yep that is very impressive. A proper job! I'm glad you admitted you had done it with just an Angle Grinder, Hammer and a Welder, in the past
I dont feel so bad about my welding now, which is not very neat;)
Watch out for my questions as i start to piece the engine back together from a total teardown by the previuos PO (s)

Barrie
 
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