The decision to fit a disc brake front-end to my 1979 XT500 was made as I slewed inexorably into the car that had just U turned in front of me. In the few seconds of realization that I was about to have a smack I noticed that the rear end was locked and skidding but the front wheel was still turning, despite the lever practically touching the handlebar.
Amazingly the only damage to the bike was a shattered front mudguard, somehow the 20mph impact into the side of the car did not bend the forks or result in any of the other usual damage!
After much research via the internet I found that the XT350`s forks are the same diameter as the 500`s (36mm)though despite posting requests at numerous sites I could not find a complete front end. I visited Allbike Spares in Greenwich and was given free rein to rummage amongst their fork collection with a vernier guage in my hot little hand, I found that the DT125LC and more modern DTR125 both have 36mm forks but didn`t feel comfortable with the thought of using a braking system designed to stop a weedy 125 2 stroke on a scale-bending XT500.
I was perusing the stock of Cheshire Motorcycle Salvage (www.cheshiremotorcyclesalvage.com) when I saw a Suzuki DR650 that was about to be broken, the huge disc(300mm) and long thick forks sold me completely and I emailed Paul the owner. He replied swiftly with the price of £250 for the front end complete, including P+P!!
It arrived with indecent haste and I was like a 6 year old kid on Christmas Day ripping open boxes..oohing and aahing. All the bits I`d asked for had been included plus a Renthall handlebar complete with all cables and switchgear, bark busters and a nice white brake disc shroud. Full marks to Cheshire motorcycle salvage.
Ok, this is the bit where I tell you how I joined the front-end onto the XT..if you have a highly technical background you might want to look away now. I`m the sort of mechanic who uses beer cans to make shims for handlebar clamps and tree stumps as centre stands.
The first thing I did was borrow a vernier guage and do some measuring;
the new steering stem diameters at the top and bottom where the bearings will sit and the diameter of the steering column of the frame at the same points. This is where I got really lucky, the DR`s steering stem diameters were the same as my XT`s...25mm at the top, 30mm at the bottom.
This meant that all I needed was a taper roller bearing set for an XT500. Dazed and confused at the simplicity of this ( I was expecting to have to go to a bearing stockist, chop and change, maybe even turn the cups down to a smaller size on a lathe,) I called Jon`s Scooters in Dalston to ask if a taper roller bearing set was made for the XT500, I realised that knowing my luck no such set existed.
`Yeah, we`ve got a set in stock..£40` said the nice man.
So I got up off the floor, jumped in the car and motored down to pick them up. While i was there I bought some brake fluid and new copper washers for the brake hose fittings at the caliper and master cylinder.
Arriving home again and with rain threatening I pushed ahead with stage 2. This is where I made a little mistake.
The length of the DR650`s steering stem is about 20mm longer than the XT`s, I`d made some 30mm and 25mm (internal diameter)spacers at work to fit at the top and bottom as required, but thought that as the taper roller bearings were 13mm deep and that the XT uses races with loose bearings(about 8mm deep)...the new bearings would act as spacers and I could space out at the top of the stem. I fitted the top cup into the steering head, nice smooth fit, then the bottom cup, then tried to get the bottom cone onto the stem. This I found really tight probably because the internal diameter of the bearing and external diameter of the stem are both 30mm.
I ended up assembling the bearing on the stem as best I could then inserting the stem into the steering column, then using the threaded collar to draw the stem up inside the column - thus pushing the bearing down the stem to it`s seat at the bottom of it. Did that make sense?
It worked fine but then I realised that I needed to have a spacer UNDERNEATH the bearing on the stem, and there was no way that the bearing was going to come off. The steel is extremely hard and has a tendency to shatter or chip if you hit it too hard.
The main problem was that at the top of the stem, the top cone sits around a 25mm diameter section resting at it`s lower end on a shoulder.
But because I hadn`t put a spacer under the bottom bearing the top bearing hit this shoulder before it engaged in the top cone. Now..,what would you have done? I decided to measure the offending distance and remove the shoulder with a grinder down to that depth so as to allow the two bearing surfaces to meet snugly. Aren`t Bosch 4-1/2" grinders great? If you haven`t got one..treat yourself. This cured the problem and the yokes were tight and snug, I used some of the 25mm diameter spacers on the top of the bearing then tightened up snugly with the loctited (is that a verb?) steering stem nut.
With that done it was just a case of assembling the front end, it was basically plain sailing from here on, I think the sun even came out at one stage.
I was sorely tempted to leave off the headlight and front mudguard, it did look awfully nice without them, but common sense prevailed,,I think I might fit an enduro style headlight unit at a later stage - the original XT headlight looks dated indeed nestled amongst the liquid shininess of the DR650`s forks. Neither speedometer nor tacho will be re-fitted.
I`d noticed that the steering stops on the bottom yoke were in a different position, turning the bars to the left the top of the fork touches the tank, turn to the right and the stop hits early, so the grinder came out again and I touched the right-hand stop on the frame down a little until the fork came within a reasonable distance to the tank.
Before test riding it I went over every nut and bolt making sure it was all buttoned up right, then before riding off I turned the bars to make sure the throttle and clutch cables operated smoothly without snagging.
Did it work? Damn right it did, although the forks look much longer than standard there doesn`t seem to be any detrimental effect. The wheelbase is definately longer but the bike still feels nimble, perhaps a very slight tendency to `tuck-in` but that might be the extremely worn front tyre that came with the wheel. The front brake is absolutely awesome..more than capable of performing a `stoppie` if only I had the guts ( and jock strap ) to try one.
If you have an XT500 with a drum brake I would seriously recommend this conversion, it looks great and one day might save your life.