1985 XC500

[gearco]

I thought I'd chronicle a project I just finished in hopes some of what i learned will help or encourage others to do similar things with these bikes. I'm not a great fan of the new 4 stroke dirt bikes; too heavy, complicated, expensive to service, etc. But new technology is a wonderful thing. Better brakes, suspension and controls to name a few. I rode a friend's modern day KTM and it was a wonderful bike but it didn't have the 2 stroke acceleration kick, and it was way too heavy IMHO. So I decided to build a "new" 1985 XC500 with modern suspension, brakes and to remedy some of the problems the older bikes had such as heavy clutch pull and overcarburetion. I've pretty much succeeded with my goal, which is to end up with a bike weighing around 220 dry and having open class power.

 

[gearco]

Here are a few pictures of the finished bike; should have taken the pictures before riding it about 10 hours because i've dirtied it up and skinned some paint off in the process.

 

[gearco]

The front suspension is from an 04 Husqvarna 450 TE; the forks are Marzzochi Shiver 50mm that allow compression and rebound adjustments top and bottom. The front wheel is also from the 04 450 TE, as well as the Brembo disk brake, brake lever/master cylinder. The steering head on the 85 frame is about a quarter inch too short, so you need a spacer on the bottom, the old inner bearing race does a good job of this; also the size of the stem is larger. You can find the right bearing size at O'Reilly auto parts for cheap; they are wheel bearings from a small Ford-just measure the inner and outer and cross reference.

The new radiators came from Ebay and made in China; the pair was $300; the stock footpegs were modified by wrapping a length of 3/16th inch flat steel around the original with spacers after cutting the teeth on a mill. Here's a pic.

 

[gearco]

The rear wheel and disk brake came from the 04 450TE as well; note the Excell wheels. There was a 22 lb weight difference between the old wheels and new ones. The old rear drum was heavy, as were the old Nordisk wheels. In order to mount the newer wheel and brake to the swingarm, the wheel had to be turned around so the sprocket is on the right side, not the left, the 85 swingarm machined (enlarged) to accept the larger axle (25mm to 45mm from memory) and a T shaped aluminum piece welded to the left side of the swingarm so the brake caliper can be pushed onto it to keep it in place. See pics.

 

[gearco]

The rear disk brake required a fabricated piece for a pedal mount as well as the master cylinder. The pedal is from the 04 450 TE that was bent after using an oxy/acetelene torch to heat it. The bracket was made from a piece of 1 inch square tubing and some angle steel. The stock rear Ohlins shock was rebuilt and powdercoated. See pics.

 

[gearco]

Forest Stahl and his son, Larry built the motor for me. The original cases were shot, and Forest found a new set of 250 water cooled cases he was able to machine out to accomodate the 500 crank. I chose to put in a WR transmission rather than the XC since I live in Georgia and our riding here is a lot tighter than the desert racing for which the bike was intended. A new 38mm Mikuni round slide carb was used with a 420 main, 45 idle and 2.5 slide. The original 85 had a 40mm carb on it and was a continual headache, hard starting, etc. I'm close to getting the jetting spot on after a few rides. The clutch pull with a new Magura lever and original arm on the motor was really hard. To fix that I welded on a one inch extender to the actuator arm and bent it up a little, then put on a new lever with ball bearing pivots. Much better. See pics.

 

[Northern Husky]

very very nice!

Trick pipe aswell. ls it a works one?

 

[gearco]

very very nice!

Trick pipe aswell. ls it a works one?

Handmade, got it on Husqvarna parts; works well.

 

[gearco]

Forgot to say that it came with a cross brace on the curvature between the engine mounting point and horizontal section below. It made the pipe too heavy, so i cut it off-wasn't needed.

 

[fran...k.]

I like seeing other folks carve these things up and re configure things. I do not believe you could get the weight savings you claim on the wheels and brake components if you use equal tires, rim locks, and tubes. Besides the origional rear wheel may not have tremendous stopping power but the diameter and angle of the spokes makes it a much stronger and more rigid assembly than the modern stuff. I am not really sure about your transmission statement, for the 400, 430, and 500 I am under the belief wr and xc transmissions are the same. Even though my comments appear critical I wish to encourage you as much as possible. I do not believe what you listed addressed the clutch pull issue much. You have a nice new bore for the clutch actuating shaft (the one the cable attaches to) and most likely put some lube on it before installing.

I kind of went a bit different way with a frame from a 1999 te 410 and the engine which belongs in this section. I didn't really think through how the plastic would work out and might add a sprung seat at some point so am not too terribly concerned about it.

 

[gearco]

i weighed the wheels side by side with tires, tubes, locks, etc. all included; keep in mind the rear wheel is a 19 inch rather than a 18 so there could be some difference there. The Excell wheels are very light and the 19 inch rear tire is lighter than the big 18. Larry Stahl confirmed the difference on the transmissions, but even then the 14/52 setup was too high. I've dropped to a 13/52, which seems a little low so I've ordered a 50 tooth rear to split the difference in the ratios. On the clutch, the new springs made it a real bear to pull. I put a new Magura lever and new cable on it and neither seemed to help. Note that the bottom of the actuator shaft is lubricated by the bottom end oil where the eccentric touches the clutch rod so it isn't a question of getting lubbed. Lengthening the lever by about an inch did help quite a bit as did the new handlebar pull. BTW, I tried on of those EZ pull contraptions and while it helped some the pressure from the clutch broke the short cable from the box to the lever.

Thanks for you comments; you've got me curious about the weight and i'm going to weigh the whole thing and post it here.

One good thing about the new bikes is that the manufacturers have lightened up most of the components because they can't get the weight off the motor. The lightest big bore 4 stroke motor seems to be about 65 lbs. The 500 2 stroke motor weighs 44 lbs, so there is an immediate 20 pound gain by using the old motor, and more by replacing the older stuff with new. Things as simple as the handlebars, for example; the new ones are half or less the weight.

 

[gearco]

Here is where I got the pipe:
CONTACT DYNO-PORT DIRECTLY
www.dynoport.com

 

[Northern Husky]

Thanks for that.

Seems a very reasonable price, are you satisfied with the quality?

ls there a weight saving on the forks and pipe aswell?

 

[gearco]

Yes, it looks like it was gas welded all around; quality pipe. On the weight of the bike, I have an embarassing disclosure to make: It ain't 220 lbs. dry; it is about a pound lighter than the original bike: 236 lbs. Tonight I drained all the fluids and weighed the bike carefully. Apparently what I lost by substituting the Excell rims and Brembo disk brakes, I gained by the larger diameter and heavier forks. 50mm compared to 40mm. This has left me in a quandry because I had hoped for at least a 10 lb drop in weight with the new parts. Anybody have any ideas about how to get additional weight off the bike? Aluminum frame? Lighter forks?

 

[Northern Husky]

Lol l was wondering about the forks.

ld bet your are still way 'ahead' though, by virtue of better stopping and suspention.

Given the power and ablity the bike will have when you have fine tuned it for yourself its not really thaaat heavy, and in the right hands a serious weapon. Dont worry you will make the KTM boys think twice

Personally now ive/its been decided it will be easier and cheaper for the rider to drop the weight.

Cheers

 

[gearco]

I'd hoped you wouldn't mention that part. but agree.

 

[adam6402]

I dont recall where I saw it on the internet, but I came across a bike where someone had spent BIG BUCKS to have a custom frame made out of titanium. As I recall it was a 70's CR 250 husky and total bike weight was reported at at less than 200lbs. So if you have cash burining a hole in your pocket........

 

[gearco]

Any idea how much the stock frame weighs?

 

[speedyauto]

I saw that the rear brake assembly is under the swing arm, did you consider a late model husky 2 stroke set up as they're still left side disc & caliper is on top out of harms way.

 

[fran...k.]

The frame weighs 19 pounds with the footpegs. I got 20 on another one with the footpegs and the coil and the regualtor thing. 88 frames. As for loosing weight a titanium spring for the shock if there is one suitable, the lightest tires and tubes, after that It gets pretty tough. You have 10 pounds in the crankshaft assembly, first has one pretty heavy gear. I got 59 pounds for my 430 engine with no sprocket and no oil. It holds over a quart of water, and didn't include the carb either. I don't think I made an error as I held the objects and subtracted my wieght. My weight ends in 8 and both of them with me ended in 9. Mine has a steel clutch basket so it might weigh a little more than an 85.

added later
I have an honest weight no springs scale good to 30 pounds and certified in 1994 and weighed some items which I believe are representative of an 85-86 xc500.

Transmission, basically everything you get from the insides of the cases
9 lb 2.5 oz

Engine cases inclding bearings and clutch actuating shaft
9 lb 14 oz

500 cylinder I weighed a few none had both the exhaust spigot and reeds/rubber carb thing
7 lbs and from 3 to 11 ounces 430cc 6lb 3 oz bare water cooled one

crankshaft with stator nut
10 lb 3 0z

clutch cover with kick start pedal and shift pedal
3 lb 11 oz

clutch assembly but no springs or bolts to hold the springs
3 lb 11 oz

If you add them all up these items are not included in above
piston
head
primary drive gear on crank, intermediate starter gear, starter gear
transmission parts inside clutch cover to turn shift drum and clutch rod and bearing
front sprocket for chain
cylinder studs bolts and nuts
gaskets, oil, water
Ignition alternator stuff spark plug

If you really were dedicated you could probably drill holes in the primary drive gear on the crank, the starter gear and perhaps first gear on the output shaft. I am not sure how to make a lighter crankshaft with the same rotational inertia but that might be possible if you were dedicated.

Fran