[warburtonm]

Gents,
I've restored a few vintage MX bikes, but I'm new to XR75's, having just picked up my first. I plan to restore my 76 as a bad-ass pit bike for when I go to vintage MX races, and I want to do it up like a '73 Elsinore clone. A question for you pros: what's the hot set up for front suspension? I'm seeing a lot of folks using XR100 or CR80 forks, but I've not seen them say that they bolt on (or not). If not, and the mods extensive? Which is preferred? Which year's forks will work?

How about the rear? I see that I can get a trick aluminum swing arm, but I am less sure about wheel sizes. What wheels do you all recommend?

Thanks!
Marc

 

[ajcmbrown]

The XR100 forks will fit but are long spindly legs (27mm?) that don't perform very well, at least the ones I have ridden have been mediocre.

The CR80 forks (31mm) are a much better fork in terms of action, damping and length. This also gives you the option of a 17" front wheel if you want a greater choice of tyres.

The CR80 front end is a bolt on fit, but having said that you will need to widen (weld) the steering stop on the frame by around 1/8" or a little more, so that the fork legs don't make contact with the tank. That is the only mod needed.
They use the same steering head bearings or you can upgrade to tapered rollers and it will raise the front by about 1" so longer (CR80) shocks are a good improvement as well to balance out the ride height and steering angle.

I even have the 16" front wheel in mine with the XR75 backing plate if I recall correctly.

The combination of the CR80 forks and shocks works great on a K4 or K5 and XR80 twin shock bikes, not sure how the rear shocks will fit on a K1-K4 though, they could be a little too long.

If I can drag my K4 out from behind the other bikes, I will take a couple of pics this weekend.
I hope this helps, Tony.

 

[warburtonm]

Thanks!

Tony,

This is just what I was hoping to learn. Pictures would definitely be appreciated. Also, how does the "K" nomenclature work? Does K1 mean a 1972; K2 a 1973; and so on? Or is there some other meaning?

Thanks so much!

 

[ajcmbrown]

Hi warburonm, the K0 through to K3 are the early (desireable) four speed models, the K4 was a different animal, engine was new, rear suspension was laid forward, still had some visual similarities though, tank looks the same though it isn't interchangeable, very little of the engine is common to the early models, if any. Forks are the same, I think wheels are the same only painted hubs, exhaust is different, you get the picture.
I will try to grab some pics so that you can see the suspension upgrades that a CR80 donor bike can offer.
Tony.

 

[warburtonm]

Tony, will any year CR80 fork work? There is a CR80R too, right? Does it have a different fork?
Thanks, Marc

 

[ajcmbrown]

Hi Marc, the only one I can vouch for is the twin shock CR80R of the early eighties, but I recall reading other posts that suggest up to '89? I think. Sorry, when I mentioned CR80 I should have given it the full title of CR80R, so yes they are the same bike, that was just me abbreviating!
Tony.

 

[ajcmbrown]

 

[theraymondguy]

80-86 CR80R triple clamp will fit in the XR75 steering neck with a simple bearing swap. 86 is disc brake.

If you're looking to keep it simple (and legit) with stock XR75 forks and a steel 17" front, CT90/110 front might do the trick - i've never done it but wanted to.

Early XR100R swingarm slides in, but the rear hub is wider than the 75/80.

 

[ajcmbrown]

I used the bearings that were in the XR75, loose balls which I will upgrade soon. They seem to work well enough for now though. No parts were required to do the swap, just the steering lock mod. The front end I used was 1980 CR80 from memory.