1987 KX fork update/swap?

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9/3/2018 8:26 PM

Just picked up a 1987 KX250-E1. Bike is rough, but it was about to be parted out. Plan to put a minimal amount in and enjoy it as a vintage racer.

Fork seals died years ago.. forks have no oil and are springy, so they need full rebuilding.

Are USD forks illegal in EVO 4 class? I ask because KTM had them on their bikes. I also have a pair of 41mm USD's from a 1991 KX250 in my shop.

Would I be better off restoring the 87 conventionals (assuming I can even find bushings) or should I upgrade to the 91 upside downers?

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Ride like a girl!!!
2016 KTM 500 EXC-F
Current project: 2007 Kawasaki KX250-R7 retro build
Current project #2: 1987 Kawasaki KX250-E1 rider/racer resto
1989 KX125 resto
1987 RM250 resto

9/3/2018 8:35 PM

Different rules for different sanctioning bodies as far as USD. I'd say pick up a set of 88-89 KX cartridge forks, those will be better than the damper rod ones that are on it and probably better than first gen USD forks.

Race Tech Cartridge emulators are another option, but I think you could find the 88-89 forks for less than the emulators will cost.

You will also want way stiffer springs. I just put stiffer springs in an 86 YZ 125 and even with no other mods, the damper forks actually aren't as bad as I expected them to be. They are KYB, probably very similar to the ones in your KX.

I rode a friend's 86 KX 250 earlier this season. If the 87 engine is similar, you are in for a treat. It had a nice usable bottom end and respectable over rev. It was very easy to use and fun to ride. Ergos were a bit weird haha but that's pretty much every bike before 1989!

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9/6/2018 9:44 AM

Looks like the body I'd race under does not allow USD forks in EVO 3. I think I have an old set of 89 KX forks around here somewhere. Wonder if the 89 triple tree would bolt right on.

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Ride like a girl!!!
2016 KTM 500 EXC-F
Current project: 2007 Kawasaki KX250-R7 retro build
Current project #2: 1987 Kawasaki KX250-E1 rider/racer resto
1989 KX125 resto
1987 RM250 resto

9/6/2018 12:51 PM
Edited Date/Time: 9/6/2018 12:57 PM

queen of spodes wrote:

Looks like the body I'd race under does not allow USD forks in EVO 3. I think I have an old set of 89 KX forks around here somewhere. Wonder if the 89 triple tree would bolt right on.

It should. I bolted a set of 89' triples/forks/wheel/axle/front brake to an 85' KX125 once. The front brake (dual piston), brake mount, and the axle/wheel spacing is different on the 89' though, so you will need everything. The one good thing about this conversion is that the bar mounts are a bit farther forward than the earlier models, so it makes the cockpit feel roomier like a newer bike.

I checked on the parts fish and the front wheel/brake setup is the same on the 87' and 88'. So it would be easier to throw a set of 88' forks on that bike, and you wouldn't have to change anything else. The 88' forks were cartridge forks, but were the standard 43mm, so they should slide right into the stock 87 triples.

Also, you can still buy stiffer fork springs for the standard 43mm conventional forks. Stiffer springs for the 89' 46mm forks are hard to come by.

Just some things to consider.

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9/7/2018 11:55 AM
Edited Date/Time: 9/7/2018 11:59 AM

Here's my 10c, The Forks are Great on the 87 though i did put the 88 internals in them in the end, I also ran 15 w oil... The shock was more of a problem as the valving made the shock way too soft on modern jump infested tracks, i got a shock off a 2000 and had it modded to fit, it was an Amazing difference, it felt like riding a modern bike! Don't put Usd forks in it will Ruin it! I love the 0ld conventional Forks smile Photo

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9/11/2018 7:02 AM

I've been thinking about doing a front end swap on my 87 KX 125 as well. I've been thinking about using 98 RM conventional forks or the 50mm WP Extreme. I'd like to use the WP's if I can find a set. Any one ever used either set of fork on a KX?

Photo

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9/11/2018 2:45 PM

The lower bearing on your 87 KX matches the lower bearing of the 98 RM forks. Allballsracing.com makes a "kit" with special sized bearings and washers that would replace the upper bearings. Check their website for what will and will not interchange.

I used their kit when adapting a complete 03 CR250 front end onto a 89 CR500. Worked like a champ.

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9/21/2018 11:52 AM

Are you going to keep this bike?. You made your 125 factory fresh and started out with a bike that was basically scrap metal only to sell it

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9/21/2018 7:35 PM

JT Hagerty, I have 49mm Showas on my 83. They came super close to bolting up. A good friend had modified the stock stem by wedding the bottom of the stem and turning it to fit. The diameter of the bottom of the stock stem was just 1mm too small.
I didn't like the gold anodizing on the lowers so I spent forever with them in a sand blast cabinet. It was son of a gun to get off.
If I were to do it again id go for a 89 front end
Where did you get that trick silencer? I need one those?

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9/22/2018 6:56 PM

kx93rfo wrote:

Here's my 10c, The Forks are Great on the 87 though i did put the 88 internals in them in the end, I also ran 15 w oil... The shock was more of a problem as the valving made the shock way too soft on modern jump infested tracks, i got a shock off a 2000 and had it modded to fit, it was an Amazing difference, it felt like riding a modern bike! Don't put Usd forks in it will Ruin it! I love the 0ld conventional Forks smile Photo

What all mods had to be done to make the 00 shock fit?

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Ride like a girl!!!
2016 KTM 500 EXC-F
Current project: 2007 Kawasaki KX250-R7 retro build
Current project #2: 1987 Kawasaki KX250-E1 rider/racer resto
1989 KX125 resto
1987 RM250 resto

9/24/2018 8:30 AM

MaxPower wrote:

JT Hagerty, I have 49mm Showas on my 83. They came super close to bolting up. A good friend had modified the stock stem by wedding the bottom of the stem and turning it to fit. The diameter of the bottom of the stock stem was just 1mm too small.
I didn't like the gold anodizing on the lowers so I spent forever with them in a sand blast cabinet. It was son of a gun to get off.
If I were to do it again id go for a 89 front end
Where did you get that trick silencer? I need one those?

I actually made the silencer. It is a Buds Racing silencer for a 2016 TC 125 Husky. I kept the silencer when I sold the bike the only thing I had to do was cut the inlet pipe shorter, weld on a little bit larger diameter pipe to fit over the expansion chamber and slide the mount closer to the front of the silencer.

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