Swapping newer forks on to an '87

Discussion specific to the various air-cooled KDX models sold in the USA
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baisleyde
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Swapping newer forks on to an '87

Post by baisleyde »

I Just picked up a 96 KDX200 parts bike , was wondering if the forks will just bolt right into the 87's triple clamps , or will the triples from the 96 install on the 87 without any modifications. Just wondering if anyone knew before I start tearing things apart. Thanks
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Re: Swapping newer forks on to an '87

Post by Kipsy »

I don't know for sure, but I wouldn't put money on it fitting. I think you would need to swap the triples, too.

On my 88 KDX, 88 KX fork tubes fit (43mm), but when I compressed the fork to check for clearance, the fork lower hit the lower triple clamp. If you look, you'll see the KX's had "gull wing" shaped lower triples to clear the extra length of the fork lower. The 88 KDX's lower triple was straight across.

I don't remember 100%, but I "think" I could have made the KX forks work in the KDX triple if I had the forks lowered to the max in the triple and removed the fork boot. Maybe not, but I don know I didn't like it and bought an 86 KX triple, which fit the KDX frame just fine.

So...... the point of the story is that the 96 KDX has the same "gull wing" lower triple as the KX's. Which would make me think the 96 KDX forks have the same "taller" fork lowers as the 88 KX forks. The 96 KDX fork does share a lot with the 88 KX fork.

Yeah, with KX triples you'd lose the headlight brackets, but you'll gain an aluminum stem and a few mm less offset. The 96 KDX forks will probably be longer than 87's. If you don't lower the forks to match, perhaps the reduced offset will compensate for the longer fork. Just making a guess on this one.

I'm using headlight mounting "bands" to mount my headlight directly to the fork tubes. I'm cutting a hole in the KDX shroud to put the bands through. It should work well and be lighter than the stock setup.

All speculation about the 96/87 fork fitment here on my end, but that's all I've got.

BTW, if you have to go for a KX triple, the 1986 moved the handlebars forward some (5mm?) compared to the 85. I am pretty sure the 87 and 88 KX triples were the same as the 86.
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Re: Swapping newer forks on to an '87

Post by KDXGarage »

I think it will work.
Check the area where the steering stops contact the lower triples.

The KDX has less travel than a KX fork. The sliders are taller on the KX fork also, if memory serves me correctly. It has been a decade or so since I had my '88 KX forks apart.
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Re: Swapping newer forks on to an '87

Post by Kipsy »

Hmmm. Good point, less travel. I actually have a 96 in the garage, as well as an 87. I will try to take some measurements today.
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Re: Swapping newer forks on to an '87

Post by baisleyde »

Thanks for the help and replies, but I've decided that I don't want to turn my beautiful 87 into a franken bike.

Image
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Re: Swapping newer forks on to an '87

Post by Kipsy »

Yeah, I think you made the right choice. If I could go back in time with my 88, I would have just bought race tech cartridge emulators and thrown those in the stock forks. Maybe add some stiffer springs. This would be much less work making things fit and I hear the emulators make the forks work way better. Plus you keep the chassis dimensions just the way the engineers designed it. I doubt we can do better then a team of Japanese engineers with the input of Jeff Fredette.

So, even though you decided not to try the 96 forks, here's the info I gathered in the garage, measuring things by eye and a tape measure while forks are on the bikes. So rough estimates here. Since I did the measuring I at least want to post it. Maybe it can help someone.

The 96 KDX forks have the same issue as the 88 KX forks. 96 has 11.4" travel, 87 has 10.6." That additional 0.8" of travel goes somewhere and it's not under the axle in these Kawasakis apparently (unlike mid-80's Yamaha's). The visible upper/inner tubes of both forks are the same length within 1/8". But the 96 lower/outer tubes are 1/2" taller as measured above axle centerline. So - you're going to have about 1/2 inch less clearance between the outer tube and the lower triple clamp at full compression when using the 87 non-gullwing triples. That would be if the 96 had the same travel as the 87. But it has 0.8 inches more, so maybe even more than 1/2" less clearance? I'll just call it a 1/2 inch for simplicity.

So...... Maybe 1/2" is still enough clearance if you remove the fork boots.... maybe. I'd just plan on using the 96 triples, though. I feel better with a margin of error between two metal parts slamming together when I'm on top of them. It looks like the 96 steering head is 3-4mm taller than the 87. So if the bearings match up and the steering stops match up (I didnt' check these), then the 96 should swap into the 87 frame with some washers/spacers to take up that 3-4mm.

FYI - as I was measuring this I remembered years ago my failed attempt to put 89-92 forks into the stock 88 triple. Same issue - outer tube made contact with lower triple. This was the frankenbike experiment that gave the "A-Ha" moment of realization - longer travel kawasakis need gull-wing triples. Coming from swapping YZ125 suspension on IT200's, it was surprising. Yamaha used the same triples and put most of their additional outer tube below the axle.

So here's the info I gathered. I hope it helps someone think through their air-cooled fork swap. And these are just my own thoughts - I'm probably wrong about half of it.
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Re: Swapping newer forks on to an '87

Post by Kipsy »

Nice bike, by the way. That tank looks like it's in fantastic condition. It's good not to tinker too much with a nice, complete, original bike.
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Re: Swapping newer forks on to an '87

Post by KDXGarage »

Nice looking '87!

Thanks for measuring! I was not thinking of that being an issue. Thanks for posting it for everyone.
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Re: Swapping newer forks on to an '87

Post by baisleyde »

Anyone happen to know what the preferred set up of the stock forks are? I got this bike last fall and only got to take it on one ride, I felt like the front forks beat me up in the rocks, they were pretty harsh. I was going to start by draining out whatever's in there and use 5W oil. I like em plush
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Re: Swapping newer forks on to an '87

Post by KDXGarage »

Make sure they are mechanically sound, then proper spring rate, then valving and oil.

If the stock springs are in there, then get the correct springs.

On damper rod forks, oil viscosity is going to factor in more on rebound than damping.

If it was me, I would completely disassemble and inspect the forks. New seals and bushings are probably called for. After that, correct spring rate and the lowest oil level in the manual for 10-weight oil. If it was harsh after all that, then the damper rod hole sizes / quantities need to be adjusted. That is what a revalve is on damper rod forks. Beyond that, Race tech Gold Valve Emulators.

With a modern theory on spring rate, 10 weight or more on fork oil would be the way to go, in my opinion. The viscosity helps control rebound. When you jump up a third in spring rate, the same old oil is not going to help as much on controlling it rebounding too quickly.
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Re: Swapping newer forks on to an '87

Post by Slick_Nick »

You might be able to get some emulators from racetech for that bike. Perfect solution for keeping the stock appearance of the bike.
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Re: Swapping newer forks on to an '87

Post by KDXGarage »

Here is a pic I took about 18 short years ago. :shock: This is from my 1987. I never rode them, so I have no ride report. :sad:
RaceTechCartridgeEmulatoron87KDX200.jpg
RaceTechCartridgeEmulatoron87KDX200.jpg (10.33 KiB) Viewed 2828 times
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