trying to make a hybrid - narrowing the cases

Tedh98 · Post by **Tedh98** » 04:40 pm May 15 2009

Last weekend I picked up a '97 kdx200. I currently have a 2000 yz125 that I'd like to put the 200 engine in. My problem is that the yz swingarm can't be cut like a kx swingarm can.

How many people have narrowed the cases instead of widening the swingarm? It looks like those steel sleeves in the case are just pressed in. I was thinking about removing them, narrowing the cases and then pressing them back in. My concern is that removing the aluminum from the cases might weaken the back end of the engine. I really don't want to have to split the cases to get an idea of just how much aluminum is surrounding the hole for the swingarm shaft bolt.

If anyone has experience with cutting the cases, I'd like to hear about it.

Thanks

ethanfoster · Post by **ethanfoster** » 05:34 pm May 18 2009

is there any bolts that line up

Tedh98 · Post by **Tedh98** » 05:43 pm May 18 2009

I haven't gotten that far on checking how the mounts fit. I figure if I can't make the swingarm work, then the rest doesn't matter.

SVandal · Post by **SVandal** » 01:10 am May 19 2009

Why can't you cut the swingarm? As for cutting the cases down, the steel sleeve doesn't go all the way through, just a little on each side. To do it right I'd recommend making a steel sleeve that can be pressed into the place of the stock on if you can't reuse the stock one. Possibly due to limited material in the cases to hold the sleeve.

Tedh98 · Post by **Tedh98** » 06:41 am May 19 2009

Unfortunately for me, the area right behind where the bearings are pressed in is hollow. In the two pictures, you can see the black rubber plugs that keep dirt out of the hollow cavity behind the bearings. From what I can tell, if I tried to cut the swingarm, I'd cut through the aluminum and expose that cavity. Plus, the yz swingarm uses two sets of bearings on each side. So there isn't that much dead space like there is on a kx.

I was really hoping I could use my yz. But I'm now thinking about trying to find a kx and then selling my yz when I'm all finished with the hybrid.

SVandal · Post by **SVandal** » 08:26 am May 19 2009

Cr's work as well

. Sorry about the swingarm, how much material do you need to take off?

Tedh98 · Post by **Tedh98** » 08:41 am May 19 2009

A total of about 15mm. But I'm not sure if I need to remove that equally or if I have to take off more on one side than the other to get the sprockets to line up.

I've been looking around for a CR. I've found a complete '01 CR and I've found a '04 KX roller for the same price.

SVandal · Post by **SVandal** » 08:48 am May 19 2009

go for the kx then. The 01 cr is the 2nd gen frame and I've heard great things about the 03 and newer kx bikes. Unless you live in Cali.

KarlP · Post by **KarlP** » 10:47 am May 20 2009

You might take one more look at that YZ frame.

What has to happen is that the CS sprocket on the motor falls in line with the rear wheel. You can't do anything to the outside of the swingarm 'cause it still has to fit the frame.

On my CR/KDX hybrid I had to shorten the case, enlarge the hole in the case, and shorten one of the inner bearing races. I've been riding it hard for over a year with no problem.

I'd set the motor on the bench, set the swingarm up with the bearings and inner races installed, and see what has to go where.

Like you said, you don't care where any of the other mounts are. You are obligated to mount the motor to the swingarm first so that the CS sprocket is in the right place

Tedh98 · Post by **Tedh98** » 03:59 pm May 20 2009

Karl - do you remember how much you had to narrow the cases? Did you ever have the cases split to see how much 'meat' was in that area?

I had an idea about the swingarm earlier today. If the machine shop took off the necessary material and it exposed the cavity of the swingarm, I think they could tig some new aluminum in place to 'box' the swingarm back up. That should retain the strength of the swing arm.

I'd really like to use the yz b/c I haven't seen anyone else putting a kdx engine into it. So I like the challenge. Plus I already have the bike and don't need to buy another one and deal with selling the yz. But I also see a lot of benefits going with the kx since that approach has been documented.

KarlP · Post by **KarlP** » 02:44 pm May 21 2009

Ted-
I think I had to take about a 1/4" off the case on the right hand side. I had to shorten the inner race of the swingarm bearing on that side 1/8".
You can tell from the parts diagrams what is going in the case halves. All was well on the left (CS) side.
This is on a '99 CR250

I had to drill out the swingarm bolt hole. From 14 mm to 17mm? It doesn't matter. There was still some of the steel inserts left. I tried to push them out at first but it was not going to happen.

I'll tell you how I cut the case if you promise not to tell anyone....Die grinder and a 3" cut off wheel

I scribed a line at less than 1/4" and cut by hand as straight as I could. I did not split the cases but the cylinder was off.
Then I mounted the motor in a drill press and used a big end mill I borrowed from work to try to flatten out the cut.

The cut ended up a bit crooked so the inner race on the right side does not sit quite square against the case.

Seems to be O.K., Ive been riding it for over a year, ran it in 4 Enduros, absolutely nothing has gone wrong on it.

No one can tell from here what you've got to do to get the YZ swingarm and KDX motor together. You'll need to have that KDX motor on the bench with the YZ swingarm and work it out.

ethanfoster · Post by **ethanfoster** » 07:31 pm May 21 2009

do the plugs hit the motor? If not why don't you cut around them?

ethanfoster · Post by **ethanfoster** » 07:49 pm May 21 2009

also has anybody ever used the kdx swing arm on a hybrid?

Tedh98 · Post by **Tedh98** » 08:08 pm May 21 2009

The plugs aren't a problem, it is what the plugs are plugging up. There is a hollow cavity behind the area of the plug. If I cut the swingarm, I'll open up that cavity and weaken the swingarm.

I bought an extra swingarm on eBay and I'm going to mock things up and cut the swingarm to see what I'm dealing with.

ethanfoster · Post by **ethanfoster** » 08:25 pm May 21 2009

well if you cut the cases you have to ream them right? If so why not ream out the alumlinum all together.

SVandal · Post by **SVandal** » 10:48 pm May 21 2009

Its not the aluminum, its the steel sleeve that prevents your swingarm bolt from eating through the case. The sleeve distributes the load from the swingarm.

ethanfoster · Post by **ethanfoster** » 02:31 pm May 27 2009

so if he had a new sleeve pressed in that went from one end to other end of the case then would that work?

SVandal · Post by **SVandal** » 07:49 pm May 27 2009

Yeah, but a two part would be more appropriate to stay with the original design. If you don't have a shop it may be costly to get the cases drilled. I am referring to drilling the bushing after pressing it into the case so as to keep it aligned. However, if you only did a sleeve on the outside like Ma-Kaw then you should be fine to drill and ream the cases to size and then just press in from each side. All sorts of fun with these things. Just don't take off too much, there isn't much else to hold onto on the back of the engine and it will see some decent loads.

Tedh98 · Post by **Tedh98** » 02:00 pm May 30 2009

Thanks for the insight and advice on narrowing the cases.

I decided not to use the YZ afterall. There are a number of unknowns with using that bike and it is in such great shape that I don't want to make it un-sellable if things don't work out.

So I picked up this '04 KX 125 roller a couple of nights ago and already started working on the swing arm. I'm using a table saw to cut the swing arm and will post those pictures in a different thread.

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SVandal · Post by **SVandal** » 02:26 pm May 30 2009

I think you'll be a lot happier with the results this way! Much better to go with a bike that you know will work, and it stays team green.

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trying to make a hybrid - narrowing the cases

trying to make a hybrid - narrowing the cases