Cartridge Fork Swap 83' CR250

3ushman
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3ushman
Edited Date/Time 5/21/2020 9:33am
I know theres a handful of guys on this forum that have done cartridge fork swaps and I need a little help please. Trying to get 86' CR500 fork cartridges into my 83' CR250. Ive got a lathe and know you need to turn down the bottoming cone. What I need help with is the washer/bushing for the compression adjuster on the bottom. Anybody have any dimensions for this, or pictures? Trying to get an idea of how thick it needs to be etc.
Thanks in Advance!
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TTperra
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TTperra 4/28/2020 2:11pm
4/28/2020 2:11pm
Forgot to answer you earlier, sorry!
I did not record the dimensions, i made a "stept washer", the smaller diameter same as the mounting hole in lower legs and the lager diameter to fit inside where the protection rubber is supposed to be.
I made mine from T6 aluminum and sealed the washer to lower legs with hydraulic sealant.
If you make it too thick, there is a risk that the adjuster dont reach the seat on compression valve.
Hope this help some
3ushman
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3ushman 4/28/2020 2:20pm
4/28/2020 2:20pm Edited Date/Time 4/28/2020 2:21pm
TTperra wrote:
Forgot to answer you earlier, sorry! I did not record the dimensions, i made a "stept washer", the smaller diameter same as the mounting hole in...
Forgot to answer you earlier, sorry!
I did not record the dimensions, i made a "stept washer", the smaller diameter same as the mounting hole in lower legs and the lager diameter to fit inside where the protection rubber is supposed to be.
I made mine from T6 aluminum and sealed the washer to lower legs with hydraulic sealant.
If you make it too thick, there is a risk that the adjuster dont reach the seat on compression valve.
Hope this help some
Thank you TTperra. I think I was just overthinking it. That makes perfect sense and answers my question about depth. So would you say the outer part of the stepped washer would be around .100 thou thick or less? If your not sure no biggie, I think you’ve got me confident enough to make them now. Thanks again 👍🏼
TTperra
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TTperra 4/28/2020 2:41pm
4/28/2020 2:41pm
Yes, i think i made it 0.080-0.100 (2.0-2.5mm)
3ushman
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3ushman 4/28/2020 4:40pm
4/28/2020 4:40pm
TTperra wrote:
Yes, i think i made it 0.080-0.100 (2.0-2.5mm)
Thank you. I’ll cut one on the larger side and turn it down if needed. Turned the bottoming cones today, turned out good.



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TTperra
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TTperra 4/28/2020 11:50pm
4/28/2020 11:50pm
I was looking in my computer for pictures, and i remember wrong about the step washer.
the larger diameter is made to fit inside the countersink part, so you can use the rubber protection.
maby you already figured that out.

Here are some pictures, not mine. dont remember where i stoled them..
If someone recognize them and dont want them here, let me know and i delete them.




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3ushman
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3ushman 4/29/2020 4:56am
4/29/2020 4:56am
TTperra wrote:
I was looking in my computer for pictures, and i remember wrong about the step washer. the larger diameter is made to fit inside the countersink...
I was looking in my computer for pictures, and i remember wrong about the step washer.
the larger diameter is made to fit inside the countersink part, so you can use the rubber protection.
maby you already figured that out.

Here are some pictures, not mine. dont remember where i stoled them..
If someone recognize them and dont want them here, let me know and i delete them.




That's what I figured since the adjuster only has so much travel. I drew up some dimensions yesterday for that 1" countersink, just need to go pick up some bar stock. That one in the picture looks to be about .100 (2.5mm) on the shoulder. I really appreciate you helping me out. I scoured the internet for a picture like that a few days ago only to come up empty handed.
TTperra
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TTperra 4/29/2020 11:47am
4/29/2020 11:47am
Glad to help
Remember to bottom the fork when tighten the adjusterbolt, so the bottoming cone is properly positioned
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3ushman
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3ushman 4/29/2020 8:54pm
4/29/2020 8:54pm Edited Date/Time 4/29/2020 8:55pm
TTperra: Thanks for the advice, ill make sure they're seated fully before threading it in.



Max Power: Don't temp me, I've already been thinking about it. I thought about making the stepped washers and having a pair of bottoming cones already turned down with a "core charge" or something to that effect. What kind of pricing would you expect something like that to be, or what seems fair?
bad juju
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bad juju 4/29/2020 9:02pm
4/29/2020 9:02pm
3ushman wrote:
TTperra: Thanks for the advice, ill make sure they're seated fully before threading it in. Max Power: Don't temp me, I've already been thinking about it...
TTperra: Thanks for the advice, ill make sure they're seated fully before threading it in.



Max Power: Don't temp me, I've already been thinking about it. I thought about making the stepped washers and having a pair of bottoming cones already turned down with a "core charge" or something to that effect. What kind of pricing would you expect something like that to be, or what seems fair?
the problem with the 83 fork is no one has outer bushing anymore, I just went all 87 with the disc, but with I could run the drum..
3ushman
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3ushman 4/29/2020 9:12pm
4/29/2020 9:12pm
3ushman wrote:
TTperra: Thanks for the advice, ill make sure they're seated fully before threading it in. Max Power: Don't temp me, I've already been thinking about it...
TTperra: Thanks for the advice, ill make sure they're seated fully before threading it in.



Max Power: Don't temp me, I've already been thinking about it. I thought about making the stepped washers and having a pair of bottoming cones already turned down with a "core charge" or something to that effect. What kind of pricing would you expect something like that to be, or what seems fair?
bad juju wrote:
the problem with the 83 fork is no one has outer bushing anymore, I just went all 87 with the disc, but with I could run...
the problem with the 83 fork is no one has outer bushing anymore, I just went all 87 with the disc, but with I could run the drum..
If your switching over internals from an 86-88 bike you would still be able to get them for those cartridge forks. Only thing that stays 83’ is the outer fork leg itself. I think the only real appeal to this mod is for people who race and want to keep the drum up front to qualify for certain classes while not killing themselves on mediocre forks.
TTperra
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TTperra 4/29/2020 10:22pm
4/29/2020 10:22pm
I wonder if anyone has made a similar modification to YZ250/465 -81 forks?
Kidkawie
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Kidkawie 4/30/2020 3:05am
4/30/2020 3:05am
Cant you cut an oring groove in it?
3ushman
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3ushman 4/30/2020 9:20am
4/30/2020 9:20am
TTperra: Not sure on the YZ forks, but if it’s possible I’m sure it’s been done.



Kidkawie: I had thought about doing that, but the flange is so thin already I don’t want to risk the integrity of the part. I’m making it a press fit to reduce the chance of any leaks.
450exc115
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450exc115 4/30/2020 10:15am
4/30/2020 10:15am
Buddy of mine just went through this when he used 05 XR650 43mm forks for the transplant. He ended up rednecking/McMaster Carr it with a washer and two copper washers to seal it up. He is a little off on the hole alignment in the cartridge but is working through it. He is also using the XR inner tubes and CR lower tubes.

As for the bushing issue the easiest way to overcome is to order 4 12mm bushings from RT and double up to match the 24mm bushing on the 83 forks. Or you can run a 20mm bushing from the KTM 43mm forks found on the 00-02 bikes but you'll have 4-5mm of gap left.

I was going to have a lug welded on my XR650 forks and even bough the reem for cleaning up the tube ID due to any local heat warpage but ended up buying the $105 bracket from Advanced Machining NW, Inc in WA. I did have to swap the bearings in my 80 CR250 front hub and then reemed the brake plate to deal with the 2mm larger axle,

I also have a set of 88 YZ125 forks that I've been meaning to pull apart to figure how to adapt to my 81 YZ465 43mm forks. The only thing I see from the outside is the lower legs of the 88 forks are definitely longer below the axle than the 81 forks. But I think we can figure it out. Smile




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3ushman
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3ushman 4/30/2020 10:23am
4/30/2020 10:23am
450exc115 wrote:
Buddy of mine just went through this when he used 05 XR650 43mm forks for the transplant. He ended up rednecking/McMaster Carr it with a washer...
Buddy of mine just went through this when he used 05 XR650 43mm forks for the transplant. He ended up rednecking/McMaster Carr it with a washer and two copper washers to seal it up. He is a little off on the hole alignment in the cartridge but is working through it. He is also using the XR inner tubes and CR lower tubes.

As for the bushing issue the easiest way to overcome is to order 4 12mm bushings from RT and double up to match the 24mm bushing on the 83 forks. Or you can run a 20mm bushing from the KTM 43mm forks found on the 00-02 bikes but you'll have 4-5mm of gap left.

I was going to have a lug welded on my XR650 forks and even bough the reem for cleaning up the tube ID due to any local heat warpage but ended up buying the $105 bracket from Advanced Machining NW, Inc in WA. I did have to swap the bearings in my 80 CR250 front hub and then reemed the brake plate to deal with the 2mm larger axle,

I also have a set of 88 YZ125 forks that I've been meaning to pull apart to figure how to adapt to my 81 YZ465 43mm forks. The only thing I see from the outside is the lower legs of the 88 forks are definitely longer below the axle than the 81 forks. But I think we can figure it out. Smile




That’s good info. Thanks for sharing. I hope all this helps the next person looking to do a fork conversion.
TTperra
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TTperra 4/30/2020 3:10pm
4/30/2020 3:10pm
450exc115 wrote:
Buddy of mine just went through this when he used 05 XR650 43mm forks for the transplant. He ended up rednecking/McMaster Carr it with a washer...
Buddy of mine just went through this when he used 05 XR650 43mm forks for the transplant. He ended up rednecking/McMaster Carr it with a washer and two copper washers to seal it up. He is a little off on the hole alignment in the cartridge but is working through it. He is also using the XR inner tubes and CR lower tubes.

As for the bushing issue the easiest way to overcome is to order 4 12mm bushings from RT and double up to match the 24mm bushing on the 83 forks. Or you can run a 20mm bushing from the KTM 43mm forks found on the 00-02 bikes but you'll have 4-5mm of gap left.

I was going to have a lug welded on my XR650 forks and even bough the reem for cleaning up the tube ID due to any local heat warpage but ended up buying the $105 bracket from Advanced Machining NW, Inc in WA. I did have to swap the bearings in my 80 CR250 front hub and then reemed the brake plate to deal with the 2mm larger axle,

I also have a set of 88 YZ125 forks that I've been meaning to pull apart to figure how to adapt to my 81 YZ465 43mm forks. The only thing I see from the outside is the lower legs of the 88 forks are definitely longer below the axle than the 81 forks. But I think we can figure it out. Smile




Have you taken the XR forks apart and looked at the compression valve?
I bought a set of NOS valves, and they look funky, some kind of cartridge where the shims bend/flex on the inside.. Nothing like my CR250 -88 valves.

Please keep us updated about the YZ forks
3ushman
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3ushman 5/18/2020 7:48pm
5/18/2020 7:48pm
Finally got a minute to make a pair of bushings. They seem to fit perfectly.

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Whymee
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Whymee 5/19/2020 8:41am
5/19/2020 8:41am
3ushman wrote:
Finally got a minute to make a pair of bushings. They seem to fit perfectly. [img]https://p.vitalmx.com/photos/forums/2020/05/18/428124/s1200_BE72182B_9DE5_4FFA_89F6_B289EE50F94B.jpg[/img]
Finally got a minute to make a pair of bushings. They seem to fit perfectly.

Are you going into production?

I am down for a couple sets...
wolfy0067
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wolfy0067 5/21/2020 9:24am
5/21/2020 9:24am
I though I had originally posted this sometime ago, here's some specs
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wolfy0067 5/21/2020 9:25am
5/21/2020 9:25am
Keep in mind you need to cut the new bottoming cones
3ushman
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3ushman 5/21/2020 9:32am
5/21/2020 9:32am
wolfy0067 wrote:
Keep in mind you need to cut the new bottoming cones
I turned my bottoming cones, but your dimensions and my dimensions are almost spot on from what I made. Thanks for the input!

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