Rmx vs rm cylinder compatibility

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7/23/2017 5:37 PM

Alright guys, another rmx250 question from me.

I have found that my bottom end on my 89 rmx250 is beyond worth repairing.

I made a bid on eBay for a bottom end to an 89 to 91 rm250 bottom end. My top end is fine. The cylinder and head and piston are in great shape.

My question is, will my rmx250 jug and head/piston work on a rm250 of the same years bottom end?

I've fished around some oem numbers and I have some confidence but I'm hoping someone more knowledgeable will give me some insight. Thanks guys and gals

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7/23/2017 6:54 PM

When you get the RM crank shaft first thing measure the journals, the RMX used different size bearings on some years.
What i mean is some RM/RMX cranks shafts don't interchange because of shaft size difference.

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7/23/2017 6:59 PM

I guess I should clarify, the full bottom end is together. Crank, rod, everything. Only thing missing is cylinder, head, piston, wrist pin. I assume being a 250cc among the same year and one being an rmx and one being a rm, that the top end would be interchangeable with the rmx having most the differences in the trans and stator.

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7/24/2017 4:29 AM
Edited Date/Time: 7/24/2017 4:32 AM

The RMX cylinder should bolt on. the power valve linkage was the same between the RM and RMX in those years as well. You might lose a little performance doing it that way though, especially if the bottom end you're bidding on is a 1991 model. The 1989 cases had a smaller volume around the crankshaft, so much the 90-91 cranks won't fit in '89 cases. My local dealer has a complete 1989 RMX250 engine on a shelf in storage...it's locked up (probably seized). If you're interested, let me know and I'll give you the contact info

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Many thanks to everyone helping me out this GNCC season: SRT Offroad, Acerbis, FCR Suspension, O'Neal Racing, Evans Waterless Coolants, Rekluse, Twin Air, Braking Brakes, Carbsport

Profile image credit Ken Hill Photography

7/24/2017 11:14 AM

The cylinders for the RMX models all interchange upward to the same cylinders for '89 and '90 RM models: 11200-28821.
The same is true for the connecting rod; all parts interchange up to this number: 12161-05D00.

Here's my guess: the bore is the same because the cylinders match. The stroke is likely the same, because the rods match. It should all bolt up and work.

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Braaapin' aint easy.

7/24/2017 11:30 AM

Thanks guys. Huge help. I picked up an 89-91 rm250 bottom end from connecting rod down. And cover to cover. Only thing I have to do is install my top end onto the rm250 bottom end. I won't have the trail happy rmx but I will be able to ride. For what I've found, the cdi brain box seems to be the same for the rm and rmx as well so I should be able to basically do a normal top end rebuild. But only rings needed and gaskets, and pray to the 2 wheel God's and give it a kick.

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7/24/2017 11:31 AM

P.s... I'll keep this post updated for future searchers in case this topic comes up again. Maybe one day I'll get some brass and split the cases and install some rmx transmission gears.

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7/24/2017 6:59 PM

I think you will be fine with what you are trying to do. I recently took an 89 RMX250 bottom end and mated it to to a 92 rm250 top end. Everything bolted up just fine, but as others have mentioned the cranks are different between them so you will have to stick to the complete RM bottom end/flywheel setup.

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7/24/2017 7:49 PM

b_kowalsk wrote:

I think you will be fine with what you are trying to do. I recently took an 89 RMX250 bottom end and mated it to to a 92 rm250 top end. Everything bolted up just fine, but as others have mentioned the cranks are different between them so you will have to stick to the complete RM bottom end/flywheel setup.

No problem there, I don't plan on using lights as it doesn't have any now. Did you use your stock electronics? Coil and cdi? I searched and found for better power to use the rm250 head gasket on the rmx cylinder and head to get the power increase of the rm. Pretty excited to get this thing together. Also your carb, did you stick with the mikuni or did you go to the keihn?

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7/24/2017 7:51 PM

Sorry I read that backwards. You used the rmx250 bottom with an rm250 top. So I'm sure you stuck with the rm stuff. But of course if the rm250 electronics work for the RMX bottom, i assume mine will work for me in the rm bottom.

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7/25/2017 6:46 AM

Yeah, I pretty much did the opposite of what you are doing. The CDI and coil appear to be the same from the RM and the RMX so you shouldn't have any trouble there. I had both the Mikuni and Kehin Carbs available to me and just stuck with all the RM stuff.

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7/29/2017 8:50 AM

Okay guys, got my engine in from fedex today, and I'm excited to get working on it. Aside from fedex treating this thing like a rubber tire bouncing it everywhere it's actually in good shape. w00t

Couple questions, is there a way to verify year of the engine by simply the engine serial number? In the pic is the code.

Also what is a good way to properly clean this out?
I want to make sure there is no trash or debri in it but unsure of how to properly clean it.

I plan to get my old engine apart and start swapping components and pray it starts and runs!

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7/29/2017 8:51 AM

harescrambled wrote:

The RMX cylinder should bolt on. the power valve linkage was the same between the RM and RMX in those years as well. You might lose a little performance doing it that way though, especially if the bottom end you're bidding on is a 1991 model. The 1989 cases had a smaller volume around the crankshaft, so much the 90-91 cranks won't fit in '89 cases. My local dealer has a complete 1989 RMX250 engine on a shelf in storage...it's locked up (probably seized). If you're interested, let me know and I'll give you the contact info

Also I wanted to let you know I contacted him when you mentioned it in another post of mine. He actually sold it a few months ago. He said it's odd because it sat for so many years and then within a few months 2 people ask for it lol

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7/29/2017 8:52 AM

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7/29/2017 8:53 AM

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7/30/2017 3:09 PM

joeyburdette1985 wrote:

Also I wanted to let you know I contacted him when you mentioned it in another post of mine. He actually sold it a few months ago. He said it's odd because it sat for so many years and then within a few months 2 people ask for it lol

Probably because I've been shopping it around for them. I have many more contacts than the dealer does, and they've taken excellent care of me over the years...went above and beyond on several occasions...good prices for me, bringing me parts at the track...pay after the fact, etc...just really good people, so I do what I can for them.

That being said, I'm going to call that a '91 bottom end. I have a 1991 RM250 that's engine # J110-112219, and a 1992 RM250 Engine that's #J110-118464.

The outer clutch basket is visually different between the 1991 and 1992 RM, so if you could post up a pic of the clutch basket, I can confirm

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Many thanks to everyone helping me out this GNCC season: SRT Offroad, Acerbis, FCR Suspension, O'Neal Racing, Evans Waterless Coolants, Rekluse, Twin Air, Braking Brakes, Carbsport

Profile image credit Ken Hill Photography

7/31/2017 4:19 AM

harescrambled wrote:

The RMX cylinder should bolt on. the power valve linkage was the same between the RM and RMX in those years as well. You might lose a little performance doing it that way though, especially if the bottom end you're bidding on is a 1991 model. The 1989 cases had a smaller volume around the crankshaft, so much the 90-91 cranks won't fit in '89 cases. My local dealer has a complete 1989 RMX250 engine on a shelf in storage...it's locked up (probably seized). If you're interested, let me know and I'll give you the contact info

joeyburdette1985 wrote:

Also I wanted to let you know I contacted him when you mentioned it in another post of mine. He actually sold it a few months ago. He said it's odd because it sat for so many years and then within a few months 2 people ask for it lol

harescrambled wrote:

Probably because I've been shopping it around for them. I have many more contacts than the dealer does, and they've taken excellent care of me over the years...went above and beyond on several occasions...good prices for me, bringing me parts at the track...pay after the fact, etc...just really good people, so I do what I can for them.

That being said, I'm going to call that a '91 bottom end. I have a 1991 RM250 that's engine # J110-112219, and a 1992 RM250 Engine that's #J110-118464.

The outer clutch basket is visually different between the 1991 and 1992 RM, so if you could post up a pic of the clutch basket, I can confirm

Photo


Photo

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7/31/2017 4:29 AM

harescrambled wrote:

Probably because I've been shopping it around for them. I have many more contacts than the dealer does, and they've taken excellent care of me over the years...went above and beyond on several occasions...good prices for me, bringing me parts at the track...pay after the fact, etc...just really good people, so I do what I can for them.

That being said, I'm going to call that a '91 bottom end. I have a 1991 RM250 that's engine # J110-112219, and a 1992 RM250 Engine that's #J110-118464.

The outer clutch basket is visually different between the 1991 and 1992 RM, so if you could post up a pic of the clutch basket, I can confirm

Photo


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Is this what you need to identify
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7/31/2017 2:33 PM

Yes it is. Apparently the cross over was earlier than I thought. That's not a 1991 clutch basket. Basket is a 1992. Looks like you got a 1992 bottom end.

Heres my 1992 clutch basket:Photo

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Many thanks to everyone helping me out this GNCC season: SRT Offroad, Acerbis, FCR Suspension, O'Neal Racing, Evans Waterless Coolants, Rekluse, Twin Air, Braking Brakes, Carbsport

Profile image credit Ken Hill Photography

8/4/2017 7:39 PM

Hey guys, a little update. I got the engine together. And set it in tonight. Still need some various parts and things tuned in but hey, it runs!! Super excited to get it moving and wheel standing! Having an issue of it idling really high and bogging when giving it some throttle so I have to figure that out.

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8/5/2017 8:59 AM

joeyburdette1985 wrote:

Hey guys, a little update. I got the engine together. And set it in tonight. Still need some various parts and things tuned in but hey, it runs!! Super excited to get it moving and wheel standing! Having an issue of it idling really high and bogging when giving it some throttle so I have to figure that out.

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It's running lean. Either you have an air leak, or your fuel screw is turned in too far.

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Many thanks to everyone helping me out this GNCC season: SRT Offroad, Acerbis, FCR Suspension, O'Neal Racing, Evans Waterless Coolants, Rekluse, Twin Air, Braking Brakes, Carbsport

Profile image credit Ken Hill Photography

8/7/2017 3:41 AM

harescrambled wrote:

It's running lean. Either you have an air leak, or your fuel screw is turned in too far.

Did some more this weekend, the throttle tube was adjusted wrong causing the high idle, and found the reeds are letting light through as well as it's puffing back through the intake. Just ordered some new carbon fiber reeds for my vforce3 and will give it another go. But I'm stoked at how far it's come.

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