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motoxhead

Complete Bottom End Rebuild - Rm250

10 posts in this topic

My 04 rm250 has to have the bottom end rebuilt. I'm going to replace everything while I'm in there. Main Crank bearing and seals, but the crank itself I'm not sure about. I've heard its very difficult to take it apart to replace the big end bearings. Would it be easier or more cost effective to just replace the entire crank assembly with a hot rods set up?

This if my first bottom end job so any tips or suggestions would be much appreciated.

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You can have your shop rebuild the crank with a new rod kit, or you can buy a new crank. A rod kit cost $100 and my shop charges $50 to rebuild a crank.

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Depends on your budget. I just did my '05 for under $600 which included a Hot Rods crank kit all new bearings and seals using a Wiesco piston kit. I also had my cyl. sleeved so that was a little more. If having a shop rebuild your old crank is more then a new kit, I wouldn't do it. I paid $200 shipped for a Hot Rods crank kit with wrist pin bearing.

Also If you've never R&R your lower end you may want to get some help from someone who has.

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Same here. I always go buy the Hotrod crank kit except I use all oem bearings and seals. I have had nothing but problems with the aftermarket seals and gaskets on my RM.

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I just did an entire motor rebuild on an 03 RM250 hot rod kit all bearings pressed in and out with a 100 northern tool 4 ton press worked great!!! and moose bearings and seals... been riding for a month no problems but what started the whole thing was the clutch side crank seal pooped the spring of and sucked oil!!!!!! I feel if installed properly and pressed in with proper tools and not beat with a socket all seals and bearings are good...My 2 cents good luck and keep track of the tranny stuff lots of washers and gears to get messed up just pull it and lay on table so you can somewhat keep track of whats there and when you put it together on the bench before its all togother and in the bike make sure it shifts throught the gears and you can get nuteral before you have it all together in the bike...

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What kind of crank truing jig did you use?

Is this neccessary if you order the entire crank assembly.

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Is this neccessary if you order the entire crank assembly.

no, they come trued.

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I totally agree on using OEM seals and gaskets. I also use only OEM bearings in the cases. The only thing the Hotrods crank kit comes with is the assembled crank assembly which includes the webs, crank pin, shims, rod & both rod bearings.

As said above, keep track on how things come apart. There are a couple shims on the shafts and I believe 2 washers in there that have to go back the way they came out.

What I do is lay the right case down on the bench and separate the left (shifter side) case first. What I've found is that's the simplest side to work with to keep the shafts assembled. Most of the time when you separate the case the washers will stay on the Drive shaft and Counter shaft, if not then their on the inside of the case and easy to see where they went.

Also make sure the washer that goes between the water pump shaft and the case goes back in place.

I would also suggest replacing all the crankshaft bearing retainer screws (there's 4 of them) and the lock washer on the clutch hub.

Alot of the small stuff is real cheap and just good insurance.

Press out the old bearings. When your putting the new crank bearings in the cases try the following method.

Put the new bearings in the freezer over night. When your ready to install the bearings heat the cleaned up case around the bearing surface with a propane torch until it sizzles when you spit on it. Get the bearings out of the freezer and drop them into place. They will just drop right in. The cold shrinks the bearings just enough and the heat enlarges the bearing surface just enough also for a perfect fit. Cool the cases then re-install the bearing retainers using Locktite.

Try to use the right tools for the job. Do not hit the new crank with a hammer trying to get back into the bearings. It really needs to be pressed with the proper tooling. I made my own. If you can fabricate and have access to a Lathe or have a friend that's a fabricator then it's actually pretty easy.

One last thing, use a good quality assembly lube around the inside of the seal when you re-install the seals and a good sealant in-between the cases with the gasket when you re-assemble the cases.

Good luck. If your careful and patient it's actually really easy.

Sorry I got into so much detail if this isn't helpful, but I got carried away.

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Very helpful marc. Would you mind giving away your trade secrets for your fabricated tool?

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