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Transmission rebuild question/bearings

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Hi all, just starting a rebuild of my transmission after it locked up a couple weeks ago. Haven't split the cases yet to assess the damage yet, but there were metal shavings on the magnetic drainplug and one piece of metal about the size of an apple seed when I drained the oil. I also had a small amount of shavings on the screen that goes up into the downtube on the frame.

I was expecting more metal than what I saw, but there was definitely metal floating around. I was way back in a wilderness area and had to drive out in first gear for 20 miles before the transmission locked up completely. Motor still runs, but even with clutch in the rear wheel remains locked. Can't shift between gears. Point is, engine oil was circulating for that 20 mile ride at 18mph.

I am going to put in ACT WR gears and want to proactively replace other potential fail elements inclulding the driveshaft, countershaft and shift bearings. My question to you is regarding the main crank bearings. It seems the tranny and crank are compartmentalized so they are not sharing the same oil bath, but the question is, is the oil filtered when it comes out of the tranny and before its sent to the crank and connecting rod bearings. Should I replace the crank bearings while in there? Parts will be a lot less than the tool I will need to pull the crank back into the case on reassembly.

Want to be prudent, but if the bearings were protected, that will be on less thing to mess with.

Appreciate any advice.

DH

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If you're spending the time to split the cases for the tranny, would you really want to do it again if those bearings are or do go bad?

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. It seems the tranny and crank are compartmentalized so they are not sharing the same oil bath,

No sir, same oil... transmission and engine...

Yes, if you have metal bits in the oil, personally I would replace the crank bearings.

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No sir, same oil... transmission and engine...

Yes, if you have metal bits in the oil, personally I would replace the crank bearings.

To clarify, same oil and engine, yes I know its shared, my point was before the oil hit the crank bearings, did it go through the strainer/filter? By compartmentalized I meant that there was a section where the transmission gears are and there seems to be a housing around the crank. Realizing the oil is circulating through the system, does the oil get filtered before it goes into the section with the crank is what I am asking. As you both suggest, changing the crank bearings probably is the safest bet, and that is the way I am leaning, but if there is no need to do that I want to save buying the extra tool . Crank bearings aren't that expensive, its the tool I have to buy (most likely) that I will only use once that bothers me.

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To clarify, same oil and engine, yes I know its shared, my point was before the oil hit the crank bearings, did it go through the strainer/filter? By compartmentalized I meant that there was a section where the transmission gears are and there seems to be a housing around the crank. Realizing the oil is circulating through the system, does the oil get filtered before it goes into the section with the crank is what I am asking. As you both suggest, changing the crank bearings probably is the safest bet, and that is the way I am leaning, but if there is no need to do that I want to save buying the extra tool . Crank bearings aren't that expensive, its the tool I have to buy (most likely) that I will only use once that bothers me.

Lube path.jpg

That is the lube path.

As for tools...

If you're splitting the case, the additional tools to replace crank bearings would be a throat plate and hyd press... if you don't have and don't need for other work, take the crank to a shop and have them remove the bearings.

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Oil collects in the engine sump, picked up by the return pump via a course screen, into the frame, out thru a course screen into the feed pump, thru the paper filter and distributed throughout the engine. Will the paper filter collect all of the debris? Hard to say. How much metal gets thrown around by the moving parts without going thru the filter? Hard to say.

In my limited experience the main bearings stay in the cases. Pretty easy to remove if the cases are heated. Probably no need for a press. Cold bearings drop into a heated case.

You need a case splitter tool to take the crank out. I don't think you need any additional special tools to replace the main bearings. There is also a special tool to draw the cases back together but I don't remember what I did for that. I probably just heated the case/bearing assembly and set it together.

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In my limited experience the main bearings stay in the cases. Pretty easy to remove if the cases are heated. Probably no need for a press. Cold bearings drop into a heated case.

MOST times, true.. but like heating the bearing to install, while it works MOST times, sometimes it does not... hence the "required" tool... Sorry, I was going for the I don't know the poster, experience level or what might happen when he splits the cases... (of note, yes I agree with Noble, most times the bearings stay in the cases... occasionally I get one bearing that will come out with the crank..

You need a case splitter tool to take the crank out. I don't think you need any additional special tools to replace the main bearings. There is also a special tool to draw the cases back together but I don't remember what I did for that. I probably just heated the case/bearing assembly and set it together.

As he was already talking about splitting the cases and the only addition was replacing main bearings.. I neglected to suggest the other needed tools. Nice catch Noble

Like stated above, heating the cases and the inner bearing race just prior to seating the case haves may work for some..and I do it even when using a tool to pull the crank .. but.. there are an awful lot of things to line up, and get perfect when these case haves go together.. .. with the heat method only you get one shot.. and if the process stalls, you're now stuck with a partially assembled motor...and scratching your head as to how you will finish the job.. THIS is the point folks start grabbing hammers, blocks of wood or moving the whole motor over to the vise and press table..... making a mess of the task and causing more damage than good.

If you're handy with fabrication you can make a crank puller..if not you can buy one, if not that, consider a local shop for just the task of putting the cases back together...

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Thanks guys, good discussion on this and it is helpful I do have a case splitter I bought for this application and a flywheel puller. Probably will replace the mains, though it sounds like from an oil flow standpoint my original question was answered by the diagram and the commentary. That being said, I don't know what I don't know, which is how much oil/metal was thrown around and perhaps still found its way to the crank?

I am planning on using a blind bearing puller on all the bearings, and was wondering primarily about the crank puller to get the crank back in the one case/bearing before assembly. Hadn't thought yet about lining everything up and getting the other side on at this point, but obviously that will take a lot of care. Suggestion of having a shop do it is a good one to consider.

Any other ideas are appreciated.

Oh, and to answer the question about my ability, I have not split the cases before on any bikes, but I am a decent, patient mechanic that reads everything three times, knows to use the right tools, and unlike my father who's theory was "use a bigger hammer", I have learned not to force things. If it isn't going together or coming apart easily, I am probably doing something wrong. The manuals and information on the internet is very helpful, but I know there are a lot of tricks I will not know and so the process will be slower than someone thats done it a couple time. Don't want to do this twice.

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