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Discussion Starter · #1 ·
Hello everyone, unfortunately I am continuing my rough start into the KTM field of things. I made a previous post discussing an excessive amount of metal shavings in the short screen. Eventually we came to the conclusion it was left over metal from the 575 bore kit and previous owner negligence on clearing out the screens. While that would make life much easier had that been the case, the bike has other plans. Last week I pulled the oil for maintenance and such and lo and behold, the same amount of shavings. I figured maybe it didn't like the clutch-less shifting (though I am very gentle with it) and decided to run an experiment using the clutch for every shift until the next maintenance. Alas it looks like I won't be reaching that for a while.

20 Miles into the service a noticeable whirring noise came about and a louder, heavier thudding began, the whirring sounds just like straight cut gears in a race car. I thought the circlip on the water pump gave up the chase so I checked that, nothing there. Next I went to the primary gear nut and that's all torqued down. This is where I noticed the excessive amount of play in the shaft.

Looking at the gear from the right side of the engine, the primary gear and components can move in all directions about 3/32". I believe KTM suggests .25 - .35mm --> .01 - .013".
102550

102551


The upper picture shows the crank pulled down as far as it will go, the lower picture shows the crank pushed up as far as it will go. Though it isn't as clear as I had hoped, it shows the play in the shaft.

Now I am comfortable rebuilding engines, that being said, I'd like to avoid it if at all possible. Being new to KTM I'm not sure what parts I will actually need, where to have the crank welded, which manufacturers I should avoid, and that sort of thing. In my time surfing KTM Forums I've read that this is a fairly frequent occurrence on the RFS engines that are supermoto'd. If I wind up rebuilding it what should I do to prevent this from happening again? Is it worth it to attempt this on my own or should I just take it to a shop and pay to have it done?

Bennet M.
 

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I would be surprised if your big end on the conrod would not also need a rebuild.

The output shaft from the crank will need a new bearing (at the least) and there is hopefully no issues with the shaft itself.

Dismantle motor to find out what is wrong. The rebuilding of a crank and fitting a new conrod I leave to the experts. But you might have that knowledge?

Good Luck!!
 
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Dirt Wizard
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Journals could've spread. I've rebuilt a couple cranks. I use to send them away until I found out the experts here just do them the same rough way I do. (Press, copper hammer and v-blocks) I haven't had the pin welded before on any though, but they say it stops them spreading. I've split and rebuilt plenty of the rfs engines, so if you're willing to have a go, I can help you out.
They're cylindrical roller bearing mains with removable inner rings, so they're very easy to split the cases. You will need a timing chain splitter and flywheel puller. You can use the balance shaft drive gear to pop the left hand inner ring off by screwing a couple longer bolts into the threaded holes gently and evenly against the counter weight and the that will draw the gear, inner ring and shim washers off.
Due to being roller bearing mains, the end float of the crank is very important.
If I had to take a guess I reckon this hasn't been checked or shimmed up properly and it's probably fried them.
Got to do them with a dial gauge.
Not like an old japper with ball bearing mains.
 
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Discussion Starter · #4 ·
Right right, thank you for the replies ya'll. I don't know if I have the experience with the rfs yet to tackle it on my own. Air-cooled VW's ok, KTM not yet. I may try to find someone in town here in Fresno, CA who would be willing to guide me through it. DW thank you for the offer, if anything comes up I will certainly ask for your advice! I am on the fence about just giving it to an engine builder and having them do the entire thing top to bottom then not have to worry about it anymore haha.
 
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