Swapping out a crank, need lots of input asap

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Mar 25, 2006
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#1
Well, at a local race on the 10th in my final moto of the day I was coming out of a gully when my bike seized. I pushed it up to the top of the hill and sat on the side of the track waiting to cross when another bike clipped mine, bending my right side foot peg, breaking the end of my brake lever off and stoeing in the side of my brand new factory fatty pipe.

So aside from my luck being that I was standing on the side of the bike that didn't get creamed and my 12 year old neighbor who ran over and was standing beside me didn't get hurt, I'm looking at a hefty repair bill.

As far as I know the mechanical damage consists of a lightly scratched cylinder that honing shold fix, and the connecting rod is seized onto the crank solid, so I'll probably need a new crank, and then the additional damage of the stoed in $300 pipe. So I'd like to know if I buy a hot-rods crank, what'd be the difficulty of putting it together myself? I don't have a service manual but am going to get one.
I read(on this site I believe) that cranks are pushed together using a 20ton press but you need a special tool when assembling the cases to make sure the crank isn't taken out of true? I'm also gonna replace the main bearings while it's apart.

So if it's conceivable for me to do this at home let me know quick, cause there's a bottom end I'm thinking about buying on e-bay for like 300ish and it's over in a couple hours.


Thanks to anyone who can help, really appreciate it.
 
Joined
Oct 19, 2006
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#2
It's easy to install install a crank, no presses are required. With carful heating with a propane torch, everything drops together by gravity. Cases are aligned with dowel pins, they don't go out of alignment. Sometimes a special tool is used to pull the crank into the case, but it's not necessary if you heat properly. Breaking a crank apart and reassembling it is what requires all of the special tools, but Hot Rods cranks come completely assembled and usually come with main bearings as well which is why they are such a good deal.
 
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Jun 9, 2007
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#3
Yes having a manual would be a good start highly reccomended and also like he says above its not to bad if u get the assembled package
 
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#4
Alright, thanks guys, sounds promising for me then. I didn't go for the e-bay bottom end, he didn't ship to canada and I wouldn't be able to come up with the coinage on such short notice anyway. Anybody else got some input? Things to watch out for when doing the re-build?

The more the merrier :cool: .
 
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Apr 26, 2007
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#5
If your rod seized to the crank, then the crank will have to be rebuilt. Unfortunately, that is beyond the means of most people, even many shops. Besides the press, fixtures are required to keep the crank halves properly aligned while being pressed back together. It also requires procedures specific to rebuilding these type crank assemblies that are very different from others such as small engines or Harleys. Bottom line, you'll need to either purchase a new/rebuilt crank or send yours out to be rebuilt. I recently contacted Eric Gore about rebuilding my crank. I discovered one of my journals was bad so it wasn't an option for me, but his reply was:

"...my friend Ryan from Finishline Engines offers crank rebuilds with parts for $125
His number is 1-920-382-2897"

As you are in Canada, I don't know if this is an option due to the additional costs involved, but it was by far the cheapest I found down here.

As far as installing the crank bearings, in addition to heating the cases, put the new bearings in the freezer for several hours prior to installation. It will also make installing the crank into the cases a bit easier if you freeze it (at least 4 hours) prior to installing it (with the cases heated).
 
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#6
Thanks for your input bud. I had planned on buying a new crank anyway because up here to get it rebuilt wouldn't cost much less and I think one of my journals(that's one of the crank halves right?) is damages as well because I can see chunks of metal in my bottom end that seem to be atatched to the crank. I'm getting a flywheel puller so I can start into it tomorrow. I'll keep this topic up to date and might put up a picture or two.
 
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#7
The journal is is the part of the crankshaft that rides inside the bearings. They are typically damaged when the main bearings seize and the crank continues to spin inside the ID of the bearing. This causes galling and tremendous heat. Because the crank is softer than the bearing, the galling removes metal from the crank, reducing it's OD. As a result, when the bearing is replaced there may be excessive clearance. Over time even a crank that's undersize by only .001" will get hammered oblong and start to cause problems. When you pull it apart the damage should be obvious, but it's possible it will look fine. Mine looked almost new, but when I measured it with a micrometer I found the flywheel side was oblong and .004" undersize inline with the crank pin.
 
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Jun 13, 2007
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#8
call midwest action cycle, they have hot rod cranks ready to be installed. and i think the kx cranks r some of the cheapest. good luck .
 
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#9
Nah, I'm not going out of country. I'm just ordering a hot rods crank from a local dealer and new main bearings.
I've got another new question, are cases sealed by gaskets or something else?
And when you split them can you do it all from the magneto side of the engine or will you have to remove the clutch basket and stuff to get it split? I'm just asking because all the case bolts come from the magneto side. I'll have the service manual to put it back together but I'd still like to take it apart asap.
 
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#10
I just got done doing my RM. I'm assuming your KX is going to be similar. There are conventional paper gaskets between case halves and the r/s crankcase cover. Yes, the kick starter assy., clutch basket, shift shaft, shifter drum pawl assy., primary drive gear, and any water pump and power valve stuff will have to come off. Once the case bolts are out the r/s case is pulled off using a case splitter, modified puller, or a non maring hammer as a last resort. The main bearing should stay in the case. Then the crank is pushed out of the left side case and again, the bearing should stay in the case. Because it's an interference fit, you should heat the cases when pulling the old bearings out to prevent damage to the case bore. Likewise, the cases should be heated and the new bearings frozen when installing them.
 
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Feb 20, 2006
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#12
i have a yz 250 and had to go through the same thing..i have a hot rod crank in my bike, its great. I read in this thread someone told you to use heat to take it apart and put it together..this is correct. this is what i did. going off of my bike...one side of the crank is pressed in and the other side isn't so heat up the bearing so it expands and just knock it out witha brass hammer..since its no good. and its definetly cheaper to get a hot rod crank than reguild the crank. (i may be wrong but thats what i found when i did this)

To get the bearings out, heat the case up around the bearing so the case expands and there isn't as much preasure on the bearing so it will come out easier.

When your putting the crank back into the side that was pressed in, ( i called a shop to see what they do to get them back in, it didn't see right what they said but it worked, i didn't have a press so i didn't really have a option) They told me to heat the bearing and very easiily and uniformly tap the crank into place with a brass hammer.

I would also definetly replace all your seals while your in there, why not, cheap insurance. and my cases where put together with liquid gasket for the two crank halves, and then with a gasket on the clutch side. Just make sure you follow the manual and don't end up with extra parts.. :laugh:

Good Luck!
 
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Mar 25, 2006
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#13
Ok, havn't posted on this in awhile but everything is hopefully going together today. My manual(on cd) that I ordered off **** never came so I still don't know torques and there's an o-ring on the clutch side of the crank that came off when I pryed the seal out and I'm not entirely sure where it goes. Now, when the main bearings are in do you have to do anything extra to make sure everything's square? or would they be fine once pressed all the way into place? And when installing the crankshaft(which I'm pretty sure on my bike both sides are pressed in) how should I do this? I understand using heat to enlarge the inner race of the main bearings and maybe even putting the crank in the freezer, but IF it wont just drop together how should I coax it into place? Would tapping the end of the crank(rubber mallet) to press it into place hurt it? Canadian riverglade national is this weekend and I really want it back together so I can ride the amateur day.
Thanks everyone, been lots of help so far just need a little more guidance.
 
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#15
cases are together, crank turns hard when bolts tightened, havn't torqued yet, HOW DO YOU GET THE CRANK TO TURN FREELY??
thankyou!