Dismantle the crank case?

Rayde

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Mar 23, 2011
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I need to pull apart my crank case to replace the clutch shaft. So far, i've managed to separate the case only slightly, and damaged the gasket in the process. I've removed everything from the clutch shaft down to the shaft itself. The crank gear is off, magneto loop is off, but not the magnet. All screws and connecting hardware are out.

But, i cannot seem to pull the case apart. Any ideas why not?
 
Hi Rayde -

I will offer the first response... I did the very same thing you are doing and had the very same problem. The key phrase you used is "only slightly". In my predicament, the crankcase bearing was getting hung up on the internal crankshaft bearing fitting.

To overcome, I heated the crankcase area around the crankshaft using a heat gun (or a really hot hair dryer). I don't recommend an open flame propane torch if the engine has had fuel run through it unless you rinse it out with gasoline and take pains to dry it out of all vapors.

The crankcase, made of aluminum, expands at a rate twice that of steel. If you get the crankcase hot enough (but not so hot to damage the rubber seals around the crankshaft), it will open the crankcase bearing fitting enough that you could tap it apart using a soft mallet or block of wood. Don't use a steel hammer.

Once apart, you will see that the crankshaft bearing is a press fit into a crankcase housing fitting. This fitting is what has to be expanded with heat.

Order spare gaskets from a dealer. Gaskets are really, really thin. It is easy to mistake a double layer when you think you have only one gasket.

Keep in mind that if you use heat to disassemble, you will need heat to assemble. (That housing fitting locks the crankshaft into a fixed position, else the crankshaft will wobble when running). I tried cooling the crankshaft in my engine, but I don't think that did much good. Heating the crankcase to "too hot to handle but below boiling point of water" worked for me.

I did this and thought I destroyed the engine. But I assembled it and have since run it over 1,200 miles.

I hope this helps.

Mikej
 
This is very Helpful. Only thing i have access to here is a hairdryer, perhaps that would work...

How difficult will it be to reassemble this? Assuming this will work, i have to reheat the crankcase bearing mount while apart, slide on the gasket, and try to get the crank bearing to seat properly back in the crankcase bearing mount? Also trying not to damage the gasket, make sure all holes are aligned, that the new clutch shaft seats correctly, etc...

Are the clutch bears press fit as well? I think i may have to replace those, they are very stiff to turn.
 
You do not have to split the case to remove the clutch shaft. If you remove the small drive gear you can tap on the end of the shaft and the whole clutch and shaft will come out as a unit
 
I thought it should as well, but mine wont. Or, it seems it doesnt want to... i have to split it now though anyway, to replace the gasket.
 
Rayde -

Reassembling is a little tricky, but not impossible. If I can do it, so can you. Heat is your friend during disassembly and reassembly. Use reasonable care. If you tear up a gasket during assembly, try again, using another new gasket. I purchased four of them; they are cheap and I usually sacrifice at least one during the learning process. I now have a couple of spares for future use.

Setting the part with the crankshaft in some books or 2x4s to keep it oriented the way you can work with it is usually very helpful.
 
I need to pull apart my crank case to replace the clutch shaft. So far, i've managed to separate the case only slightly, and damaged the gasket in the process. I've removed everything from the clutch shaft down to the shaft itself. The crank gear is off, magneto loop is off, but not the magnet. All screws and connecting hardware are out.

But, i cannot seem to pull the case apart. Any ideas why not?

http://www.motoredbikes.com/album.php?albumid=808
 
here's a really dumb question....
you did take the cylinder off before you tried to split the case right?
 
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