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How to Split Your Motorcycle Engine Crankcase


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To service your transmission gears, crankshaft, kickstarter, etc. you’ll need to split your engine cases. On many motorcycles you can split the cases without removing the top end. If you only need to work on the transmission, this can be a good option and will save you some work.

Remove the Motorcycle Engine from the Frame

To split your motorcycle engine cases, you’ll need to remove the engine from the bike frame.

After the engine is out of the frame, you’ll remove the engine side covers, the oil pan, the shift mechanism, and possibly the clutch.

Loosen the Crankcase Bolts

You’ll then remove the bolts on the top and the bolts on the bottom of the motorcycle crankcases.

When you remove the bolts, keep track of where the came from. An easy way to do this is by tracing a pattern of the top and bottom cases on a piece of cardboard and sticking the bolts in the relative positions when you remove them.

How to Split the Motorcycle Engine Crankcases

Horizontally split crankcases open like a clamshell, and you’ll be able to lift the bottom crankcase half from the top. Certain engines will require that you drive out the primary shaft bearing before you pull the cases apart.

Once all the bolts are removed, you can try to gently tap on thicker areas of the motorcycle crankcase with a rubber mallet to help it loosen. Be very careful not to strike anything thin or to strike it too hard.

If the cases won’t come apart, double check that you removed all of the screws. Sometimes there is a screw in the very back of the crankcase that can be easy to miss.

You can purchase a crankcase splitter or engine case puller tool to help split the cases if they are really stuck together.

If it still won’t come apart, you can try a heat gun or very, very gently prying on a thicker area of the case. Do not pry and damage where the cases meet or they will not seal properly and you will have an oil leak.

If you are having no luck, walk away and try again later. Sometimes the case will loosen itself after being unbolted for some time. Try to get some penetrating oil near the knock pins of the crankcase if you suspect they are rusted in.

Reassembling the Motorcycle Engine

Keep everything in order and clean when your engine is apart. When you are ready to put it back together, follow the installation sequence as specified in the shop manual.

If you are unsure, it can help to assemble things in a dry run to make sure you can shift through the gears and that everything spins properly.

Place a small amount of liquid gasket along the crankcase surfaces and shut them back together. Make sure all the knock pins are in and the cases seal properly. If they don’t, be sure that everything is aligned properly. Do not bolt the cases shut if they are not sealing back together correctly – something is likely wrong.

Refer to the shop manual for the proper torque values and tightening sequence for the crankcase bolts.

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