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Rcndn

2002 yamaha bigbear 400 4x4 top end rebuild need manual..

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Posted (edited)

I have a 2002 yamaha bigbear 400 4x4 with a seized engine. I was able to free the piston with the old "fill cylinder with oil and let it soak" and it worked. So I bought a top cylinder rebuild kit , but now I have no idea the process to fix this . I need a service manual.... 

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Why was the engine seized ? Water in the cylinder head ? If it’s freed up now all you would need to do is run a honer through the cylinder to clean any rough spots.  I’ve seen engines where people either take the spark plug out and have not put it back in allowing water to get in. Or having a water cooled engine where a head gasket went bad bike was put away with water in the cylinder.  

Also are you sure the main bearing on the bike is ok ?  

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I don't know about main bearing. I don't have a clue how to begin this project without a guide. Its air cooled. It ran out of oil and seized. Filled cylinder head with oil and let it soak, and eventually the piston freed. I don't have access to a honor so I bought a cylinder kit, came with new cylinder, piston, rings and gaskets. Now I don't know how to begin the project, where to start. That's why seeking manual.

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Got all that. Why I was asking is to prevent you from possibly buying parts that are not needed.  But that may be too late. If the engine ran out of oil the main crank/bearing should have went bad also which is located on the lower half of the engine and much more involved then taking the head/cylinder off.  Your able to download manuals after 10+ posts in the forums. As far as taking the head off it’s not that difficult if your mechanically inclined but just need to be aware of the engine timing etc.   

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Ok, good to know. Top end parts already bought, and I am sure I can do the work, if its more or less nuts and bolts. But now the (main crank/bearing) I never would of thought of that, thanks. By chance would you  have an image what this bearing looks like and part cost?   Thanks

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Aw man, I just googled where the bearing is, and what it entails to get to it. I don't think I'm equipped to handle a job like that. I guess I better look for a repair shop. Is there any possibility that the bearing might be fine, and how could I tell without tearing it all apart?  Thanks

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The main bearing and crank shaft assembly is the main component that makes the engine run.   I don’t want to put the cart before the horse here and have you ripping the engine apart for nothing. So you have to pull the head off no doubt. The you have to move the the crank (rotate it) up and down to see how it moves.  And there should be no play (wiggle room) up and down. If this bearing is bad then the entire motor has to come off the bike and split apart.  It’s not just a nuts and bolts thing unfortunately. It’s huge undertaking.  I posted some images from the manual for you. 

9995BC51-BA08-484D-9EA5-EB75677EB5AB.jpeg

ABAF9919-22C9-4A23-8DBC-20673798F413.jpeg

8910192D-653F-46C7-9288-DDEB3ECB6371.png

DBE9C66B-0FB0-46E6-9737-D32F1807E82B.jpeg

AAE5D4B9-667A-42CB-B408-C49039D46D7E.jpeg

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Oh, by the way it does turn over, and no noise is heard while starting. Just won't fire up. If that helps.

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It will turn and prob will start but you will hear a knock.  Are you positive it was ran out of oil ? I’m assuming you have some background history of the bike ?

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Thanks for the images and the fast reply back. Yes it was ran out of oil. I was going across a wood slashing and the oil hose that runs Into the oil radiator pulled off, drained all oil out before I knew. First it stalled out on me then restarted after a few cranks. Drove about 100 yards stalled out again smoking. Every time tried to turn over smoke would bellow out of Carb filter and no start. Grabbed other vehicle and towed it home. Then realizing that it  wouldn't turn over, I did the oil in the cylinder trick to free it. Bought the top end kit because figured the cylinder and rings were shot. I had hoped that's all I needed to fix.

 

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Well I’m an optimistic kinda guy so let’s say you got lucky and pulling the head has to be done anyway so get after it and get the head off and we will go from there.  First things first get the piston to top dead center and a big piece of cardboard.  Put the cardboard up against a wall and as you take bolts out punch a hole into the cardboard and stick the bolt in the cardboard and write on the cardboard what bolt its for. That will help you keep track.

Spray the exhaust bolts down long ahead of time, they are rusted and always a problem and snap easy so go gentle with them. 

 

 

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Great, sounds like a plan. Thanks for the help. So when you coming over to help me with this....jk. I'll keep you posted.

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Lol I wish I could give you a hand brother but we have walked many through some tough projects here.  Lots of pics and ask as many questions as you need to.   

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