Hi, I have owned a few 400ex's and sold them all off and have now started building up a different quad. I bough a 2003 400ex bottom end that the chain busted a hole in the left crankcase. I have bought the new left crankcase on ebay. And I am planning on splitting the case and installing everything into the new case and reassemble.

I am a master certified auto technician and have done tons of mechanical work on atvs, BUT the one thing I have never done is split the case on a atv engine. I know the bearings are pressed into the side cases and will need to be pulled apart, my question is. Are there any tricks to this that the service manual don't address? How hard is it to split the case. Will I need the special puller or will I be able to be carefully tap it apart with maybe the aid of a hairdryer on the case around the bearings to expand the aluminum. Any tips or special tricks would be very much appreicated. And yes I have a factory service manual coming in the mail. thanks for all the help. mike

 

Welcome to the forum 400exbuild1, with your experience you should be fine. From my experience with splitting the cases on a thumper you will probubly need some sort of puller but may get away with out one. I have needed one to press the crank thru the cases and to get the crank out of the other case half. The gears/shafts in the cases usually stay on the clutch side during splitting, so you dont have to worry about gears falling out. The manual should cover all your problems along the way. I usually read thru the section Im going to be needing before tearing anything down. It helps to familiarize you with the project.

 

Thats sounds good, since the gears and shafts stay on the clutch side then maybe I can just pull the left cover off and leave the crank and everyting on the right side and install the new left crankcase. I guess its better that the left one is broke and not the right side? thanks any other suggestions please comment.
mike

 

That sounds like a good idea to me.

Should make it easier thats for sure.

Just move slowly as you split the cases and have good lighting to look inside as they split to make sure everything is staying to one side. If not try and push it to one side with a wooden dowel or something that isnt metal. Unless your very careful. Also dont pry between the cases with a screw driver or anything metal. Usually there is a lip in the cases you can use. If you have to go between the cases use a plastic spatula or something similar. You dont want to ding the gasget surfaces.

 

thanks for the suggestions, I was also thinking; should I remove the right side outer cover and strip that side of the motor down to the case also or can I get by with leaving the right side of the engine together and just removing the left side cover then splitting the case, installing the new left case and then installing the left side cover again. will the crank stay in the right side case or will it pull out with the left case. Anyone know the best way to change the left crankcase on a 400ex. anyone have experience with this?

 

That is the normal way.

I was thinking about this earlier and think its possible. Id sure give it a try.

It wil definitely stay in if you leave the right side together.

There has to be some one here who has done this before. Im sure in a day or 2 there wil be more replies.

 

looks like we were both thinking the same thing, Surely someone on here has the experience to confirm this.
anyone?