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Discussion Starter · #1 ·
I bought a 06 400ex off of a buddy for 500.00
Plastics and everything is in good shape. The motor not so much... He said that he put diesel in it on accident one day and that it wouldnt start. For 500.00 I didnt care what was wrong with the motor. I pulled the plug and installed a new plug and cleaned out all the fuel system. That didn't change anything either. I put my finger over the plug gap and didnt fell much if any compression when trying to turn it over. I then checked that the plug was getting spark and it was. The carb is getting fuel too.
I drained the oild and it was dirty and I got less than half a quart out of it... Does this sound like the motor is sezied? I have started to teardown the motor but I am stuck on the timing chain... How do I release the tension so that I can get it off and find out what this thing needs to run??
If it is seized whats the best budget rebuild option? 416?426? 440?
Id like to run a cam down the road but for right now I just want to get it running with a pump gas friendly compression level
 

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If the engine is turning, when trying to start it, it isn't seized. If it doesn't have compression, you probably have piston, ring, and/or cylinder problems.

To loosen the timing chain, just remove the timing chain tensioner. It's located on the back of the cylinder and only has two bolts holding it on.
 

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Discussion Starter · #3 ·
so regardless of what it is I would most likely need to install a new piston correct? If I am going in there I should just redo the piston and rings. Any advice on what size to go with?? 416 426 440?? I am looking for a fun reliable trail bike with some added power so that I have more than it did stock. Id like to keep the compression 91 octane friendly
 

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If you don't have good compression, it's more than likely, the piston, rings, and/or the cylinder walls. You won't know for sure, though, until you tear it apart and see.

I like to keep my quads as close to stock as I can, because of the reliability issue. If I wanted more power, I would probably just go with an aftermarket pipe and filter and rejet, but that's just me and I'm a utility guy. I mostly ride utility ATVs. Some of the other guys on here that ride sport quads can give you better advice than I can about the mods.
 

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Your gonna get most of your power with getting a bigger engine. If you make it a 440, it will prolly last a year on rings due to heat. I would go with a 416 and be on the safe side. A 416 actually pulls harder than a 440. To start out with jetting, what kinda pipe is it? What brand, Slip on or full exhaust? For more air flow, put a nice foam filter like Twin air or UNI. I mention foam because if your doing trail riding, a K&N is gonna get really dirty unless you have an Outerwears on it. Jetting is gonna be around a 168 if its full exhaust and a filter. The best thing to do with that timing chain is to get a Service manual and I think they are like $50? It will show you how to do everything on that bike. good luck. oh and btw, if you get the Wiseco 11:1 High Comp piston, I dont think it requires race fuel but i think you can mix 50/50. I mix 50/50 anyways with my stock bore and 10:1 compression.
 
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