OK, here is some information you will need to know about getting the YZ conversion completed in a 400ex frame. For this conversion I used the YZ400F over the Yz426. The motors are the same just diferent bore and stroke. Use the same mounting,cases ect. The reason why I did choose the 400f over the 426 was do to reliability. The 426 is known for clutch problems and some transmission problems. The yz400 is up to par with the 426 or if not faster overall.

1)First you will need a custom made sleeve for the YZ motor to work with your stock swing arm bolt. The ex pivot bolt is too small of OD to fit snuggly in the pivot bolt hole of the motor, so you will need to knock the two bushings out that are already in the hole, and replace them with a custom machined bushing/sleeve that is 3.5" long. But 3.5" long will fit everything snug.

2)OK, now you half the motor bolted in correctly after you put in the bushing. Now u need to shift the motor to the right so ur motor shifts to the left about .6000 of an inch, so your motor is lined up with the sprocket set up. Now you will need the front motor mounts which I can get for you at a certain price (E-Mail me for details). Once you get the front motor mounts you can begin Step #3.

3)For this big of a performance motor in a quad frame you are going to need a oversized radiator because these YZF thumpers run hot by nature, and with sticking it in a quad frame your going to want to make sure it gets adequate cooling. I personally run a radiator from Denton Racing which retails for $399, which should get the job done quite well. And you are gonna need special water sprockets so you can hooke up the radiator ends properly. You can prolly get away jeryy riggin but I like to do stuff the right way on this quad . Also you are going to need a custom oil tank which K&K ATV sells for $269.95, but don't waste your money yet, I am working with CFM Performance to make some and they make some of the best oil coolers and airboxes in the business.They make the oil tank for $150. If you do choose the CFM oil tank . For mounting cut the stock existing mount tabs off and relocate them to where the cfm will bolt to them and re-weld to your frame so you have a professional look that is free.

4)For this much horse power in the 400ex frame you are going to need some custom re-inforcements for the motor to fit in correctly. You don't want to have little spacers anywhere...They just weaken the motor's stabibility and that causes cracks on your frame. So for the radiator to fit you will have to make special brackets for it to fit properly.

5)After that you are now ready for the final stages, which the first is gusseting the frame so its alot more sturdy and stronger. I guesseted mine by the stock shocks mounts,steeering stem area,and put some oversized beads on some of the weak OEM ones. Also when I did all of the welding I moved my bottom oil tank support to hold the CFM tank and I gusseted that braket up to. When doing this if you are running nerf bars make sure you have them on so u can weld the oil tank support to fit around the nerfs. I made the mistake by welding the support with out the nerfs on and then later I had to cut it off then re-weld it with the nerfs on.

6)The real final stage is getting the YZ exhaust to fit better. For this you will need to cut some angles and bends for it to fit like your 400ex exhaust is suppose to. With the exhuast uncut it will stick up about 1ft. above your subframe and it won't work with your plastic. Also now that you have the motor in you are going to need a kick start attachment which retails for $200,but wait again i can get you one made for $100. For the exhaust situation I orderd a speacial pre-cut exhaust from the makers of Power Pro Racing which was $470 shipped and there is about a 6 week wait. Power Pro's make all of CT,Trinity,graydon and a few other big companies products. I give them a A+ the pipe hauls ass and sounds very nice not to loud or to quiet. I personally cut mine about 2 finger in width which is about 2" as it came a little long and I didnt want it to get hit in a holeshot if some jackass rear ends me.

7)Now that I got the quad pretty much wraped up I was very happy with the performance it gives. It has 5 times as much torque and just overall performace over my modded 400ex motor. Just a few pointers suggest always put "Anti-Seeze" on the YZF spark plug threads as the YZ is known for the spark plug seezing when motor gets to hot. If it does get seezed as mine did just get the motor pretty hot by riding and then loosen it back and forth till it comes out. Another thing you will need to do is cut the rear fender about 8" so you are able to kick it.

8)Another problem I had was the intake manafold hooking up the proper way. For this I had to cut out the left OEM gusset near where the subframe mounts up at the top. If you dont cut it the carb will hit it in return not allow any room for your airbox boot to hook to the carb properly. But when you do cut the gusset out make sure you re-inforce that area,dont leave it ,or you will have a cracked frame sooner or later.

9)Some of my information maybe a little out of place...these are just some problems I have encounterd so far during my YZ conversion...I wil continue to update my site as I learn new things about getting this motor to work correctly in a 400ex frame.

10) Well I have had the YZF quad out enough times to be able to understand the power and see its great points. It seems as the YZF has alot of Low-mid power as where I can hammer the throttle and be able to rely on the power. Well before I did this I had a pretty modded EX with port &polish,rev box,cam,Exhaust and the other mods needed to suseed in the MX racing. Well put it this way my bone stock YZF motor would walk circles over my old EX motor. My furthur plans are to maybe get a 440 big bore maybe and definately get port&polish. This motor has the drive of a dirtbike where I can handle jumps with the same speed as dirtbikes where my 400ex was always up a gear from the dirtbikes when jumping decent jumps.