350X 400EX Transplant Build!

[Matt85'350x]

I’ve been wanting to put a 400ex engine in a 350x for a few years now. When I originally starting searching I couldn’t find anyone who had actually completed the project; just speculation or in some cases abandoned projects. Then came along “Top Notch 350x” who was actually successful in the idea. Whilst he didn’t write a long detailed build of it, he did post some really important details and so thus far I believe he’s the only one to actually go through with it.

The bones of the project:
I originally bought this 350x back in 2011. The frame was trashed so I bought a pristine 86 frame from someone here on the boards. I actually ended up selling and rebuying this same 350x twice. It’s not going to be sold again, it’s a solid foundation for what I want to do. Here’s what it looked like the day I brought it home (with the bad frame):




This is what it looked like before I started tearing it apart:


Part of the reason I haven’t started until now was because I was waiting for the right deal to come along for a 400ex. Ebay has engines priced for what I can get a whole quad for which if I bought the quad I would also get the carb, electronics, exhaust, etc. So it didn’t make sense to buy just the engine. I found plenty of good deals on first gen 400ex’s but I wasn’t going to do it unless it had reverse too so I needed a 2005 and up. Finally the right deal came along-I traded another 350x I had for a 2006 400ex with first gen plastics. This thing was hideous and was obviously ridden hard but the engine ran good and that’s all I really cared about.





I had quite the time getting this engine out as the swingarm bolt was seized to the bushings. Had to cut it out.


Got the engine out and traded the roller for a kx80 project which I then sold on craigslist. So overall I did much better than buying just the engine online, plus this way I could hear it run.


And here’s the engine sitting in the X for the first time. Only the bottom bolt is holding it.

[Jmoozy27]

Looks good. Do you plan on modding the swingarm so the bolt goes through the motor. It's probably your best shot to make everything fit tightly. Just remember to measure twice and cut once...

[Matt85'350x]

Looks good. Do you plan on modding the swingarm so the bolt goes through the motor. It's probably your best shot to make everything fit tightly. Just remember to measure twice and cut once...

Nope. I actually used the mount right below the swing arm mount. I'm further than what's in the above post. I have more pics but it's hard to post from my phone. More to come tomorrow.

[RIDE-RED 250r]

This build has my interest. As much as I love the 350x, it's hard to deny the plethora of aftermarket support for mods with the 400 mill! Plus there's the issue with worn cam journals making paperweights out of 350 heads and the fact that there are less good 350 heads out there as time goes on makes this problem get steadily worse as time passes.

Reverse, just cool.

What's your plan for the battery??

[DohcBikes]

Joe, are you aware that the trx350 heads 86-89 are a direct replacement?

Unless I'm making that up, like the rest of my stories.

Yep all I can think is 440x.

[350xtrike.rider]

Wow definitely going to be following this build! I've been wanting to do one of these too with my 350 roller.

[Matt85'350x]

I'm planning to use a really small motorcycle battery. There are some that are the size of a multi meter. I'll figure out somewhere to mount it. Probably in place of or on the opposite side of the tool box.

[dman10]

Keeping tabs on this one. Got a 350x frame here that needs a heart

[RIDE-RED 250r]

Joe, are you aware that the trx350 heads 86-89 are a direct replacement?

Unless I'm making that up, like the rest of my stories.

Yep all I can think is 440x.

Yes Sir I am aware. But are there many of those still out there these days?

[DohcBikes]

Well I guess I didn't make it up. How unlike me to be honest.

http://m.ebay.com/sch/i.html?_nkw=Tr...+cylinder+head

Be sure to spot the 4 valve heads.

Here's a nice one. http://m.ebay.com/itm/86-89-Honda-Fo...EAAOSwvU5XM4sU

Even have fresh rebuilt listed there somewhere.

Seems pertinent to the thread. Carry on.

[BOB MARLIN]

What are the advantages you are looking for over the 350x motor ?. I have thought of this conversion off and on through the years and ended up talking myself out of it many times. The only real advantage I came up with was the electric start. I think the ex motor was only about a 1 hp gain ( may be very wrong on this) and the big problem I had with it was having to find somewhere to mount a oil tank. Maybe engine parts are more available ?.

[Matt85'350x]

What are the advantages you are looking for over the 350x motor ?. I have thought of this conversion off and on through the years and ended up talking myself out of it many times. The only real advantage I came up with was the electric start. I think the ex motor was only about a 1 hp gain ( may be very wrong on this) and the big problem I had with it was having to find somewhere to mount a oil tank. Maybe engine parts are more available ?.

The advantages for me are as follows:
-Electric start
-Reverse
-Lighter engine (don't know the exact numbers but I do believe it's lighter)
-More aftermarket support/parts availability

Other than that I don't know what to tell ya. It's something that I've wanted to do for a while. The overall idea is to end up with a more modernized 350x. A 450 hybrid would be cool but a bit out of reach for me plus I really like the 350x so a modernized version of it really appeals to me.

[Matt85'350x]

Motor Mounts. The only mount that lines up is the bottom 220mm long bolt. The spacers don't work but at least you can get the bottom bolt through so that the rest of them can be worked. on. I decided to start with the front mount since it was the easiest to access for measuring purposes. I measured and designed the mount in CAD and than cut the design out with a laser. The mounts are made of 5mm thick stainless steel! Plenty of strength here:


Here's the first mock up of the front mount:


I went ahead and upgraded all of the bolts to M10's. The front mount previously were M8's but the sleeve was big enough for an M10 so and M10 is what it got. I wasn't happy with the way the mount contacted the engine block so later I went and trimmed the design and recut the front 2 mounts on the laser.

[Matt85'350x]

Next I decide to tackle the upper mount. For this I first had to replace the rocker cover as I didn't notice the mount was broken when I bought the quad.



Ended up getting a good deal on a cover off of someone on Facebook. While waiting for the head to come I decided to go ahead and see where the engine needed to sit to line up with the sprocket, carb, etc. Center of the mounts seemed to be where everything lined up well:



Chain is just laying in this picture, that's why the bottom looks tweaked.



Exhaust doesn't really fit without a fight. The end of it will need to have the angle reduced in order to work properly.

[Jmoozy27]

Those mount plates look badazz. It sure beats a cut off wheel and shaping with a bench grinder for hours.