Taking her apart

[Dritto]

So, as I decided in my previous thread I'm going to take my 400ex fully apart, mainly because it needs a repaint, but I'll also do a few mods and maintenance.
This is my first time taking a 400ex apart, I've only once taken another quad apart and it was a Blaster.


First off I'll do maintenance like checking valve clearance, checking bearings and the condition of various things.
Next thing I'm going to do is mods, like removing the choke and installing HID lights.
But there are somethings that I'm wanting to know about before I decide. And before I start, you should know that I don't like to sacrifice durability.


As high compression ratio for 4-strokes is very effective, I'm think of putting a 11:1 Wiseco piston with stock bore (Btw I'll put all the links below). Is this a great idea? Do I need to change anything else than the piston, or adjust the valve timing and spark timing? I know this mod will put more stress to certain parts, but will this affect durability much?
A thing that a lot of 400ex owners do, is to replace the camshaft with a Hotcam stage #1 or #2. What does it really do? Is it just like a sprocket mod, increase top-end but lose low-end? Why do so many people do this mod?
I also seen some replace the timing chain with a crf250 one. Why's that?
Manual or automatic tensioner. What benefits will I get with this?
I went on Sparks website and found a 39mm FCR Carb Conversion Kit. What improvements are achieved with this expensive kit?


Are there any other mods that I should consider through out the quad?
As this is my first time parting an 400ex out, do you have any tips for specific items to check, replace and look out for?

I'll appreciate every help that I'll get, please feel free to post anything.


Links:
Hotcam 1/2/3: http://www.hotcamsinc.com/ProductSearch.aspx?page=1
Wiseco 11:1 piston: http://www.wiseco.com/ProductDetail....008&AppID=1202
39mm FCR Carb: http://www.sparksracing.com/39mm-fcr...trx-400ex.html

[CJM]

-You will be happy with the wiseco piston kit, just make sure to measure your cylinder. If its worn out you need to bore it out to the next size.

-Stage 2 hotcam is what I would run, had one in my EX and liked it alot. Buddy ran the same setup as me with a stage 1 and was unhappy-power signed off early. Cam changes the duration the valves open/close. See here for more info: http://www.atvriders.com/vbb/showthr...mparison%29&s=

-Save your money on the sparks carb, WAY to much money for what you get. Either keep the stock carb, go to a CRF carb and buy an adapter (noss machine can make you one) or use and 04-05 450r carb.

-You want to buy a crf450r timing chain, I know 2002 works but I think its the same part for a few years. Its a heavier duty timing chain and works great. Stick with the stock tensioner. Check your guides and tensioner when you have it apart. The tensioner turned tight should spring back easily if you let the screwdriver go-it doesnt buy a new one.

[Dritto]

-You will be happy with the wiseco piston kit, just make sure to measure your cylinder. If its worn out you need to bore it out to the next size.

-Stage 2 hotcam is what I would run, had one in my EX and liked it alot. Buddy ran the same setup as me with a stage 1 and was unhappy-power signed off early. Cam changes the duration the valves open/close. See here for more info: http://www.atvriders.com/vbb/showthr...mparison%29&s=

-Save your money on the sparks carb, WAY to much money for what you get. Either keep the stock carb, go to a CRF carb and buy an adapter (noss machine can make you one) or use and 04-05 450r carb.

-You want to buy a crf450r timing chain, I know 2002 works but I think its the same part for a few years. Its a heavier duty timing chain and works great. Stick with the stock tensioner. Check your guides and tensioner when you have it apart. The tensioner turned tight should spring back easily if you let the screwdriver go-it doesnt buy a new one.

Thanks for the link, but still a bit confused with the cams.
Titanium valves are they only for durability, or is their also benefit for their lightness?
I see that the 450r carb has a 40mm flat-slide with TPS. Benefits? :P And does the 400ex one have a round-slide?

[CJM]

The 450r carb from 04-05 is a round slide carb, it is larger overall inner diameter and improves throttle response and power. The FCR is a flat slide carb with a TPS, you dont need tps on any carb.

Dont need titanium valves, they are stock on 06+ 450r's but most replace them with steel b/c they were. 400ex valves loosen and need adjustment-450r valves tighten and need shims.

Overall what ya want is a stage 2 hotcam, trust me its the preferred cam to run and will leave a smile on your face.

[Dritto]

The 450r carb from 04-05 is a round slide carb, it is larger overall inner diameter and improves throttle response and power. The FCR is a flat slide carb with a TPS, you dont need tps on any carb.

Dont need titanium valves, they are stock on 06+ 450r's but most replace them with steel b/c they were. 400ex valves loosen and need adjustment-450r valves tighten and need shims.

Overall what ya want is a stage 2 hotcam, trust me its the preferred cam to run and will leave a smile on your face.

Ok thanks
I know I ask a lot of questions but I have to.

Now I'm considering a 416cc piston 11:1. What's your opinion? 416cc 11:1 vs 397cc 11:1. Will I need HD head studs in both applications?
Also when I'll order XR400 gasket, should I order a gasket for the cylinder and cylinder head, a total of 2 gaskets?

I appreciate your help

[CJM]

I honestly liked my 416 the best, BUT if your planning on keeping the EX for awhile it would be smart to simply go to the very next size up from stock which is 402. This way you can bore it again down the road, if you do 416 off the bat 426 is next then 440. Friend and I did a 407 and it revved just as good as my 416 did.

You dont need the studs, but for 100 dollars (bought and installed) they are cheap insurance. The key with 400ex and those studs isthe following: Since the EX is aircooled you MUST jet it right, excessive heat goes right to the exhaust and those studs start to get heated up and pull out. So jetting it right is important.

As for gaskets, I personally like cometic brand MLS gaskets (they are rubbery coated steel). Although they are thicker and you do lose a slight bit of compression. You will need all the gaskets, base (bottom of cylinder), and the head gasket. Everything else is metal and can be reused.

My fav build with my 400 was the following:
11:1, Stage 2 hotcam, 450r carb, outerwears lid, and 416. That sucker liked to rev but also had some nice torque. My final build before I sold it was the same but a 426. I wound up going to a 36T rear sprocket b/c it revved so fast and I ran out of gears-there was plenty of torque. This i the same build I and some other vets on here always recommend and it puts a smile on many faces.

[Dritto]

I honestly liked my 416 the best, BUT if your planning on keeping the EX for awhile it would be smart to simply go to the very next size up from stock which is 402. This way you can bore it again down the road, if you do 416 off the bat 426 is next then 440. Friend and I did a 407 and it revved just as good as my 416 did.

You dont need the studs, but for 100 dollars (bought and installed) they are cheap insurance. The key with 400ex and those studs isthe following: Since the EX is aircooled you MUST jet it right, excessive heat goes right to the exhaust and those studs start to get heated up and pull out. So jetting it right is important.

As for gaskets, I personally like cometic brand MLS gaskets (they are rubbery coated steel). Although they are thicker and you do lose a slight bit of compression. You will need all the gaskets, base (bottom of cylinder), and the head gasket. Everything else is metal and can be reused.

My fav build with my 400 was the following:
11:1, Stage 2 hotcam, 450r carb, outerwears lid, and 416. That sucker liked to rev but also had some nice torque. My final build before I sold it was the same but a 426. I wound up going to a 36T rear sprocket b/c it revved so fast and I ran out of gears-there was plenty of torque. This i the same build I and some other vets on here always recommend and it puts a smile on many faces.

My quad probably only has 100hours on it, when do you think it will need to be bored up? As I do live in a very small country, who can bore it up? Auto mechanics?
As for the gaskets, are the stock gaskets reusable or is it the Cometic ones?

Is there nobody else that have any opinions? As for now I've only heard from one person, and he has helped me a bunch. But would be great to hear others opinions.

[DragonGunner]

My quad probably only has 100hours on it, when do you think it will need to be bored up? As I do live in a very small country, who can bore it up? Auto mechanics?
As for the gaskets, are the stock gaskets reusable or is it the Cometic ones?

Is there nobody else that have any opinions? As for now I've only heard from one person, and he has helped me a bunch. But would be great to hear others opinions.

When it starts to smoke alot its time for a bore or if your loosing power....these things go forever if you do the jetting and oil changes. If you do a rebuild you want new gaskets.

[CJM]

Any machine shop can bore it, but they will need the piston to do it. Cant reuse gasketws except for the metal one at the valve cover and timing chain tensioner gasket.

[Stickman400]

I don't think anyone else is commenting because CJM has it covered, he hit the nail on the head. Nearly everyone on this forum has the exact setup CJM mentioned, including me, except I went with a 407 to have 2 more bores left.