400ex Smoking

[Potter20]

I have a 2002 400ex. It has been smoking pretty bad from the exhaust. It's white smoke. It only did it at start up first but now it smokes almost all the time. I have changed the oil and everything so I know its not low on oil or anything. Would it be the valve seals causing this? As far as I know its never had any seals or rings put on it so I think this may be the problem?

[CJM]

Compression test, should at least be 100 psi. But chances are the smoke although appearing white is bluish and that means your bore/rings are shot.

[Potter20]

Okay I'll test my compression here shortly. I'm kinda new to this stuff, but how much would just the parts run? Just a rough estimate.

[Honda.rider5871]

If you just need rings , meaning your cylinder isnt egg shaped, they run roughly $30. IF you need a whole top end kit , they can run anywhere from $100-170 depending on brand and where you buy it . You wont know what you need most likely until you tear into it. I would also replace the timing chain with a crf450 and replace the guides while you have the motor open also

[Potter20]

Okay thanks a lot. I'll tear into it in a day or two and see exactly what I'm going to need. Thanks for the help.

[honda400guy]

ok its probobly the rings or the valve seals i would replace both to be sure

[Potter20]

You think you guys could post a link to the valve seals and rings I will need from your preferred site. I am a complete noobie when it comes to stuff like this. I have a cousin that told me he could install them for me. Thanks in advance.

[BeefySTi]

Valve stem seal- #1 on diagram:
http://www.motosport.com/atv/oem-parts/HONDA/2002/TRX400EX/CAMSHAFT-%2B-VALVE

Rings- #2 on diagram
http://www.motosport.com/atv/oem-parts/HONDA/2002/TRX400EX/CRANKSHAFT-%2B-PISTON

Can probably find them cheaper somewhere else, however I have dealt with motosport a lot, and their customer service has been top notch.

[Potter20]

Thanks a lot! Yeah I like them a lot as well. I have ordered a couple set of tires from them before. Hopefully this will fix the smoking. I will let you guys know how its doing when I get the parts ordered and installed.

[CJM]

Its important before you even bother ordering the rings to check your current ring clearances. This will let you know if you need to do rings or bore itup next size and new piston.

Take the rings off and put then in the cylinder using the piston to push them evenly down and measure the gap. It depends on the bore but iirc its like .017 and .020.

Honestly, chances are your going to need to bore it and do a piston if you have a good bit of hours on it. Valve seals will not smoke all the time, just when it starts up and once warmed up it will be fine.

id recommend boring it out to a 407 and doing an 11:1 high compression piston. The only thing needed is to run 93 octane and you will LOVE the boost in power you get.

[Potter20]

I'm not exactly sure how many hours it has on it. I bought it about 2 weeks ago for a great price and I knew I was going to have to dump some money into it to fix the smoking. Is it hard to bore one out and install new pistons and all that for someone with hardly any experience on 4 stroke engines? Or would I be better off paying a little more and taking it to someone who knew what they were doing?

Also some of my friends were wanting to go riding this upcoming weekend... Would you think it would be alright to ride for 5 or 6 hours this weekend?

[CJM]

your call, if you ride it enough it will need a new piston and could lock up. Personally, if it smokes as bad as you say Id not chance it.

If it has some hours on it, skip the rings and do the bore job. Go to ebay and look for seller apex racing, hes cheap and sells excellent parts. Should be able to get a piston for 120 bucks . Bore job can be done at a machine shop for about 100 or less. Then all you need is gaskets. Cometic MLS viton coated steel is all I use,t hey hold up.

In total 300 bucks maybe, its not that hard to do really if you can follow a manual and asking here if need be. If your not sure have someone do it.

[Potter20]

Yeah it smokes quite a bit. So I'll probably just wait until I get it fixed.

Would you recommend going ahead and getting a timing chain as well, since I'll have it apart already anyways?


Probably another stupid question but which of these pistons? I didn't know whether to get a big bore piston or a standard... This is the apex racing store on ebay like you recommended.

http://stores.ebay.com/apex-racing-store/Honda-ATV-/_i.html?_nkw=piston&submit=Search&_fsub=670764012&_sid=733442432

[CJM]

This one: http://www.ebay.com/itm/HONDA-TRX400EX-400EX-WISECO-PISTON-KIT-040-10-1-99-08-/320858278935?pt=Motors_ATV_Parts_Accessories&vxp=mtr&hash=item4ab4a4cc17

Its a 407 10:1 compresion. Enough that you will get a boost, but not enough to need say heavy duty head studs.

id do the timing chain, guides if needed and replace the tensioner to make sure thats all good. Check everything first to make sure its ok, replace the chain anyways. Pull tensioner off, pull of small screw, turn the mechanism with a small flathead and let go. it springs back nice its good, if not buy a new tensioner.

Heres the gaskets you need, same guy I get mien from: http://www.ebay.com/itm/cometic-Top-End-Gasket-Kit-Honda-TRX400EX-TRX-400EX-99-/170637729570?pt=Motorcycles_Parts_Accessories&hash=item27bacd1f22&vxp=mtr

[Potter20]

Okay thanks a lot!
So I am most likely going to need...

Piston
Gaskets
Timing Chain
Valve Seals
Get it bored to a 407

and possibly chain guides and tensioner. Sound about right?

Also would you recommend getting a stage 2 hot cam? I have heard that they help out quite a bit.

[CJM]

If your gonna go all in, then yes stage 2 hotcams worth it.

[Potter20]

Okay, I guess I'll just have to see how the money situation is looking when I order haha. But once again thanks, I'll definitely keep you updated when I get everything figured out.