2008 400ex smoke

[engr400]

Hello, I am new to the forum. I recently purchased a used 2008 400 ex. It is in great shape and still has the original tires. Everything on is tight and the engine is quiet and doesn't make any abnormal noise. However, once it gets to operating temp. it starts burning oil. It is not bad but for a bike that looks as good as this one it seems like this is a little premature. I have adjusted the valves and installed a dynojet kit. The exhaust and intake are stock. The dynojet helped it run better and by checking the plug it seems to be running at the correct AFR. Enough of that, I was just wanting some advice on what to do. I have a few ideas:
1. Run it like it is till it gets bad.
2. Buy a head gasket and pull the head for inspection of head and cylinder.
3. Buy a base gasket and head gasket and inspect piston and rings.
4. Spend money now and go ahead and buy new .010 oversize piston and rings.
5. ?????

Thanks

[OZ-T]

I typically follow the old saying "don't fix it til it's broke" and just wait.

My 02 burns a little oil, I just keep on top of checking my oil and adding some when needed. Been doing that since I got it in November and been riding it pretty hard up until my axle bearings went tits up about a month ago..:(

[CJM]

Smoke is bad. Either its time for rings or piston and bore.

[Ryan02400ex]

Could be valve seals too. Mine smoke blue like a 2 stroke and when we took it apart the cylinder, piston, and rings were in great shape. ( that's what we thought the problem was). The valve seals were just bad

[engr400]

I think it could be the rings because it was running lean when I bought it and it seemed to run a lot hotter than it does now with the jet kit.

[2001400exrida]

Is it smoking or are you actually losing oil by checking the dipstick? If it's losing oil but not smoking, check other avenues such as oil plug. If it's smoking it could be too rich, some machines smoke when they're running rich, especially under acelleration. IF it's smoking and losing oil then it's definitely the rings.

[Ryan02400ex]

Mine was smoking and losing oil and the rings were fine. What I'm trying to say is check it before you spend the money on parts when your not sure what's wrong

[2001400exrida]

valve seals typically only smoke on startup Ryan. This OP is describing that his machine is smoking once it's warmed up which is almost always rings, bore, or piston.

[Zakradu398]

valve seals typically only smoke on startup Ryan. This OP is describing that his machine is smoking once it's warmed up which is almost always rings, bore, or piston.


Bad valve seals will smoke on decel also.

[Ryan02400ex]

valve seals typically only smoke on startup Ryan. This OP is describing that his machine is smoking once it's warmed up which is almost always rings, bore, or piston.

Mine smoked all the time with bad valve seals

[engr400]

I don't think it is the valve seals because it doesn't smoke at all until it is completely warmed up and i would think that if it was the valve seals it would smoke all the time and be worse after it had sat for a while. I am thinking that i will just buy a base and head gasket along with new rings and see if that fixes the problem. Should I lightly hone the cylinder when I do this? And is there anything else i should do when I have the head and cylinder off? What brand gaskets should I buy or should I go back with honda?

[Mtndew99]

Just keep feeding her oil and since it burns oil you really never have to change it since your putting fresh oil in it it actually renews ( an old diesel mechanic teacher at the tech school told me this) and a stock 400 will run forever so I wouldn't worry about it unless its losing power

[shaggy01]

my '07 just started this as well. Its jetted for roughly 1000 ft but when i took it to utah last week and rode in the dunes (high rpm for long time) which is about 6000 ft, it would smoke on decel after running it hard. Wouldn't smoke on start up, wouldn't smoke when warmed up, only smoked when i would let off of it after a high rpm run up a dune. Atlest thats what i saw. im thinking either rings or valve seals. any other ideas? like someone said, it could just be cause it was too rich while up there.

[engr400]

I dont think this is a good idea. The oil will eventually break down and lose some of its lubrication properties and it will create sludge. Neither is good on any moving parts in the engine.

[Mtndew99]

If the oil is being burned and you add new oil then how does it break down? Not trying to argue but just like learning new things

[engr400]

Well, i pulled the cylinder off today. I found light scoring on the cylinder walls. Everything else looked good. However, when I pulled the cam out I could not find the decompression plunger or spring, I don't think it fell in the case but i could not find it anywhere. Now I just got to order a gasket set, piston, rings, and the decompression stuff. as for just adding oil while it burns it off, the oil will break down because the clutch will add crap to the oil that will not get burned off. Also if it is burning oil then the blow by will add more deposits in the oil. None of this is good for the engine.

[CJM]

Are you sure it is a stock cam?

[engr400]

I think so. Is there an easy way to check? Also what brand gaskets and pistons should i order?

[HondaRacing83]

Cometic gaskets. Wiseco, Je, or Cp pistons only. Do not buy those namura or pro x pistons they are junk and will break and blow. My valve seals are bad. Smokes alot on startup then smokes bad on decel when its hot. When its normal it usually doesnt smoke on decel. Blue smoke it burnd oil. Doesnt burn alot hardly noticable. Ill dump a little gn4 in there every once in awhile and top it off if im goin on a long ride. I still change the oil and filter every once in awhile i dont just add oil because i know its burning it.

[Stickman400]

Isn't the '08+ 400s the ones that don't have a decompression spring or plunger anymore? I could have sworn that member 05DodgeDakota or what ever his name is found that out the hard way after tearing apart his entire bottom end and checking everything with a fine tooth comb, only to find out his was the first year to not have one.

[engr400]

Yep, I just checked and the decompression stuff is not listed on the 2008 models and newer. This is a relief. Also, i will probably just go with a honda piston because i can just go .010 over instead of .040 over with the wiseco.

[HondaRacing83]

I think id still probably go wiseco. Maybe bump up the compression a little while your in there

[ben300]

Yep, I just checked and the decompression stuff is not listed on the 2008 models and newer. This is a relief. Also, i will probably just go with a honda piston because i can just go .010 over instead of .040 over with the wiseco.


agreed. go with a wiseco, 11:1 compression. your gonna get better power and torque with nearly the same reliablity. not to mention, order it off ebay because its cheaper than RMATVMC and motosport and you get more size options than just stock or .040 over..