Top End rebuild ques.

[acw592]

I just bought a 400EX that has a little white looking smoke every now and then. It doesn't do it when you start it up or when it's idleing, just when you gas it, but not all the time. The main jet is too big-155. Has the stock silencer on it until I get the white bros. I bought, but I didn't think that would make it do it. It kind of has that oil burning smell when it does do it. Does that sound like it needs a new top end? Should you have anything done to your valves when you rebuild the top, or can you just bore the cylinder and get by with just the new piston. I want to stick a Hot Cam stage 2 in it, might as well do it all at once. Thanks

[acw592]

???

[Bullrider21]

usually white smoke is not enough fuel. but if it smokes just a little i wouldnt worry to much about it. You can check your valves by shooting lubricant down into them and if they leak out the sides at the bottom you really need to replace them. What size piston are you wantin to put on there? If you do a piston you really need to do a hotcam at the same time. Because if you just do the piston you wont see the full potential without the hotcam.

[acw592]

Doing a search, it almost looks like it could be a valve seal leaking.
I wasn't quite following you on how to check the valves, could you re-explain that? Do you have to take the head off? If I do have to rebuild the top, or when, I was just going up the next size.Thanks

[m1ke]

valve seal's don't leak at high rpm (far as i know) you sure its not bluish white? they are notorious for burning oil............ check the bore and piston skirt.

[Rico]

Sounds to me like your running rich, too much gas basically.

NO rebuild needs to take place or anything else so don't worry about it.

[acw592]

thanks everyone for the help. It is jetted to big, until I get my slip on. we'll see what it does when it's not too rich.

[m1ke]

guy if you smell oil its burnin the ****, there's no way around it. besides at high rpm smoking and none at idle is rings/bore/piston.... i would know i was there.

Besides, if your jetting was too rich you would CLEARELY see BLACK SMOKE. white smoke is coolant, but since this bike isn't water cooled your either taking on water or your bike is burning oil. Go ahead, search the net for black smoke symptoms.

Mike,

[ballz2thewall]

Not sure how much this will help but I had the same problem with Honda's G4 oil, it would burn if you were on it. So I fixed that by going to another type of oil ( Amsoil).

[m1ke]

Yes. They will smoke if you use too thin an oil in a worn engine. The thicker oil doesn't seem past the rings near as easily if at all. Typically in the summer months you should use 15W40/20W50 High Temperature Engine Oil as it's designed for high-heat engines, which means the oil doesn't break down.

The only problem with using thick oil in the winter/cold is that it's like molasis and you get "dry-starts" cause the oil can't be moved through the system as quickly.

[acw592]

So if I do the top end, what is recomended for the valves. Do they need attention? (I need to buy a clymer's). Is doing the valves by hand with valve grinding compound all that needs done? Also when I looked in rocky mountains catalog they only listed two wiseco pistons, std. and .040 over. Should'nt there be a .010,.020,.030 available?

[Buffalo400]

Honda has some oversized pistons (std compression).... but you can go with bigger bore with aftermarket compagny pistons like Wiseco, Je, Ross..... go with a HC piston and head studs kit if a motor job is needed for more HP....

if you don't have blue smoke, don't worry and hit the trails...

[m1ke]

Do a leak down test before you tear it down. This will give you an idea how much it leaks, and where. Other than that, it's a matter of taking it all off and seeing what's worn. (Connecting rod play, scores or worn bore, valve damage/wear, etc. The rebuild should not cost you hardly anything. You will need a clymer's manual, and with this, you will be able to do this with ease.

When my bike was smoking it would not smoke at all at startup, and when you revved it, it wouldn't smoke at all until it warmed up (oil thinned out) then when you give it a good rev the puffs of smoke would come out and you could distinctively smell that oil burning (kinda like if you burned grease). I knew then I wasn't going to ride it smoking like that. When I rode the engine would just cough it out once it was hot. You'd of thought it was a 2 stroke. Anyway, so I rebuilt it and everything is good now. I'm glad I fixed it...

Once you remove the head you should do a visual inspection as well as a leak test with keroscene. if they leak they need lapping...

Good luck.

[acw592]

Thanks for the help. This is exactly like yours was, but it doesn't smoke much. when I rode today I didn't see it at all. I would think it was just dust from the tires but I deff. saw a little come from the pipe when I was behind my son riding one of the other quads a couple days ago. It has plenty of power and runs great except for bottom end from the jetting. Would a compression test tell the same thing?

[m1ke]

Hi again,

With a compression tester, the only thing you can do is get a reading in psi (pounds per square inch) of how much compression the engine is producing. This can be very valuable for telling how worn your engine is. If I remember correctly, the engine is a 9:1:1 compression ratio, and the compression ratio in this engine for a stock engine is from 100-128 psi. But that can only tell you so much. What was bizarre was mine produced 120 psi cold! I was stumped. I couldn't figure it out. It turned out to be scores in the cylinder walls. A trick with the compression tester is to do a cold dry test, and then a wet test. Doing this involves adding 1 table spoon of engine oil. Now, do the test again. if you get a higher reading, your piston rings or bore is leaking. if it does not change, it's most likely valves/head gasket.

So basically if you want a good idea of what could be wrong you should do a leak down test with a leakdown tester. They are a little expensive but if you have alot of used vehicles/machinery they are a great tool to have. You will need an air compressor for this tool to work. What a leakdown tester does is measures how much the engine is leaking compression. To do this, we thread the device into the spark plug hole, allow 100 psi to flow into the cylinder, and then we check the guage to see how much pressure loss occurs. If the press drops from 100psi to 90psi you have a 10% leak (decent), if it drops from 100 psi to 80psi you have a 20% leak, (not so good...) and if it drops lower you have a big problem. With that done, you can now LISTEN for where the leak is coming from. Listen in exhaust/intake ports, and crankcase to tell where it's leaking from when you hear an audible hiss of air.
This is also good for telling if your valves are sealing properely.

Hope this helps. You can have a honda shop do a leakdown test for you for about 1 hours labor ($65-70) Good luck!

Mike,

[m1ke]

If you're not sure you want to rebuild, you can try adding some smoke-stop or putting high temp engine oil 20w50 and it should be ok however this is not a permanant fix.

best of luck.
mike,

[acw592]

A leak down tester sounds like a good tool to have. We have 3 quads, 4 if you count the one I'm putting together, a go cart, 3 vehicles, mower, ect. ect. I actually wouldn't mind doing the top end in this once we get our garage built. At least I have a couple others to ride while that one's down. I would like to put in a wiesco piston and a stage 2 hot cam and see how it compares to my other which is a 99 basically stock (slip on & uni filter). Thanks again for all the help, this is a great site!