Logical explanation why 400EX's smoke [Archive]

ImWhite

12-21-2005, 12:56 PM

Originally posted by speedyquad
i have a 2000 400ex and it has never smoked...a little on start up, but after a few little puffs, that is gone...every bike i have had has had the little bit of smoke on start ups...

same here on my 01,never rebuilt yet and it only smokles alittle bit on start up(in cold weather)....*knock on wood* just incase lol

atvracer980

12-21-2005, 01:23 PM

what is done after start-up, If your not patient enough to let the oil get circulating after start-up , that'll cause premature wear- if you feel you must rev the motor right after start-up then your the cause of smokeing, the 400ex needs time to get the oil pumping throughout the motor after start-up. Lack of timely oil changes- I personally change my oil after each race, each trip to the sand dunes or after about 6-10 hours of casual rideing. Running to high of compression piston will prematurely wear your rod out and oval the lower part of your cylinder. I run a larger oil res. and a 4-row oil cooler to circulate cooler oil all the time. Heat is the worst enemy for the 400ex- spend alittle money to reduce the heat factor or spend more money on piston replacement.

fitethesystom

12-21-2005, 02:04 PM

Ok, Smokey's apart. I'm going to take a picture of the valves & piston crown, it has dried carbon on it, but is fairly clean. Cold compression test showed 120PSI COLD, Which blows me away. That's almost FULL compression (128 being peak according to Clymer's manual). Im replacing all rings & honing and hoping for the best. cylinder sleeve looks excellent. I'm hoping the oil ring is gone?! What are your thoughts? It's smoking at high-rpms, only once it's warmed up. Am I on the road to recovery?

Mike,

fitethesystom

12-21-2005, 02:09 PM

Might I add that the 120 psi reading was a dry test.

mike.

stc416rider

12-21-2005, 02:51 PM

mine hasent ever smoked

F-16Guy

12-21-2005, 03:45 PM

Originally posted by fitethesystom
I would like to know if anyone can tell me why this fourstroke engine is so prone to smoking regardless of wear. I'm baffled.

Mike,
Because people who don't know what they're doing try to work on them. Mine has never smoked; at startup or otherwise.

fitethesystom

12-21-2005, 03:49 PM

False. They have a weakness. Engines that have never seen a wrench smoke with low hours. Personally I believe they run really hot and thing's get a little out of kilter. Just an idea.

Mike,

ImWhite

12-21-2005, 04:06 PM

Originally posted by atvracer980
what is done after start-up, If your not patient enough to let the oil get circulating after start-up , that'll cause premature wear- if you feel you must rev the motor right after start-up then your the cause of smokeing, the 400ex needs time to get the oil pumping throughout the motor after start-up. Lack of timely oil changes- I personally change my oil after each race, each trip to the sand dunes or after about 6-10 hours of casual rideing. Running to high of compression piston will prematurely wear your rod out and oval the lower part of your cylinder. I run a larger oil res. and a 4-row oil cooler to circulate cooler oil all the time. Heat is the worst enemy for the 400ex- spend alittle money to reduce the heat factor or spend more money on piston replacement.

well let me fix my words from the first post i made....mine only smokes in the cold...i let my quad warm up b4 i ride,i rev it alittle but not much at all...i change my oil about every 3 rides which is about 2-3 hours each ride sometimes less....i dont race so mine r just casual rides

balls2da-wall

12-21-2005, 05:15 PM

you all must be getting lemons or something...I bought a 2003 400ex and raced it a full season on XC..NEVER SMOKED...put a 440 kit on it my self and raced it another full season of XC...NEVER SMOKED...have that same quad today and it still doesnt smoke. No quad is supposed to smoke...they are supposed to burn a LITTLE oil but all engines are supposed to...but not enough to cause smoke. Ive never seen a 400ex smoke at the races i go to except one that blew there rings out.

DEAL

12-21-2005, 05:32 PM

fitethesystom

12-21-2005, 05:35 PM

Mine never smoked either.
The only time it did smoke was after I lost my airbox at a race and sucked dirt into the motor, once I replaced the piston and rings it worked great.
after that the only time it did smoke was on startup because it wasn't a stock piston.

- That's encouraging. I hope my bike does the same thing with these new rings. If not....ill be really pissed off. lol

balls2da-wall

12-21-2005, 05:39 PM

are you guys just changing the pistons rings and praying like hell its solves the smoking problem? Or are you honing the cylinder too to remove the scratches which CAUSE smoking...you also need to check the tolorances to see if it will need bored or just honed. If your JUST changing the rings thats like beating a dead horse...your just wasting your time.

fitethesystom

12-21-2005, 05:42 PM

I'm going to hone it also. It has 120psi compression. I don't know.

Mike,

WheelerBob

12-21-2005, 05:46 PM

I agree with f-16 guy, 400ex's are probably one of the best selling quads ever, everyone and there brother has or has had one at one time or another, for many years the 400 was their best selling quad. What i'm trying to say is you have to look at complaints vs units sold, so for every yfz or 450r there are 4-5 ex's. Since the 450's came out the 400 has gotten to be a bargin, and alot of used ones have been apart at one time or another by someone who thought they knew what they were doing. My ex is an 04 and doesn't smoke at all, it's stock and has never been apart. Take this for what it is, personal experience and nothing more. And btw i've been riding Honda for about 20 years now and have had very few problem's that i didn't cause myself.:D :D

Rip_Tear

12-21-2005, 05:52 PM

Mine smokes when I have the choke on a bit at start up, but other then that it's never smoking... The tires smoke a bit... but thats something totally different...

fitethesystom where in Ontario are you?

ImWhite

12-21-2005, 06:04 PM

wheelerbob where in maryland r u?im in hagerstown,lookin for some new people to ride with....

fitethesystom

12-21-2005, 06:06 PM

Hey, I am in Hamilton Ontario Rip_tear. This is blue smoke i'm talking about.

Mike,

CDCHONDAS

12-21-2005, 06:11 PM

Just honing your cylinder may not solve your problem either, you should have someone measure it to be sure its not out of round and check the clearance, normally its best to bore it over a size, also putting in new valve seals would be a great idea.

fitethesystom

12-21-2005, 06:13 PM

how often would these cylinders get 'out of round'

-mikey

CDCHONDAS

12-21-2005, 06:29 PM

Well it would have alot to do with how hard its ran and how often the oil is changed but its not all that uncommon or anything, basically its better to have it checked than to put it together wrong, what happens is since the piston has side load from the connecting rod one piston skirt will drag going up and the other coming down and since this is only happening on one plane it will create and out of round effect, the problem with putting a new piston and rings in an out of round bore is that the rings are meant to fit in a round hole and the bore may or may not be creating a bad seal? get it?

malibuj

12-21-2005, 06:56 PM

There are certain diagnostic tests you can perform prior to a tear down to determine the source of the oil burning. You can do a compression test, if you have a baseline compression value to compare it to. (If it's stock I believe it is 128psi) The problem is that if you have changed the piston and/or cam the compression will not be 128psi due mainly to the timing events of an aftermarket cam or the higher compression piston creating more pressure in the cylinder. The best way is to do a leakdown test on the motor. (do a search on the web)Through a couple of steps with this procedure, you will be able to determine whether it's your rings or valves that are the root cause of your oil burning problem.

If you're going to tear it apart anyways, you must check the cylinder for both out-of-round and taper. Just a quick hone and new rings is a waste of time if you're trying to achieve an efficient seal with the rings. Also check the valve seats(lap them or get them cut) and guides for wear/damage. Measure the valve guide clearance as well and be sure to install new valve stem seals while you are there. These are the steps necessary to ensure a smokeless 400ex and prevent you from doing a couple of teardowns to get it right. These are the basic service rules for all internal combusion engines.

On a final note, I have witnessed both my machine and others smoke due to overfilling the oil. Mine has always been a pain to check. I believe the service manual says to get the machine hot and wait 5 min or so before checking the oil level. You are not supposed to just fill it up to the top of the dipstick when it's cold. Will be overfull for sure.

Just a few of the things I've learned over many years of screwing things up myself!
malibuj

fitethesystom

12-21-2005, 07:44 PM

if my engine had an "out of round cylinder" wouldn't i have low compression? 120psi of 128 peak.

Mike,

WheelerBob

12-21-2005, 07:54 PM

Maybe , maybe not if you have a tapered cylinder caused by the piston skirt contact, the wear would be much greater at the bottom of the cylinder than at the top, because of the angle of the connecting rod, as the piston comes up the side load decreases resulting in less wear on the top half of the cylinder. Most of the compression is made in approx the top 2/3 of the piston travel, so you could have good compression and still have a slightly out of round cylinder. Hope this helps.:D

WheelerBob

12-21-2005, 07:57 PM

ImWhite - I'm in baltimore, thinking about heading to Greenridge soon.:eek2:

bwamos

12-21-2005, 07:59 PM

fitethesystom,

Have you done an A/F ratio test?

I swear to god, most smoking 4-strokes, are people rejetting their quads using some bogus setup off of the internet that is way too rich, and not actually doing "proper" plug checks and/or A/F ratio testing.

For example most people running the old 330ex run a 145-150 main jet. I am running a 138 main jet and I'm running at 13.8:1 A/F ratio. A 150 has to be around 11:1. That's horribly rich.

2-Strokes are supposed to smoke a little.. ;)

fitethesystom

12-21-2005, 08:03 PM

Yeah, but this smoke is clearely blue. I wish it were A/F problem.

My motor's in pieces currently. I'm throwing new rings in and honing the cylinder. I may buy a new piston. I just want the smoking to stop and i'm one happy camper. This out of round **** sounds like a real nightmare.

Mike,

bwamos

12-21-2005, 08:07 PM

Is the blue while it's at high rev after warmed up, or at startup?

Warm at high rev, you just need new rings as the others have said.

If it's at startup, you need to replace the valve seals.

I wouldn't worry too much about the out of round. Check it, if it is out of tollerance, just bore it out 0.5mm (0.020") and use the +0.5mm piston. ;)

Should be easily fixed for a low $ value.

CDCHONDAS

12-21-2005, 08:08 PM

like Wheeler Bob said with a tapered cylinder, or for example out of round would be worse at the bottom than the top (essentially taper) because the bottom of the skirt never gets even close to the deck of the cylinder. also your old rings probably conformed and wore to some extent to the out of roundness, the only way to check is with a precision bore gauge.

bwamos

12-21-2005, 08:09 PM

A leakdown test should tell you if you're getting blowby at the bottom of the stroke, no?

fitethesystom

12-21-2005, 08:10 PM

too late. it's apart.

Rico

12-22-2005, 06:46 AM

muffler bearings seem to let the oil pass thru...:mad:

malibuj

12-22-2005, 07:04 AM

Rico, I already thoght of that, I'm runnng a dual-row muffler already!:devil:

Rico

12-22-2005, 07:08 AM

Originally posted by malibuj
Rico, I already thoght of that, I'm runnng a dual-row muffler already!:devil:

Tapered is better, trust me. I"ve rebuilt my motor 3 times this year and know WTF i'm talkin bout...:scary:

ImWhite

12-22-2005, 07:40 AM

Originally posted by WheelerBob
ImWhite - I'm in baltimore, thinking about heading to Greenridge soon.:eek2:

thats cool,blatimore is only like 1.5 hours from me,any good places down there?it sucks here lol,where is greenridge?

malibuj

12-22-2005, 08:53 AM

To answer bwamos's question:
A leakdown test could be used to determine if you are getting blowby at the bottom of the stroke. But usually is not. You are primarily concerned with ring seal at the top of the stroke. This is were the compression takes place, and the most potential for power loss. As for cylinder taper, most times the cylinder is the largest at the top of the bore. This is where the piston has the most loading, right after the fuel mixture is ignited.

To touch on another point, incorrect jetting(way rich) can definately cause minor smoking. All too often it's incorrect jetting, lean or rich, that leads to the rings losing their ability to seal efficiently. Then it's smokey time!
Another big thing rings don't like is dirt. Keep those filters clean and oiled!

Rico, thanks for the tip! I'll PM you my plans for installing an old hairdryer in your airbox! 6hp garanteed! :cool: I'm painting my engine side covers yellow for an additional 2hp as we speak!:blah:

bwamos

12-22-2005, 09:41 AM

Originally posted by malibuj
To answer bwamos's question:
A leakdown test could be used to determine if you are getting blowby at the bottom of the stroke. But usually is not. You are primarily concerned with ring seal at the top of the stroke. This is were the compression takes place, and the most potential for power loss. As for cylinder taper, most times the cylinder is the largest at the top of the bore. This is where the piston has the most loading, right after the fuel mixture is ignited.

Aye, I was thinking more of the intake stroke. Negative pressure in the cylinder. At the mid-bottom of the stroke it could suck oil up past the rings causing the smoke.

That was my thought process. Right or wrong, that's what I was thinking.

fitethesystom

12-22-2005, 10:16 AM

So what do you figure is wrong with my engine? My engine produces 120 psi of compression on a cold dry test. My oil ring or something not doing it's job causing it to leak past the top ring? Did the ring gaps move? Glazed cylinder? Are my valve seals shot? I need IDEAS. It won't smoke when it's cold. Which makes me believe the oil thins out, and is seeping past the rings. Just an idea. Once it is fully warmed up you can definately smell and see the smoke. And yes, it's blue. The piston has carbon buildup on the intake side, and carbon build up on the valves are black as night with carbon build up also. no burnt valves here. I don't think there's anything wrong with the way the valves are operating as i have excellent compression. Ideas??... I need to put it back together ASAP.

Mike,

12-22-2005, 10:24 AM

I havent bothereed to read this whole thread. but from the last poast I would say to replace the valve seals.

coryatver

12-22-2005, 10:29 AM

Originally posted by Rico
Tapered is better, trust me. I"ve rebuilt my motor 3 times this year and know WTF i'm talkin bout...:scary:

I don't know what honda was thinking why didn't they put grease zerks on those dang muffler bearings?:mad:

Trevor

12-22-2005, 12:31 PM

my 300ex dosen't smoke but it dose go down a little on oil a verry little bit!

400exrules

12-22-2005, 03:40 PM

i dont wanna sound stupid but how does oil get up to the piston if the oil sump is below the crankshaft? this is a a model of a car engine, but the 400ex is a dry sump engine, so it looks the same right?:

http://auto.howstuffworks.com/engine1.htm

fitethesystom

12-22-2005, 03:46 PM

Nobody has any idea's?

-also i saw someone said they put a 440 kit (which means new sleeve) in there bike and it still smokes.... how the hell is this possible? valve seals?

12-22-2005, 05:26 PM

Originally posted by mittimj
I havent bothereed to read this whole thread. but from the last poast I would say to replace the valve seals.

wilkin250r

12-22-2005, 05:47 PM

Originally posted by fitethesystom
My engine produces 120 psi of compression on a cold dry test.

I don't think there's anything wrong with the way the valves are operating as i have excellent compression.

120psi is not excellent compression. Your motor, in stock form, should be at least 165psi compression.

If you have carbon build-up and you're blowing blue smoke, it sounds to me like your rings are gone. Time for a rebuild, and a fresh bore.

fitethesystom

12-22-2005, 08:05 PM

Originally posted by wilkin250r
120psi is not excellent compression. Your motor, in stock form, should be at least 165psi compression.

If you have carbon build-up and you're blowing blue smoke, it sounds to me like your rings are gone. Time for a rebuild, and a fresh bore.

120 cold isn't good compression?!?!?!?..........................What the HELL are you smoking? If my engine was hot I would have even higher compression. The manual clearely says 100-128psi for Compression specs....................................... I dont see how that's low AT ALL. It's only an 9:1:1 Compression ratio. 165 psi would NOT be in the honda's operating range. Maybe if you had a HIGH COMPRESSION piston.

Cylinder compression: 100-128 PSI. (686-863 kPa)

You need to straighten your facts out son.

Mike,

12-22-2005, 09:26 PM

Originally posted by fitethesystom
120 cold isn't good compression?!?!?!?..........................What the HELL are you smoking? If my engine was hot I would have even higher compression. The manual clearely says 100-128psi for Compression specs....................................... I dont see how that's low AT ALL. It's only an 9:1:1 Compression ratio. 165 psi would NOT be in the honda's operating range. Maybe if you had a HIGH COMPRESSION piston.

Cylinder compression: 100-128 PSI. (686-863 kPa)

You need to straighten your facts out son.

Mike,

never argue with. walkin250r. never mind insult him. your about to be proved wrong...

fitethesystom

12-23-2005, 10:42 AM

Prove the Clymer's manual wrong - Make my day.

Make sure you provide hard facts that 165psi is correct for the 9:1:1 compression ratio 400ex engine, god almighty one.

biff440ex

12-23-2005, 10:55 AM

You are taking into consideration that moisture gets into your exhaust and possibly the motor when it sits or you wash it, and it takes a while for the moisture to burn out. Just making sure you understand that. Unless its blue and does it after its warmed up don't worry about it .

wilkin250r

12-23-2005, 11:30 AM

Actually, he's right. I forgot about the decompression mechanism. It's been so long since I've done diagnostics on the POS stock engine. :p

But don't talk down to me and call me "son" or "almighty one". I've forgotten more about engines than you'll ever know.

And between you and me, YOU'RE the one that can't figure out your smoking problem, so I don't think I'm the stupid one. ;)

fitethesystom

12-23-2005, 11:54 AM

I have to agree the engines kind of a POS. But, I have a good idea of the situation and with this there is no obvious reason. Obviously if my compression was low I would know right away it's rings. However it could be bore, oil ring & rings, taper, or valve seals. Other than that I think it's fine.

4 out of 5 honda mechanic's think it's valve seals.

Mike,
:)

wilkin250r

12-23-2005, 12:15 PM

If you're blowing blue smoke and have lots of carbon build-up on the piston and valves, it sounds like oil, as you have already guessed.

If it is indeed oil, there are only two paths it can get into the cylinder. Either from the bottom, through the rings, or from the top, through the valves. It certainly isn't coming through the cylinder walls, and I would hope it's not coming from the carb. ( there is also a very small chance it's leaking through a gasket somewhere)

Personally, my bet says it's NOT the valve seals. If it was, I would expect to see it when the motor is cold.

malibuj

12-23-2005, 12:55 PM

It's still kind of beating a dead horse here. You refer to doing your compression test "cold" and it being a "dry" test. Assuming you understand what both of those terms mean, I have no idea why you wouldn't do a wet test (preferably when the motor is hot) to determine whether it was the rings or the top end. You're at the point now where if you want to be sure what's causing your oil burning problem, you need to measure the cyinder for taper, out of round, and check your valveguide clearances. Seals should be something you do for sure.
The main problem here is that you didn't perform the preliminary diagnostics properly. Don't get frustrated when you realize none of us are clairvoyant here. Every motor is different. One motor may smoke for a different reason than another.
I would strongly suggest you take it to a shop or someone with the proper tools and know-how to properly diagnose and correct whatever problem you have. In the end, you'll be glad you did. :rolleyes: