2001 400EX burning oil. Job difficulty? - Honda ATV Forum
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post #1 of 12 (permalink) Old 05-11-2011, 08:57 AM Thread Starter
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2001 400EX burning oil. Job difficulty?

so my 2001 400EX that i got for very cheap is burning quite a bit of oil lately. i always check/add oil as necessary before and after every ride, but i'm getting sick of leaving a big cloud of blue smoke everytime i get on the gas.

it smokes both under load (this is the rings) and also a bit when letting off the gas at a standstill (like after a rev...this must be the valve guide seals).

i have already ordered a new OEM ring set, and also a full top end gasket kit (head gasket, valve guide seals, etc).

my question is this: how involved is the job to do both of these items?

i understand that the top end has to pretty much completely come off, and then be disassembled for the seals to be installed. however, to do the rings, i'm assuming that i'll need to remove the cylinder case that's around the piston?

i have also heard that i should throw a new timing chain in there while i'm at it. anything else that i should do as a precaution?

any specialty tools that i'll need? like a valve spring compressor? anything else?

i'm trying to decide if i should do this now, or wait until wintertime and do it then.
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post #2 of 12 (permalink) Old 05-11-2011, 09:59 AM
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If you have the service manual it walks you through step by step. Pull the head, cylinder, and your piston is right there attached to the rod. Off the top of my head you will need the valve spring compressor and a torque wrench but not really any other special tools.

Once you do one they are all really similiar. I tore my 110 engine top end down and put a new piston in it in a couple hours earlier this week.

If you want to do the job right, get it bored 10 over and get the matching piston kit. I skimped once on a 185 trike and just replaced the rings and it still smoked after I put it back together. Talk about disappointment. I didn't make that same mistake on my 200x. Next overbore and Wiseco piston kit and no more smoke. You get a like-new ring to cylinder wall seal.

It will cost you about $150 more to get the bore/piston kit, but it's the same amount of work once you have it torn down that far.

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I've owned several Hondas over the years, with 2, 3 and 4 wheels.
Currently have a 1979 ATC 110 and 1985 XL350R enduro.

Last edited by dr. feelgood; 05-11-2011 at 12:24 PM.
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post #3 of 12 (permalink) Old 05-11-2011, 10:25 AM
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it dont matter by the sounds of it it cant get any worse and its not gonna hurt anything riding it like that just wont have to worry about mosquitos anymore lol
and your friends will hate riding behind you
but other than that wait till winter unless you wanna spend a whole weekend working none stop on it sometime
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post #4 of 12 (permalink) Old 05-11-2011, 11:21 AM
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To replace the piston rings (please keep in mind that I’ve never done this before) I believe all you have to do is remove the case surrounding the piston. I think it would be a good idea just to go over everything (timing chain included) if and when you break the motor down since your 400 is 10 years old. Good luck!

2008 TRX400ex

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post #5 of 12 (permalink) Old 05-11-2011, 12:46 PM
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I would not just do the rings. Do a small bore, buy the piston first then get the jug bored for that piston. You could do a 10:1 compression with out messing with the head studs. The timing chain is a good idea to replace while you are in there, also check the guides for damage or wear. Dont buy cheap gaskets. Get a manual and good torque wrench and you will be good to go. Any other question just ask. This is a great site for assistance. Its not to hard, read the manual a few times before you start.
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post #6 of 12 (permalink) Old 05-11-2011, 01:25 PM Thread Starter
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thanks for the replies, guys. yeah, i do have a shop manual, and am pretty mechanically inclined, but have never done any work that required precision machining.

i think i'll just keep an eye on the oil level for now, and ride it out for the season. but when it does come time for the rebuild, i might think about the bore out, since i'll be used to the power by then
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post #7 of 12 (permalink) Old 05-11-2011, 01:30 PM
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I wouldn't tear down a running quad during riding season either. Run it and then rebuild during winter. The small bore jgar and I mentioned isn't for a big improvement in performance. It just gets your cylinder/piston back to factory fresh. You don't even have to rejet. A first overbore is 1/4 millimeter shaved from the cylinder wall, very miniscule.

Rob

I've owned several Hondas over the years, with 2, 3 and 4 wheels.
Currently have a 1979 ATC 110 and 1985 XL350R enduro.
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post #8 of 12 (permalink) Old 05-11-2011, 01:34 PM
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i would definitly have it bored out to the next oversize. that way you wont have to worry about smoking, costs probably $50 for a bore job and you can rest assured its been done right.
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post #9 of 12 (permalink) Old 05-11-2011, 09:42 PM
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dont DONT DONT do a big bore kit when ya bore it over just do a 416 kit or 426 dont do a 440 tho because they make the 400 to unreliable and there tedious to work on plus they over heat easy so you had better put a bigger oil tank and air shrouds and a fan on it so stick to the smaller bore kits and get a higher compression piston
ask if ya want anymore advice
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post #10 of 12 (permalink) Old 11-03-2016, 05:26 PM
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I'm new here and don't know a lot about atv's but I have a 2007 honda 400ex and I checked the oil the other day and it was a little low so I filled it up i went and checked it last night and it was empty it's not leaking anywhere and it don't smoke at all and it don't have a oil burning smell I can not figure this out if anyone has any ideas please help
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