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Discussion Starter #1
hey guys im new to the fourm, hopefully someone can give me a little insight on my problem here. i bought an 09 Honda 420 from a friend that had just put a fresh top end in it. about 2 hours after the rebuild it started smoking again so he shut it off and decided he wanted to get rid of it. anyway, he says he called a mechanic and they told him it sounded like the camshaft bearing and the oilpump. does this sound accurate to you? im pulling the motor out soon and wanted to get some opinions. thanks!

-mike
 

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IMO a camshaft bearing and oil pump have nothing to do with smoking.

Smoke is caused by either oil or water entering the cylinder and being burned off.

Whiteish smoke is caused by water leaking into the cylinder via a blown head gasket (if water cooled)

Blueish smoke is caused by oil, a ring sealing problem.

The rings may have been replaced but if the cylinder is damaged or egg shaped the new rings might never seal.

I would suggest doing a compression check on the motor and reporting your findings. If you're going to tear into it remove the cylinder and have it checked by a competent machine shop to have them check the condition of the cylinder. They will be able to tell you if the cylinder is within spec as far as wear and roundness. As well as evaluate the overall condition of the cylinder walls

If it isn't within spec an oversize piston can be used and the cylinder bored out It isn't an incredibly hard job.

As for the shop that told you camshaft bearings or oil pump. I wouldn't go back there for advice. Come to think of it I've never seen bearings on a quad camshaft. They may exist but our of five engines of various makes and models I've been into I've never seen cam bearings.


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Sounds like he did a shoddy rebuild to me.

Oh btw welcome to the forums
 

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Discussion Starter #4
Thanks for the replys guys, there is a cam bearing in the bike i havnt torn into the motor yet. As far as the smoking it is oil burning because of the blueish tint to the smoke, he said he got it bored .50 over by a machine shop and has the right rings for it. He also said the valves were in good condition so he didnt put new valve seals or anything. So you guys think just the rings arnt creating a seal and thats what is causing it to smoke? Any other things that could cause this problem?
 

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That sounds like what it is to me. Is it drinking any oil?

Bluish blackish smoke can also mean unburned gas.








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How much oil is it burning and has it lost power? If it hasn't lost it's power but has a consistent but slow loss of oil it's probably a valve seal. If it burns it really bad and you lost a lot of power then it is probably rings. What the mechanic told you doesn't even make any sense, don't listen to him or let him work on your stuff.

Edit: Ill add this in as well. If you think it is valve seals, it's possible to simply take your exhaust/carbs off and look in the ports. My brute was burning oil, I took it apart then looked in 1 of my exhaust ports and found black sludge stuck to the valve stem and going right into the combustion chamber. Sure enough it was valve seals.
 

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Discussion Starter #7
Im scared to run it because i have been told it can scar the cylender. I did run it for about 5sec and the smoke wasnt thick at all. The muffler does have a slight smell of unburnt gas in it so im not too sure how bad that is.
 

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Correct me if I'm wrong guys but it'll only scar the cylinder if debris gets in it or if the piston were to swell?

If its burning oils it's getting a little extra lubrication lol.






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If the cylinder was bored out of round yes it would damage but really it's already damaged and needs to be fixed either way.. Same if the rings are the wrong size then they need to be replaced anyway. Shouldn't have an issue of running it just make sure you check your oil and keep it topped up.

The first thing I would do is a compression test. If your a full compression its very likely a valve seal which is an easy fix.
 

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Discussion Starter #10
Thanks for the tips this is my first time tearing into a smoking engine and a 420 at that so im clueless haha.. So is there a way to see if the cylinder is ( ) besides bringing it to a specialist. How much does getting it re-honed cost?
 

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Agree with the compression test, THEN if its low compression Start tearing it apart. You'll be able to tell if it's scared or not. In fact when I get home I'll run by the mechanics and take a couple pics of a scared cylinder.

Does he have to pull the whole motor in a rancher or can the top end be torn down in the bike?






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I may be way off but wont a bad over fuel cause it to blow some dark smoke? He said he smelled gas out of the exhaust. does the oil smell like gas?Im unfamiliar with a honda but have you explored any possibilities of this? I may be wrong so honda guys or anyone smarter than me correct me.
 

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Yeah my brute blow out thick black smoke when I first got it. Had never been properly jetted after the msd.







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Discussion Starter #15
Alright guys heres the update.. Tore the head off today only to find that the piston and ring kit that was put in was a STD size and he bored it over .50 needless to say the rings wernt even making contact with the cylinder wall! Looks like i just need a new piston and rings for the right size and im good to go! Any company suggestions for a DECENT price? I found some on ebay for about $130.
 

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Are the cylinder walls scared? Sorry I didn't get a pic.






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go with highlifter. they have the right piston you will need with the rings!
 
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