When is it time for a new top end?

15 replies to this topic
  • yzfmxer

Posted July 01, 2004 - 06:40 PM


Ive got an 02 426 and have ridden probably 75hrs total. but recently i have noticed a slight burning oil smell when im riding, and it blows some black smoke when its cold. So is it time for a new top end or do the valves need adjusted?
I just checked the valves about 9 riding hours ago. so i thought they would be fine.
but toamrrow im going to check the valves and see what ive got for clearences. all info is appreciated!!! :thumbsup:

  • berudd

Posted July 02, 2004 - 08:13 AM


I thought the service life of our pistons was over 100 hours but that may be BS. I would try new rings and see if that helps.

  • bushy

Posted July 02, 2004 - 08:34 AM


The some is caused from the valve guides leaking or rings blow by. Im guessing its the rings, but why you have it apart might as well put a new piston in it as well! :thumbsup:

  • Hamish

Posted July 02, 2004 - 11:30 AM


and it blows some black smoke when its cold

black smoke is fuel, indicating a rich fuel condition.
If the smoke occours when you give it a rev in nuetral, it probably indicates that your accelerator pump duration/timing is wrong. Have you done the BK mode???
If not check out motoman393's site.

  • yzfmxer

Posted July 02, 2004 - 11:39 AM


Yes i have done the BK mod, but i have been noticeing that its been a little rich latly, probably because of the increased heat outside. so i leaned it out a little so maby it will stop? i run bel ray thumper oil in it. and change it regulary. But like i said, there is s alight burning oil smell in the exhaust?

  • DoctorRzed

Posted July 02, 2004 - 03:19 PM


Dont worry about rebuilding your engine. I put well over 200 hrs of mx riding on my 426 :thumbsup:

  • tool

Posted July 02, 2004 - 03:57 PM


Dont worry about rebuilding your engine. I put well over 200 hrs of mx riding on my 426 :thumbsup:

i would estimate that ive got around 450 hrs on my 426. ive had to split the cases 3 times. im still on the stock piston, rings(!) and cam chain. there is no type of oil smell in my exhaust. smells like air. regular oil and air filter changes really help the life of a 4 stroke top end.
having said that, it usually smokes a little when i start it cold. no worries. :devil:

  • x654

Posted July 02, 2004 - 07:31 PM


Dont worry about rebuilding your engine. I put well over 200 hrs of mx riding on my 426 :thumbsup:


I am no pro or anything but for the peace of mind of not having a piston shell or rings break and tear everything up i replace mine once a year... i usually run 10-14 x-c races and ride 2 times a month... the $180 and 2 hours it takes to do it is well worth the troubles of knowing i may save a lot more later. just my thoughts.

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  • silveradoss

Posted July 03, 2004 - 05:55 AM


I noticed the oil smell too on my bike and found out it was oil on the bottom of the engine that dripped down when I changed my oil filter. I clean it up with some simple green now and there is no burnt oil smell.

  • yzfmxer

Posted July 03, 2004 - 12:31 PM


I just got done checking the valves, and they are all perfect. Im mean PERFECT! so i know thats not it. maby its just me? Maby i dont know the difference between a rich condition and oil burning??

  • tool

Posted July 03, 2004 - 01:00 PM


i believe GRAY smoke is unburnt fuel, black smoke is oil, and blue smoke is burning coolant. i could be wrong. :thumbsup:
if its gray and only when you first start it, i wouldnt worry about it.

  • redrider77

Posted July 03, 2004 - 03:16 PM


I'm not an expert on the color of smoke, but this is what I have been taught...

Blue -> Oil
White/Gray -> Coolant
Black -> Fuel


Posted July 03, 2004 - 04:20 PM


I would say pull the spark plug and look at what kind of deposits are on the plug- if its black and sooty that might be a rich mixture, oily deposits-rings/valve guides.

  • yzfmxer

Posted July 04, 2004 - 08:38 AM


I Pulled the spark plug when i checked the valves, and it was fine, the outer ring below the electrode was black, but the electrode was a little on the white side.I have the iridium plug in there now. Im thinking that it could have been smoking because i had a gas jug that i used for a 2 smoke, but i just started using it for my 4 stroke, i rinsed it out sevearl times with straight gas, but there could have been some oil reidue left? I just started runing a 50/50 blend of 91 and 111 octain race gas. it has a different smell to it, but i cant smell any oil now?

  • Hamish

Posted July 04, 2004 - 10:31 PM


the small amount of oil left in the jug would be insignificant. I once had a sticky valve and ran my 426 for about 10 minutes on a 60:1 2 stroke mix. Even at 60:1, there was virtually no sign of smoke, so you can discard that theory. Black smoke if fuel, Grey smoke is oil. You'd do well to remember that, can save you a lot of trouble in finding the cause of your problem. When reading a spark plug, look at the porcalin around the electrode. To get an accurate plug reading you need to go WOT in top gear almost to redline, pull in the clutch and hit the kill switch. If you crusise to a stop you wont get an accurate reading.

  • Vet28

Posted July 08, 2004 - 01:40 AM


Do a compression test. If that looks OK, do a leak down test. That's all you need to assess ring/piston/cylinder wear.

I don't think you have enough hours to warrant a new top end, but do the tests first.

Vet28 :thumbsup:

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