Why? Greyracer!


11 replies to this topic
  • fishkiller

Posted December 15, 2010 - 11:17 AM

#1

Have a quick question.
80 hours of MX on my 09 450. Strict oil and air filter changes. Anyway pulled my motor for a good frame cleanin and was checkin my valves, very carefully.
Exhaust are both border line at .20 mm but my intake has me baffled!
.28mm .25mm .30mm right center left. Why would they be so far off? Have never adjusted but have checked before and knew they were too big but just wrote it off to improper measurement technique. Now that I have her sittin on my work bench I can see with my eye that the gap is larger on my intake side! Crazy! Could this have been messed up from the get go? What are your thoughts on adjustment? I realize your gonna say if its out its out and adjust but dang. Just wanted a little advice before I go cracking into her.
THANKS!

  • KJ790

Posted December 15, 2010 - 11:26 AM

#2

Chances are the shims are wearing where they contact the top of the valves. You can pull them out and see if they have little circles worn in center of the shims.

  • fishkiller

Posted December 15, 2010 - 11:38 AM

#3

After 80 hours? really feel like they have been big for a while. Thanks for the comeback though.

  • grayracer513

Posted December 15, 2010 - 01:59 PM

#4

Regarding the exhausts, Yamaha builds their engines with the valves set at the minimum because it's technically better that way, and they can. I can't explain the intakes unless it was a production error, like maybe the gut doing the head didn't get the jig squarely in place. Things the would make clearances go wide due to any kind of changing condition in the engine are:

  • Carbon on the backs of the valves
  • Worn valve shims
  • Worn valve stem tips
  • Worn buttons on the underside of the lifters
  • Worn or damaged cam cap
  • Assembly error

Items 1-4 seem very unlikely because they only rarely occur, and because the variance from spec is so uniform. If you can't find any of the first 5, assume it was a mistake, shim them and check them more frequently for a little while.

  • fishkiller

Posted December 17, 2010 - 06:46 AM

#5

WHile I have the motor out should I pull the head for more inspection? How bout replacement parts such as pston or rings?
Looking down my intake ports with a flashlight I can see that my middle valve is clean and shiny on top and my outside intake valves def hav a little black on top. I assume this is because the one in middle gets the most direct shot of fuel but is it something I should investigate further?
Thanks.

  • KJ790

Posted December 17, 2010 - 08:06 AM

#6

WHile I have the motor out should I pull the head for more inspection? How bout replacement parts such as pston or rings?
Looking down my intake ports with a flashlight I can see that my middle valve is clean and shiny on top and my outside intake valves def hav a little black on top. I assume this is because the one in middle gets the most direct shot of fuel but is it something I should investigate further?
Thanks.


That's typical on the 5-valve heads, the center valve is always cleaner, no need to worry there. Personally I would put a new piston in it at 80 hours, especially if you have the time to do it over the winter. I know a lot of people would just run it as is though, but that's not me.

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  • fishkiller

Posted December 17, 2010 - 08:15 AM

#7

Thanks for the quick reply KJ!
Thats kinda what I was thinking. Whats your opinion on piston, OEM or aftermarket? Wanna go ridin of course, but first of Jan gonna knock it out.
Also my stock shims out of my three intakes only one of them has a number on it, I have a quality tool to measure with just a little surprising. Seems like there just worn off ink, not stamped.
What about timing chain or tensioner? Replace?
Thanks dude.
DJ

  • fishkiller

Posted December 17, 2010 - 08:26 AM

#8

One more and I will leave yall alone!
My timing marks on flywheel, when I have timing marks on my cams aligned perfectly with head surface, are not perfect through the timing sight hole in cover, bout an eigth of an inch off. Has anyone ever noticed this? I am gonna go with my cam marks aligned with head but just curious. It is not far enough off that jumping a tooth one way or the othe would correct it, only make it worse or mis timed.

  • KJ790

Posted December 17, 2010 - 08:32 AM

#9

Thanks for the quick reply KJ!
Thats kinda what I was thinking. Whats your opinion on piston, OEM or aftermarket? Wanna go ridin of course, but first of Jan gonna knock it out.
Also my stock shims out of my three intakes only one of them has a number on it, I have a quality tool to measure with just a little surprising. Seems like there just worn off ink, not stamped.
What about timing chain or tensioner? Replace?
Thanks dude.
DJ


I like OEM pistons if I'm staying with the stock compression ratio. Obviously you have to go aftermarket if you want high compression. OEM pistons are so cheap compared to aftermarket (1/3 the cost), and I have never had any issue with an OEM piston on these bikes. Yes they are cast, but as long as you don't run them for a million hours they last just fine.

Definitely change the cam chain if you haven't yet, they are a weak point on these engines. They stretch very quickly and if you run a stretched out cam chain it destroys the sprocket on the end of the crank, which is made on the crank, so it will force you to replace the crank. I change mine every 50 hours, it's cheap and easy to do. Worn out cam chains also tend to jump teeth on the cams, which causes bent valves and damaged pistons. Much cheaper to just spend the $25 on a new cam chain often.

As far as the tensioner, some people say replace them every time you replace the cam chain. Personally I don't really see a reason to do that. I have had one Yamaha automatic tensioner lose tension and cause the timing to skip which resulted in bent valves. The thing is that it was on a motor that was very built up (very aggressive Web cams, heavy duty valve springs, high compression piston, etc), and the engine only had 45 minutes of run time on it, so obviously the tensioner was not worn out or anything. When I took it apart the tensioner still functioned completely normal. After talking to some top engine builders I learned that when running aggressive cams with heavy duty valve springs, automatic tensioners can lose tension momentarily when the throttle is chopped.

Moral of the story, if you are running aggressive cams and heavy duty valve springs, ditch the automatic tensioner for a manual one, those can't fail. I run the stock tensioners in my stock engines and have never had a problem. Just inspect it to make sure it is working properly when you have it out. If it is working fine, I have no problem reusing them and have never had a problem from doing so.

  • KJ790

Posted December 17, 2010 - 08:40 AM

#10

One more and I will leave yall alone!
My timing marks on flywheel, when I have timing marks on my cams aligned perfectly with head surface, are not perfect through the timing sight hole in cover, bout an eigth of an inch off. Has anyone ever noticed this? I am gonna go with my cam marks aligned with head but just curious. It is not far enough off that jumping a tooth one way or the othe would correct it, only make it worse or mis timed.


If the cams appear to be retarded slightly then it could be caused by a worn cam chain. Of course the dots are just a guide and aren't absolutely perfect, they are just there to give you an idea of what the cam timing should be, but the more stretched the cam chain gets, the farther off the marks become.

  • fishkiller

Posted December 17, 2010 - 08:44 AM

#11

That was what I was thinking! Thanks a bunch dude! Gonna go ahead and order piston, rings, chain and check my tensioner!

  • rdefonce

Posted December 17, 2010 - 09:33 AM

#12

Definitely change the cam chain if you haven't yet, they are a weak point on these engines. They stretch very quickly and if you run a stretched out cam chain it destroys the sprocket on the end of the crank, which is made on the crank, so it will force you to replace the crank. I change mine every 50 hours, it's cheap and easy to do. Worn out cam chains also tend to jump teeth on the cams, which causes bent valves and damaged pistons. Much cheaper to just spend the $25 on a new cam chain often.


is the '10 and '11 cam chain in same league; weak point that should be replaced occasionally?
or did they change something to make it more durable.
Lastly, is that the same issue with all the Japanese bikes' cam chains???





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