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Yz450f feels weak

By SH3A,
in YZ400F/426F/450F/450FX

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SH3A

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Recently bought a yz450f '09, every time I started the bike It smoked bad, it was blue, it would continue to smoke as I rode it for a good 15 min, after 15 min the smoke was very minimal and could only be seen inter a heavy load from the bike. The bike had a lot of power. I knew it was a time for a rebuild, instead of going through the hassle of working inside that tight frame I removed the motor and started tearing it down, I got down to the cylinder which looked good and was not warped, the piston looked fine so I replaced only the rings, new OEM, then I honed the cylinder and started rebuilding, I took the valves off so I could install some new valve seals, and while the valves were off I cleaned the carbon buildup off of them and lapped them so the were even again, I used a valve spring compressor for reinstallation. I put it back to top dead center to install the cams, placed the cover back on, """torqued everything down BTW""", put all back together, put in fresh oil filter and oil, kicked over the Motor by hand with the kick starter just to make sure everything was moving, then I went to start the bike as usual started on like the 10th kick, let it idle for about two minutes and the header with glowing red "I know this is normal for an idling bike" I was breaking in the rings but just driving slowly up-and-down the road. I gave it another oil change and change the oil filter. I took it back in my woods and could already tell it's so different there was not as much exhilaration and felt as if when I gave the bike throttle with the clutch out it didn't actually move until the RPMs fell and I gave it more gas I had to gradually get up to speed, sidenote "If I'm in first gear with the clutch held in and I rev my bike it will start to move forward, I know there was a power loss because when I tried to spin the tires by exeleration the bike got into high rpms but didn't spin tires would this be caused by a worn clutch?

I am willing to remove the clutch cover if anyone has any ideas what's wrong

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Grand Master

grayracer513

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A couple of things to touch on first.  One, you should absolutely not ever lap titanium valves.  Ever. No matter who says otherwise.  They're coated with an extremely thin (less than .0006") layer of a Ti Nitride compound to make them serviceably hard, and lapping will degrade the coating and shorten the service life of the valve.  Just don't.

 

Second, I trust you are aware of the cylinder head torque procedure being a 3 step process, the last of which involves rotation angles, not torque wrenches.

 

With that out of the way, as to your clutch, start by being certain that you have at least the required 3mm of free travel at the clutch lever, and that the same travel exists at the cable end of the release arm.  If you have play, then the slippage you report indicates a faulty clutch.  

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Grand Master

grayracer513

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If you don't have a manual, get one here:

 

http://api.viglink.com/api/click?format=go&jsonp=vglnk_14456101137259&key=fd4d0c8927dbf2331e83bbda32ac7c21&libId=ig3qxg26010004is000DL9wpsycvdqvyn&loc=http%3A%2F%2Fwww.thumpertalk.com%2Ftopic%2F378677-common-threads-look-here-1st-mods-maintenance-common-issues-and-faqs%2F&v=1&out=http%3A%2F%2Fwww.yamaha-motor.eu%2Feu%2Fservices%2Fowner-manuals%2Findex.aspx&title=Common%20Threads%3A%20Look%20here%201st!%20Mods%2C%20Maintenance%2C%20Common%20Issues%20and%20FAQ%27s%20-%20YZ%20400%2F426%2F450%20-%20ThumperTalk&txt=http%3A%2F%2Fwww.yamaha-mo...uals%2Findex.aspx

 

http://api.viglink.com/api/click?format=go&jsonp=vglnk_144561012565210&key=fd4d0c8927dbf2331e83bbda32ac7c21&libId=ig3qxg26010004is000DL9wpsycvdqvyn&loc=http%3A%2F%2Fwww.thumpertalk.com%2Ftopic%2F378677-common-threads-look-here-1st-mods-maintenance-common-issues-and-faqs%2F&v=1&out=http%3A%2F%2Fwww.yamahaownershandbook.com.au%2F%3Fr%3D0&title=Common%20Threads%3A%20Look%20here%201st!%20Mods%2C%20Maintenance%2C%20Common%20Issues%20and%20FAQ%27s%20-%20YZ%20400%2F426%2F450%20-%20ThumperTalk&txt=http%3A%2F%2Fwww.yamahaown...ook.com.au%2F%3Fr%3D0

 

If the hard coat on the valves is worn through, the symptoms are simply that it won't stay adjusted.  You will set the clearance, and then after no more than two rides, you'll find that the clearance has closed up already.  Then, it's time for new valves. 

 

Here is the head torque procedure: 

 

https://www.thumpertalk.com/topic/873863-cylinder-head-tightening/

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SH3A

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Absolutely will, if it even starts.

Go to yamaha's website and download the factory service manual for free and it will explain the cylinder torquing procedure.

Ok, idk if you would know why but in this case what would cause the loss of power? Because the valves are still fully closing and opening, right?

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SH3A

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If you don't have a manual, get one here:

http://api.viglink.com/api/click?format=go&jsonp=vglnk_14456101137259&key=fd4d0c8927dbf2331e83bbda32ac7c21&libId=ig3qxg26010004is000DL9wpsycvdqvyn&loc=http%3A%2F%2Fwww.thumpertalk.com%2Ftopic%2F378677-common-threads-look-here-1st-mods-maintenance-common-issues-and-faqs%2F&v=1&out=http%3A%2F%2Fwww.yamaha-motor.eu%2Feu%2Fservices%2Fowner-manuals%2Findex.aspx&title=Common%20Threads%3A%20Look%20here%201st!%20Mods%2C%20Maintenance%2C%20Common%20Issues%20and%20FAQ%27s%20-%20YZ%20400%2F426%2F450%20-%20ThumperTalk&txt=http%3A%2F%2Fwww.yamaha-mo...uals%2Findex.aspx

http://api.viglink.com/api/click?format=go&jsonp=vglnk_144561012565210&key=fd4d0c8927dbf2331e83bbda32ac7c21&libId=ig3qxg26010004is000DL9wpsycvdqvyn&loc=http%3A%2F%2Fwww.thumpertalk.com%2Ftopic%2F378677-common-threads-look-here-1st-mods-maintenance-common-issues-and-faqs%2F&v=1&out=http%3A%2F%2Fwww.yamahaownershandbook.com.au%2F%3Fr%3D0&title=Common%20Threads%3A%20Look%20here%201st!%20Mods%2C%20Maintenance%2C%20Common%20Issues%20and%20FAQ%27s%20-%20YZ%20400%2F426%2F450%20-%20ThumperTalk&txt=http%3A%2F%2Fwww.yamahaown...ook.com.au%2F%3Fr%3D0

If the hard coat on the valves is worn through, the symptoms are simply that it won't stay adjusted. You will set the clearance, and then after no more than two rides, you'll find that the clearance has closed up already. Then, it's time for new valves.

Here is the head torque procedure:

https://www.thumpertalk.com/topic/873863-cylinder-head-tightening/

Ok phew, I did do the whole 14lb and then 180° turn thing, I've never torqued anything to that before, they are measured right now to like 75ft/lb, I didn't torque it to 75 but I wanted to see what kind of pressure was going on a those bolts.

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Grand Master

grayracer513

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Ok, idk if you would know why but in this case what would cause the loss of power? Because the valves are still fully closing and opening, right?

 

You stated that you lapped the valves.  I don't know whether you performed that task correctly, and I don't know whether you checked them before the head went back on to see how much they leak, if at all, but if the the valves operate well enough that you have detectable compression resistance at the kick starter, and the bike starts and runs, whatever leakage you may or may not have will not cause a loss of power that most people would notice, and would definitely not produce the symptoms of revving up under power without an associated amount of acceleration or wheel spin. 

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SH3A

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You stated that you lapped the valves. I don't know whether you performed that task correctly, and I don't know whether you checked them before the head went back on to see how much they leak, if at all, but if the the valves operate well enough that you have detectable compression resistance at the kick starter, and the bike starts and runs, whatever leakage you may or may not have will not cause a loss of power that most people would notice, and would definitely not produce the symptoms of revving up under power without an associated amount of acceleration or wheel spin.

If that doesn't than what do you think would cause the power loss, it ran fine with power before the rebuild, I got all new OEM parta
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SH3A

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Sounds like possibly a compression leak. Also, alot of people say you need to ride kinda hard on breakin to seat rings properly (like first 15 minutes) need some somewhat heavy acceleration. May be cam timing is off??

I've ridden for a good hour on the rings and it feels like my bike is just getting weaker the more I ride it, I haven't ridden it since GREY RACER, told me its time for new valves, and I know the timing is correct, hmmmm
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FORMA MOTO

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I've ridden for a good hour on the rings and it feels like my bike is just getting weaker the more I ride it, I haven't ridden it since GREY RACER, told me its time for new valves, and I know the timing is correct, hmmmm

 

You have been told what it probably is, and you can confirm the issue by doing a leak down test.

 

Riding it more is not going to make it run better..........

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SH3A

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What did you use to hone the cylinder and how much did you hone it?

The nikasil coated cylinders are not really meant to be honed although a couple quick passes with a ball-type hone is okay.

ImageUploadedByThumper Talk1446030568.881432.jpg
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grayracer513

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Fixed stone hones like that are the wrong tool for any simple re-ring or piston replacement where the cylinder is not being re-bored or replaced.  A brush/ball hone is better because it only refinishes the surface without trying to "straighten it out" or restore a perfect shape to it.  Nikasil plating is typically only .002-.003" thick, so you have very little to work with.

 

https://www.thumpertalk.com/topic/399309-new-piston-06yz450f-advice-needed/#entry3565759

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SH3A

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Fixed stone hones like that are the wrong tool for any simple re-ring or piston replacement where the cylinder is not being re-bored or replaced. A brush/ball hone is better because it only refinishes the surface without trying to "straighten it out" or restore a perfect shape to it. Nikasil plating is typically only .002-.003" thick, so you have very little to work with.

https://www.thumpertalk.com/topic/399309-new-piston-06yz450f-advice-needed/#entry3565759

Would it be worth it to get replated or should I just get a new OEM cylinder, and when I install I read to not apply oil inside the cylinder to help seat the rings, is this correct?
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SH3A

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Personally, I would just replace it with new.

The wet/dry build debate is a whole other can of worms. I always have and always will smear a film of oil, just a light film, on the cylinder walls, the piston skirt, and the top/bottom surfaces of the rings.

Ok, cuz yea I've always put a small layer of oil, well thank you for your help, I believe that should be all I need. ?
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