Tight valve clearances on your low-hour 450?


5 replies to this topic
  • Adammoto

Posted November 07, 2009 - 05:19 PM

#1

If you have a low-hour YZ450F with slightly tight valve clearances, try loosening the cam cap bolts and re-tightening to spec (10 Nm). Just about every bolt on my 09 YZ450F was way overtightened at the factory, including the cam caps. At ten hours, I measured one intake at .09mm and one exhaust at .18mm. All valves came into spec after resetting to the correct torque. Obviously this only applies if you have never removed the cam cap bolts before.

Lots of people have posted with this issue but I could not find a consensus on what to do. I didn't want to shim the valves to the wide end of the spec just because they were a tiny fraction of a mm tight. Now they are all in spec with no new shims. Hopes this helps...

Edited by Adammoto, November 07, 2009 - 05:20 PM.
plural


  • grayracer513

Posted November 07, 2009 - 05:54 PM

#2

If you check the torque required to loosen most bolts including the cam caps with a torque wrench after they were correctly installed and have been in use for 5 hours and/or 5-6 heat cycles or more, they will universally indicate far more than the specified torque was needed to break them free. This is completely normal, and I fail to see how you, or anyone, for that matter, is or was able to determine whether the bolts were overtorqued from the factory.

Also very questionable is the idea that one can use a feeler gauge to determine accurately the difference between .10 and .09mm. That's .0004"

In any case, would be no need to shim to the wide side of the spec in most cases, since the OEM installed shims are quite often odd sizes used by the factory, and if you just can't get Yamaha shim in an increment of .05mm that makes you happy, you can used Honda shims, which are sold in increments of .025mm instead.

It's also not that critical in the first place, since the difference between the min and max spec is only .002".

Still, it's an interesting tale, and it makes some sense to try reseating/retorquing the caps in the event a low hour bike is off by .01 or .02mm. Can't loose more than a little time by trying it.

  • MR2turbo4evr

Posted November 07, 2009 - 06:04 PM

#3

I noticed the same on my bike. It's a low hour 06 (even had the original tires on it when I bought it, so I doubt the valves clearances have moved much from when it came from the factory) and the exhaust valves are at 0.18mm. I can slide a 0.0mm feeler gauge in, but there is quite a bit of drag, more than normal I would think. I'll definitely try the re-torque thing and see if it makes a difference on my bike.

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  • bakeyz426f

Posted November 07, 2009 - 08:23 PM

#4

i cant get i torque wrench on one of my cam cap bolts because the frame is too close to the bolt. should i just torque that one by feel with a regular wrench?

  • Adammoto

Posted November 08, 2009 - 06:51 AM

#5

i cant get i torque wrench on one of my cam cap bolts because the frame is too close to the bolt. should i just torque that one by feel with a regular wrench?


Get an extension and/or universal joint.

If you check the torque required to loosen most bolts including the cam caps with a torque wrench after they were correctly installed and have been in use for 5 hours and/or 5-6 heat cycles or more, they will universally indicate far more than the specified torque was needed to break them free. This is completely normal, and I fail to see how you, or anyone, for that matter, is or was able to determine whether the bolts were overtorqued from the factory.


I'm not an expert, and I certainly don't want to give anyone false information. Just saying this fix was easy and, at least according to my particular set of feeler gauges, effective on my bike.

  • grayracer513

Posted November 08, 2009 - 12:15 PM

#6

i cant get i torque wrench on one of my cam cap bolts because the frame is too close to the bolt. should i just torque that one by feel with a regular wrench?

Either use a 1/4" drive torque wrench (I prefer a flex beam type), or a box end torque adapter mounted at right angles on your wrench. Universal joints should be avoided because they can easily distort the torque reading.

I'm not an expert, and I certainly don't want to give anyone false information. Just saying this fix was easy and, at least according to my particular set of feeler gauges, effective on my bike.


As I said, it isn't unreasonable to believe that removing and reseating the caps could have that effect, but it is unreasonable to expect to be able to gauge how much torque was originally applied to a bolt by measuring the torque required to remove it. As small as .01mm is, it isn't unusual to get that much variation in clearance by simply turning the engine over a few times, either.





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