Checking the valves after rebuild - important?

11 replies to this topic
  • vomitbomb

Posted August 30, 2012 - 05:21 PM


Hi all,

The mechanic said I should come in and have the valves checked at 12 hours after the rebuild. I'm almost there now but it's kicking over fine and running smoothly. Is it worth having them checked? I don't wanna risk blowing the thing up again. If it's that important I'll just make some time and get it done.

It's a '10 yz450 and they are SS valves if that makes any difference.


Edited by vomitbomb, August 30, 2012 - 05:23 PM.

  • Theeebalz

Posted August 30, 2012 - 05:26 PM


if he said to have em checked i'd check em yourself! not toohard!

  • vomitbomb

Posted August 30, 2012 - 07:17 PM


if he said to have em checked i'd check em yourself! not toohard!

But I'm a scared pansy girl and I don't want to go opening up the engine!

I would definitely be getting the shop to look at it for me. The question is, should I be in a rush to sort it out?

  • Theeebalz

Posted August 30, 2012 - 07:31 PM


i wouldn't be in a huge hurry i'd probably wait for the end of the season if you're not riding it like a raped ape.

  • Charlie755

Posted August 30, 2012 - 08:30 PM


The only reason they are saying that it to make sure everything is in good order. I do the same on any bike I rebuild. I dont charge to check them after the rebuild and I would hope they dont either. If you arent having any starting or runablility issues you are most likely fine. :thumbsup:


Posted August 31, 2012 - 01:47 PM


How's the bike running after the rebuild? What did you have done?

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  • crf450319

Posted September 01, 2012 - 06:06 AM


Learn to do it yourself, with the tank/shrouds off it takes all of 20 min. It is very very easy. Watch this (go to 2:50)

  • vomitbomb

Posted September 09, 2012 - 12:40 AM


How's the bike running after the rebuild? What did you have done?


Bike has been running great after the rebuild. I actually had the top and bottom end rebuilt after drowning it in a river. It basically deteriorated over time and started burning through oil. Doesn't feel as touchy on the throttle as it used to but I assume that was because of the SS valves that were put in instead of titanium.

Learn to do it yourself, with the tank/shrouds off it takes all of 20 min. It is very very easy. Watch this (go to 2:50)

Hi crf450319,

Firstly, thanks for the vid.

I sacked up and gave it a whirl - checking the clearances anyway. Bought myself some feeler gauges and started pulling it apart.

The valves were way too tight! I checked each one about 10 times to make sure I wasn't messing up the measurements (I could still be wrong). Anyway here's what they worked out to:

0.076mm (.003") - 0.051mm (.002")
0.152mm (.006") - 0.127mm (.005")

From the manual they're supposed to be between (imperial values rounded):

0.100mm (0.004") to 0.150mm (0.006")
0.200mm (0.008") to 0.25mm (0.010")

To give you an idea of the gaps between the sizes of the gauges, they went up in the following order: 0.051(.002"), 0.076(.003"), 0.102(.004"), 0.127(.005"), 0.152(.006"), 0.178(.007")

OK so my question is, is this a serious problem? Has it been bad for the engine running on such tight valves? Strange that it has been running fine.

I guess I'll go get some pads and install -0.05mm(0.002") on every valve seat except the rear right exhaust valve where I will install -0.1mm(0.004")?

It's been an interesting experience so far. I hope I am able to do it all myself.


  • crf450319

Posted September 09, 2012 - 12:25 PM


I don't have a lot of time to post (have to go to work) but intake valves being at 0.003" isn't a big deal. It's not desireable, but not the end of the world either. 0.002" obviously isn't any better and IMO requires some immediate attention.

Most people will try to shim so they end up closer to 0.004" as opposed to 0.006", less slapping around in there.

Here's a good calculator to use/try, the only thing I don't like about it is that it's metric....


Posted September 09, 2012 - 04:16 PM


So I assume that its better to have a tighter tolerence if you cant get the shim gap perfect.

  • crf450319

Posted September 09, 2012 - 07:49 PM


So I assume that its better to have a tighter tolerence if you cant get the shim gap perfect.

Tighter but still within spec, when ever I've had to shim my bikes or my buddies (read: Honda's) I try to get them to 0.004 or 0.005. If I shim them and the clearance comes out at 0.006 and I've figured out that going to the next smallest shim in my Hotcams kit will drop me below 0.004, then I'll leave it at 0.006". The reason for shimming them closer to the lower end of the specification as opposed to the higher end is that when the clearance/lash is too great, tappet noise is present and the impact between the lifter and valve parts increases... or so I've heard.

Here's another calculator to try...

and an measurement conversion calculator

Of course you need to know your existing shim size to use the calculator, make sure you keep each shim seperate as it's quite easy to mix them up.

  • vomitbomb

Posted September 09, 2012 - 11:17 PM


I had the day off today so I thought I could take some time to learn how to re-shim the valves myself. I knew I needed 0.05mm off every shim except the rear right exhaust where I needed 0.10mm.

I got the shims out and took them to the shop where they measured them for me and swapped my old ones for the new sizes - cost $5 per shim still but I was happy.

Went about installing everything back in. The fact that I don't know much about mechanics at all made it a pretty slow and calculated process. Torqued everything to specification and made the interesting discovery that the cam chain tensioner is self tensioning - didn't know that.

I saw in one of the threads posted above that it was a good idea to mark the chain and the cam gears with a permanent marker. This allowed me to see exactly where my cam was in relation to the chain when I re-installed them.

Checked the alignment, then checked again about 10 times. Each time it came up perfectly. One thing I was unsure of was how much tension was meant to be in the chain and if the self-tensioner was working properly. I assumed it was all OK then put everything back on the bike.

At this point it was either do or die but I eventually built up the courage and kicked it over. It started second kick and ran beautifully. Ran it for a few minutes then turned it off. Waited a minute or two then kicked it over again - first kick.

It felt like it was almost running better than before. I did question whether or not it was psycho-somatic though.

I'll be keen to see how it goes on the next ride. Hopefully no dramas.

Edited by vomitbomb, September 09, 2012 - 11:19 PM.

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