Valves are way too tight, how to select proper shim? Help!


6 replies to this topic
  • BMW doc

Posted December 04, 2008 - 06:45 PM

#1

I am checking the valves on a friends 450. Using a .0059 in. feeler, I can't even get it into the exhaust side. :thumbsup: My feeler gauge set goes down to .0026 in. and it won't fit in either side. I have checked and double checked that I am at TDC, and the cam lobes are pointing in the correct direction.

So how do I go about shimming, since I can't even get a feeler gauge to check the current clearance? Fwiw, the bike is nearly impossible to start 'cold'. Once its at operating temperature, it starts fairly easily. So the symptoms for tight valves are definitely present. I am just at a loss for how to go about getting the proper shims. Since I don't have a shim kit, just dropping a few shim sizes and measuring won't be too cost effective for me. If thats what it will take, I'll just have to buy a shim kit though.

Ideas? Thoughts? Surely someone has developed a method........

  • Smokeslider

Posted December 04, 2008 - 06:56 PM

#2

yeah, you could take a look at the other shim numbers, put the smallest one back in the tight spot, re-torque and recheck, might be able to get a feeler in there and give you an idea of what you need. Otherwise, the moto shop might let you take some shims back that you don't use..... $.02

  • 642MX

Posted December 04, 2008 - 07:54 PM

#3

I am checking the valves on a friends 450. Using a .0059 in. feeler, I can't even get it into the exhaust side. :thumbsup: My feeler gauge set goes down to .0026 in. and it won't fit in either side. I have checked and double checked that I am at TDC, and the cam lobes are pointing in the correct direction.

So how do I go about shimming, since I can't even get a feeler gauge to check the current clearance? Fwiw, the bike is nearly impossible to start 'cold'. Once its at operating temperature, it starts fairly easily. So the symptoms for tight valves are definitely present. I am just at a loss for how to go about getting the proper shims. Since I don't have a shim kit, just dropping a few shim sizes and measuring won't be too cost effective for me. If thats what it will take, I'll just have to buy a shim kit though.

Ideas? Thoughts? Surely someone has developed a method........


If the valves are zero'ed out and you can't slide a feeler gauge in, then pull the head and put some valves in it. Be sure to have the seats cut before installing the valves. If you want to pro to do it, send it here: http://www.mxtime.com

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  • grayracer513

Posted December 04, 2008 - 11:53 PM

#4

Minimum intake clearance is .15mm. If your intakes are at 0, you would need a minimum of a .15 smaller shim to correct it, probably more. With that much wear, the valves are shot. If you continue to run them, even reshimmed to the correct clearance, you may very well drop one and destroy your engine.

Like the man said, it's time for a valve job.

  • black_dog

Posted December 05, 2008 - 05:33 AM

#5

My feeler gauge set goes down to .0026 in. and it won't fit in either side. I have checked and double checked that I am at TDC, and the cam lobes are pointing in the correct direction.


Yeh, sounds like its time for new valves doc.
Might be a slim chance that its been badly gapped by the previous owner.:thumbsup:

  • motox88

Posted December 05, 2008 - 09:30 AM

#6

Minimum intake clearance is .15mm. If your intakes are at 0, you would need a minimum of a .15 smaller shim to correct it, probably more. With that much wear, the valves are shot. If you continue to run them, even reshimmed to the correct clearance, you may very well drop one and destroy your engine.

Like the man said, it's time for a valve job.


exactly.. right method, but he said EX. so the spec, at least on a new bike, on EX is .20-.25.

so say if you currently have a 2.00 mm shim in there you would need at least a 1.80mm 1.775mm shim. You can fix it to a point but expect it to move as you ride it more.

A head job with new piston will probably run you close to $600. About what it cost me to have my honda done.



edit: I see that he said he tried both sides. yea, if both EX and IN are 0 then there are major issues. I've never seen them both go to 0. eeek!

  • grayracer513

Posted December 09, 2008 - 06:36 AM

#7

exactly.. right method, but he said EX. so the spec, at least on a new bike, on EX is .20-.25.

...in which case the wear is even worse, isn't it?

I've never seen them both go to 0. eeek!

It's more common on the 250F, as the 426/450 wears the valves so little, but once through the hard coat, they wear quite rapidly.

The way they go beyond zero has to do first with the fact that valve clearances on this engine are greater when warm than when cold because the aluminum head expands more than the valves from heat, moving the cams farther from the valve seats. This is why an engine with worn valves will run OK hot, but have no compression cold. Additionally, once at zero, the valve head can vibrate at right angles to the valve stem, wearing the valve face further. When the engine cools and clearance is checked, it is found to be zero, and may actually be held open slightly.

Here's what they look like:

http://members.cox.n...yzer/valves.htm





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