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Screw it, gonna mess with the valves.

  • Thread starter Thread starter Draketh
  • Start date Start date
D

Draketh

Guest
Ok, I'm sick of the bike not running right so its time to play with the valves. I have a basic understanding of what I'm doing by looking at basscliffs site, but how exactly do I adjust the valves themselves after I check them? I've heard people talk about "shims". I have no idea what these are but are they something that has to be replaced, or do I have to get correct size ones or what?

Basically after I check it with the feeler gauges where do I go from there to tighten or loosen the valves? It should be pretty easy to get done since I'm only dealing with two cylinders here.
 
Preface: If it's like my bike...

When you take the cover off you will see the cams. They have lobes... like a rounded off triangle. As the cams turn the "point" of the triangle points down as part of it's revolution and pushes against a round piece of metal like a silver dollar that sits in a little cup (the "shim" sitting in the "bucket"). Under that cup is the valve. You use either a special tool, or the zip tie method to hold the valve open so that shim is as far away from the cam lobe as it will ever get. You are measuring how far that farthest distance is and adjusting it by replacing the little round metal disc (the shim).
 
doctorgonzo said:
Preface: If it's like my bike...

When you take the cover off you will see the cams. They have lobes... like a rounded off triangle. As the cams turn the "point" of the triangle points down as part of it's revolution and pushes against a round piece of metal like a silver dollar that sits in a little cup (the "shim" sitting in the "bucket"). Under that cup is the valve. You use either a special tool, or the zip tie method to hold the valve open so that shim is as far away from the cam lobe as it will ever get. You are measuring how far that farthest distance is and adjusting it by replacing the little round metal disc (the shim).
Click to expand...

Ok cool. So can these be adjusted or the only way to do that is to pretty much get a new shim? What kind of shims, where do I get them? Are the clearences pretty much the same for all the bikes? I got the specs from the valve adjusting pdf so do I just buy shims in that spec?

1982 GS450GAZ
 
Draketh said:
Ok cool. So can these be adjusted or the only way to do that is to pretty much get a new shim? What kind of shims, where do I get them? Are the clearences pretty much the same for all the bikes? I got the specs from the valve adjusting pdf so do I just buy shims in that spec?

1982 GS450GAZ
Click to expand...

Hard to know for sure until you look. Here is mine as an example...

6 of the 8 were too tight. Of the too tight ones ...
1 had a 2.55 mm shim,
2 had 2.65,
3 had 2.60 mm
so increase the distance I needed...
1 2.50
3 2.55
why only 4..... not 6....
because 2 of the 2.60 that I changed to 2.55 could now be reused (the 2.60 shims) to take the 2.65 to 2.60

Z1 has them, maybe local bike shop has a dusty box full. There is a thread here for trading them.
 
See, thats what confuses me, why would there be different size shims in there? Or do they just naturally change size over time?
 
Draketh said:
See, thats what confuses me, why would there be different size shims in there? Or do they just naturally change size over time?
Click to expand...

They change over time, wear unevenly, maybe the valves, or valve seats, or whatever were slightly different size from the factory. I mean we are talking about distances of 5/100th of a mm, maybe 15 years ago one valve got burned and was replaced, but not all of them, lots of potential reasons. Again, we are talking about TINY variations here. The "good' range clearance is .03 to .08 mm that's not a whole lot of space.
 
Hi Mr. Draketh,

It's not the shims that change size, it's the valve clearances that tighten up. Therefore you need to put thinner shims in the buckets that are under the lobes.


Thank you for your indulgence,

BassCliff
 
Last edited:
There are different size shims to make up the minute differences in clearances on each individual valve between the cam and the bucket that sits over the valve. It would be too hard and expensive... especially back then, to manufacture engine components to such exacting standards. Plus you would have no way to change or adjust anything as parts wear/move/stretch. Thus, you have an adjustment system - shims. By using a shim of the correct size, you can make keep each individual valve-to-cam clearance within spec - not too loose, not too tight. This will vary from valve to valve and will change over time (generally the clearances get tighter and you will likely alway be changing to smaller shims... don't ask me why).

Shims seldom wear any measurable amount and are made of hardened steel. Unless you run your engine without oil the shims will not wear.
 
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