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Valve shim rules, tips or hints?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Hi again, same bike--the GS750E. I've pulled the valve shims out as the clearances b/w them and the cam lobes was less than .001" Is there any cut-and-dried rule regarding downsizing the thickness of the shims?

i.e. no clearance with a 2.80, get a 2.70 or no clearance with a 2.75, drop to a 2.60?

that would be extremely helpful as they're all almost the same size shim (2.70 is the smallest, i have one, 5 2.80's a 2.75 and a 2.85.)

thanks a bunch


Chris
 
shim

shim

Its easest to use a shim chart like whats in most all the manuels,with 0 to.02 you want to drop to the next size down 2.80 at 0 would take a 2.75
 
If you have no clearance, it's a question mark. You'd have to find (buy) a shim thin enough to provide some clearance, measure that clearance, and determine your final (you hope) shim thickness.

There really isn't any easy way out. What's the thinnest shim in your 'arsenal''?

Just be thankful you have only eight valves to worry about. Makes you wonder how long a CBX takes.
 
they should take the person who came up with using shims out back and put a bullit in em!!
 
There are also "fat" shims. They have an "X" after the number. A fat 2.70, will actually be 2.72 or even 2.73, etc. Just be sure to measure when the bike's stone cold.
 
another tip, do not use a magnet to pull the shims out, it magnetizes them and they will in turn want to stick to the cams and can come out while the engine is running. not good.
 
I don't mean to scare anyone, but...

back when I was young and ignorant, I was driving myself nuts chasing a zero clearance shim problem in exactly the same manner with a limited supply of shims.

Finally, I ordered up the smallest shim available (2.15mm), figuring I'd check the clearance with that installed and at least get in the ballpark.

Still zero clearance. Uh oh.

I checked the compression, and had no compression in #2 and #3, even with a bit of oil in the cylinder. Drat.

After a rushed cylinder head-ectomy, I found what I had feared -- the exhaust valves looked like miniature models of Grand Canyon. Each had several notches eroded in it. Double-drat squared, and other comments.

Here's what I finally figured out after a few years of perusing theGSresources.com.

It all started with bad intake boot o-rings. This caused a very lean mixture and no end of carburetion problems, which I chased for months. I continued to ride the bike anyway, since it mostly ran OK as long as I didn't want it to idle consistently.

Finally, the incredibly hot exhaust gasses spawned by the lean mixture started to eat into the exhaust valves on the hottest cylinders (#2 and #3). As the erosion got worse, power dropped off drastically, to the point where my once-proud GS850G couldn't maintain 80mph on the interstate.

I'll spare you the saga of the motorcycle shop owner that vanished with my cylinder head and $500. (I'll find you one day, you $#@!*!)

A year and a half later, salvation finally arrived in the form of a cylinder head purchased from Nick Diaz (All hail Nick!).

And now, my GS850G runs like a watch!

So anyway, if you have a zero clearance valve, check that compression. And those intake o-rings. You could try the smallest-shim trick if you're pretty sure it's just tight and no damage has occured yet.

Valve temps go up drastically and they tend to melt when there is no valve clearance -- they can't make firm contact with the valve seat, so the heat can't escape to the cylinder head. Not good.
 
i'm just now getting around to responding to my own thread. the problem right now, is that i'm not sure. i don't wanna pull the head apart to find out that there's nothing wrong.. i figure investing $6 in a shim is cheaper than worrying about pulling the motor apart. i've got compression issues, and i've been trying everything to make sure that it's the same every time. i'm hopeful there's no valve damage, but at this point in time, it's hard to assume there's none..

the bike's got ~26,000mi on it, it's got 4 2.80, 2 2.70, 1 2.75 and 2.85 (that's 8 right? lol)

but. i tried swapping in the 2.70 i where the 2.85 was, but had no change in clearance; so i'm not quite sure what i should do at this point. my manual is MIA, so i don't have the chart, but i would think that a switch from a 2.85 to a 2.70 would increase the clearance a lot.
 
You can go down to 2.30 (somebody wanna double check this for me?), so there's plenty of room before you need to panic. To save your sanity, just order a couple of really slender shims, maybe a 2.30 and a 2.50, and you should be able to zero right in on the shim you need.

Without having a shim set, like a factory tech would have, this is about your only option, other than a WAG.
 
2.10 is the smallest listed in the parts diagram, but I would be more concerned about going down from a 2.85 to a 2.70 and it still being so tight. That seems like a big jump with no noticeable difference, but maybe that's not uncommon

I have a rule that when things seem crazy and don't make any sense, go back to the basics and check all my assumptions. In this case:

Am I using the right blade on the feeler gauge - .03 mm not .03 inches
Is the cam in the right position for the measurement?

I made myself a cheat sheet from the info in the factory manual when I did my 750 recently:

turn crank until
#1 exhaust cam lobe pointing forward parallel with the top of the head
- check #1 exhaust
- check #2 exhaust

rotate crank 180 degrees
#1 intake cam lobe pointing up perpendicular to the top of the head
- check #1 intake
- check #2 intake

rotate crank 180 degrees
#4 exhaust cam lobe pointing forward parallel to the top of the head
- check #3 exhaust
- check #4 exhaust

rotate crank 180 degrees
#4 intake came lobe pointing up perpendicular to the top of the head
- check #3 intake
- check #4 intake

If you're using the right gauge and following the proper procedure and still too tight, I agree with Robert get a couple of shims, say a 2.60 and a 2.50, or maybe even a 2.30 and give them a try. My local dealer charges only $4 if you return one that still has readable numbers. You might see if they will give you a similar break. If those still don't give you some clearance, then maybe bwringer is right - something very serious is going on...
 
shims

shims

Are you wiping out the puddle of oil that is under the old shim, and putting a light coat of oil on the new shim,(both sides) before you in stall it, a large amont of oil, under the shim will take up several thou, I also rotate the motor over after I put the new shim in to seat the shim then I recheck it, when I stated zero clearance I mean zero not a negetive measurement, like( -.03 mm ), one way you can get an idea if your below zero is by feel, does the shim rotate around by finger easily or is it tight feeling and hard to rotate meaning it is very tight or less than zero?
 
ptm said:
?

I made myself a cheat sheet from the info in the factory manual when I did my 750 recently:

turn crank until
#1 exhaust cam lobe pointing forward parallel with the top of the head
- check #1 exhaust
- check #2 exhaust
................................
Click to expand...

Excellent idea, Cut and paste this and print it off and paste it to a sheet of card or even better laminate it and repeat the process for all the maintenance jobs you need to do on the bike and put them in a file/folder or stick them on the wall.It's better than handling the manual because you can actually read it whilst you're doing the work whereas using just a manual means you are constantly getting lost in a lot of words
 
Going down one size is reasonably normal..more than that and I would suspect that the clearance has closer up for a while, and lead to further damage of the valve seat/valve due to the valve being kept open. Keep it at the right clearance and and it may be ok. Once the valves settle in they rarely need adjustment.
 
[/quote]

I think Gee-s-is may have your answer. When you fit a different shim, use a big wrench to turn the crank over a few times then measure the clearance again. The action of the cam on the new shim should displace any oil underneath and give you a correct reading.
 
Just don't forget to dribble a little oil on to the cam so it doesn't rub agianst the new shim dry. Use the oil puddled in the head.

Harrison
 
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