GS850 Valve adjustment reprise
GS850 Valve adjustment reprise
Hi,
I know this is a little out of sequence, but I wanted to give you some illustrations of all the the lobe positions when checking clearances and pictures of the steps I forgot to take pictures of. Reference the diagram below:
This is looking at the right side of the motor (as you sit on it), cylinder #4. The exhaust cam lobe of #4 should be pointed toward the front of the bike when you check exhaust #3 and #4. Reverse this view when checking exhaust clearances for #1 and #2 and point the #1 exhaust cam lobe toward the front of the bike.
In the picture above, the intake cam lobe of #4 will be pointing straight up when checking the clearances for intake #3 and #4. Reverse this picture when checking intakes for #1 and #2 so that the #1 intake cam lobe is pointing straight up.
Intake valves are on the carburetor side of the motor. Exhaust valves are on the exhaust pipe side of the motor.
Here is a diagram for the shim tool placement in order to depress the bucket and allow removal of the shim.
Place the shim tool (tappet depressor, #1 in the above diagram) next to the cam lobe on the side nearest the center of the engine. Insert the tip as above then take care to keep the tool firmly against the camshaft and perpendicular to the shaft as you apply downward pressure. It takes some practice and if you slip you'll get some oil splatter. Here's a picture of the beginning of the process.
Once you have the bucket pushed all the way down with the shim tool, the tool will be held in place by the pressure of the valve spring. Hopefully you have remembered to spin the bucket so the notch is pointing up and is accessible. You may need a little pressure (and perhaps a very small flat blade) to break the surface tension seal of the shim in the bucket. Then remove the shim with tweezers or similar tool. Reference note: The picture below is the intake valve of cylinder #4.
Even if your clearances are within spec, it's a good idea to inventory the shims in your motor. If you know your current shim size, you'll be able to know better what shims you may need for future adjustments. Document all clearances and shim sizes.
Now a little about the shims themselves, sizes, calculating what sizes you need, and extra tools to help you. The shims used in the "2-valve per cylinder" Suzuki motors are 29.5mm in diameter. These motors include the inline 4 cylinder "8 valve" motors and the 2 cylinder "4 valve" motors. (The later GS motors with 16 valves do not use shims.) The shims come in various thicknesses ranging from about 2.20mm to 3.10mm. You can view Z1 Enterprises' selection of shims
here. (Note: Z1 also has the best prices on individual shims that I've found online. You can also by a "shim kit" which includes a selection of different sizes. I've also been told that some Suzuki shops will trade shims for a couple of bucks.)
Let's talk about calculating shim replacement sizes. I'll use an example from my experience. When I measured the clearance for the #1 exhaust valve, my .04mm feeler gauge would not fit. So I assumed that the clearance was at .03mm or less. (Note: The spec is between .03mm and .08mm for all clearances.) When I removed that shim I found the number 2.70 on the bottom. This is a 2.70mm shim. In order to gain more clearance I'll have to replace that shim with the next smaller size, or 2.65mm. After I replaced the shim, spun the motor a couple of times to make sure the shim was seated properly, I measured the clearance again and found it was .07mm. Right in spec. That means the original clearance was about .02mm. In effect we added .05mm to the clearance when we replaced the 2.70mm shim with the 2.65mm shim. .05mm plus .02mm equals .07mm. Do you see how the math works?
One more thing about shim sizes. Some shims will be marked with an "X". For example: 2.60X. This means that the shim is actually a little bigger than 2.60mm. This can come in handy when you have a big enough selection of shims and you really want to "dial in" your clearances. Another example from my recent experience was when I measured another clearance at less than .04mm. The shim was a 2.70mm. I dropped in the next size down, 2.65mm. But when I measured the clearance was still barely .04mm. I decided to go down another size, 2.60mm, but that made the clearance too big. So I found a shim marked 2.60X and used it. That brought the clearance for that valve to .07mm, right in spec.
Another handy tool to have is a digital vernier (caliper or micrometer). With it, you can measure each shim for exact thickness. It's also very handy when you find a shim that has had the numbers worn off. Some used shims may have a little wear in them. I found one in my borrowed shim kit that was labeled 2.70mm but measured 2.68mm. I actually used that one to fine tune one of my clearances.
Here is an example.
I hope this write-up makes it a little less daunting for those of you who've never checked valve clearances. For those of you familiar with this procedure, please let me know if anything needs editing for clarity or completeness.
My thanks again to Mr. IanFrancisco for his help, and Ms. SqDancerLynn1 for the use of her shim kit and assorted tools and parts.
Thank you for your indulgence,
BassCliff
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