Continuing the investigation of the loss of compression in Cylinder No. 3 I am removing the valves and checking them against the wear limits and tolerances identified in the service manual for the 1981 GS650L.
As with most tasks, any parts removed from the engine that you plan to reinstall should go back to the same location that they came from. Therefore, it is important to keep things organized.
First was the removal of the valve shim buckets and shims. An old egg carton is handy for keeping these pieces organized for re-installation later.
Next you can use a valve spring compression tool to depress the valve retainer against the spring and remove the valve keepers. It is very easy to compress the springs with this kit that I have from Pit Posse. I have seen people use large C clamps and old sockets with the side of the socket hacked off, but that seems like more work than using this kit.
Here are the components of each valve when removed. Intake valve shown, but both are setup the same.
There was a bit of carbon built up on the backs of the intake valves, most likely from some oil dripping on to the backsides of the valves, and more build up on the exhaust valves. I soaked each pair of valves in parts cleaner for 48 hours +/- to try and remove some of the build up. The before picture is on the left and the after on the right.
Now the fun part to determine if the valves are still within specification for Valve Face Wear, Valve Stem Runout, Valve Head Radial Runout, and Valve Stem Wear. These measurements are measured in hundredths of a millimeter or thousandths of an inch. The gauges that I already have available will measure to thousandths of an inch.
The wear limit for the thickness of the valve face is 0.5mm or 0.02″. Not the easiest thing to measure, so I just set the calipers to this minimum measurement to make sure that all were greater then the minimum. No problems were found.
Next was valve stem runout which has a service limit of 0.05mm or 0.002″. This will determine if the shaft of the valve has been bent. Here is my setup to test the runout of each valve.
Handy to have the nice smooth surface of my table saw and the magnetic locking base of the clamping system. The V blocks are machinists blocks that are about 3 lbs each so that they don’t move around very easily as your are rotating the valve.
None of the valves exhibited any valve stem runout except for the No. 3 intake valve, but it was still just within the service limit.
Next was the valve head radial runout with a similar testing setup as the valve stem runout. The service limits for the valve head radial runout is 0.03mm or 0.012″.
Again, every valve was well within the service limit except for the No. 3 intake valve. Most valves were about 0.004″ of runout. The No. 3 intake valve was 0.020″ of runout. Almost double the service limit.
The last measurement was for valve stem wear. The valve stem limits are 6.960-6.975mm (0.2740-0.2476″) for the intake valves and 6.945-6.960mm (0.2734-0.2740″) for the exhaust valves. All valves were still to the upper end of the service limits. An intake valve is shown below.
All parts are kept together by their respective cylinders and intake or exhaust valves until they are ready to back into the cylinder head.
Looks like I will only need to find a replacement for the No. 3 intake valve as expected.