Valve Grinding
After disassembling the cylinder from the crankcase, I removed the intake and exhaust valves. The process is fairly simple -- I used a pair of needle-nose pliers. With the cylinder upside down on the bench, the open pliers can be inserted in the valve lifter holes like an inverted "V", compressing the outer rim of the valve spring washer, 180 degrees apart. With the valve spring thus compressed, it's a simple matter to remove the C-clip from the valve stem with a second pair of pliers. This releases the spring washer and spring, and the valve can be removed through the top of the cylinder.
The condition of the valves is about what I expected: not great, but not too bad. The exhaust valve showed some pitting, but was not burned. The intake valve showed more wear, and rather uneven wear, though it was not pitted as much as the exhaust valve. After cleaning and a light wire brushing, this is how the valves looked (exhaust valve on left):
Given that new Whizzer valves seem to be a rather scarce commodity, and expensive when they can be found, I decided to try regrinding the original valves. As a fun alternative to having the valves serviced at a commercial small engine shop, the job can be performed by the do-it-yourselfer fortunate enough to have a shop equipped with a small lathe, and a die grinder ("pencil grinder").
The process consists of rotating the valve slowly in the lathe by its stem, while passing a small grinding stone across the valve's margin and face. The grinding stone is held in the collet of the die grinder, which is in turn mounted on the lathe's compound, carefully set to a 45 degree angle. I would advise against using the compound's degree scale to set the angle -- they cannot be relied upon for precision. I mounted a magnetic base indicator to the compound, and passed it along a 45 degree angle block held against a spindle-mounted faceplate. With the compound's locking screws only snugged up, the compound can be lightly tapped one way or the other until the indicator reads zero. Then tighten the locking screws.
The valve stem needs to be mounted with a high degree of concentricity. In other words, we want the ground surfaces of the valve to be as concentric as possible with the stem. Some kind of collet setup is ideal. My lathe uses 3-C collets, and I have them at 1/32" increments, but the valve stems are an odd size (.230" dia.) So, I made a brass split bushing to adapt the stem size to an 11/32" collet:
Making such a bushing is a simple operation, and the "split" can be made with a bandsaw (as I did) or a hacksaw. Here's what the valve looks like with the bushing in place:
(A possible alternative to the collet system would be a 4-jaw chuck, but it would necessitate accurately centering the valve with an indicator.)
The die grinder is mounted to the lathe compound by means of a boring-bar holder. Once again, a brass reducer bushing serves to adapt the grinder body's OD to the holder's ID. Don't tighten the boring-bar holder's clamp screw too tight -- the grinder body might be compressed to the point of locking up. Just tighten enough to hold the grinder securely against very light cuts, which is all this method is capable of making.
A word of caution is appropriate here: The abrasive dust that this kind of operation produces can be VERY DETRIMENTAL to the precision bearing and sliding surfaces of a lathe. Therefore, take steps to shield the lathe from grit. Also, using a lathe in this fashion should be no more than an occasional thing, not a frequent occurrence, unless you are prepared to accept a shortened useful life of your machine tool.
Here is the basic setup. (Note the plastic film and mounds of shop rags employed to keep grinding grit out of the lathe):
The lathe is run in reverse (against the direction of the grinding stone) at a moderately slow speed. Very light passes are made across the face of the valve, until the surface "cleans up". Heavier passes can be taken at first, but as the surface becomes smoother, more surface is exposed to the grinder, and lighter cuts must be taken. Here's another view of the setup, showing how the grinder is mounted in the boring-bar holder:
Once both valve faces have been ground, reset the compound angle to 90 degrees, and grind each valve's "margin" (the cylindrical portion at the valve's large diameter) until it cleans up at around 25-30 thousandths wide. Here's the finished valve grinding job:
It should be noted (and obvious) that regrinding a valve reduces it's size. It's entirely possible that the dimensions of a reground valve may no longer fall within factory specs. This may result in the valve sealing too low in the valve seat -- not an optimal situation. I think these valves will be ok, but we will see how it looks once the seats have been re-cut.
Paula