Rudi has asked me to show the component lapping procedure, as it would apply to a Cub carburetor body. As I didnâ€™t have a Cub part available, I used a generic carburetor part, that was laying around my shop.
Lapping is a very simple procedure, which requires only a smooth, flat surface and various grades of sand paper. My set-up, for this demo, is a piece of Â¼â€ tempered glass, on top of a piece of Â¾â€ plywood. Any piece of glass will do, as long as it is on top of a flat rigid surface. Iâ€™ve used window glass many times. For this demo, I used three grades of sand paper, starting with 80 grit, next using 180 grit and finishing with 400 grit. Hereâ€™s my set-up.
Here, I am using adhesive backed paper, but it doesnâ€™t have to be, it just makes it a lot easier. You can put a light coat of spray contact cement or spray gasket sealer on the back of the paper, or just hold the paper in place with your free hand. Because Iâ€™m lapping a small item, my pieces of paper are small as well. If youâ€™re lapping a large item, full sheets of paper may be required.
Hereâ€™s the part, before starting the procedure. To make the results show up better, in the photos, I sprayed a light coat of machinist bluing on it.
I first take a couple passes across the 80 grit, to see how uneven the part is.
You can see, in the photo, that it only made contact in a few places.
After a few more passes on the 80 grit, itâ€™s beginning to take shape. As I sand, I rotate the part to sand in various directions.
At this point, I have near full contact and can move on to the 180 grit.
After a few passes on the 180 grit, Iâ€™m making full contact, although reflections in the picture make it look a little darker in some areas. At this point, almost any gasket would certainly seal, but for the sake of illustration, weâ€™ll take it one step further.
Hereâ€™s the finished product, after lapping with 400 grit. In the photo, it doesnâ€™t look much different, but is actually a much smoother finish.
It took me all of about ten minutes, including photos, to get this part in shape. Larger or badly warped items will obviously take longer, but itâ€™s very rewarding when youâ€™re finished.
By the way, if you know someone who is getting rid of an old refrigerator, with glass shelves, grab the shelves, theyâ€™re good heavy tempered glass.