Vernier cam timing

OK, so yesterday I tried adjusting the CAM timing.

The thing in the middle is the vernier used for adjusting the CAM timing. Its called “gear timing flange” in the Velie Installation and Maintenance manual. This gear is running at 1/6th of the crank shaft.

By removing the 4 bolts, moving the front disk a bit and screwing the bolts into the next hole, the whole timing is moved by about 10 deg or that’s what I thought.

That was a bit to much, so I thought if I hold the front disk and rotate the prop one hole turn then I might be able to get smaller steps. But it looks like its exactly the same 🙁 or that’s what it looked like.

_1398587297

So how does the CAM vernier work:

The front disk driving the CAM has 16 holes with thread in it. This is 22.5 deg per hole.

The disk behind, is driven by the crank shaft has 20 holes with thread. This is 18 deg per hole.

So by removing the bolts, moving the crank shaft a little, and putting the bolts back in the next lot of 4 holes, the CAM timing is shifted a bit. In fact it’s a step of 4.5 deg (22.5 – 18 deg). This is less then what I had seen yesterday, but oh well….

Another thing that can be done is when the bolts are out, is holding the front disk with the 16 holes, and spin the prop one full revolution. This will move the CAM and the disk with the 20 holes, 60 deg (360 deg / 6) as the CAM moves 6 times slower then the crank shaft. The 60 deg is 3 times a 18 deg step plus 6 deg. In combination with the 4.5 deg from the paragraph above, this gives a 1.5 deg minimal step!!! So in total there are 240 possible positions for the CAM for one complete full 4 cycle of the engine.

So I am thinking that what I have now is maybe 1.5 deg different from before and that’s why I don’t, or hardly see the difference !!!!

Leave a comment