With the camshaft bushes lined up properly I now had to get on and make the cams – I hadn’t done this before and it looked difficult. The method for making cams described by Len Mason in the mastiff book looked far too complicated and it’s no surprise that a few other ways have been published. After a lot of searching around on the web I found the work of Rod Jenkins, as modified by Ron Chernich, and this looked like the way to go considering the workshop gear that I have. The hassle of running Java code on Windows (and the usual desire to find out what’s inside anything) motivated me to re-write the software in Python 3; when I’m convinced that the cam-follower velocities and accelerations are OK I’ll let the program loose. The offsets needed for cutting cams look good and text files for the Mastiff inlet and exhaust cams are attached. These are tabulated at 1° steps but cutting at 3° intervals worked well for me.
The cams started as two lengths of ½” silver steel which were necked down to leave four cam blanks in a row:
Transferred to the dividing head on the mill the blanks were (rather laboriously) cut to the base circle radius for 240° (inlet) and 230° (exhaust) in 3° steps. About now the urge towards CNC became even stronger.
The rest of the cam profiles were then stepped through (this is the second set where I added tailstock support to improve the surface finish a little):
An outbreak of stupidity made this process much harder than it should have been – when going “over the top” of the cam I twice messed up by, completely without realising, changed the direction I was turning the dividing head handle. Must be something in my psychology?? Anyway, I’m not into analysis so I decided to fix the problem mechanically and burrowed in to 40+ years worth of “things that would come in handy sometime” (known to someone else as “all that junk down there”). What I found was a pair of gears (original use long forgotten) with a one-way clutch between them:
With a simple adaptor sleeve this fitted neatly on to the dividing head drive shaft:
Now it didn’t matter what happened inside my head, the shaft could only turn anticlockwise and the two sets of cams were ready for polishing and parting off. The cams were much easier to polish as a solid set than as individuals:
Each cam was then faced to length on a taper mandrel:
And the final results look like:
A bit of tweaking of lengths and “selective assembly” in the block made it important to keep track of which cam was which during hardening, cleaning and final assembly:
To assemble the cams on the shaft core I followed the method described by Mick Knights in his “The Mastiff Plus” series in Model Engineer (Parts 8 and 9 in #4521 and #4523). This needs a guide pin machined to fit the cam noses:
And centred over the core mounted in the dividing head:
Then slid along the core at the correct (I sincerely hope!) angular location with some Loctite 638 on the core:
With the bearing journals added the final product looked like:
In the block it looks good!
Phew! That took longer than I thought…
It is also going to be a long wait before I find out if the cam angles are correct but for now I’ll move on to finishing the timing end gearing, oil pump etc.
DT