I’ll describe the rocker subassembly next. Probably a familiar theme by now, modifications to some parts require changes to other parts. At this stage when examining more complex assemblies in CAD I kind of adopted a new habit. If something caught by attention, or didn’t look right, or needed later examination in context of another part or a motion, I immediately take a screen grab right then while it’s staring at me, rather than trust my memory or doodle a sketch. I now use this method more often finding it quicker & more reliable. I’m left with a number of snapshot/notes which become the To-Do list for another day. Sometimes a good thing happens where a bunch of seemingly unrelated issues can be resolved simultaneously with one single modification. Hopefully without too much boring detail, I’ll show such images & then onto the end result.
The rocker box is mounted to the angled facet surface of the head with an M3 screw. The inboard base hole straddles the valve with a locating ring boss on the underside. The two vertical members either side in the middle contain the rocker shaft & rocker arm within and snugly fit the inside of rocker covers to laterally retain them in position. The outboard hole in the base faces forward & accommodates the pushrod tube. The result is fully enclosed pushrods and rocker mechanism. The holes for pushrod tubes showed some pesky dimensions on the plans. Drill centers with asymmetrical offset distances & drill angles projected in 2 planes. The angled hole axis make sense of course because the pushrods come through the bottom of the rocker box originating from different positions on the nose case. The intake & exhaust lifters are positioned over their respective cam plates, which are orientated in fore & aft to one another. A longwinded way of saying 2 different rocker boxes are required, one for intake & one for exhaust dictated by these different pushrod holes.
It may not be apparent but the pushrod action is actually slightly 3D, not linear, which is why they are ball ended. The bottom end mates the cam lifters which operate linearly. The top end mates with the rocker arm adjusters rotating through a different plane. The resultant 3D motion has a wider envelope on the top. The point of all this is to say that these motions need to be accommodated without interference of the pushrod within its tube & wide tubes don’t look pretty.
Because of these angles, the pushrod tubes are of slightly different length and need to be mitered differently on either end. On the bottom it mates the lifter bushing. The plans called for as a conical shape bushing to kind of contain the tube at a 3D angle which I initially thought this was a good idea. But I wasn’t particularly fond of how the tubes were retained upstairs in the rocker box. Plans suggested a teeny set screw laterally through the base into a key hole in the (very thin walled) tube. Then there was the issue of wear & tear, engine vibration acting on these small contact areas, oil seepage etc. I knew I would have to deal with these issues eventually but hopefully could defer to when the engine was assembled to this level & things became clearer. I decided to proceed making them, for now omitting the holes. If push came to shove, I would omit the tubes & run open pushrods. But then why have rocker covers with naked pushrods, they kind of go hand in hand. Hey, maybe that’s why many model radials skip this stuff! I’ll return to tubes & lifter bushings later in the story.
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