My design criteria for the camshaft includes the following:
- Turns on two ball bearings (all shafts turn on ball bearings, crank, gears and camshaft)
- A center bush in addition to the two out board ball bearings
- Oil delivered to the four cam lobes and the center bearing
- Cam Lobe definition – covered later (lift 3/32″)
- Firing Order – (1-3-4-2)
- Direction the cam turns – (counterclockwise when viewed from the front)
- Center bearing diameter – (1/4″)
- Ball bearing selection – (same as the timing gears 5mm X 10mm X 4mm)
- Method to deliver oil to the camshaft-
- Method to retain cam timing gear – key and nut
- Method to allow cam timing adjustment – the timing gear can have multiple key slots, each with a slightly different timing.
My tentative solutions are above in parenthesis.
Also my current thinking is not consistent with the cambox design and will require changes to other major components to deliver oil to the camshaft.
I need to get oil down the middle of the camshaft and there are three ways to do this: Through the back end, through the middle bushing and through the front end. Getting oil delivered to the middle bushing does not look possible as there is not enough material in the cam box to drill an oil gallery. Sending oil down the cambox cover likewise does not seem feasible. Bringing oil in through the front of the camshaft is complicated with the presence of the cam timing gear, so.. First I look at brining in oil through the back of the camshaft
Below is an example of a technique I have used in the past to deliver oil to the center of the camshaft. Oil is delivered to the bearing holder, then to the center of the camshaft through the back.
Pros of this method are it will be easier to get oil through the backend, but the cons include the extra distance the oil has to travel from the front of the crankcase to the rear. Also I am a little concerned using the 1/16″ thick rear motor mount as a cover for a very long oil channel up the back of the engine.
The other alternative is to bring oil up directly from the oil pump and into the camshaft through a bushing. Does it replace the ball bearing or work in conjunction with it? Do I just use the aluminum cambox as the bushing? Then do I abandon using ball bearings on the camshaft?
That front camshaft bearing wants to be mounted in the rear gear tower to maintain predictable gear meshing. But on the other hand the camshaft needs to be securely mounted in the cambox. Now I am thinking that using ball bearings on the camshaft is causing more problems than it is solving.
I am going to think about the bearing and oil delivery system a bit more so I am going to move on to the cam lobe design. The design parameters are:
- Lift – 3/32″
- Major diameter – 7/16″
- Base Circle – 1/4″
- Bearing diameter – 7/32″
- Exhaust Lobe duration – 110 degrees
- Intake Lobe Duration – 125 degrees
- Exhaust Lobe nose radius – .025″
- Intake Lobe nose radius – .050″
These data give the exhaust cam lobe shape shown below
I would like a way to adjust the camshaft timing after the engine is built. Becasue there are 36 teeth on the camshaft gear, I can only get 10 degree resolution by moving fromone tooth to another.
If the camshaft timing gear is held on with a nut and its registration to the camshaft is achieved with a key, there could be 5 keyways cut in the gear. This would give us 2 degree resolution in our adjustment of the camshaft timing. 36 teeth times 5 keyways divided by 360 degrees. This can be seen by looking at where the lines emanating from the center intersect the gear teeth.
I have deleted the camshaft ball bearings and am having the camshaft ride directly on the cambox, at least for now.
This is where I ended up for the day, an exhaust camshaft sitting in the cambox. Alignment between the cam box and gear tower needs to be perfect to get correct gear mesh. Does not look much different than where I started.