We have turned one eye to the business of the drive train and prop-shaft for Befur.
I have concluded that I am putting a CV joint in the drive train, to allow the engine to be mounted horizontally, and also going to use a toothed belt drive from the engine to the prop-shaft, so allow me to install the engine off-centre, and improve internal layout.
The sequence of elements in the drive train are:
Engine crank, toothed (cam) belt drive to 1.25″ “jackshaft” supported in 2 plumbers blocks, CV joint (ex Ford Sierra XR4!), with attached shock absorber, thrust bearing, stern gland/stuffing box prop-shaft (with 2 cutlass bearings (it’s 7 feet long!)) and Prop (21.5″d x 23″ pitch)
You can see the approx layout below (although one of the two jackshaft support bearings is yet to arrive, and a dual v-belt pulley is substituting for the final (smaller) toothed-belt pulley (oh, and yes the engine is not in place yet 🙂 !! )
Making a half-shaft
As part of this process we will need to make a “jackshaft” to take the place of the original half-shaft fitted in the Sierra. This involved cutting a 25-spline shaft. Having never done this before I decided to have a trial run.
The idea is to hold the shaft in a dividing head (rotary table) on the milling machine and then use an end-mill (actually a slot-drill in this case) to cut “slots” (each pair of slots leaving a spline in between).
So firstly we turned the trial bar to the O/D of the splines (as measured from the CV joint) – Of course as there are and odd number of splines we can’t actually measure the diameter, but some “mark-1 eyeball interpolation” provides an answer that works
Then (after some head scratching) realised I needed to arrange the cutting edge of the mill 50% of the radius of the bar forward of the centre line of the shaft; this means that the vertical and horizontal faces of the cut we make will each be at an angle of 45-degrees to a normal drawn at the point of the cut (easier to see than describe!)
Then we just need to index the shaft round 14.4-degrees for each slot, and keep feeding in until we get a fit (e.g. when the bottom of the slots equals the ID of the splined hole in the CV). I actually wound up “climb milling” to get better visibility, but the solidity of the Ramboudi mill meant that this was no problem at all!
The pic and video below explains all;
I also managed to find a stern gland on ebay. Fortunately it arrived slightly smaller than advertised, so I could re-cut the shaft hole, so it’s as good as new 🙂 …. and then found an untouched cutlass bearing casting at the SBA Auction, so machined this to take an ex-ebay cutlass bearing – all in all I saved several hundred pounds when compared to purchasing these items from new – pics below: