I mentioned at the end of a previous blog on rebuilding the crankshaft that one of the consequences of using “K” mainshafts and MOV flywheels is that the assembled inner distance between the flywheels is about 1/8” less than the standard “K” crankshaft which means that the mainshafts are 1/16” further inboard.
This ended up having a few knock-on effects; in no particular order:
- The big-end nuts foul the bearing outers
- The crankshaft shock-absorber meets the crankcase casting before the taper grips on the drive-side mainshaft
- On the timing side, the woodruff key on the crankshaft barely reaches the slot to engage with the bevel gear
The first of these needed to be addressed before I could make any progress on the others because it was not possible to assemble the crankshaft into the crankcases.
As I mentioned in previous blogs I have been using solid steel “bearings” that have the same ID/OD/t as the correct bearings
throughout the build rather than continually using the genuine items as the latter have a slight taper to ensure a good tight fit onto the mainshafts – it’s just easier this way. Modifications were first tested using the dummy bearings and then 0.040” was removed from one side of the bearing outers on both the new MC22 bearings that I had purchased
and making a similar modification to the inner side of the bearing housing in the crankcases (shown below with one of the dummy bearings)
and by using 0.015” of shims on both sides of the crankshaft allowed the crankshaft to be fitted without interference with the big-end nuts, gave a slight (couple of thou) oversize on the overall crankshaft length and positioned the connecting rod exactly in the centre.
The second issue – non-engagement of the shock-absorber on the mainshaft taper - was quite straightforward to fix. The drive-side crankcase was put on the milling machine and material removed from the timed breather extension of the crankcase casting
until the crankshaft and shock-absorber tapers mated (plus a bit of clearance). There is also a consequence of this – the crankshaft sprocket will be further inboard and will be out of alignment with the clutch chainwheel but this can be easily fixed (at a later date – when the engine is in the frame) by making a thicker K-145 shock-absorber fibre washer.
The last “gotcha” was that the Woodruff key barely reached the bevel gear and had minimal engagement. There are 2 main factors that position and hold the bevel gear in place on the crankshaft: the key and the tightness of the LH threaded nut. As this engine has a lot of gears in the cambox (with their associated inertia etc) the drive train will need to be as strong as possible to survive.
A new key was made from an 18” length of ½” x 3/16” key steel. The picture below shows the new key together with a standard Woodruf key.
Fitted to the shaft (and with the dummy bearing in place) the new key provides the best possible level of engagement with the bevel gear.
The material is O1 tool steel and will be heat treated in due course to improve its properties (see eg here). And I have over 17” of this key steel left over!
The bevel gear is designed to be a close fit in the timing-side crankcase casting to maintain oil pressure in the lower bevel chamber. I found that the fit with this particular bevel gear and casting was a bit too tight – the bevel gear would not even fit into the hole. The crankcase was therefore back on the milling machine and the boring head used to open it up slightly.
As the changes to the lubrication system that I have made will not require a pressurized lower bevel chamber the larger diameter hole will not be an issue.
With a 0.020” gasket on the K-46/2 bevel gear housing there is perfect engagement of the lower bevel gears.
Not shown in the above picture, I have made a ½” x 20 TPI LH thread nut (removed here for clarity) to replace the usual K-114 LH ball-valve nut and the crankshaft bevel has been pushed “home”.
In preparation for the next sub-project – making the eccentric studs, I have put helicoil inserts into the 4 3/8” BSF threaded holes that support the barrel. These must be put in very accurately to avoid the studs sprouting out at weird angles like the spines on a porcupine. Each crankcase half was bolted, in turn, to the large angle plate on the milling machine and the digital level box used to set the top face horizontal (with the milling machine table as the reference).
However, when I checked this by using the position of the vertical head when a 5/8” diameter ground bar first contacted the surface
I found that the level box method was not sufficiently accurate and I could get a better and consistent result by using the contact method.
For the X-Y positioning I machined one stud on the lathe with a small “pip” in the centre and used that in conjunction with a small centre in the collet chuck, under a magnifying glass, to locate the on-axis position.
Whilst this might seem crude it has proved to be accurate. At the time of writing I have completed most of the machining of the eccentric studs – and the barrel slides down over them perfectly.
For any particular helicoiling exercise I never seem to have the size I want and invariably end up buying another kit.
I have also helicoiled 2 of the 3/16” BSW threads that hold on the K-45/2 timing gear cover.
That just about concludes the work on the bottom-end for now. The oil pump drive gear alignment will be checked and modified if necessary at the final build (when the oil pump is inserted) and I will need to remove a bit of material from the back of the inner timing case to clear the piece of additional aluminium that I have added for the crankshaft oil feed quill.
The next step is to complete work on the eccentric studs so that the cylinder barrel can be put in place properly.
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