Having completed the “top-end” of the engine the “bottom-end” was next on the list for attention.
Although I have had all the aluminium components vapour blasted and their appearance suggests they are nice and clean and ready for assembly the reality is that the cleaning process often adds to the decades of accumulated crap deposited in threads and oilways. I therefore clean all threads by running a bottoming tap down them and oilways by brushing in cellulose thinners and blasting with an airline.
The oil pump, which has been stripped, cleaned and checked for any damage is popped in first. Grove Classics sell new ones, if needed, and I’ve used these on both the AJcette and AJS V-Twin projects. As I’ve mentioned in the past, I have 2 ovens for heat treatment and the larger, lower temperature oven that I use for tempering is extremely useful for heating aluminium castings for removing and dropping in bearings etc. This also applies to the oil pump which is an interference fit.
If it is not held together, the oil pump quickly dismantles itself! The shim, K-110, that goes on the back of the pump holds the gears for the scavenge part of the pump in place and if it is removed or the pump is positioned drive-side up the gears simply fall out.
The way that I insert the pump is as follows:
Two 3/16” steel rods with a 3/16” BSW thread on one end are screwed into 2 opposite holes in the crankcase that support the oil pump.
The crankcase is then heated in the oven to 180 - 200 0C. The oil pump, with 2 of its countersunk screws inserted in the holes that will NOT be used with the 2x 3/16” rods, is then held face down (to prevent it falling apart) and offered up (the right way round!) and engaged with the 2x rods protruding from the facing-downwards heated crankcase half. With a bit of jiggling, the oil pump can be inserted fully into the crankcase and the crankcase can then be turned over and put on the bench and the threads of the 2 screws engaged,
the rods removed
(I use a tailstock chuck – because it’s convenient. The alternative would be to thread both ends of the rods and use a couple of locknuts) and the other 2 screws inserted. Needless to say, a good pair of welding gloves is needed to avoid a visit to A&E.
I have fitted a new timing-side bearing.
These (and the drive-side roller bearing) are a metric size – ID = 22mm, OD = 50mm and t = 17mm. These bearings were also fitted to vintage Nortons (I know because I’ve replaced them in the past) and probably other bikes and they are available from Vintage Bearings or Veteran Triumph. As can be seen, they are also now available with an oil seal which is very convenient for the Velo engine which requires pressurization of the bevel drive chamber. However, this does not mean that the K-150 shim can be omitted because this would affect the positioning of the bevel gear.
I have found both the original and new bearing to be tight fits on the crankshaft and to avoid applying a lot of force on assembling the crankshaft into the crankcase it was much easier to fit the bearing onto the crankshaft so that the force is applied directly onto the bearing inner using a short length of aluminium tube and then drop the crankshaft + bearing into the heated crankcase.
The next step was to set up the crankshaft end-float and the bevel drive. There are a number of possible ways in which the crankshaft end-float can be determined; my preference is by direct measurement of the distance between the mainshaft boss that contacts the drive-side bearing and the contact face of the timing-side crankcase half
and the corresponding distance between the drive-side bearing and the mating surface
on the surface plate (it’s actually a granite block). I concluded that the end-float would be 0.041” – not too good for reliable engagement of bevel gears.
As I think I’ve mentioned before, shims are available at remarkably good prices on eBay UK. I paid 9 GBP for this collection (10 of each) in various mm thicknesses and with 22mm ID and 32mm OD.
I decided that I would set the end-float to zero which can be done with 2x 0.019” plus 1x 0.003” shims. The question now arises as to how to distribute these as this will affect the position of the bevel gear and my starting point was to put all the shims on the drive-side (which positions the bevel gear at its most outward position) and check the engagement.
There is a good synopsis of setting up the crankshaft bevel drive (and many other aspects of Mk 1 cammies) in FT 238 by Denis Drake and downloadable from the VOCs website. More recently, Richard Boldry has also written a comprehensive article on bevel gear meshing in the latest (at the time of writing) copy of Fishtail (FT 507) so I will only add a couple of points that I have found useful here.
The bevel gear needs to be pushed right up against the abutting shoulder on the crankshaft and rather than putting the K-34 gear on the end I simply made up a small spacer to allow the left-hand threaded K-114 nut to be tightened.
In this way, the engagement can be more easily seen when the lower bevel gear + housing is fitted; if the K-34 gear is fitted it is more difficult to see the engagement.
The objective is to get smooth rotation of the crankshaft by adjusting the positions of one or other (or both) of the gears, with both gears fully engaged and without backlash. The crankshaft bevel gear can be moved inwards (in this particular engine build) by redistributing the 22mm ID shims that are on the drive-side or outwards by adding shims (K-111/X available from the VOC) behind the bevel gear. The bottom bevel can be moved vertically upwards by making gaskets using different thickness of gasket paper acting as shims or moved downwards by machining material from the bronze bush (an option of last resort).
The picture below is a partial screen shot from a listing which offers gasket paper in various sizes from 0.25mm to 2mm – perfect for making and testing gasket shims.
It turned out that with 0.041” of shims on the drive-side of the crankshaft, no shims behind the crankshaft bevel and a 1mm (0.039”) gasket under the bottom bevel that I got full engagement and smooth rotation. To get to this point, a few gaskets with different thicknesses were made and tested. It is not so easy to photograph with the whole assembly so I have removed the spacer and LH nut to get better access.
Prior to setting up the meshing, I found that the threads on either or both of the K-46/2 housing for the bevel gear bush or the K-52 nuts can be poor after 90+ years of assembly and disassembly. The external thread on the housing can be cleaned up using a 24 TPI thread chaser and holding the other end in the lathe chuck.
The K-33 bevel gear is pressed out (it is held in by the K-27 locating collar) prior to machining and pressed back after machining and cleaned up to avoid any swarf finding its way inside.
On this topic, it can happen that the locating collar is so tight on the bevel gear shaft that the bronze bush (K-46/3) is pressed out instead. A Sykes-Pickavant type bearing separator is then needed to extract the bevel gear from the bush.
I have been refurbishing these parts for the other engines that I am building and this happened on one of the bevel gears.
An internal thread chaser can be used to clean up the threads on the K-52 bevel gear gland nuts ….alternatively and if the nuts are in poor condition, just buy new ones from GroveClassics.
With the oil pump in place, the crankshaft end-float and bevel gear meshing sorted out the crankcases were sealed with Honda liquid gasket (it’s expensive but I’ve been using it for years without any problems) and bolted together. There are 3x ¼” diameter permanent studs and 4x 3/8” studs (or bolts) that are in place when the engine is in the frame. I use all of these to make sure that the two crankcase halves are firmly clamped together after the sealant has been applied and for the remainder of the engine build.
I measured the piston ring gap in the bore which came out at 0.030” (!!). This is nearly 2 ½ times the recommended limit of, typically, 4 thou per inch of bore which gives around 0.0125”. However, with a nominal diameter of ~ 80mm the slipper piston that is fitted is not original Velocette; so, where to find new rings?
This measurement could also be interpreted as 79mm+ 0.020” or 79.62mm (within the limits of accuracy on old used parts) and which manufacturer fitted nominally 79mm pistons? Norton of course. And the form of the piston is very similar to, if not the same as, this Norton International piston.
Manufacturers did not change much if they didn’t need to and the piston rings from other Norton motorcycles – Model 18, 16H etc have the same dimensions for the ring thickness and radial thickness and this set of rings
which I found on a well-known auction site cost around 20 GBP and fitted perfectly. The ring thicknesses are even given on the front of the packet. These are quality rings, made by Wellworthy, and were almost certainly manufactured in their Lymington works (South coast of UK near Southampton) prior to the close of the factory in 1981.
I measure the ring gap at 0.013” and these were fitted without change.
The next step was to set up the Oldham couplings for the vertical shaft. These need some vertical clearance to avoid putting an axial load onto the shaft and which would be transmitted to the bevel gear meshing. But how much clearance? Phil Irving in his book Tuning for Speed simply states “a small amount of end-clearance”, Peter Miles gives “at least 12 thou” in FT 141 and “not more than 25 thou” in an article on Building OHC Velocette Motors and Burgess gives “not less than 12 thou” (Thanks Gerry).
Different thickness couplings are available from both VOC Spares and Grove Classics, however, by taking a measurement of the gap (there are a couple of washers and shims under the feeler gauge in the picture below)
I could not find a combination of the available couplings to get close to these figures; this is a consequence of having a Norton slipper piston fitted that requires an aluminium spacer (which can be seen in the above picture between the crankcase and cylinder base) and has changed the cylinder base – to – cambox dimension.
The easiest way for me to resolve this was to make a new lower Oldham coupling
from O1 tool steel, fitted (before heat treatment because it’s much easier to fettle) to give a clearance of 0.015”
and then hardened and tempered.
As this blog is getting quite long, I’ll leave the rest of the engine build to the next time.
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