Depending on the year of manufacture three different designs of camshaft spindles can be found in post 1937 M20 engines, shown in the picture below...

On the left are a pair of the earliest type...These have the oil hole in a different orientation to the flat that is used to position the spindles within the crankcase when fitting...The spindles were drilled right through, with the hole at the inner end later filled with lead..This can be seen in the photo.Note that the short section of the spindle that fits into the crank case is completely circular...There is also a hole drilled though this part of the spindle that serves no purpose when fitted...I surmise this may have been used for jig location during production...

In the centre are a pair of the 'intermediate type'...These have the second hole deleted. They are also not through drilled so no lead filling is needed...The oil hole lies in a different orientation to the location flat when compared to the earlier type...The short section of the spindle is still completely circular...

Finally, on the right are a pair of the last type...These have the oil hole in the same orientation as the intermediate type...The major difference here is that there is a flat machined onto the short section of each spindle where it fits into the crank case. The spindles are marked 'IN' and 'EX' (inlet and exhaust), the reason for this being that the flats are machined on the opposite sides of each spindle, making them 'handed' for fitment...
The reason for this last change was that it was found that the degree of fit of the spindles into the crank case combined with the proximity of the spindles to the main bearing housing was causing distortion of the housing...The flats served to relieve this pressure at the point nearest to the housing...
Consequently, these later spindles would be the best choice when rebuilding an engine....Ian

email (option): ian@wright52.plus.com

Hi Ian, the pair on the left are used in the 1939 B series engines KB21/23/24/25/26. The oil hole in the side of the portion which fits into the crankcase is the oil feed to the cams/spindles as this is supplied internally from the timing side main bush.
The notch in the flange is an indicator for when they are fitted to make sure the holes in crankcase and spindle line up. The solder plug on the inner end stops the oil escaping there as they are drilled hollow from that end. No reason why they couldn't be used on M Series engines if they are also drilled hollow from the other end?
Just building a KB24 engine and had to modify some new M Series spindles to replace the worn originals...
Regards, Rupert.

Thanks for that information...These were removed from an M Series engine some time back...It would be interesting to determine whether these were a non standard fitment by a previous owner or were used in both engine types...Do you have part numbers for them?....Ian

email (option): ian@wright52.plus.com

The 1939 parts book says 65-2422, same part for inlet and exhaust.

PS, same spindles used on M series in 1939 except the M22 which retained the previous live spindles running in bushes. Looks like once the B series models (B29/30) adopted the M Series bottom end in 1940 the cam spindles were changed to suit only being fed oil from the outer end.