Featured Rickman Triumph Project

The 3 holes would work ok as you only req a small amount of oil to lube the chain, the other 2 holes have been used to remove the outer race of the main bearing. I would get all 5 holes welded up and revert to a timed breather and use a spare pair of rocker cover caps to vent each rocker box as i do on our bikes.

 

63-65 speedo drive.

 

I've always found the inner gearbox drive to weep slightly no matter how many times I get an o ring in there and because they are a right fiddle to get to once the engine is in I run these with an external driven speedo.



The drive is held in with a threaded screw that you have missing. The inner worm gear is also gone on yours. It looks like someone had a battle getting it out on yours but there's still some thread in there. Order the countersunk screw (70-3728 I think) and put the drive sleeve back in. I then use the open nut from the speedo cable with a small cap inserted and screw onto the threaded sleeve.

Or you can always buy a later 'preloved' inner gearbox cover, they don't usually run to too much.

Or just weld the hole up completely of course.

 

The bearings come in several tolerances. That is how tightly they fit together in themselves, not how tight they fit into the hole or over the shaft.
The lettering for their tolerance is confusing but the easiest way is as follows:

C2 bearings are the tightest tolerance
then
CN bearings which are ‘normal’ size and are looser than C2
then
C3 bearings which are looser than CN
then
C4 bearings which are the loosest of all

Each model of Triumph's and BSA's unit engined bikes take different toleranced bearings on the crankshaft. Obviously the more powerful the bike the closer the tolerance needed to be to stop the crankshaft ‘knocking’ and/or mashing up the bearing.

From CBS: (T.S. timing side D.S. drive side)

 

that thing on the top of your primary is an old-style fuel petcock. since you dont have a seal on the crank and hes drilled the three holes its clear he was venting through a hose on that petcock.

that will work fine but the inside of the petcock is only 3/16 or so and it really should be larger. if you keep the later style venting you can replace that petcock with one of these from CBS:

https://www.classicbritishspares.co...parts-tools-accessories/products/57-2166-vent

check with kyle to make sure the threads will work. i have one that does not screw into a 1967 case half. or maybe it wont fit the 1970s? cant remember.

the three little holes are an engineers boondoggle. in the stock, higher position they dont do anything except maybe spray oil onto the chain. they are way above the actual level of oil in the chaincase which varies between about 3/8 and 5/8 inch. they are below the level of the main bearing in all cases anyway. as near as i can figure out, the holes were there to allow oil to drainback beneath the level of the main bearing if the machine was laid over somehow and a large quantity of oil from the spine flowed into the chaincase through the upper vent line.

when running the oil sprays in and out of the main bearing, and is not controlled by th ethree holes.. i run dry primaries in my race motors, and drill the stock holes out to 1/16 inch (iirc) and then tap in patent plate rivets. but your holes are drilled by the PO, so theres no telling what size they are. i have drilled and tapped oversize OP-modified holes for 5-32 (not 5/32) screws and epoxied em in.

 

Always a hard one if you have not ridden the bike as i have seen horrible parts come out of a perfectly good working box lol, you could chance what you have with new mainshaft, M/S high gear bush and lay shaft low gear bush. Also M/S bearings and L/S thrust and needle rollers as a minimum. I always fit a new detent plunger and spring as well.

 

I would go with a new mainshaft myself if you don't have the correct drifts to remove and refit the bushes then it's better to give the job to someone that has, most bushes don't req reaming, i have never had to ream one myself but have been told others have.

 

The dowels ensure the two engine parts, in this case, the barrels and the cases, align correctly.