The primary side case is puzzling. I can see there is no seal on the crank bearing. It has the 3 small holes which are too low. However there are 2 other holes on either side of the crank bearing housing. I have not seen or read about this before and wonder if someone knows about this kind of alteration. Depending on how the rest of the engine is, I would likely seal all these 5 holes up and go to the original rotary venting on the cam and install a crankshaft seal. I appreciate any comments on this!
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.
OK. What is this! On the Gearbox inner cover on the bottom, front edge is a fitting that looks like it is a modification. The fitting is also plugged. Does anyone have an idea of what this would have been for? I may have it welded up if it is not necessary. Thanks.
Here are a few more photos. The brass cylinder is what came out of the hole. It was not threaded into the case, just fixed in there with some silicone or black goo. Plus, the cylinder itself was plugged with goo. It doesn't look like a standard item.
OK, Darkman, of course you are right. So I thought this was a 67 motor, but obviously this part is from an older bike. So filling it in was the right thing to do. I'm curious if anyone has a good technique for filling this in if one is not using a speedo? Perhaps just fill with silicone?
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.
Left and right crankshaft bearings - Question. I did not realize there were about 3 different bearings for the left and right side of the crankshaft, marked CN, C2 and C3. I didn't realize this when building my last engine, and will have to look through my receipts to see what I installed. Can anyone explain this issue and how one determines which bearing to use in a 1967 T120R engine. My parts book says the part number are E2879 for the main bearing left, and E1591 for the main bearing right. Thanks for any advice!
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)
OK, very clear information. I appreciate your help to allow me to learn something new most every time I ask a question. I would have never thought this had to do with tolerances internal to the bearings!
Transmission main shaft a bit worn. So I disassembled my transmission and it all looks pretty good except for the transmission main shaft. I don't know if this kind of wear makes this unserviceable and would appreciate any comments in this regard. Thanks!
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.
OK, this is a bit new to me. So the 4 speed transmission only has 2 bushings, apart from the clutch rod bushing. So I was planning on replacing all the bearings in this already. Are you suggesting that a replacement of the M/S high hear bush and the lay shaft low gear bush "might" be ok with the current mainshaft? Or is it obvious the current mainshaft needs replacing? And . . . I've replaced cam bushings before but not these transmission bushings. Is this done by heating the part and driving them out? Then is there generally a need for them to be reamed? Thanks again!
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.
Thanks speedrattle. I am planning to revert this engine back to the rotary breather system. I'll fill in the holes and make sure I've got the vent pipe open, etc. I may have the holes welded shut on this case.
Yes, the shaft is pretty bad. I think I've found a used one that is not damaged and is a reasonable price and hope that will work out ok.
Cylinder base dowels. On my motor, two of my cylinder stud holes have a cylinder base hollow dowel recess for the dowel that is in the cylinder. I am unsure of the purpose of this setup and would appreciate any comments to explain this. Thanks!
