View Full Version : Are these holes supposed to be there??

06-01-2012, 6:54 AM
1966 BSA A65. Opened up the primary side outer cover to adjust the clutch springs. Found about a half quart of engine oil had "leaked" in. Found these two 1/8" holes with trails of oil running down. No signs of oil leaking around the crankshaft, or any behind the clutch into the trans. Are these holes supposed to be there, or did the previous owner do some mods?

06-01-2012, 11:05 AM
Im rebuilding a 63, Ill take some pics for you

06-01-2012, 11:33 AM
Do you have a big bore ? Is there a exrta hole added to the top of the primary ?

06-01-2012, 11:51 AM
No, standard size bore when I bought it. No extra holes at the top of the primary. The level of the holes allowed the oil to fill the primary side enough so that the clutch plates were about 1/2" in the oil.

06-02-2012, 1:15 PM
NO they are not standard for 66 . In 66 you should have a cam drivin case breather . it uses a vacuum caused by your pistons going up to draw the oil from a cam followers back to the case . With those holes in it you can get a oil leak from the head gasket area inbetween the cylinders . It was common to drill extra holes into the primary to add in lowerend preasure while running big bores for racing . but they would add a vent to the top of the primary and the valve cover . It should not really afect you clutch or a a real issue since the bike should only have 100cc of oil in the sump while running or sitting for a short time . If it wet sumps from sitting which is common on these old twins then the primary will fill up add it will not be drawn out once the bike is started since the case preasure is higher then the primary . Your bike does run a wet clutch so a bit of oil is no big deal.

06-02-2012, 3:07 PM
Thanks Trumpnut, that's what I was hoping to hear. I'm thinking of plugging those two holes with setscrews since they don't really seem necessary. I was thinking it had to do with racing. Thanks!

06-02-2012, 5:27 PM
Make sure you still have the main case vent stil efore you do that . Just in case the plugged it or somthing .

06-05-2012, 8:38 AM
Thanks Trumpnut. The case vent is there, I put the engine together from a box of parts, so i think I'm good to go. Appreciate the warning!