Oil leaking through primary drive case bolt holes on crank case

Dear Dave,

On my 750 the 3 threaded holes that retain inner primary vase also go through so no surprises here, only problem with this is if you strip thread and helicoil it as a repair these can pass through as well. I didn't know commando has alternative sprockets - or are you running a belt drive?

martin

Previously dave_lee wrote:

Hi , I wonder if anyone can answer this apparently bad problem ,

I have just removed the primary chain case to fit a bigger drive sprocket , think the engine must have wet sumped which I am familiar with , but horrified to see oil pouring out of lower 2 primary case bolt holes , do holes go all the way through or are the bolts too long and have punched a hole into crank case ? seems a bit strange to have bolt holes all the way through would have thought they were blind .

Thinking I might have to strip motor and get crank case welded , hope Im wrong !!!!!! please help

Dave

The casing is quite thin so using screws that pass right through it will give a few extra threads to spread the load when tightening the screw. A SMALL dab of none hardening type sealant on the thread on reassembly will both help to seal the thread against oil leakage and help stop it coming undone (though each bolt should have its own tab washer to prevent this).

On my 1970 Fastback, the three holes in the LH crankcase are already helicoiled probably from new. If you are getting oil through the lower two bolts then the oil level in the crankcases must be above the screws. Crankcase pressure will just squeeze it through the threads and past the oil seal as well if the level is high enough. Eventually the clutch will be swimming in engine oil and the engine will be running low. If you only use the bike occasionally you could drain the crankcase and tip the oil back in the oil tank. Easy on the engines with a small drain plug but a good mod on the big drain plug engines would be the smaller drain plug in the big plug filter body.

When you re-assemble the inner chaincase, degrease the three threads and use welseal on the screws.

Avoid the NRV anti wetsump valves unless you, like me, need to check your engine re-building skills after a big end seize and a £500 bill