Got a couple of annoying oil leaks on my B31.Primary chain case and sump plate.
Looking at making my own gaskets from cork nitrile bonded sheet.It comes in 1mm,1.5mm and 3mm thickness.What thickness should I use?
Hi,
I would use the 1mm or 1.5mm but make sure the surface of the case is flat.
Over the years they get a bit abused. Ideally do this when inner and outer are both off the bike. Assuming that it is a swinging arm frame model this means two surfaces to do.
A piece of plate glass that is bigger than the case is needed. As this could be expensive get a quality glass kitchen chopping board. They are very strong and flat.
I used this on the primary case of a '51 Flash and I needed 2 A4 sheets of emery paper held to the glass with double sided tape. Cover the whole of the back of the emery to avoid any lows and highs at the joints. Use some WD40 for lubrication and spend a bit of time cleaning up the surface.
Before starting just try a feeler gauge at several points to see how much needs to be done.
With gentle pressure move the case in a circular motion. Use open hands to avoid any 'rocking' pressure. It is vital that all parts of the surface move exactly the same amount so rotating is a 'nono'. After a few minutes you will see how much un-evenness there is. Once all of the surface is of a uniform you should have a good flat case to help keep the oil in.
Dave.
Another issue with alloy chain case is that it can be distorted when mounting. You have the three wired screws into the crank-case and the bolt at the rear lower edge to the frame plate. You need to make sure the case does not get pulled out of shape when this bolt is done up. There is a spacer in the parts list but sometimes you just need a narrower spacer (a variable stack of washers assembled to right thickness is also an option.
People are selling the rubber gaskets for these that you glue onto one surface with Permatex or similar.
Agreed. You need to get the inner case pulled up on the engine then check the gap to the frame plate at the rear. Then pack it with washers so there's no bend in the case.
I use grease for primary chain case on my B31. This remidied the leaks , as when I used oil, no matter what I did it always leaked.
Another source of oil leaks on the alloy cover are the through drilled and tapped bolt holes on the inner cover especially at the oil drain and oil level bolt locations. I found that oil migrates from the scallops cut in the casings at these locations along the bolt threads and out the back side of the inner case.
I made short plugs from 1/4-20 cap screws with fibre washers and installed them on the back side of the inner housing. I also place fibre washers on the BOM drain and oil level screws.
Jim