Oil leak confusion

[Pete A10]

Re the washers and their effect on the head gasket. Without a washer the nut cannot be properly tightened as the aluminium head under it will distort. The thicker the washer the less deformation there is in the washer which allows the nut to be torqued down much better thus giving much more compression on the gasket resulting in a better seal.

[Bess]

Hi Mick,
            A thicker washer amongst other functions, spreads the face pressure over a larger surface area hence increasing the effectiveness of the gasket.


Best wishes...

[Mick Boon]

Today I've been educated thanks.

[Calum]

It is a bit confusing! The CEI threaded components that we have on BSAs (mainly 26 TPI but also 20) need Whitworth size spanners. The spanner size relates to the shank diameter not the head.

BSF/UNF/UNC spanner sizes all relate to the measurements 'Across Flats' (AF) so use common spanners although they have varying thread profiles.

To make it more confusing, there are some sizes where one spanner size is near enough to fit both Whitworth and (e.g.) BSF.

This link may clarify! http://classicmechanic.blogspot.com/2011/06/mm-af-bsw-bsf-spanner-conversion-chart.html

My suggestion would definitely be to invest in a set of Whitworth spanners.

Finally.... You will find that you can't get a socket on to some of the head nuts and an open-ended spanner can't get the torque. In which case I suggest getting one of these: https://www.amazon.co.uk/gp/product/B00BH3QVA2 it's metric but adjusts to grip and does a good job!

Cheers,
Bernie

BSF use the same spanners as BSW. For post war fasteners, the same diameter thread in both BSW and BSF use the same spanner size. Prior to that, the Whitworth fastener would have a bigger head than a BSF fastener of the same diameter. Hex sizes were reduced to save material, and never changed back. What makes it confusing is the markings on spanners never changed - even brand new ones will say 5/16" Whit for example, when in fact it will fit a 3/8" Whit bolt and nut (and 3/8" BSF, which the spanner will correctly state)

Unified series threads (UNF/UNC etc) use AF spanners, as you say across the flats sizes.

CEI (later adopted as BSCy) should use BSW sizes for the head flats, but I've found a mix on aftermarket nuts between BSW and AF size hex (should be the former on standard fasteners)

[Mick Boon]

Re the washers and their effect on the head gasket. Without a washer the nut cannot be properly tightened as the aluminium head under it will distort. The thicker the washer the less deformation there is in the washer which allows the nut to be torqued down much better thus giving much more compression on the gasket resulting in a better seal.

I have the correct washers on the way.   Thanks for the info !

[AdrianS]

I've got the same leak on my A50.
Rebuilt the engine , new head gasket, same leak still present in the same place as yours.
Only leaks when on the side stand and engine running. It can tick over on the centre stand for 5 minutes with no leak.

[DAVE BRADY]

Hi,

This seems to be a recurring theme.  One of my A65s did this when I got it. It was not really a problem but more annoying than anything else.  I cleaned the joint and made sure it was dry to see exactly where the oil was coming from.  The main area was on the front to the left hand side and nothing elsewhere.  Eventually I did change the head gasket and it stopped.  Although there is still a hint of oilyness on the joint it is not enough to run and drip.  I think the main culprit is where the drain holes are near the exhaust valves.  If the head is not perfectly flat and the gasket not torqued properly this seems to be the spot that leaks.  At some point, officially or unofficially 'O' rings were fitted to solve this.  The hole in the gasket is big enough for an 'O' ring to be squashed by the head and make a good seal.  I have done this on both bikes recently but have not done enough miles to say if it works long term.

Dave.

[Mike Farmer]

 

I am about to reassemble an A65 as a result of the same problem. oil was bubbling up alongside one of the head studs. Maybe partly my fault as a result of a bad torqueing of one bolt, but strangely on the opposite side of the head. Who knows we'll have a better idea tomorrow??

Mike

[DAVE BRADY]

Hi,

A slightly different issue as that indicates that gasket has not sealed around the stud.  So along with very clean threads to ensure proper torquing it is worth making sure that the gasket is perfectly flat around the holes.  They appear to be stamped out and this can cause slightly raised edges on what I would call the underneath of the gasket so remove any burrs or raised edge.
I think with all of these things it is marginal gains to get the best result.

Dave.

[Mick Boon]

Hi,

This seems to be a recurring theme.  One of my A65s did this when I got it. It was not really a problem but more annoying than anything else.  I cleaned the joint and made sure it was dry to see exactly where the oil was coming from.  The main area was on the front to the left hand side and nothing elsewhere.  Eventually I did change the head gasket and it stopped.  Although there is still a hint of oilyness on the joint it is not enough to run and drip.  I think the main culprit is where the drain holes are near the exhaust valves.  If the head is not perfectly flat and the gasket not torqued properly this seems to be the spot that leaks.  At some point, officially or unofficially 'O' rings were fitted to solve this.  The hole in the gasket is big enough for an 'O' ring to be squashed by the head and make a good seal.  I have done this on both bikes recently but have not done enough miles to say if it works long term.

Dave.

I have noticed when the bike is on the center stand that the exhaust is a slightly smoky on the leaking side,   maybe it's leaking internally too ?

[DAVE BRADY]

Hi Mick,

It is possible that some oil is being drawn into the combustion chamber.  Check the plug but also consider that there could be a worn valve guide or bore but if the engine has not done enough miles after a rebore it could be that the rings are not quite bedded in yet.    If you are going to fit the washers then as you will have the head off check everything.

Dave.

[Mick Boon]

Hi Mick,

It is possible that some oil is being drawn into the combustion chamber.  Check the plug but also consider that there could be a worn valve guide or bore but if the engine has not done enough miles after a rebore it could be that the rings are not quite bedded in yet.    If you are going to fit the washers then as you will have the head off check everything.

Dave.

There are washers under the bolt heads beneath the rocker box cover but they look like ordinary washers, they are not thick.

My bike was made in 1968, but if memory serves you said earlier the thick washers were introduced in 1970 .   

I'm wondering if I should mess with the bolts under the rocker box cover.   What do you think ?

[DAVE BRADY]

Hi,

I would think it best to a least re-torque all the bolts as you will be undoing the outer nuts and then torquing them again.  There is a sequence for tightening in the handbook and it is worth following this for undoing a bit in order to re-torque. 

Dave.