Sq4 Mk1 oil leak

[DaveC]

Hello All, I have recently acquired a Mk1 - the head is leaking oil and I am in the process of tackling this. (Yes, I know!) The head and barrels are flat according to my precision straight edge. It had the correct Otto gasket with what looks copper silicone sealant, but over the whole gasket area, not just a bead around the pushrod tunnels as per current guidance. The bolts were maybe a bit tighter than the latest recommendations from Drags, but not massively so.

Most oil was emanating from the front and rear of the head and front and rear between the barrels, and looks to have come from central void area between the cylinders. The actual head joint and gasket faces looked pretty uniform with no particularly obvious leak paths. The seatings for the sleeve nuts are rough and need machining and could be a path if the head gasket hasn’t contained it. What’s bothering me before I fit my new and expensive Otto gaskets is the amount of oil, staining and crud up in the central void of the head above the inlet ducts. It's probably blown up there during use, but the bike has clearly had very little use since an extensive rebuild.

Is there any history with these heads of cracking or having casting flaws up in this area which could lead to oil leaks? There appears no sign of machining that could have broken through to the voids.

Thanks in advance for any wisdom you may wish to share.

[Roger Gwynn]

The MKI heads frequently crack from the front and rear centre across the gasket surface from the edge as far as the triangular shaped hole. I have never known the crack to cause any problem or to go any further and other than extreme abuse, which is not unknown, they do not suffer from the sort of problems that you ask about. Check that the ally has not pulled up around the studs because this will prevent the head from seating properly.

[simon.holyfield]

The rocker oil feed union - is there any staining around there? One of my early discoveries in Mk1 ownership was the folly of using a conventional fibre washer in that position...

[DaveC]

Roger, Simes, thank you for your replies.
I don't think I have any of the things you mention, but I think I shall run some some dye pen over it now to be on the safe side.
Cheers, Dave