Oil Leaks


True surfaces, new gaskets and new oils seals properly fitted can result in an oil tight motor, particularly with the later 650/750 twins.

Nigel Sprocket was working on a revolutionary solution to oil leaks in a secret department at Meriden and recalls – “after years of intensive research we discovered that the polarity of crude oil atoms is reversed in the refining process – thereby creating an attraction between the oil in your motor and the subterranean reserves of crude. Ah yes I can see a few of the more astute TOMCC members taking notice now. Yes that is the reason oil consumption increases as you cross the Taranaki oil fields. We discovered injecting a small amount of uranium into the oil feed changed the polarity back and we all know, well those of us that managed to finish primary school, like poles repel. Simple innit. (At this point Joe Lucas’ nephew, Smoky assures members that kits would have been supplied with a syringe of weapons grade uranium for direct oil line injection in the unlikely event of there being insufficient smoke available to drive the injector pump). Regrettably the project was halted when apprentice Wokey Mills (no relation to current TOMCC president Glenn Mills who I am assured has only two ears at present) Mum complained about the extra ear growing on Spotty’s for’ead. This one still puzzles me, me Mum was always complaining that I had no ears while repeatedly thumping what was patently obviously an ear – wot’s wrong with and extra one I  ask you fellow members? Oh an there’s an opportunity out there for the more entrepreneurial TOMCC members – fit an oil level gauge to the old girl, monitor it while riding around this fine country, and when consumption goes up bingo! No charge for this little gem, just remember yer old mate Sprocket when you hit the mother lode seam.

Right that’s enough of that crap, joints first, I lay a sheet of emery on a piece of plate glass and dress up the surfaces of both components until I have a shiny surface all round. Make sure you wash all traces of grit off with petrol and assemble with a new gasket. The photo on the left shows the head of my 69 Bonnie and the head joint has clearly been leaking.


A very light dress up on the plate glass fixes this, removing hardly any metal, see photo on the right. While this is not a simple oil leak situation the other surfaces on my top end when I took this photo were perfect and the principal is the same. Rocker box joint surfaces are often not true.  Tighten bolts evenly but don’t overtighten. Socket sets are partly responsible for this, the handle has the same leverage on a 3/8” nut as a ¾” nut – a 3/8” ring spanner is much shorter than a ¾” spanner making it harder to overtighten.

Oil seals should all be new, and if there’s a spring around the lip then the spring faces where the oil is. Careful with Hinkely fork seals, some have a lip and spring both sides so note which way round it is before taking the old one out. Smear oil around the seal and fit the components together carefully so as not to damage the seal.

Don’t overdo silicon sealant but I always smear the pushrod tube seals with silicon and that stops the leaking. I just use the standard ‘o’ ring type seals but every time I order new ones British Spares send different types. Last time they sent a rectangular section sealbut it was too big. Always check the thickness of seals by placing the pushrod tubes, seals, head gasket and head loosly in place and measure the gap between the head and barrels/gasket. It should be about 1/32″ (31 Thou”), if it is much more or less than this it won’t seal either by being not tight enough or by crushing the seal , I have heard of ones that needed trimming to fit providing a perfect seal but haven’t used them – anyone out there who can comment?