Rockers over oiling

[V500]

True. Everyone assumes that the old British factories knew little or nothing about breathing when the opposite is more accurate, and while adding additional breathers may help in some circumstances they're not a cure-all for other engine problems.

[JulianS]

About 18 months ago I determined to reduce the rockerbox oil leaks on my iron head A10, having tried various methods as detailed below. I checked the metal to metal joint by removing the rockers then bolting the box to the head and then checking for the gaps. The worst gaps were on the outside of the exhaust compartment.. With head removed from bike and valves out I lapped the box to the head, quite labourious, but the result is no leak after sealing the joint with an SRM gasket ane Wellseal.

Some gaskets are not quite the correct shape especially at the front of the inlet compartment giving a narrow joint. Some gaskets do not seem to resist being squashed when the fixings are tightened and seem to settle and appear to need to be retightened. When retightened the gasket starts to creep out from the joint. Leaks follow.

I tried the simple version of Bunn, really just a rocker breather with a non return valve similar to an aquarium air pump non return valve. It did not seem like the valve could keep up with the engine. I tried a rocker breather on a Dow finned cover, both with the original small bore outlet and with a much larger one. Not convinced that it helped. Tried a breather on both covers. The same result.

I sealed a freezer bag to the Dow breather tube, expecting it to slowly inflate when the engine ran. Well it did not, it seemed to suck a little more air in than it expelled.

Those breathers now blanked off. Not needed following the work on the joint.

[DAVE BRADY]

Hi,

I salvaged another valve from an old inner tube and threaded it into the open end of the tube from the rocker box. This has been in place for many year/miles and still works.  When the engine is running a flow of 'air can be felt but no obvious oil vapours being emitted.  Almost like the std timed breather.
As the engine can suck as well as blow the valve serves to keep out fresh air and any muck that could find its way up to the rocker box - I had noticed this in the past.

Dave.