MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Tappet cover breather pipe.

In my consideration of fitting a Derrington head with an aluminium rocker/tappet cover I am thinking about the breather pipe. I am also fitting K&N filters in the standard filter casings.
I have read that with K&N filters it is not advisable to have the breather pipe going to the filter. I'm not sure why? Any thoughts or experience with the K&N filters with the vent.



John Francis

Can't speak specifically about the Derrington head, but I've been running K&N filters for many years in the original Vokes housings with the breather pipe without any issues. Although I have the original cover on my head, I've seen aluminum covers which needed to be modified with the addition of a breather port & pipe, while others switched to a breather cap to avoid the need.
Nick Kopernik

John,
so long as your engine doesn't have a lot of piston blow-by, which pressurises your crankcase, it shouldn't be a problem to connect the rocker cover breather pipe.

The breather pipe is designed to draw clean filtered air from the air filter which flows down past the valves, via the tappet holes, through the crankcase. From there it exits via the tappet cover vent where it is drawn out by the slight suction caused by airflow passing by the vent pipe beneath the car.

When my 1950 cc engine was running in, it did blow a bit of oil out through the vent pipe and made a mess of the underside of the car.
So I fitted an MGB oil-trap style of tappet cover into the front position on the engine, which cured the problem.

My car has a Weber 45 DCOE and there is only enough space for the Pipercross sock style air-filters on the bell-mouths which have no provision for the breather pipe.
So I have installed a separate K&N crankcase filter onto the bulkhead which seems to work well.
Colyn

Colyn Firth

Generally the aluminium rocker covers can be partnered with the chrome oil filler caps that have a small hole in the centre of them, these are not so good for breathing as the original style black plastic oil filler caps.
Nigel Atkins

I just spotted this option on the Twin Cam Group and wondered if it would be an easier alternative?

The K&N filter has a spigot that pushes through a hole in the filler cap, I believe the filler cap is a generic plastic one for the B-Series Engine.

Colyn


Colyn Firth

Would it really need to be that big as the K&Ns I've seen on V8 rocker covers (just one side?) have been half that size.

And a smaller size would leave more room to get at the oil filler cap to remove and replace it at topping up or refilling with oil.

Looks very smart though, a red cap would gain more points though. :)
Nigel Atkins

This thread was discussed between 29/02/2020 and 01/03/2020

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.