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MG Midget and Sprite Technical - Catch Can

Hi
New to all this Mg midget stuff
I have a 1275 engine with a webber carb and i am thinking of installing a catch can as there is nowhere to run the breather pipe from the canister that is on the crankcase
Hope this makes sense
Any help would be great
R Deans

First step is to understand and decide what you want the breather system to achieve. There are two systems to consider:

1. A passive venting of the engine crankcase and innards to the ambient atmosphere to prevent build up of pressure caused by piston blow by and the movement of pistons. For this you need as much free ventilatilation as you can get, by one or more exits and these can vent via a catch tank to collect any oil in suspension.

2. An active Pressure Controlled Ventilation that sucks vented fumes out of the engine with the purpose of clearing fumes AND creating a negative pressure inside the crankcase which reduces or minimises oil leakage, specifically from the rear of the crank where there is no conventional oil seal. This may also vent via a catch tank but this must then be a sealed type, and itself is part of the reduced presure system. Extraction suction is provided by either the carbs (SUs, but your webbers don't have a vacuum point) or by connection to the inlet manifold. If to the latter, then a PCV valve is needed at the manifold. There are other types of systems providing the extraction suction but these are not commonly used on Midget engnes.

Image shows my extraction catch tank made from a coffee can as part of an active PCV system on a 1275 engine



GuyW

I use a PCV from a Japanese application on the B. There is a Moss kit with a generic PCV for a larger U.S. engine but it was too big and oil consumption went through the roof.

With the Japanese PCV (Toyota/Mazda), there is no oil consumption at all. It is ported to the Weber manifold.

I run the S.Us on the Midget so I haven't had the need to adapt a PCV, but it should work fine as on the B.





Glenn Mallory

Thanks for all the info
R Deans

This thread was discussed between 25/05/2023 and 27/05/2023

MG Midget and Sprite Technical index

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