1920's-1931 All Models - Crankcase 'Clack Valve' Breather Spring - Each

Product no.: 1112 BrthSpring1

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This item is for a spare spring - of the type that were fitted into the distinctive 'Clack Valve' breathers in 1920's OHV and Walter Moore CS1 breathers - an original dismantled clack valve (shown in photo) providing the spring pattern.  We will shortly be manufacturing the complete breather/clack valve unit. 

Price is per spring

Backgound:  This distinctive breather/clack valve unit was normally fitted to both OHV and early Walter Moore CS1 engines in the 1920's through to the early 1930's.  Sorry, but I cannot be definitive about which year they were first fitted, and which year they stopped using them - but the accompanyning photos of engines shows them fitted to the crankcase of CS1 Walter Moore engines (normally either behind or in front of the barrel), and in the timing case of 1920's OHV models.

The pattern we are using came from an original 1928'ish Walter Moore CS1 engine and looked to be complete and untouched for many years (lent to me by a close friend Norton collector).  It has a small steel disc that sits in the chamber of the main bottom banjo union, and is held against the breather hole by a spring that sits in a similar receptor/chamber of the top union connection.  The spring keeps the disc flat against the hole - the idea being that gasses can escape out, but outside air cannot be sucked in.

This design was replaced by the 'normal' Norton 1/4" BSP 'One Way Valve' (our Item 0248) with a ball valve, screwed into the crankcase above the driveside mains housing - from approximately 1933 ownwards.

Although it is very difficult to be definitive about 1920's components still being original (so often they got worn out and replaced), the spring that was fitted to this breather looked to fit perfectly in this breather - and the wear marks on the top of the steel disc corresponded to the spring - so we took this spring as being original - and have now had it replicated.

We are selling it seperately, for those that might have an original breather - with insides missing or worn, but at a later date (hopefully later in 2022) - we will be manufacturing the other parts of the breather assembly.  For the moment - the spring is available seperately (apologies not cheap - but we had to pay setup costs for manufacture of a spring which we are only expecting to sell very small numbers of).

For those trying to find more information on this type of breather assembly - you can email us on sales@racingvincent.co.uk.  Something worth noting about this type of assembly - although the actual circular banjo looks like later 'normal' oil fitting banjo's - on this earlier type - it had conical top and bottom faces, with corresponding conical faces on each union - rather than relying on red fibre washes to seal the banjo.  We are looking at having a small number of these banjos cast and machined.

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