SOHC Pressure Release Adjusting Screw and Locknut (Price is per pair)

Product no.: 0243 A11/42+43

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This is the oil pressure adjuster (and locknut)  that sits behind the inner timing case and controls the oil pressure to the entire lubricaton system on SOHC engines. 

We CNC manufacture these adjuster bolts to be identical to an original Norton SOHC adjuster bolt, but ours are made from stainless steel, and come supplied with the correct 'half nut' locknut.  The hex head is the correct Imperial spanner size - and is now very difficult to obtain - so we mill both the hex and screwdriver slot to ensure it is correct (which is why this adjuster is more expensive than standard bolts - this requiring 3 seperate operations).  They are also quite pretty and do not rust.

Price is for the special adjuster bolt, and correct Imperial Half Nut (do not try and fit a full nut)

SOHC Oil Pressure Adjuster Fitting and Operation:

As can be seen from the photographs, this special little bolt has an extending shaft that presses against a small ball bearing, which itself seats againt one of the oil ways, with a spring placed along the shaft of the bolt and pressing against the ball.  If the bolt was screwed in to its fullest amount - the tip of the shaft would push the ball bearing against its seat in the crankcase, stopping any 'bypass' of oil from the main feed circulation oilway, and therefore providing the maximum oil pressure.  But in normal use - this bolt is normally screwed back slightly (i.e. anti-clockwise) from from 'fully home', allowing the small ball (our Item 0244) to push against the spring (our Item 0245) and allow the ball to rise of the seat in the crankcase against the pressure of the spring, until it comes into contact with the ball and allowing oil to escape through a 'bypass loop', thus reducing the overall engine oil pressure.

Turning the screw anticlockwise (and then locking it with the special 'half nut') by different amounts will both allow the ball to raise off its seat by a greater amount, but will also reduce the spring pressure against the ball.

In the definitive 1950's Workshop guide called 'Norton Motor Cycles', by Edgar Franks - Technical Manager for Norton Motors in the 1940's/50/s, he recommends screwing the bolt fully home first (to ensure it is locking the ball to the seat), then turn it anti-clockwise two and a half to three turns back from fully home for normal operation.  

When stripping your engine down (providing it is functioning as normal) you should take a note how many turns from fully in this screw is set - so you can replace it in the same position.  If building an engine for the first time - first, ensure the ball bearing is seating correctly in the crankcase, then place spring on shaft and screw in this adjuster first - without half nut finished - so you can ensure it does fully lock the ball down, before it runs out of thread (just in case your crankcase has got a different depth to the ball seat from the 'standard' depth that this screw adjuster is deisgned for.  Once happy it is fully locking the ball to the seat, you can remove - fit the half nut, then lock down again, then screw outwards (i.e. anit-clockwise) until you are comfortable you have your initial starting position for running the engine.

It should be noted that Edgar Franks also highlights this area of the engine (with the ball seating in a taper within the crankcase hole) as one of the areas of the engine that can cause 'wet sumping' on these SOHC engines (along with wear to the oil pump gears being another major culprit), if the ball behind this bolt is not seating properly, or if dirt is trapped behind the ball.  Therefore he suggests, taking the ball out to check and clean periodically - and when placing the ball back in the crankcase, and it is on its seat - giving the ball a sharp blow with a (soft punch) and hammer - to help the ball seat properly. 

We CNC manufacture these adjuster bolts to be identical to an original Norton SOHC adjuster bolt, but are made from stainless steel, and come supplied with the correct 'half nut' locknut.

Note: We sell both the correct ball and spring seperately - Items 0244 and 0245.


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