Aluminum valve stem torque

Does anyone know what is the correct tightening torque for the screw on type aluminum valve stems (part #174166) for 550 and 575 OEM once piece wheels?

I bought new OEM 550 and 575 wheels for my 456 which do not come with the valve stems. So I bought separately and want to install them on the wheels before sending to tire shop.

Being aluminum I don't want to over tighten and risk breaking these valve stems.

So far can only find general info indicating 4Nm (or about 35 inch pounds) for metal screw on valve stems.

 

113 views without any reply so I guess nobody knows the answer. So today I did a bit of reverse engineering and measured the torque necessary to slightly further tighten the existing aluminum valve stem on my 550 wheels.

It took between 5.5Nm to 6Nm, which is about 49 to 53 inch pounds, to break loose the nuts that have been on the original 550 wheel valve stems since 1998. Assuming some stiction from 18 years my best guess is that the valve stem nut torque should be 5Nm or about 44 inch pounds.

This is not too far off from the generic info I found on the internet.

I also found out 550 and 575 one piece OEM wheels use different valve stems.

550 uses valve stem 174166 which is prior to tire pressure sensor days. This requires a 14mm socket for the nut and 16mm socket for the stem base.

575 uses valve stem 185328 which is for tire pressure sensors same as what's on my 599. Valve stem nut uses an 11mm socket. 174166 valve stem will fit inside the 575 wheel recess but there is not enough clearance to put a socket on the 14mm nut so won't work.

As for the 575 modular wheels they use another valve stem part number. Don't know the spec on that one as I don't have modular wheels.

 

John, I have now found specific info. Valve stem 185328 for TPMS equipped 575/599 and others is supposedly designed and manufactured by Alligator Ventilfabrik GmbH for Huf/Beru which supplied them to Ferrari. And the correct torque is 4Nm. Huf part number is RDV001. Huf's improved version of this valve stem is RDV021 which has extra rubber seal on the nut side of the valve stem and with a better design for the small screw that secures the TPMS sensor to the valve stem. I will post this Huf part info on your interchangeable parts thread.

 

Here are photos of valve stem 174166 and 185328. Note the reduced nut size design on 185328 to fit into the smaller valve stem wheel recess diameter of 575 and 599 wheels.
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