New replacement thermal bulb for AAV available

(John) #41

Teflon lube will be the first to try :wink:

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #42

Will a lube stay put?

(John) #43

No it will not last forever but I think it will be better then liquid lubricants in this aplication. Anyway any lube or coating will weal out eventually. Idea behind stainless steel piston is that it will have less friction then original aluminium piston to start with.
Aluminium to aluminium sliding friction coefficient is ~ 1,4 while aluminium to stainless steel is only ~0,5

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #44

The lower friction is good, but the big issue is probably galling. Aluminum to aluminum will gall something awful. I don’t know about SS to aluminum. Is there any way you could press a brass sleeve into the cylinder? Polish up the outside of the SS piston, and it should slide smoothly forever.

Alternatively, you could apply the same sort of teflon treatment used on piston skirts in Nikasil engines. I think the things might even be a peel-and-stick thing, I dunno. If so, you could get some from a Chevy and just cut out pieces to wrap around that little AAV piston. Of course, you’d need to machine the piston a bit smaller to allow for the thickness of the teflon.

(John) #45

I think nikasil coating is electroplated

(John) #46

I think it is possible but first I will polish the piston and see how it works with aluminium body. I bet it will be much better then original.

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #47

The nikasil coating to the cylinder is plated or something. I’m talking about what’s done to the pistons, which involves a patch of teflon on each side of the skirt. It’s apparently what keeps the skirt from galling the nikasil liner.

Here’s a pic of a piston with the skirt treatment, in this case in a pattern with the manufacturer’s logo!

(Aristides Balanos) #48

What if one press fitted a machined Teflon sleeve to the piston, or even did the piston entirely out of Teflon ? Just a thought…
Don’t know how the heat would effect it though.

I made a bearing for my Record Player, high polished Stainless Steel axle on a Brass bearing with a Teflon sleeve insert.
It worked very well, has Zero Tolerances, Zero Noise (very important) and almost Zero Friction.

Nevertheless, when I rebuilt my Auxiliary Air Valve I’ve just sanded and polished the aluminium piston to give it some more clearance and it works fine 13 years since…!


(Dr.Quail/ Jon Wallace) #49

Thermal bulbs is not as much of a problem as the “oily sh…that builds up in the cylinder walls….I always hone both the piston and sleeve…if you really want to do something important, make new pistons from Delrin or? so they don’t gall
and hang up. Best, JW

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