Doesn't Z-Therapy advertise on their website that part of they're
re-manfacturing process is to "match" domes with pizza?
Mike H. 67-1600
----- Original Message -----
From: "Stan Chernoff" <az589@lafn.org>
To: <Keith0alan@aol.com>; <datsun-roadsters@autox.team.net>
Sent: Thursday, July 29, 2004 6:30 PM
Subject: Re: Carb cleaning tip, what not to do
> Keith,
>
> Dean should be able to give a definitive answer on matched pistons and
> domes. He carries Z-Therapy remanufactured complete carburetors for the
> same price as Z-Therapy with an added free gasket bonus. At least he
> should be able to supply the acceptable clearances.
>
> Z-Therapy is one of the recognized authorities on the Hitachi S-U carbs.
>
> Stan
> ===============
> At 06:11 PM 7/29/2004 EDT, Keith0alan@aol.com wrote:
> >Well since I'm a testing kind of guy I decided to experiment a little. I
> >pulled 6 dome/piston pairs from carbs I've recently done. The dome to
piston
> >clearances were all between 1.5 and 3 thousanths of an inch. Pretty tight
> >tolerances. Then I took the springs out and plugged the holes in the
> pistons. Turning
> >them upside down and dropping the pistons in they took between 2 and 6
> seconds
> >to leak down. Not as consistant as I was expecting. Then I tried
> something, I
> >wet the piston edge with silicone spray. One thing you will notice when
you
> >pull your domes is that the piston edge is wet with oil or gas. With the
> piston
> >edges wet the pistons did not leak down at all. One thing I noticed was
the
> >grooves on the outside of the piston. This is a technique used on some
small
> >engines. The grooves hold oil that acts as a piston ring sealing the
space
> >between the piston and wall with very little friction. I dragged out the
> piston and
> >dome tht hat been sandpapered. It took about a second to leak down dry
and
> >about two seconds wet. The piston to dome clearance was about 6
thousanths.
> >
> > I can't say for sure that pistons and domes were matched at the
> >factory but the tolerances are awfully tight. I can say for sure that
this
> piston
> >and dome were ruined by being sanded.
> >
> >keith williams
>
> >
> > I heard that they were matched sets, but you know how rumor and inuendo
> go. The other interesting point here would be how many times these parts
> have been taken off the cars over the past 30 years and cleaned in a
> solvent tank and the parts switched by unknowing mechanics and put back
> incorrectly no longer preserving the "matched set".
> >
> >Dean
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