[TR] [EXTERNAL] Small coolant leak - blueing the tapered surfaces

[Reihing, Randall S.]

My restored 1948 C85 Taylorcraft has a wing tank pet cock in the cockpit on the passgenr side under the panel. Recently, it started a very slow seep. An occasional drop but not quite a steady drip. The valve is a petcock that rotates 90 degree from full off to full on. It has a tapered bore and tapered stem. The fix was to remove and disasseble the valve, apply the finner grade of Clover Valve Grinding compound followed by Clover Lapping Compound. Prussian Blue was used to verify the two surfaces now perfectly matched. The vlave was reassembled and no longer leaks, even with 6 gallons of AV gas above it.

Sincerey,
Randall Reihing
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From: Triumphs <triumphs-bounces at autox.team.net> on behalf of aribert neumann <aribertn at gmail.com>
Sent: Wednesday, September 16, 2020 9:59 PM
To: triumphs at autox.team.net <triumphs at autox.team.net>
Subject: [EXTERNAL] [TR] Small coolant leak - blueing the tapered surfaces

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From: Michael Marr <mmarr at albiontechnical.com<mailto:mmarr at albiontechnical.com>>
To: Jeff Scarbrough <fishplate at gmail.com<mailto:fishplate at gmail.com>>
Cc: David Friedlander <forzion7 at gmail.com<mailto:forzion7 at gmail.com>>, TR3 Triumphs <triumphs at autox.team.net<mailto:triumphs at autox.team.net>>, New England Triumphs <net at newenglandtriumphs.org<mailto:net at newenglandtriumphs.org>>
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Date: Tue, 15 Sep 2020 21:46:56 +0000
Subject: Re: [TR] Small coolant leak
The drain “valve” is actually a petcock. It doesn’t have a gate and seat, as such.  The best fix is to relap the plug to the body, using valve grinding compound.
Mike


There is a product called Prussian Blue.  Here is a link to one mfg of it (not the only one) :   https://www.permatex.com/products/specialized-maintenance-repair/rebuilders-aids/permatex-prussian-blue/<https://urldefense.com/v3/__https://www.permatex.com/products/specialized-maintenance-repair/rebuilders-aids/permatex-prussian-blue/__;!!LoBwcKfm!1RXucXzoCkVKqGafAKDtvc3yQPgJ__WX-6aY8mEpm7cUqWmH0XXmsiU-g0XKUZlgjepx5yw$>  Should be available at any large industrial supply or machining supply type of store.

I bought a 1/2 or 1 oz tube about 25 yrs ago - still have 90% of it and use it maybe one or twice a year.  This stuff is nasty, it is infinitely divisible, it will get all over your hands and clothing if you are not careful.  I store my small tube in a zip lock bag and frequently I'll only get a rubbing of blue off of the **outside** of the tube (previous sloppy handling, hence the zip lock bag).  Put an extremely thin film (almost translucent) on one of the two mating parts, asm and rotate a few times.  The high spot(s) should transfer over to the mating part.  Now you know how bad the mating parts are with respect to one another.  Lap the parts as mentioned above.  Redo the bluing to check the match.  Once the entire surface around the water port on the cone/socket is showing faint traces of blue, you are done lapping.  You now have a new skill and someone in the future, at your estate sale, will have a royal mess on their hands when they open the tube to find out what it is.
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