Hylomar universal blue failed to seal oil?

If it is still of interest the data sheet/instructions for the 3 grades of Hylomar Universal Blue can be found here.

Martin

Usually the thread is not supposed to provide the seal on such fittings. There will be an o-ring or flat cicular gasket that fits between the screw on ring and the threaded boss on the mill. On some there will be a flat circular gasket on each side of the glass. The thread is purely for retention and to apply pressure on the gasket/s or o'ring. No oil should make it as far as the start of the thread if yours is one of that type

Clean up all parts free for oil with acetone and apply RTV or FIPG silicone gasket and reassembly.

This thread has indicated that while hylomar has been re-formulated in recent years it is still an effective sealant.

As per Hopper’s post, it is amazing the number of times I have come across hydraulic fittings where threads have been sealed instead of fixing the metal contact seals in such as water pipes (olives are deformed to provide the seal - not the threads between fitting and retaining nut). Only tapered threads, with filler/sealant between male and female parts are used in low/medium pressure situations.

Braking systems and even higher pressure hydraulic/pneumatic systems (gas storage bottles at 200Bar, or more, for example) rely on meta/metal seals with no extra sealant. They work perfectly.

This application is one of minimal static pressure. A very few inches water gauge or a few milliBars pressure. Time to draw conclusions as to the source of the failure in this instance, I think. I have.

I assume that the 2BA thread you are referring to is the cap head bolt at the bottom left in your picture. If this assumption is correct the threaded part of the cap head would not be exposed to any oil in the gearbox. If so then the leak past this cap head might well be due to a failure of the gasket between the flat face of the gearbox and the cover allowing oil to seep through to the unthreaded shank of the 2BA screw and show up as a leak around this cap head bolt. It is relatively simple to confirm if the tapped section is blind or open to the inside of the gearbox. Remove the cap head bolt the fill the gearbox with oil, if it runs out then the threaded section is not blind, if no oil appears then leave it for a few hours or longer and check again and if no oil leaks then it is a fair chance that it is a blind hole.

The Hylomar data sheet states, and I quote: "Hylomar Universal Blue can be used to seal joint faces or threaded parts." While the data sheet specifies surface smoothness limitations for the three grades it does not give any gap filling limitations for threaded parts.

Hope this is of some use to you.

Martin

PS

If the threaded portion of the hole is blind then wrapping the threaded sect with PTFE will not be effective.

Edited By Martin W on 24/06/2020 10:38:45

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Very useful, Martin ... Thanks

MichaelG

NEVER ,EVER use the wrong blue Hylomar on a petrol line.

.Unless you like removing blue torpedoes from the line for years to come.

EDIT TO MY PREVIOUS POST

I assume that the 2BA thread you are referring to is the cap head bolt at the bottom left in your picture. If so then I would expect this to screw into a blind hole in the case of the gearbox. If this assumption is correct the threaded part of the cap head would not be exposed to any oil in the gearbox. If so then the leak past this cap head might well be due to a failure of the gasket between the flat face of the gearbox and the cover allowing oil to seep through to the unthreaded shank of the 2BA screw and show up as a leak around this cap head bolt. It is relatively simple to confirm if the tapped section is blind or open to the inside of the gearbox. Remove the cap head bolt the fill the gearbox with oil, if it runs out then the threaded section is not blind, if no oil appears then leave it for a few hours or longer and check again and if no oil leaks then it is a fair chance that it is a blind hole.

The Hylomar data sheet states, and I quote: "Hylomar Universal Blue can be used to seal joint faces or threaded parts." While the data sheet specifies surface smoothness limitations for the three grades it does not give any gap filling limitations for threaded parts.

Hope this is of some use to you.

Martin

PS

If the threaded portion of the hole is blind then wrapping the threaded sect with PTFE will not be effective.

Edited By Martin W on 24/06/2020 10:38:45

Should have included the sentence highlighted in italics.

OOPS Bad day at the office

A quick and dirty way that may fix the leak is to fit either a copper or fibre washer under the head of the bolt having coated all parts with Hylomar and assemble while still wet. If this doesn't work clean up parts and try assembly dry. The advantage is that you already have the Hylomar and if neither option works all you have lost is the cost of a small washer.

Martin