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MG MGA - Indicator / Turn Signal - Stuck Bleed Screw


Does anyone have any suggestions on how to free up a very stuck (possibly glued) bleed screw on the back of the turn signal switch.

I've soaked it for day's with WD40 and even tried to heat the screw with a soldering iron.

I'm using so much screwdriver force, it may snap the bakelite.

Thanks in advance.
Mark



Mark Hester

WD40 is mostly mineral spirits, definitely not a penetrating oil, and it most likely would not attack any glue. Try a few drops of lacquer thinner.
Barney Gaylord


Good idea.

Thanks Barney
Mark Hester

Mark, If that boss does snap off as mine had already when I first got the "A", you can use a small tap to make a thread in what's left of the plastic. (I used 6BA) Screw in a screw with a nut as a lock nut and instant vacuum adjuster to time the 20 second indication.
You could perhaps try soaking your screw in a silicone oil/aerosol... That bakelite should be pretty immune to most solvents.
Pete
P N Tipping

If the bleed screw is steel you may be able to take advantage of the difference in expansion coefficients. Bakelite expands two or three times more than steel so heating the whole thing up to, say, around 100 deg. might loosen it.

If the screw is brass, which it appears to be from the picture, this may not work as bakelite expands only a bit more than brass.

I suppose a last resort would be to drill out the screw but doing this would almost certainly damage the bakelite.

As a penultimate resort and if the screw is brass, I would try dissolving it away with dilute (50%) nitric acid (if you do try this do it outside!) but unless you know a chemist then getting hold of the acid will be nigh on impossible...............Mike
m.j. moore


Unlike the photo off the Internet mine appears to have a steel screw.

Placing it in the oven may work but may also crack it or make it brittle would it not?

Thanks
Mark
Mark Hester


Put it in the oven for 15 mins my lazer temp gun said 76 degrees C but still can't unscrew it.

Looking for acetone nail polish remover now.

Mark
Mark Hester



Acetone did nothing to aid removal of the bleed screw

Reading up on Bakelite it appears 120 Degrees C is OK.
Should I be trying to get it hotter to loosen the grip on the screw?

http://en.wikipedia.org/wiki/Bakelite

I've really put alot of force onto the screwdriver and surprised it's not snapped the boss.

Barney ?

Thanks
Mark

Mark Hester

Isn't there a rubber bellows inside these units? If so I don't think heat is a good idea.
Max Irvine



I've removed all those internal parts.



Mark Hester

No rubber, just a leather washer.
Art Pearse

Assuming you can increase the temperature by about 100 deg C and that the diameter of the screw is 3/16" then the relative increase in the hole diameter will be a bit less than half a thou. This doesn't seem enough to me. However have one last go with your oven at 150 deg. and perhaps pre-cool your screwdriver in the deep freeze for half an hour.

If this doesn't work and you've tried everything else then perhaps dissolving the screw could be your last best bet.

If you can't get hold of nitric acid then hydrochloric or sulphuric (battery acid) might work given time. As long as you don't go to the highest strengths the acid shouldn't attack the bakelite. You'll then have the problem of finding a replacement screw!....................Mike
m.j. moore



Thanks Mike.

But what is the temprature I should not exceed on the oven with bakelite ?

This Wiki pages does not state the melting point.

half a thou is not much but you never know till you try... Yes I will also put the screwdriver into the freezer. Good tip.. thanks

Have a good weekend

Mark

Mark Hester

Mark:

Ultrasound might be a better bet.

Alex
Alexander R

Try a high power soldering iron applied to the screw
dominic clancy

Mark,

Soak it in a mixture of 50% automatic transmission fluid and 50% acetone for a couple of hours - or even overnight - that works wonders on rusted bolts/nuts and no reason it shouldn't be able to seep between the bolt and the bakelite.

Gene
Gene Gillam

Bakelite is not a thermoplastic. it will not melt. It will char but at a much higher temperature than you will be at.

You might try some freeze mist directly on the screw alone. It might shrink the screw. Thermal shock of the freee mist might help too. Start directly from the warm oven.
Chuck Schaefer




Perfect, got the Bakelite body up to 133 degrees C in the oven, so says my laser thermo gun and screw driver in the freezer.

Screw was very rusty when fully out.

Many many thanks to all.

Cheers
Mark

Mark Hester

Sorry for my ignorance...I am familiar with the screw, but what does it actually do?
Edward
Edward Wesson 52TD

Ed, there is a bleed hole which the tip of the screw regulates to adjust the pneumatic timing of the return.
Art Pearse

Ed:

At the innermost end of the regulating screw, there is a small cotton "pill" which acts in the manner of a valve for the air displaced by movement of the cup on the switch shaft. If the pill is missing, regulation of the timing will be too coarse - if it works at all.

Alex
Alexander R

So, tighten to make it slower, and loosen to make it faster?
Edward
Edward Wesson 52TD

Edward:

That's the theory. Original regulating screw had a shouldered inner end, which prevented it being done up too tight. Check for this with care, as the cotton pill can pull out along with the screw.

Internally the leather vacuum cup needs to be in good order; best kept conditioned by washing with a paste of saddle soap and then re-oiling with neats' foot oil. Hope you find a good working unit.

Alex
Alexander R

Has anyone "successfully" tried replacing the leather with a piece of inner tube rubber (more available to me than a piece of leather)?
Gene Gillam

I looked into these leather cup washers some years ago and got the impression that getting hold of one would not be too difficult.
Sizes are:-

Lucas direction indicator - 1.375 x 1/4"
Sutty tyre pump - 1.125 x 3/8"

Have a look at Ebay item 250864087551 if you know four other people wanting one !

There are also sites which tell you how to make them.

In the end I didn't need one because my old washer responded to a bit of caressing with vaseline and engine oil and is still working a couple of years later......................Mike
m.j. moore



I've found over the years you done need to replace the leather. Just place a spacer behind it.
I used a tooth paste tube foil / plastic
You can cut a strip and fit it up to the ridge.

Under the bleed screw is a tiny filter

Barney has a page on changing the leather plunger.

Thanks
Mark
Mark Hester

This thread was discussed between 20/06/2013 and 24/06/2013

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