Vacuum/Economy Gauge Piping

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Monty-4
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Vacuum/Economy Gauge Piping

Postby Monty-4 » Wed Feb 21, 2018 12:15 pm

I'm a sucker for old gadgets such as these and this one was both shiny and colourful, I had to buy it! So now I've got to connect it.

My engine is currently running twin HS2s on a old style manifold (AUE1020). The vacuum advance connection on the carb is the type that is really close behind the carb butterfly so doesn't give a reading at idle, but does once the throttle is opened just a little. As such I don't think the gauge would really work properly if I just add a t-piece in there somewhere. What does the forum's collective mind think would be the best way to rearrange or add to this for the gauge? Once aspect I've been wondering about is whether it would be best to pull the vacuum 'signal' from both carbs for the vacuum advance and the gauge.

So how about I;

1. Add a take-off on the manifold (no idea what the thread is though) or a single manifold spacer with a take-off and run straight to gauge (don't touch the vacuum advance connection).
2. Add two manifold spacers with take-offs to cover both carbs and join with a T-piece (don't touch the vacuum advance connection).
3. Switch the vacuum advance pipe to the manifold or a spacer (or two) and add a T-piece for the gauge closer to the dizzy.
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philthehill
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Re: Vacuum/Economy Gauge Piping

Postby philthehill » Wed Feb 21, 2018 12:34 pm

Just fit a vacuum take off into the manifold using one of the blanked holes.
The large plug thread should be 5/8" UNF.
If you have the smaller blanking plug(s) fitted post the dia on here and I will give you the thread.
BMC did make an 5/8" UNF adapter to enable the vacuum to run vacuum operated windscreen washers on the MGA.
If I can find the adapter I will post a picture.


Monty-4
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Re: Vacuum/Economy Gauge Piping

Postby Monty-4 » Wed Feb 21, 2018 2:39 pm

The blank that secures the vacuum flame trap looks like the best candidate, others are taken by the PCV valve and the throttle cable bracket. Looks like a coarse thread to me, UNC? BSF? BSP? 1/4 or 5/16... something. :)
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philthehill
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Re: Vacuum/Economy Gauge Piping

Postby philthehill » Wed Feb 21, 2018 5:29 pm

Thanks for posting

What you have described and what you have shown in measurement (0.3125 Dec) leads me to believe that the thread is 5/16" x 18 TPI UNC.

The threads in a BMC manifold are normally either UNF or UNC.

Is that hole blind or does it go right through into the inlet manifold tract?
Phil


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Re: Vacuum/Economy Gauge Piping

Postby Monty-4 » Wed Feb 21, 2018 6:09 pm

Straight through into the tract. :)
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philthehill
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Re: Vacuum/Economy Gauge Piping

Postby philthehill » Wed Feb 21, 2018 6:13 pm

Thank you for the detail.
If that is the case I would relocate the flame trap and use the drilling to fit an adapter.


SteveClem
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Re: Vacuum/Economy Gauge Piping

Postby SteveClem » Wed Feb 21, 2018 8:13 pm

I can almost see why you want one :lol:

philthehill
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Re: Vacuum/Economy Gauge Piping

Postby philthehill » Wed Feb 21, 2018 11:19 pm

Can also be used as a good indicator of driving efficiency.


Monty-4
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Re: Vacuum/Economy Gauge Piping

Postby Monty-4 » Thu Feb 22, 2018 10:52 am

Any ideas where I could find a 5/16 UNC (to 1/4" or 1/8" pipe) hose tail? They all appear to be BSP!
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philthehill
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Re: Vacuum/Economy Gauge Piping

Postby philthehill » Thu Feb 22, 2018 12:45 pm

If you cannot find one make your own.
Centre drill a 5/16" UNC bolt and solder or braze a piece of brake pipe into the hole. A piece of old brake pipe with the nipple on the end would be ideal.
Before doing anything confirm that the existing hole is 5/16" UNC.

The normal vacuum take off union for the servo is also shown below. The thread is 5/8" x 18 TPI UNF.

The bottom photo is the vacuum take off fitted to a MGA inlet manifold to provide a vacuum source for the windscreen washers.
The thread is 5/8" x 16 TPI UNS.

Both of these vacuum take off unions would normally be fitted into the unused bosses of the twin carb manifold shown above
Phil
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Monty-4
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Re: Vacuum/Economy Gauge Piping

Postby Monty-4 » Tue Apr 03, 2018 10:49 am

Thanks again for the help and advice - here is a wobbly video taken by my passenger today. I think I'm saving fuel already trying to get the gauge to show as high as possible!

https://youtu.be/KXcjanrie5U
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Re: Vacuum/Economy Gauge Piping

Postby pgp001 » Tue Apr 03, 2018 1:09 pm

Hi Monty

Can I ask you to give us some details of how you made and fixed the new dash panel into place please.
I am just at the point of doing exactly the same thing myself.

Thanks
Phil

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Re: Vacuum/Economy Gauge Piping

Postby Monty-4 » Tue Apr 03, 2018 1:53 pm

Sure thing. Not an expert job but here were the steps:

1 - Made a paper template of the shape of the glove box arround opening, plus 3-4mm, with circles for planned gauges, and stuck it to cheap 1mm steel sheet.
2 - Cut steel to shape and used circle cutter for holes, filed burr off edges.
3 - Stuck veneer (smoked sapele) on with basic wood glue, cut holes with scalpel.
4 - Teak/reddish stain, followed by clear varnish.
5 - Bonded panel to back of glove box surround with Araldite, sealed a couple places where it lifted with Sugru (the back is not entirely flat, a more flexible metal such as aluminium would have been far easier).
6 - Gauges are held in by interference and the normal clamps.

Good luck. :)
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philthehill
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Re: Vacuum/Economy Gauge Piping

Postby philthehill » Tue Apr 03, 2018 3:05 pm

Well done and thanks for the video.
A description and a photo of the fittings to the manifold would be appreciated.
Phil


Monty-4
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Re: Vacuum/Economy Gauge Piping

Postby Monty-4 » Thu Apr 05, 2018 1:15 pm

I'm embarrassed to say I 'cheated' - lacking a pillar drill and my normal drill being knackered I didn't think trying to bore out a bolt would be fun.

Instead I dug out a spare carb spacer and fit it with a tail for hose of approx 4mm ID (5/32"?), the same as the tail on the back of the gauge. After doing this I realised I didn't have a long enough length of hose to reach friom the manifold to the gauge panel (using offcuts of braided fuel hose from another job), so have two reducers and a length of 3mm (1/8") hose between them, nipped up with jubilee clips as it leaked vacuum without them. The slimmer hose and reducers will likely stay in place indefinitely as it helps it squeeze into the existing hole in the bulkhead that carries the wiring loom.
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Last edited by Monty-4 on Thu Apr 05, 2018 10:05 pm, edited 1 time in total.
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philthehill
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Re: Vacuum/Economy Gauge Piping

Postby philthehill » Thu Apr 05, 2018 7:14 pm

Monty-4
Thank you for the post above.

As you have twin carbs did you put the same or similar thickness spacer between the other carb and manifold so as to keep the carb linkage parallel with the manifold?

Also where does the pipe to the PCV valve come from?
Phil


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Re: Vacuum/Economy Gauge Piping

Postby Monty-4 » Thu Apr 05, 2018 9:53 pm

I did indeed put a matching spacer on the other side so the carbs are equally spaced, getting them back on with the linkages not falling through the engine bay is always heaps of fun. :roll:

The pipe from the PCV valve routes under the airboxes to a tappet breather canister (from a Mini I think) stuffed with stainless steel dish scrubbers.
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oliver90owner
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Re: Vacuum/Economy Gauge Piping

Postby oliver90owner » Thu Apr 05, 2018 10:33 pm

... as it leaked vacuum without them ...

Can’t help but be pedantic on this! I have never ever experienced a vacuum leaking anywhere. First there would be nothing to leak and secondly it would (usually) be air that was leaking through any orifices into the lower pressure area. :D

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Re: Vacuum/Economy Gauge Piping

Postby philthehill » Fri Apr 06, 2018 12:45 pm

Monty-4
Thank you for the pictures and description.

An observation:-
The flame trap in the vacuum advance pipe should be vertical so as to stop any unburnt fuel getting into the distributer and being ignited when the points open. Being vertical also stops the diaphragm in the vacuum advance unit from being contaminated by petrol.
Phil


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Re: Vacuum/Economy Gauge Piping

Postby Monty-4 » Fri Apr 06, 2018 1:17 pm

That makes sense regarding the flame trap, thanks for the tip Phil. I well get on that as I'm running an "electronic" dizzy currently but will be switching back to trusty old points when the original 25D comes back from having it's timing curve changed and a general refurbishment.

oliver90owner, I'll have to let m'lady know that I've met my match when it comes to pedantry, she'll be quite surprised to hear it!
68' 4-door Saloon, another 'Monty'.


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