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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Vacuum advance pipe fuel separator bulb

Here's a bit of an anorak question for some well informed person. Is there anything clever or scientific about the fuel separator bulb in a vacuum advance pipe? ie. is it simply, as described in Barney's words, a cavity filled with wire wool, or does it have a one way valve or other "things" inside it. I have a new one from Moss Uk and it just seems bunged up to me, or there again there might be more to it than that!
Bruce
Bruce Mayo

Bunged up? You mean it won't pass air?
Must check mine, still in the box.
Art Pearse

Sorry Art, yes, should have been more specific. Indeed, it resists passage of air in either direction, hence my wondering if it there is something a bit cleverer in the fuel separator bulb than I had originally thought.
Bruce
Bruce Mayo

Should be free flow in both directions, although fairly slow flow with the small tubing.
Barney Gaylord

Thanks Barney. So this one is going back to Moss. I suspect it might be blocked where the pipe is braced to one end of the fuel separator bulb. Perhaps a bit of flux or braze in the wrong place.
Bruce
Bruce Mayo

Add it to the faulty part list, Barney?
Peter.
P. Tilbury

Bruce,

Is the vacuum advance pipe intended for your Twin Cam?
The Twin Cam had a modification to remove the vacuum advance completely.
Are you intending to fit ant-vibration "soft mounts" to the SU's and then refit a vacuum advance?
Current thinking is that SU vibration, not over advanced ignition, caused the piston melting problem.

Mick
M F Anderson

It is way too early to brand this part number as globally faulty. There is no direct reason (yet) to believe all other parts will be similarly bad. It is quite likely a single bad part, which the supplier will toss out and replace with a good one.

It is "interesting" (like a human interest story) when someone publicly reports one bad part, but the only good effect of that action is perhaps for other public domain people to remind the customer of the proper procedure for reporting and returning bad parts. Always report the problem to the supplier first, and see if they provide a suitable resolution.

When the part is returned with a known reason why it is a bad part, it should trigger a sample inspection of parts remaining in inventory. In simplest form it could be a note saying to inspect the very next part before shipping (especially if it is the replacement part). If even one other similarly bad part is found, that should trigger 100% inspection of inventory and disposal of any bad parts. But the world doesn't always work that way.

The supplier might replace the part, then continue shipping parts without inspection. If there are no more customer complaints, the world is happy. This is a statistical returns policy. If very few parts are returned it is assumed to be a good part and sales continue. If there are more customer complaints and more returns of bad parts, that may then trigger an inspection and/or stop on sales of that part number. From the customers' point of view, that sucks, as the supplier is using the customer base as the quality assurance inspection crew, which means some bad parts are guaranteed to get through before the issue can be corrected. That's when "stuff" hits the fan and the supplier gets a justifiably bad rap in public.

What triggers a Faulty Parts web page (on my web site) is a known generic problem with design or construction of the part that will show that all other parts from the same production batch are likely to be similarly faulty. Even then, if the supplier is informed of the problem and immediately stops sales of the parts, the problem is gone (except for parts already sold), and no need for a Faulty Parts web page.

The Faulty Parts web page is a last resort when a supplier refuses to acknowledge a known problem and continues to ship known bad parts.
Barney Gaylord

Barney. Agree completely. I'm not slagging off Moss (yet!). To be fair to them they have listened to my phone call, brought in a technical guy on the phone as well, and concluded that I should return the pipe and they will check it over and replace with another. Where they then go re QA I'm not sure but at this stage of the proceedings it's just possibly a bad part and they are responding OK. Let's see.
Mick. Yes, for the Twin Cam. I keep returning to the simple thought that it's just a pretty normal engine, and, given that the olden day piston burning problems were, I understand, nothing to do with ignition but leaning of the mixture due to vibration at long periods of high revs, my curiousity demands a (very gentle!) trial of the original vacuum advance setup. Anyone else gone down that route to share experience?
Bruce Mayo

Bruce,

You are making the same mistake that BMC made all those years ago.
The problem is not at high RPM and full power, they tried that, with no piston melting.
It relates to to engine vibration. It is worse at about 4500 RPM and little or no load.
It also needs you to have the 9.9 CR pistons.
If your engine was ever changed to 8.3 CR, as with later engines, the problem does not occur. The problem is only being masked.
Only some engine had the problem and they would melt the pistons more than once, even many times.
Most engines never had the problem, including mine.
The balancing of the engines was a bit hit and miss.
With "soft mounted" SU's the refitting of the vacuum advance would probably be OK but I do not know any examples.

Mick
M F Anderson

This thread was discussed between 22/11/2012 and 23/11/2012

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