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MG MGA - Setting timing with a vacuum gauge

Working on my friends TR has introduced me to the concept of setting the timing advance using a vacuum gauge.

Its pretty easy because there are a number of vacuum fittings on the TR manifold.

Has anybody ever tried this on a MGA using the vacuum fitting for the distributor advance?
T McCarthy

The vacuum used for this procedure must be manifold vacuum. I believe that the vacuum advance port on the MGA is the same as on the early MGBs, a ported vacuum on the carburetor and will not work for timing purposes. I seem to remember that there is at least one hole in the MGA intake manifold that is plugged with a bolt, where a barbed vacuum fitting could be installed to do the timing. The barbed fitting could then be capped or removed and the original bolt reinstalled. Cheers - Dave
David DuBois

I drilled my balance pipe midway between the carbs and installed a fitting with a cap. This allows easy measurement of manifold vacuuum. That said, I've never considered vacuum reading to be an accurate method of timeing, only a trouble shooting tool. Too many other variables I think. I could be wrong....

GTF
G T Foster

Tysen - This is a technique that interests me - tell me more.
dominic clancy

All you are doing is determining the maximum idle speed, hence highest vacuum produced for a given throttle opening. Not a good way to set timing (or mixture, which is also done this way); it will wind up too far (sometimes a LOT) advanced (or too lean) but useful for diagnostics.

FRM
FR Millmore

Dominic,

Here's a good description.

http://automotivemileposts.com/garage/v2n8.html
T McCarthy

Tysen -
Please don't believe this Malarkey.

"Timing chains can slip over the years,"
***Very unlikely, and if they do then the engine either quits completely, or will do so soon, possibly doing severe damage.
Timing chains do wear, causing late cam and spark timing. Fix it, since that also can do damage and certainly kills performance and mileage.

"harmonic balancers can move,"
***A balancer that has moved is a fragmentation grenade ready to go off. Fix it!


" and the bottom line is you are no longer able to verify where top dead center is using the old methods."
***Certainly not at this guy's competence level. The rest of us can, or have enough sense to find out how from someone who does.

"Plus, with today's fuels, it's more difficult to reach the point where your old engine performs both efficiently and reliably without sacrificing performance. Following the steps below, you will be able to minimize pinging, have reliable starting under all conditions, and easily get maximum performance from your engine using today's fuels."
*** Yeah and pigs fly with a carburettor that uses a cup of gas per thousand miles, Shut up!

The rest of it is not bad as a general description of how to approximately to set up the engine to get your 1928 Whatzit out of the Arizona desert after replacing the rod bearings with pieces of your boot sole, Mr Joad. I can do as well or better by just eyeballing the thing

" Your engine is now optimally timed to run on today's lower octane, no lead fuels."
**** NO, 'tain't!

FRM
FR Millmore

As above. I have been in the motor trade as a mechanic and automotive instructor since 1953 and it was an old wives tale then. Denis
Denis4

This thread was discussed between 21/09/2009 and 22/09/2009

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