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MG MG Y Type - Engine timing for XPAG

Can anyone let me know what the ignition timing is best set at for the XPAG engine (in the Y type) given modern fuel characteristics. Can I set it with just a simple xenon/neon timing light and do I need an RPM meter? Any advice welcome and what other checks do I make first before doing it? A simple how to guide would be welcome and how often one needs to do it. Saves getting a garage to do it and after all these years about time I had a go!
D MULLEN

It is generally agreed that the XPAG on modern fuel can be given a few degrees pre-ignition, instead of the recommended zero degrees static.

How much however depends on your engine. Compression, camshaft profile and condition of the distributor itself are unique to any individual engine.

Take out a tape measure, measure the circumfence of the camshaftpully, divide the measurement by 360. You then have a guide how much per degree you have to turn the engine.

I would time any XPAG at about 4 degrees before TDC (static). Don't overdo it however because too early timing destroys engines with the high-speed knocking which you won't hear.
Willem vd Veer

David,
Willem is spot on - there is only one correct setting for your engine - mine is 10 degrees before TDC => but this is only after the distributor was re-built and re-mapped for modern fuel.

If you just start advancing, you could do damage, so absolutely no more tha 5 degrees without having the dizzy re-built.

As the original dizzy's wear over time, they tend to over advance right through the rev range which can be dangerous. Considering the importance of what the distributor does in an engine - it should be the first component done in an engine re-build.

Modern fuels burn slower that 1950 fuel, but have more bang, so you want to be sure all the combustion is done before the piston starts rising on the exhaust stroke !. That's why it needs a bit of advance, to give the piston a good push all the way down.

The best way to time is at static - even at idle speeds, the XPAG distributor has started to advance.

Cheers - Tony
A L SLATTERY

Re-reading my post I see that I advise to measure the (non-existent) CAMshaftpully.

What I meant was the CRANKshaftpully.....
Willem vd Veer

I had the distributor rebuilt last year - what a revelation in starting the car....runs well too so I thought I would check the timing after fitting it. Static timing it is - thanks. If this seems a daft question forgive my ignorance but how do I go about the static timing on the XPAG - weird that I have done just about every other job on my Y type but never this!
D MULLEN

Static means that the engine is not running.

Assuming you have these, the adjusting of timing should be covered in the Workshop Manual and maybe even the Drivers' Handbook.

If not it roughly goes like this:
First you adjust the point gap to the recommended gap.

Then you adjust the timing. Factory recommended timing is 0 degrees, which you achieve by putting the cylinder no.1 in TDC, at which point the notch in the crankshaftpully should align with the pointer on the distribution cover.

With No.1 at TDC you then turn the distributor so that the points just start to open. You can do this by eye, but it's better to use a lamp that goes off when the points open or a cigarette paper between the points that is released when the points open.

To achieve 4 or 5 degrees advanced timing (which is a better term then the pre-ignition that I used earlier) read my earlier post and see if you know what I meant. If not, please ask again.
Willem vd Veer

Many thanks Willem and Tony - I will have a go at this at the weekend and also refer to the manual. When you look at the crankshaft pulley from the front of the car (ie by the radiator) BTDC (ie before TDC)refers to a position just to the left of the notch on the crankshaft pulley. I can work out the distance OK but just checking its to the left when viewed from the front of the car.
D MULLEN

At the bottom of this page you will find all you need to know:
http://www.chicagolandmgclub.com/techtips/mgt/tune_up1.html

An excerpt:
Adjusting the Static Advance To 5º or 10º Before TDC

The diameter of the crank pulley is 95mm or 3.74 inches.
Multiply that by the magic Greek pi (? = 3.1416) and you get 11.75 inches, the circumference of the pulley.
5º is 1/72 of 360 degrees.
11.75 : 72 = 0.163 inches.

Standing in front of the engine and facing aft, make a mark on the pulley 0.163 inches to the right of the original timing mark. Use a file or mark with paint.

The distance is roughly equal to the height of three stacked dimes.
Making the mark to the right of the original TDC mark advances the timing.
Readjust (statically) the timing to the new mark.
Double the distance for 10º advance.
Willem vd Veer

Many thanks Willem!
D MULLEN

Bear in mind (when you are setting an engine up after a rebuild especially) TDC occurs twice per engine revolution but only once for TDC on cylinder #1.

Paul
Paul Barrow

I think Paul meant to say "twice per four stroke cycle", (as TDC occurs with every revolution), but the TDC we are looking for is the TDC at the start of the combustion stroke - both valves closed & piston going down !.

Follow Willem's detailed post - clear & concise, you can't go wrong there.

cheers

Tony
A L SLATTERY

This thread was discussed between 28/10/2012 and 01/11/2012

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