Setting up vacuum advance on distributor

[minormarc]

Hi everyone.
Whilst taking the engine out of my ’69 Minor to repaint it, I noticed whilst cleaning the outside of the distributor that the vacuum advance pipe allowed me to suck and blow quite happily through it meaning that the diaphragm inside the unit is probably not working. It’s as if I was blowing through a toilet roll tube, like one does!
I’ve ordered up a new vacuum advance unit and am happy to swap it over but is there an easy way to set it up or is it very complicated? I have read on the internet about hooking up vacuum gauges, driving round noting the readings etc., increasing idle speeds and noting readings and then subtracting one from the other….. which all sounds like a lot of faff. I was hoping to attach the new advance unit and wind the advance adjuster up until it just starts to move the plate inside the distributor and then backing it off a fraction. Then I was going to take the car for a drive once the engine is back in place (of course) and see how it went and making any adjustments I need.
Am I being hopelessly optimistic? No doubt I probably am. Any advice would be gratefully received.
Thanks all.

[philthehill]

Measure the protrusion of the vacuum advance screw beyond the nut - make a note of that measurement - remove old vacuum advance - fit new vacuum advance - adjust the protrusion of the vacuum advance screw so as to replicate the old setting - jobs done.
May require slight adjustment either way after road testing.
There is a spring clip that stops the adjustment screw rotating - make sure that you do not loose it and refit it when fitting the adjusting nut.
Good luck.

[minormarc]

Hi Phil. Ahh. The old unit is already off and I didn't take any measurement. I'm also thinking that the previous maintainer of the car may not have known how to adjust it properly and so it may be an idea to start from scratch, although I take your point and recording the protrusion would probably have been a good starting point.

I did notice that clip and spring and have them securely in a sealed bag and I do have an idea of where the adjuster wheel was before I removed it (I photographed everything before removal). The plate was also loosely stuck because nothing moved until I carefully probed it with a screwdriver which may mean the wheel was adjusted willy-nilly and wasn't actually doing anything, hence my reason for starting from scratch, if that makes sense.

Unless there are any other good ideas, I may set it up as closely as possible to where it was and go from there. Thanks for the quick reply.

[philthehill]

It is always a very good idea to take photos of the status quo before dismantling anything.
The photos will be a very helpful reference when reassembling the distributer or any other parts.
I use the 'I' pad camera all the time for the purposes of reference.
When I took the head off my 16 valve Suzuki which has variable inlet valve timing I took photos of everything and marked the valve drive train with indelible marker pen before dismantling. Made the job so much easier.

[minormarc]

Hi Phil

Yes I agree with you. In actual fact, the rusty mark and the darker mark where the wheel sat for years on the screw thread is a bit of a give away as well, so I'll not clean it before reassembly otherwise those tell-tale signs will be gone.

The iPad does take a good shot and there's many a time when the photos have saved me especially when replacing the oil seals on the BMW VVT. I must admit to 'clenching' when I started that up for the first time afterwards.

I have posted on here before about the repainting of the engine (gold seal) so I'll pop some pictures of the finished job when it's done. It's getting new a new timing chain set including the gears as well as sump gasket (including the crankshaft seals), new heater hoses, thermostat, radiator hoses etc. Should look good and go well when finished.

Thanks for your help and advice.

[stuffedpike20]

How do you set the vacuum advance unit if you do not have any reference points, such as a rusty mark?
Thanks, John.

[philthehill]

You make sure that you have the reference point (which can be either a visual or measured point) what ever that may be before you dismantle.

[JOWETTJAVELIN]

There should be a graduated scale on the vacuum advance, each segment of which equates to a few degrees of timing adjustment. Set it to the large line on the scale, which is in the middle of the range and start from there. Any large variation in ignition timing has to be achieved by moving the distributor itself, slackening the clamp. I do this first, with the engine hot and running, and advance it until the engine note sounds harsher and rougher, then back off a bit until it smooths out again. That is when you finish off by using the micro adjuster, but you might find it's alright as it is.

[liammonty]

You make sure that you have the reference point (which can be either a visual or measured point) what ever that may be before you dismantle.

If it's impossible without a reference point, surely setting up the first one ever was impossible, with nothing before it

Surely a rough setting can be reached by measuring advance from tickover at very light throttle openings, to get near the correct setting? There are specifications for degrees of vacuum advance, are there not?

[minormarc]

Thanks everyone for your help.

I would have thought though that being that the vacuum unit is supposed to advance the timing, there is little point setting it up in the middle of the range because why would you want to retard the timing using the screw? If the initial timing has been set correctly at idle by twisting the distributor with the vacuum capped off, you should from there only ever want to increase the timing or am I wrong? Or is it that by turning the screw the other way you are delaying the advance of the timing?

I'll try the tried and tested Morris Minor method of using the rusty mark and see how it drives. I am surprised, along with Liammonty that there doesn't seem to be a proper procedure written anywhere being that the diaphragms on the 50 year old distributors don't last forever.

[liammonty]

I think that the purpose of setting the unit 'midway' as per JOWETTJAVELIN's comment (which is exactly as per the Workshop Manual) is to allow scope for either retarding or advancing the timing to compensate for differences in fuel grade or quality in years gone by - it meant 'minor' adjustments could be made at the roadside without the need to have a spanner handy to loosen the distributor clamp. You're right though, insofar that doing so would essentially reduce the amount of vacuum advance available. I really wouldn't worry about it - do as JOWETTJAVELIN suggests and set halfway, or throw caution to the wind and set it to allow maximum vacuum advance. then adjust the timing by adjusting distributor position. In my experience, I've never had an issue with too much vacuum advance - as it only occurs at part-throttle, and not under full load with wide open throttle, it's never led to pinking on my cars. When that's happened, it's always been due to too much centrifugal advance.

I think that sometimes we worry too much about these things. If you ask about setting the timing according to recommended settings on here, you'll be told that's bonkers and you should do it by ear, so I don't know why there's so much fuss around the procedure for setting up the vacuum advance unit!

Good luck

[philthehill]

This is all getting overly complicated.
If you are starting from scratch set the vacuum advance knurled knob in the centre of the vacuum advance adjustment screw thread.
Set the static timing by using the static timing marks on the front of the engine and then adjust the timing by either using a strobe or road testing.
The settings (both static and dynamic advance) quoted in the manual are settings for the petrol used at the time of the manual publication.
Those settings can only be used as basic settings. The only way to get the timing exactly right for the engine in question is to road test the car or put on a rolling road. No two engines are the same.

[geoberni]

Thanks everyone for your help.

I would have thought though that being that the vacuum unit is supposed to advance the timing, there is little point setting it up in the middle of the range because why would you want to retard the timing using the screw? If the initial timing has been set correctly at idle by twisting the distributor with the vacuum capped off, you should from there only ever want to increase the timing or am I wrong? Or is it that by turning the screw the other way you are delaying the advance of the timing?

I'll try the tried and tested Morris Minor method of using the rusty mark and see how it drives. I am surprised, along with Liammonty that there doesn't seem to be a proper procedure written anywhere being that the diaphragms on the 50 year old distributors don't last forever.

Have you looked in the Manual?
Section CC.10 (2)
There's your 'proper procedure'. Don't forget these cars are from an era when such stuff was 2nd nature to any 'man with a car', because you were doing it that often!

Dizzy.JPG (162.41 KiB) Viewed 1618 times

[liammonty]

This is all getting overly complicated.

Indeed!!!

[JOWETTJAVELIN]

Just one more thing worth mentioning that I've noticed over the years. Not all engines pink when the timing is too far advanced, but a sure way of telling is when starting up from cold, if the starter motor struggles on each compression stroke, try retarding a little for the next cold start.

[minormarc]

Thank you all so much for your invaluable knowledge. I have installed the new unit with the marker set to the heavier line midway, as pretty much all of you have suggested. I didn't notice the graded scale on the old unit as it was cruddy but the amount of screw thread poking out the end is, as near as can be seen with the naked eye, the same as before. I'm sure that will be fine.

I do enjoy tinkering around with the Minor although I will be happier when the engine is done and I can get out and drive it.

Thanks again everyone.

[liammonty]

Just one more thing worth mentioning that I've noticed over the years. Not all engines pink when the timing is too far advanced, but a sure way of telling is when starting up from cold, if the starter motor struggles on each compression stroke, try retarding a little for the next cold start.

That's a great point - I've had this on a few engines over the years too. So the "advance the timing till it pinks a little" advice doesn't always work.