Ignition Timing

[Mike Stevens]

Did manage to swap batteries on 2 vehicles and convert one from 4 x 6v batteries to 2x 12v ones and get a Leyland Atlantean (11.25 litre 6 cyl diesel) to start and run for the first time in over 2 years. Just needed the fuel system bleeding - bit like a PI, only slightly larger scale.

Hi Kevin,

Your efforts makes my stuff here seem somewhat tame!

Cheers,
Mike.

[Greeks]

I think this thread shows just how shot a lot of people's distributors must be!

Lucas ones don't seem to last too well. Tend to develop a fair amount of lateral wear in the shaft. Remove the rotor arm and move from side-to-side. I've got a reconditioned one next to me and there's no discernible movement. (They do move up and down a bit though).

I can confirm also that you should be able to get the vacuum advance to move quite easily by sucking... however what nobody mentioned is that it should 'hold', too. So suck on the tube and then stick your tongue over the tube. The plate should not return (obviously you need to make sure the tube doesn't have a hole in it ... they can get brittle, I've had that happen before).

However, i've never noticed a great deal of difference at idle on the advance, surely it's when the hammer's down that the advance operates and it needed ... or are are we talking about the vacuum retard mechanism???

[David Withers]

This is my understanding.....

The vacuum unit has two purposes:
1. To advance the timing a little to improve fuel economy when cruising on a light throttle
2. To help the engine run a little sweeter in general by tweaking the advance according to the load, whereas the centrigual weights set it to the rpm alone.

The vacuum unit is ineffective on a wide throttle. It also has minimal effect at idle as the vacuum drilling in the carburettor is just on the intake side of the throttle valve. This appears to be drilled, on the SUs at least, in line with the edge of the fully closed throttle valve (i.e. the edge that moves inwards as the throttle is opened).

For that reason I'm not sure that it is strictly necessary to disconnect the vacuum pipe when using a strobe to set the timing at idle, but it does seem a good idea. The advice used to be to disconnect it and plug it so as to avoid any change to the air/fuel mixture or idling speed when checking/setting dynamic timing.

[Umquat]

I cant help feeling mine is well past its best. I took the cap off last night at it would appear that the rotor arm is coming into contact with it - fine score line. Time to replace I think! Might try a 123 out seeing as they seem to have good press

Regards

Gavin

[sorbs]

I wonder if 2500S distributors are different? The consensus seems to be that 2000 vacuum units are difficult to operate by sucking on the pipe. I'm not convinced that it indicates a problem.

I understand that when the engine is running on a trailing throttle, it takes a long time to draw the mixture into the combustion chambers past the closed carb butterflies so the ignition is advanced a lot to burn as much of the mixture as possible; better economy and reduced emissions as Dizzy says.

Alec, my car is a 1969 mk2 2000 with the Lucas 25D6 distributor, I'll look for a specific number later on. Any info about when the vacuum advance is supposed to operate and at what vacuum would be appreciated!

I've jusr been out enjoying the sun in the 2000, a nice 60 mile round trip and it's running so well that even if the advance thing is a bit sticky, I'll probably just leave it alone!

*Edit*

I found the number 41314 A stamped on the base of the distributor.

It also has the numbers 40 69 which I assume represent the date of manufacture, ie. week 40, 1969?

Some info here:

http://www.teglerizer.com/mgstuff/advance_curves.htm

[Alec]

Hello Sorbs,

the unit you have should have a vacuum unit 2/7/10(y) which means that 2"hg is the start figure, 7" Hg gives maximum advance and the 10 is the amount of distributor advance. (No idea what the y means) These figures agree with the Triumph manual.

The reference that I looked at is an old Speed and Sport publication (Remember Car and Cars conversions magazine) called tuning Lucas ignition systems and has pages of distributor settings up until about 1970.

Interestingly there is a substantial variation in the next series of 2000 engines with the 25D6 unit.

Early:- mechanical advance 24 degrees at 5,000 rpm (+- 2 degrees), 20 degrees vacuum and 8 degrees static. Total 52 degrees possible advance at above 5,000rpm, light load (very I would guess, down a steep hill?)

Later (ME50001 to ME92300):- Mechanical advance 18 degrees at 3,600 rpm, 12 degrees vacuum advance an 10 degrees static. Total 40 degrees possible.

I don't know if the deviation in settings was in compensation for deteriorating fuel ratings, or indeed if Triumph unlike Rover with their 2000 series specified 100 octane. It just seems such a large drop in advance.

Alec

[sorbs]

Thanks Alec. It'd be interesting to get hold of a vacuum gauge and see when my engine generates the level of vacuum described.

[Greeks]

I wonder if 2500S distributors are different? The consensus seems to be that 2000 vacuum units are difficult to operate by sucking on the pipe. I'm not convinced that it indicates a problem.

In my time I've sucked on various distributors My GT6 had a 25D6 with electric tacho, the S originally had a 49D6 (unusual Aussie model I think), and has since had a 45D6 and now has 25D6 ... same for all of them, and the diaphragm has lost its hold on a couple.

You're right though, it could be that your springs are much stiffer.

[Mike Stevens]

I wonder if 2500S distributors are different?
I found the number 41314 A stamped on the base of the distributor.

It also has the numbers 40 69 which I assume represent the date of manufacture, ie. week 40, 1969?

2500S and all cars after about 1974 ('Face-lift') used the 45D (?) distributor. I have no idea why.

That number is the Lucas reference number which Triumph quote in the manual with the relevant mechanical and vacuum advance figures. Alec has put up the figures. 40 69 is also likely to be the date code too!

I do have a 'vacuum' gauge complete with 'T' piece. I meant to put that on the PI distributor that I have, but I have spent most of the weekend (finally) fixing down the rear body on the Herald Convertible and getting the doors to fit. I tell you, you may think that getting Big saloon doors to fit is difficult - that's nothing on a Herald (or Vitesse, or Spitfire or GT6)! I'm hoping that today's efforts may be the last time I have to play with the body fit. Maybe at last there is light at the end of the tunnel - as long as it's not a train coming the other way!

Cheers,
Mike.

[mikeyb]

Took my car for a run saturday (it looked a right shambles ) but it needed it.

anyway after freeing the clutch slave off so it would move (!!) I drove it about 6 miles to the petrol station and topped it up with a few litres of tasty unleaded and some lead replacement stuff.

Paid, got in the car, wouldnt start.

Turning over a bit, started, thought no more of it.

Went about 1/2 mile to a mates house for a chat and a coffee, parked up for about 30 mins, then wouldn't start when I came to leave.

Checked connections etc, then got a strobe gun, no spark.

Turns out the dizzy cap and arm were "furry", a quick sand and it all fired up fine.

Although it wasn't running as smooth as before. Now i do have a new cap and arm.

So, after that long ramble my "on topic" question is, how much does the timing need to be altered for lead replacement? It also had an octance booster in it too.

Mike