15 replies to this topic

[mk=john]

Hello

I will be collecting an 850cc engine that has been professionally rebuilt etc. I am assuming the cam and valves follow original spec, or close to original. but I am not sure about this

My question is about distributor advance. If I were to purcchase a distributor which is for an 850cc engine, such as 25D, could engine damage result if the advance curve isn't correct for the engine. There are so many distributor numbers out there it's a minefield.

So, would a wrong advance curve just be detrimental to performance, or can it cause engine damage.

I can live with a small drop in perfrmance for now. I was hoping to purchase this distributor from Minispares today:
http://www.minispare...id=34708&title=

Cheers
John

Edited by mk=john, 03 September 2011 - 10:01 AM.

[Dan]

Shouldn't cause damage unless it's horribly far out. Generally it just means that it won't be as good as it might potentially be. In the real world, it might give you some trouble pulling away from junctions and decelerating and things like that because the engine won't be setup to behave as expected under all circumstances.

[minimender]

As it doesn't state how much advance is built in to the distributer you will need to look at the number stamped on the baseplate in order to set it right.

The engine needs around 30 degrees ( more or less depending on engine ) full advance at high revs.

The number stamped on the base plate must be doubled and subtracted from 30 (example 13 x 2 = 26 ,,,, 30 - 26 = 4 that means set at 4 degrees static)
.................................................................................................................................( example 10 x 2 = 20 ,,,, 30 - 20 = 10 that means set at 10 degrees static)

This will give you your basic timing, the engine may like more than 30 at high revs you will just have to try it and see.

As long as it doesn't pink under load then no damage to engine.

[lrostoke]

Sorry Dilligaf I really aren't trying pick fault

But I'm pretty sure the 2 x the stated figure is the amount of mechinical advance.


But just to clarify are we all talking about the same number, the one I'm talking about is stamped on the cam on the advance mechanism, The 2 advance springs connect to it

http://www.jcna.com/...h/tech0015.html

Pretty extensive article on tuning lucas dizzys. A few year back I logged my advance curve topic in here somewhere , figures stand up to whats shown in article.

One of the examples in there shows 6 degree @ 1000 rpm rising to 36 degree at 3500 rpm using a 15 advance cam. Which makes sense 2 x15 = 30 plus 6 degree initial figure

Edited by lrostoke, 04 September 2011 - 07:44 PM.

[minimender]

10 on the weight inside the dizzy means that the dizzy can advance the ignition by 10 degrees when the bob weights have fully opened out..............

If that was correct then an MG metro would only be getting 20 degrees advance at high revs and the engine needs 30+

(10 deg static and 10 on the baseplate = 20....not enough unless you double the baseplate figure to get 30)

Try it with a light, the mechanical advance will be exactly double the base plate figure, ....promise

[lrostoke]

Just a thought I think I can see where the confusion may come in.

We are talking dizzy advance and crank advance.

crank spins twice for every turn of the cam, So with the dizzy being driven by the cam, to get 26 degrees of advance on the crank timing marks we need 13 degrees at the dizzy.

[minimender]

Just a thought I think I can see where the confusion may come in.

We are talking dizzy advance and crank advance.

crank spins twice for every turn of the cam, So with the dizzy being driven by the cam, to get 26 degrees of advance on the crank timing marks we need 13 degrees at the dizzy.

exactly and nicely put

[lrostoke]

But surely everything mentioned is part of the same subject.
The advance on the dizzy is normally measured by the timing marks on the crank,
So for every degree the dizzy advances the measurement at the crank is double.

[minimender]

As I said I wasn't disagreeing with the post just adding to it, after all if it says 12 on the bob weight does it not advance the dizzy 12 degree's ?

Trying to keep it simple as advance mechanisms can seem complicated to some people

[lrostoke]

DILLIGAF is entirely correct in what he says which was why I posted this after my initial post

We are talking dizzy advance and crank advance.

crank spins twice for every turn of the cam, So with the dizzy being driven by the cam, to get 26 degrees of advance on the crank timing marks we need 13 degrees at the dizzy.

[minimender]

10 on the weight inside the dizzy means that the dizzy can advance the ignition by 10 degrees when the bob weights have fully opened out..............

Sorry but this quote could give people the wrong impression, 10 on the dizzy plate advances the ignition by 20 degrees not 10

The numbers on the outside dont tell you what spec the dizzy is, the number on the baseplate does and you need to know what it means

To add to the confusion not all diaphrams are the same either so vac advance may be different but that's another argument.

I do not know anything about electronic ignition but I have fiddled with mechanical ones since the sixties and know how they work

[Gulfclubby]

Then you'd surely know how much dynamic and static advance an Aldon Yellow dizzy with Vac advance gives? I'd be interested to know:)

[minimender]

Then you'd surely know how much dynamic and static advance an Aldon Yellow dizzy with Vac advance gives? I'd be interested to know:)

Never had anything to do with Aldon I have always altered my own distributers.
The yellow spec will be for what engine ? are all yellow specs the same?
All engines are different and need different maximum advance, some are 30/32 some are 36 some are less depending on design and spec.

Each engine has different needs and that is why adjustable electronic ign like meggasquirt or whatever its called is so good. Not available in my time I'm afraid that's why firms such as Aldon were successful, they initialy did what I do , altered things and then sold the distributers on. If they know what cam you have and the head spec they can make you a dizzy but it wont be as good as mapable electronic systems.

It isn't difficult to alter a distributer but you need testing facilities, I had a stop watch and a piece of measured road where i could measure the cars performance after each modification.
If you understand the basics you can sort your own timing out for very little outlay and that's what most Mini owners need to be able to do unless they have loads of spare cash to spend on letting someone like Aldon do it for them.

[Gulfclubby]

It's a 1380 with a 276 cam. The car is running fine, but it's hard to find experts with rolling roads who still know how to adjust timing and SU-carbs here in Switzerland, so I'm trying to find as much information as I can do to it myself. I'm sure there are some extra bhp to be had in there. I guess I'll have to take a look at the dizzy myself, one rainy day.

[minimender]

It's a 1380 with a 276 cam. The car is running fine, but it's hard to find experts with rolling roads who still know how to adjust timing and SU-carbs here in Switzerland, so I'm trying to find as much information as I can do to it myself. I'm sure there are some extra bhp to be had in there. I guess I'll have to take a look at the dizzy myself, one rainy day.

Found this site which may help you to understand why modified engines need different timing.

http://www.s26261265...rews/timing.htm

Hope it helps