Dizzy's and engine numbers

[aspira]

Hi,

I'm putting on a new dizzy as part of my re-build. It's an SVDA and should be setup at 7.5% BTDC at 900 RPM with the vacuum pipe blocked.

I just wondered, as I read through my old Haynes, they talk about different engines that have different ignition timing setting as per their engine numbers; So, AE numbers at 5 degrees ATDC and AD numbers at 7.5 degrees BTDC for example.

Is that simply because they assume different engine numbers run different dizzys?

 

[aogrady]

Hi,

I dont know either, i have bought a degree pulley to get it right once and for all, I have a TP AE engine, but running ICT's, but with matching numbers for engine dizzy.

So what settings would you use if you had a replacement non gen vac dizzy?

I wondering if it's something to do with USA emissions regulations? :?:

Someone must have the right answer?

Cheers,

Alistair

 

[aspira]

Funnily enough, I did the same and bought a degree pulley. I've got a couple of Dell 36's and wanted to get everything running spot on, especially the advance .

 

[aogrady]

Funnily enough, I did the same and bought a degree pulley. I've got a couple of Dell 36's and wanted to get everything running spot on, especially the advance .

We're in the same boat then! :lol:

I don't know enough about firing timings to fully understand ATDC and BTC, and how 2 engines the same type (TP) can be different, emiswsions is the only think i can think of.

What does everyone else set them on 7.5 ATDC?

BTW, is ATDC towards the right, and BTDC the left? :msn4:

Do you know BTW, if you can fit a degree pulley without removed the rear vanence, rear tin, bumper etc....i.e, can i just undo the bolt, remove and fit with new and re torque....? :msn4:

Cheers,

Alistair

 

[aspira]

7.5 BTDC is the correct setting for my VAC. So the marks are before top dead centre - to the right.
My engine's out at the moment so it was easier to get my stock pulley off. I say easier but it was still a bit tricky and tight. I managed to get it off by knocking the back of the pulley by the key, then the opposite side but had to give it quite a knock. If your's is tight I guess it would be more difficult in situ but not impossible

 

[Trikky2]

The original timing specifications were listed by engine number because any particular engine number series from the factory would be fitted with a specific distributor.

This was done for simplicity at the time when these units were new.

In the real world the timing is relative to the distributor type being used.

In view of the age of these vehicles it is now common for the dissy and/or carb to not be the original and not matching the engine number code.

It should be noted however that some distributor types should only be used in conjunction with the carburettor model associated with it. For instance, the somewhat troublesome double vac dissy (used for a while to meet US emission regulations) will only work with the solex carb with twin ports for the two pipes on the vac can. It is however perfectly acceptable to use this twin port type carb with an svda unit as long as the secondary (rear facing) carb port is blocked off.

There is information available on which ones went with which originally, here :- http://www.oldvolkshome.com/ignition.htm#B6970" onclick="window.open(this.href);return false;

The svda type distributor performs better than either the vac only or the weights only (009) models.

In view of this one should always check and set the timing in accordance with the dissy type or number rather than by engine code these days.

Ps. For the same reasons its also important to check that the timing marks on the pulley are correct.

Wrong timing can easily result in overheating and premature engine failure so it is important to get it right.

 

[aspira]

Thanks for the clarification. Just what I thought but wanted to be sure I wasn't missing something.