Spitfire Spitfire Static Timing, Conflicting Data?

[dklawson]

I tried the search feature to see if this had been covered before but I didn't find what I was looking for.

My sons and I now have our project '72 Spitfire Mk4. As part of the basics I want to go over setting the points and static timing. I have Haynes, Bentley, and the factory documents on a Heritage CD. Prior to this all my LBCs have set the static timing between 5-8 BTDC. Haynes says this 1300 engine should use 6-8 BTDC, Bentley and the Factory owners manual say 6 ATDC. Under the bonnet, the factory tech sticker remains and it says to use a dynamic (idle) timing of 2 ATDC.

The distributor appears to have a vacuum retard unit without vacuum advance. Is Haynes wrong and are Bentley and the factory manual correct? Is the static timing set to after because of the retard only vacuum unit on the dizzy?

We're just getting started with this car and things like this are quite a bit different than on our GT6. All advice is welcome.

 

[Andrew Mace]

I'm not positive, but I'm guessing that the Haynes figure might based on a nonemissions setting? Regardless of any of the books, I'd want to at least start with the "dynamic (idle) timing of 2 ATDC as specified on the underbonnet sticker. A similar spec. sticker on my long-gone '69 Mk3 proved to be pretty accurate. Not that the factory didn't make the occasional mistake, but.... :wink:

 

[DrEntropy]

I'm with Andy, Doug. Things were kinda goofy in the early days of emissions "standards". See how it runs, tweak it a bit then p'raps swap out that diz for an earlier unit with vacuum/mechanical advance later.

...that an' a pair of HS2 SU's... :wink:

 

[TR3driver]

Different every year, and different for different markets. Anything BTDC has to be without vacuum retard (or with it disconnected). But US regulations at the time required the timing to be set with the retard connected and operational (so the Haynes is simply wrong).

As a starting point, I'd make sure the retard works (idle rpm should rise sharply if you pull the connection off the retard and cap the line with your finger); and use the 2 ATDC figure.

 

[TR3driver]

Just noticed the title of this thread ... if you are looking for a static timing figure (with the engine not running), I'd use the 6-8 BTDC. That's plenty close enough to get the engine running, so you can check again with a timing light and use the 2 ATDC with the vacuum retard in operation.

 

[dklawson]

Thanks all. The first series of tasks will be to undo the disassembly performed by two or three previous owners. A general tune up will be part of that.

Once we have the engine running I'll make the dynamic adjustments to achieve the 2 ATDC at idle (assuming the retard diaphragm is intact). Randall, I am still concerned about the static timing figure. I would normally be very comfortable setting the static timing to 6-8 BTDC but the factory and Bentley manuals both say to use a static timing of 6 ATDC.

Dr, you brought up a point I have been considering, swapping this dizzy for one with vacuum advance only as opposed to retard. However, would the carb have the proper tap for that? I imagine that the carb and manifold I have now must be using manifold vacuum to retard the timing at idle and part throttle. Wouldn't I need a different carb (with a ported vacuum tap) to use a vacuum advance dizzy? Certainly using a vacuum advance dizzy connected to manifold vacuum would give way too much advance at idle... wouldn't it?

EDIT: Andy, I understand that you're an acquaintance of Jamie Palmer. Jamie trailered this car home for us and will be our local support for it.

 

[TR3driver]

Randall, I am still concerned about the static timing figure. I would normally be very comfortable setting the static timing to 6-8 BTDC but the factory and Bentley manuals both say to use a static timing of 6 ATDC.

There were some Spits that were timed that way, but they did not have vacuum retard. Since your distributor apparently does have the vacuum retard module, the static timing should be faster than the dynamic (idle) timing. Basically by the amount that the vacuum retard retards.

But if you want, you can use the either the 6 ATDC given in your manuals or the 2 ATDC on the sticker under the hood. The engine will still start and run that way; just won't make much power (and probably need the fast idle cam to idle). Then with it running, you can adjust to the sticker.

What distributor do you have ? Should be able to look it up on the web (Marcel Chichak published a table of distributor specs by number, so did Paul Tegler) and find out how much retard the vacuum module gives. Add that to the 2 ATDC on the sticker; should be the correct static timing.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Wouldn't I need a different carb (with a ported vacuum tap) to use a vacuum advance dizzy? [/QUOTE]Yes, exactly. The 'retard' port only supplies vacuum at idle, while an 'advance' port only supplies vacuum off-idle.

 

[dklawson]

I've got Marcel's dizzy database both at home and at work. I'll check it when I get home and can look at the dizzy. However, I suspect the dizzy on the car is a Delco unit, not Lucas and therefore won't be in Marcel's list.

I may arbitrarily set the timing to 6 BTDC and use that value to start the engine. Once the idle is set for the specified 800-850 RPM I'll check the dynamic timing and adjust as necessary. If I have to make any major changes to the dynamic advance I'll work backwards and turn the engine over to see where the static timing falls and record it for future reference.

All of this assumes the previous owners haven't mixed and matched components and that I can still go by the sticker under the bonnet.

On other LBCs I've worked on there has only been vacuum advance (not retard). What I prefer to do is remove and plug the advance line and bring the engine up to 3500-4000 RPM and set the max advance to around 32 BTDC. I've never worried much about idle or static timing except in a case like this where I just need to get the engine started from cold (and getting the car in pieces). Can you handle vacuum retard the same way? Can you plug the tube and set the max advance to 32 BTDC?

 

[TR3driver]

The concept is sound, but I don't know how much total advance a 1200 Spit motor likes. The specs I have handy are for a 73 1500 model, and call for only 30 degrees at 4800 rpm.

I thought Paul had the Delco distributors listed, but it looks like his "4 cyl" section is a duplicate of the "6 cyl" section and only covers to 1970 anyway. Oh well. Maybe someone else has info for a late Mk 4 ?

 

[dklawson]

I checked the car carefully against the documentation last night. When you use the dizzy number and the engine block number to read into the Bentley and factory manual tables it appears that my car falls into a group of cars that used the vacuum retard without advance. The static timing for that particular combination of dizzy and block was specified as 8 BTDC and as listed earlier, dynamic timing of 2 ATDC at 800-850 RPM. If the retard diaphragm is intact I think I understand from the description how this dizzy will behave compared to those I'm more familiar with.

Thanks to all who posted.