Ignition timing

[IainP]

I know this has been done to death, but I’m being thick and the combination of the WSM, Buckland and Wilkins are confusion me. Especially Wilkins who has very confusing dizzy figures…….he’s mixed up Dizzy and crank rpm. Although his note says it’s Lotus!

Background.
Distributor removed for refurbishment by Distributor Doctor.
Engine BV.

Do I set the crank and number 1 piston to TDC and then insert the distributor?
Or do I set the Crank No 1 piston to the static 12 degree BTDC?

When I insert the distributor number 1 lead is at 11 O’clock. I believe this is correct?

Thanks in advance

[512BB]

Make sure No 1 cylinder is on the compression stroke. Move the crank pulley round to 12 degrees. Then insert the dissy. On all my cars, the rotor arm is pointing to No 1 lead in the cap at 1.30 and the nylon connector block on the dissy will then be roughly adjacent to the block, or at about 12 o clock in English.

If your dissy cap leads are wired the same way, ie your No 1 in the cap is at about 1.30, then your setup will be the same, but if your No 1 lead is at 10.30 ish, then you have to insert the dissy so that the rotor arm points to that, so first, determine where your No 1 lead is in the cap.

After inserting the dissy, I connect up a meter to tell me when the points are just opening, and that is pretty well spot on. Put a timing light on the engine after firing up.

Good luck,

Leslie

[IainP]

Thank you.
I found the answer after much searching last night.
Apparently the later WSM does not have a very useful page on Distributor replacement.
What I had done was correct, however what was fooling me was the fact that the engine ran best and performed best with an 18 degree btdc reading with a strobe. This is according to that page of the bible correct. I’ve been trying to reduce this back to the static value given of 12degrees……..the result being a very unresponsive, hesitant engine. ( Dwell is 60 degrees)
Every day is a school day.

[111Robin]

The static timing figure is really just given as a position to enable you to get the engine running for initial setup (or if you don't have a strobe), it shouldn't be used as a definitive advance value. Using your strobe light and the engine running around 3000rpm rotate the distributor to achieve around 32 degrees of advance (assuming the mechanical advance is working properly). The static advance will be whatever it is at this setting, probably closer to the 18 degrees you mention.

[2cams70]

The static timing figure is really just given as a position to enable you to get the engine running for initial setup (or if you don't have a strobe), it shouldn't be used as a definitive advance value. Using your strobe light and the engine running around 3000rpm rotate the distributor to achieve around 32 degrees of advance (assuming the mechanical advance is working properly). The static advance will be whatever it is at this setting, probably closer to the 18 degrees you mention.

That is not correct. If the static figure is not where it should be in order for the engine to run well there is definitely a problem with the distributor springs or your engine has non-standard internal components or you are reading off the timing with the engine running at too high an RPM.

[rgh0]

You need to be very careful around generic statements regarding the "correct" ignition timing. Lotus used different advance curves over time and different curves for Stromberg versus Weber head. my observations are

1. With most modern fuels a road Weber twin cam needs around 28 degrees max advance at arounf 3500 rpm, a well developed "typical" competition engine needs around 32 degrees at 4000 rpm (whatever "typical means )

2. Static advance of more than around 12 degrees will give you a problem cranking the engine.

Beyond that you're on your own trying to decipher the data that is published with so many errors and vagueness by Lotus and subsequently others adding to the confusuon. The Standard , SE and Sprint cams, Stromberg and Weber , emissions and non emissions, should all need different timing but this is not made totally clear in any of the manuals as to what curve applies to what engine. i am sure Lotus adopted some non optimum timing in some circumstances to keep production simpler.

cheers
Rohan

[IainP]

Thanks all. It does seem that a lot of the literature is poorly written and error strewn….
Never mind, with the help on here all appears solved.
Iain

[111Robin]

The static timing figure is really just given as a position to enable you to get the engine running for initial setup (or if you don't have a strobe), it shouldn't be used as a definitive advance value. Using your strobe light and the engine running around 3000rpm rotate the distributor to achieve around 32 degrees of advance (assuming the mechanical advance is working properly). The static advance will be whatever it is at this setting, probably closer to the 18 degrees you mention.

That is not correct. If the static figure is not where it should be in order for the engine to run well there is definitely a problem with the distributor springs or your engine has non-standard internal components or you are reading off the timing with the engine running at too high an RPM.

Whereas it may not be "by the book", it is a fact that static timing values are pretty irrelevant, the advance needs to be fully in at the engine speeds that you will be requiring performance at, who cares what it is at idle ?. I agree you may be overcoming other issues, especially modern fuels that dictate different advance curves anyway, but at the end of the day if the engine pulls more cleanly then it's better than sticking to the book, in my opinion.

[2cams70]

For reference attached is the Ford data for the Lucas 41189A distributor used on the LTC (non emissioned, Weber head, SE cams). It's probably more accurate than anything Lotus ever published. Indeed for this particular spec. it was probably Ford and not Lotus that did the final tuning. Probably not the case for the emissioned engines however because by the time they were being developed Ford was well out of the picture and more interested in the BD series engines.

For what it's worth it says that maximum advance was 12 degrees static + 14 (+/- 2 degrees) = 26 degrees at the crankshaft at a crankshaft speed of 2,400 RPM. No further advance after that.

In the Ford parts listing the same part number is given for both distributor springs (so single stage advance rather than two like the regular pushrod engines). This correlates with the shape of the curve given which is single rather than 2 stage.

Ford probably had no involvement with the US emission calibration and so sorry can't help in that case if the Lotus supplied data is unclear.

[IainP]

Very useful, this is the data used by Distributor Doctor to rebuild my 41189a. His reference being the original Lucas Printed Manuals.
Iain

[mark030358]

You need to be very careful around generic statements regarding the "correct" ignition timing. Lotus used different advance curves over time and different curves for Stromberg versus Weber head. my observations are

1. With most modern fuels a road Weber twin cam needs around 28 degrees max advance at arounf 3500 rpm, a well developed "typical" competition engine needs around 32 degrees at 4000 rpm (whatever "typical means )

2. Static advance of more than around 12 degrees will give you a problem cranking the engine.
Rohan

Beyond that you're on your own trying to decipher the data that is published with so many errors and vagueness by Lotus and subsequently others adding to the confusuon. The Standard , SE and Sprint cams, Stromberg and Weber , emissions and non emissions, should all need different timing but this is not made totally clear in any of the manuals as to what curve applies to what engine. i am sure Lotus adopted some non optimum timing in some circumstances to keep production simpler.


Hi Rohan,
Interesting re the standard and "developed" timing...

Given my head is ported and run 420 Cams, I guess it falls into the "developed" world.

Attached is my distributor curve after a refurb with no changes. So if timed with a 12* advance I would have 32 degress at 3500, with the dizzy advance being all in at 4000 rpm.

cheers

Rohan[/quote]

[IainP]

Interesting curve, Martin has applied his considerable knowledge and given you distributor more advance and at higher rpm.
Cf mine. I believe my engine to be a standard Sprint Specification.

[mark030358]

Iain,
When I have stripped and cleaned the distributor in the past I noted the bob weights are stamped with the number 10. I would be interested to know what your weights are? However I guess all depends on the springs fitted.

cheers
Mark

[rgh0]

Yes looks like a good starting curve for a developed engine. May be a bit much advance for a non full competition engine so maybe you could back off the static advance a couple of degrees. However without dyno runs with the actual fuel your using its all guess work. The distributor doctor probably knows better than me what works with current UK fuels ?

cheers
Rohan

[2cams70]

Iain,
When I have stripped and cleaned the distributor in the past I noted the bob weights are stamped with the number 10. I would be interested to know what your weights are? However I guess all depends on the springs fitted.

cheers
Mark

That number if memory serves me correctly is stamped on the cam. It Indicates the maximum advance possible when the cam rotates and hits its limit stops - ie 10 degrees at the distributor in this case. If you want more advance than that you would need to machine the cam where the limit stop hits the spring post. Similarly to reduce the maximum advance you’d need to add metal to the cam.