mk1-forum.net

Hello

I have a lucas 25D4 fitted on my cooper mk2, référence 41238 (probably 1300GT or inno)

What could be the best timing, the engine is modified with a freeflow exhaust and some aluminium rame pipes for the carbs,

I will work with a timing lamp of course

I didn't find any advance curve on the web..

Could you help me guys?

All need to know about Lucas distributors is contained here.
http://www.starchak.ca/tech/pdfs/lucas.pdf
BUT your modifications pertain more to the air/fuel mixture than the timing of the spark advance. That's where I would be devoting my time and money. You'll need a richer than standard needle if you're running an SU cab. Without putting your car on a dyno and measuring exhaust gas emissions and air/fuel ratio its a bit of a trial and error process of making educated guess changes and then observing the colour of the spark plug deposits. There are web sites that will guesstimate the needle based on your engine modifications.

Charlynsane wrote: référence 41238 (probably 1300GT or inno)
I didn't find any advance curve on the web..

I found a .pdf file with over 500 Lucas Type distributors that will fit into a Mini...
It came from "the internet", but unfortunately cannot vouch for its accuracy,
although it does look quite comprehensive.

It looks like it's the same document that LarryLebel links to: There is a reference to "41238A":

Service number,Model,rot'n,ECM curve,RPM 1,Advance1,RPM 2,Advance2,RPM 3,Advance3,RPM4,Advance4,no advance below,vacuum code,Connection,years,make,comments
41238A,25D4,CCW,,3000,12,1400,12,500,2,,,200,4/11/7 (y),push,1968-72,"BMC Austin 1800, MG 1300 MK II and Riley Kestrel 1300, Wolseley 18/85"

Sorry, but I was unable to add the file containing this info to the post.
It's in ".csv" format, so you can copy and paste it into a text file, rename it to 41238A.csv,
and then open it in Excel of LibreOffice.

It looks like this, as a .pdf... Don't forget, these timing figures are the distributor's curve only, you will need to
ADD on the amount of static timing you intend to use...

Ian

I'm currently using a 41238 25D4 on my 1330, , this particular dizzy definitely came off a 1300GT.

I have it timed up for 8 deg btdc static, with the 12x2 centrifugal advance this gives you max 32 deg advance.

Depending on the petrol, cam, and compression you have on your motor you may find it pinks slightly at lower rpm range even with 99 octane fuel. I got around this by using a slightly stronger primary advance spring.

Hello,

thank for all these informations,

I already put richer needles, and the mixture is fine. The engine runs well

I used to tune ignition timing without tools, only ears and eyes,

But i would like to have a more precise timing,

So what advance can have I to put at 1000 rpm??

thank you guys

Since your engine is no longer standard and the fuels are different than they were when the car was new, I would not focus on your idle advance or published values for it.

Use an advance timing light (the ones with the knobs on the back or the digital equivalent). Bring the engine to operating temperature, then raise the engine speed to 4000 RPM using the idle adjustment screw. Set the timing light to 32 degrees. Shine the timing light on the marks and align the "zero" marks by turning the distributor. When the zero marks are aligned, clamp the distributor down and return the idle speed to where you want it.

Now test drive the car. Accelerate uphill in "too-high" a gear. Make the engine work. Listen for any bad noises like pinging or knocking. If you hear any, retard the timing by 2 degrees and repeat your test drive. Keep doing that until you hear no bad noises.

At this point you will have found the maximum advance your engine can tolerate for its state of build and the fuel you are using. You can measure the advance at idle and use that value in the future.

Thank you,

I will try to find the good timing!

hi sirs,
the informatin is very useful.
however, i have question. what is "zero" mark? is it shown on the flywheel? how can we find 32degree on the flywheel because there are only 1/4 5 10 degree shown.

warm regards
ink

matic wrote:hi sirs,
however, i have question. what is "zero" mark? is it shown on the flywheel? how can we find 32degree on the flywheel because there are only 1/4 5 10 degree shown.
ink

As mentuioned a one you use a Advanced timing light, these flash at TDC. Internally allowing for the advance the lights set to.

To elaborate a bit and for clarification I will post some pictures from the web.

First the timing light. As mentioned, the light I am talking about is an "advance light". It uses internal electronics to fire the strobe ahead of when the spark occurs. You use a knob or electronic buttons to tell the light how many degrees ahead of the actual spark to fire the light. This allows you to use the "zero" (TDC) timing marks on the engine rather than look for marks that are not there. (As Matic said, there is no 32 BTDC mark unless you make one).

Note the knob on the back of this light. Modern equivalents use push-buttons and digital controls to do the same as the knob.

Next the timing marks. Depending on what vintage your engine is, the timing marks will be on the flywheel or front pulley. The 1/4 flywheel mark corresponds to Zero (TDC). The front pulley marks are more obvious.

You set the knob/controls on the advance timing light to 32 BTDC and aim the light at the timing marks, then turn the distributor until the zero (TDC) marks line up.


and

If you haven't got an advanced timing light a standard one can strobe can be used.

Measure the diameter of the bottom pulley
Use a compass to make a template
Use a protractor to mark 32degrees on the template
transfer this to the actual pulley and mark the 32degree line on the pulley with a paint/tipex
then use your standard timing light
if it is set at 32degrees it will line up with the tdc mark on the engine

dklawson wrote:Since your engine is no longer standard and the fuels are different than they were when the car was new,
I would not focus on your idle advance or published values for it.

I totally agree with this statement, although I appreciate that others may not...

dklawson wrote: Bring the engine to operating temperature

Ditto, I agree with this. Temperature is very important.
See my thread "Temperature vs The Likelihood of Pinking"
viewtopic.php?f=3&t=9182

dklawson wrote: , then raise the engine speed to 4000 RPM using the idle adjustment screw.
Set the timing light to 32 degrees.

Given your opening sentences, we are in complete agreement about
not specifying exact figures for people to use.
However, when you say 4000 RPM, please confirm that you mean that
the engine should be set to such an RPM level high enough that the distributor
is running on the flat/fixed part of the curve. This would imply that any
RPM within the fixed/flat level band would, in fact, be appropriate. It would
also ensure that the advance would never go higher than 32 degrees.

dklawson wrote: At this point you will have found the maximum advance your engine
can tolerate for its state of build and the fuel you are using.

Very well put! It will more than likely not be the best set up, but given
the current parameters, it will the best available with the existing parts.

Ian

ianh1968 wrote: However, when you say 4000 RPM, please confirm that you mean that the engine should be set to such an RPM level high enough that the distributor is running on the flat/fixed part of the curve. This would imply that any RPM within the fixed/flat level band would, in fact, be appropriate. It would also ensure that the advance would never go higher than 32 degrees.

Ian

Yes, that is what my post meant to convey. Very few people will know exactly when that flat transition occurs for their distributor. In general most vacuum advance equipped Lucas distributors seem to be "full on" at or before 4k RPM (I have seen others quote 3500 RPM). Therefore, I am suggesting 4K RPM as it is reasonable to assume that in most cases full advance will have occurred by that speed. If in doubt, the reader can refer to Marcel's distributor database (linked by others earlier) to see if it provides sufficient information for their particular distributor. If you can find a service that still offers distributor re-curving they could determine your distributor's unique and specific advance curve.

The 41238 has a very heavy secondary advance spring, so may not 'flatten out' until pretty high rpm is reached.

This might well be at more than 4000 rpm... others can comment further.

dklawson wrote: *** The Pictures, posted Sun Mar 16, 2014 10:52 pm ***

What a really good idea to paint the flywheel white and scrape out black the numbers...

I had always tried to paint the numbers, but your method looks like it would be
far better and I will certainly be doing it this way round in the future.

Thank you for sharing this "Top-tip" with us...


Just one small point to note: Always check the flywheel AND the pulley,
certainly at least in the first instance. I was trying to strobe-check the
timing recently on the pulley end on one of my engines. Even with a
"wind-back" strobe, I could not get the pulley "nick mark" to line up with
the "fingers".

When I checked the flywheel end, it appeared that the 1/4 (zero) flywheel
mark and the pulley "nick" were not in the same place, by quite a long way...

I am not sure if there are "different" pulleys around, but whatever the reason,
mine was wrong. What I did was to set the flywheel at 1/4,Zero,TDC, and then
mark the pulley with a chinagraph pencil. Everything then worked out as
expected.

Ian

Well, for what it's worth, this is what the curve should look like;-



As for whether it is suited to your engine is a bit of a guess. What to time it at is also a bit of a guess, however you could do it by road testing, advancing it gradually until you could hear it pinging or you notice a loss of performance and then backing it off a little, however this is rather onerous without a dyno session by someone who knows what they are about.

There has been a bit of chatter on here of late about distributor curves and modifying them. It can be done on the car, however it is quite an exceedingly fiddley job. It easiest and more accurately done on a distributor test bench, this is mine;-



These Test Benches are only for testing the dissy itself, they are not used for determining what dissy curve a particular engine needs, a dyno is the tool for that.

Ian, thanks for the compliment but the flywheel shown with the paint is not mine. I simply grabbed pictures off the net to show early and late timing marks. Like you, I have always tried to fill the numbers with paint.

Spider, you have your own dizzy machine? I am impressed. I have a DC controlled hobby lathe that I use with a tach, timing light, and dummy ignition system to map things out. If I did more mapping it would be wonderful to have a machine like yours!

So... it looks like the 41238A would have full advance slightly before 3000 RPM. That's a lot lower than I would have expected. Thanks for posting the curve.

Spider, that looks like a great bit of kit you have there for checking out distributor advance curves.

Now - with apologies to the OP - I am putting my anorak on.

There is information about Lucas dizzy advance curves on the web, for example the data I have seen in a big table of Lucas dizzy curves gives the following for 41238A : 12 deg advance at 3000 rpm, 12 deg advance at 1400 rpm, and 2 deg advance at 500 rpm.

In an old Speedsport book 'Tuning Lucas Ignition Systems' dated 1972 the data for 41238A is very different, it states 12 deg advance at 3000 rpm, 8 deg advance at 1400 rpm, 3 deg advance at 500 rpm, with no advance below 200rpm.

I have no way of proving which one is correct, but based on visual inspection of the advance springs my guess is the Speedsport data is much closer to reality.

All of the above rpm speeds are distributor rpm, multiply by 2 for crank rpm. So the 41238 may not advance fully until 6000rpm...

carbon wrote:Spider, that looks like a great bit of kit you have there for checking out distributor advance curves.

Now - with apologies to the OP - I am putting my anorak on.

There is information about Lucas dizzy advance curves on the web, for example the data I have seen in a big table of Lucas dizzy curves gives the following for 41238A : 12 deg advance at 3000 rpm, 12 deg advance at 1400 rpm, and 2 deg advance at 500 rpm.

In an old Speedsport book 'Tuning Lucas Ignition Systems' dated 1972 the data for 41238A is very different, it states 12 deg advance at 3000 rpm, 8 deg advance at 1400 rpm, 3 deg advance at 500 rpm, with no advance below 200rpm.

I have no way of proving which one is correct, but based on visual inspection of the advance springs my guess is the Speedsport data is much closer to reality.

All of the above rpm speeds are distributor rpm, multiply by 2 for crank rpm. So the 41238 may not advance fully until 6000rpm...

Yes, it's hard to know which data is right. Maybe if the OP wants to send his dissy, I'll test it!

My guess here is that the RPM is engine based and the degree angle is distributor.

Thus we would have 24 (2 x 12) degrees crank rotation advance at 3000 RPM,
which would sound quite feasible... Add in the static, and we have something which
would look like a fairly "normal" curve.

Do we know for sure what the RPM figures are? A certain amount of mix-n-match
tends to go on here...

Ian