Distributors

[Chris Cole]

I have a Lucas distributor. It has three lots of numbers stamped on the body. Fisrt is '952' which I believe means September 1952. Next is 'AJ41' and lastly, probably the model number, is '40317 A' and an arrow indication anticlockwise rotation viewed from the points end. Can anyone tell me the model name, like DM2 of D45 etc. etc. And has anyone the vaumun advance curves for this at various RPM's? Is it a diect replacement for my worn DM2?

[PAUL BEAUMONT]

Chris, in the first instance visit www.telusplanet.net/~chichm/tech/lucas.pdf
According to them its a DM2P4. The site also gives other data related to the distributor which is listed as for the Javelin and Jupiter
Any help?

[Tony Fearn]

Hello Chris.

I'm in uncharted waters where Javelins are concerned, but I followed the link in Paul's posting, and it came up with a very interesting list. I note what Paul said, but if you go down to page 8 on the list, service no. 40795A, model 25D4 ccw rotation is said (on the extreme rhs of the list) to be a recommended alternative to 40115H and 40317A for the Jowett Javelin.

Regards,

Tony

[Chris Cole]

Paul, Many, many thanks for the Lucas informaion. The pdf file holds over 3,000 distributors - amazing. I found the two that I have and was able to see that thy were both DM2P4 models with the same advance charateristics. Thansk to for Tony's supprt.

[Drummond Black]

In April this year I fitted a Lucas 41427 ( 45D ) distributor to my Jupiter. See Jowett Talk on Jupiter. This unit works well with added power and smooth running. The only disadvantage of this unit is the lack of a fine setting Advance and Retard system. Apart from that I am very satisfied with this unit....
Drummond

[Forumadmin]

http://jowett.org/jowettnet/dt/tech/Dis ... ibutor.htm
Why not search on jowett.org first!!!!!! It has been there for about 7 years!!!

[Keith Andrews]

Has anyone looked at recurving cenrteifical and vac advance vac response pionts range to suit moden petrol?
No need for a dyno to run a ping curve or performace if u have a hill to test on, a handfull of diff weight springs out of random old dizzys at the wreckers, a in car vac gauge, and a file, hand vac pump to establish the vac adv canister vac range, timing light and tach.
Tuning a dizzy is like tuning a carb, what works on 1 engine will be a little different to the next engine.
There are some very dramatic economy and performance gains to be made even on a stocker engine.
Looking at the specs (I assume these are Cam degs not crank) lighter springs, maybe widening the cent advance range, change of vac advance canister degs and vac range.

[Forumadmin]

Many distributors on Jowetts are either not the right ones or are worn. The result is that the spark occurs in a random fashion around or about where it should do. The first thing to do is to recondition the dissie so that the spark always occurs within 1 degree at 3000 revs. An oscilloscope or stobe helps here; although, be careful, as some timing lights with some electronic ignition systems give incorrect readings. Found this out on the Allfrey Jup!

Next check you have a good spark of the correct polarity through the coil.

Next wait for a dark, damp night and make sure none of that spark is leaking to parts it should not do. It can be like a lightning show under the bonnet with poor cap, leads or plug sockets.

Now check the advance is no more than the maximum (20deg +/- 2deg for Javelin/Jup at crank) at 3000 rpm and that static is TDC +3 deg/- 0deg. If it is then I humbly suggest your dissie is not set correctly. A quick check on the dissie cam should show a 10deg mark (20 deg at crank).

If all this is OK then start playing with vacuum or advance curves. Springs and weights can be altered. The cam can be re-profiled with weld. I check mine on the bench with a drill on the dissie drive shaft and a disk protractor to show the advance.

Different vacuum units can be fitted. 5 degree(at crank) is standard. I think from memory. Check by sucking or using a vacuum pump and gauge.

Anybody know what the vacuum codes mean in the Lucas table?

You also may like to experiment with different size vacuum pipe, reservoirs in the vacuum circuit or just disconnect the thing like the racing boys do! I do not recommend the latter for road use.

[Keith Andrews]

Recurving on a dyno takes a couple hrs, assuming one doesnt have to machine or alter anything to change range and I would think, looking at the old curves modern gas there would be some both in the dizzy and vac advance.
Note all Degs here are crank not dizzy degs.
Centrifical:
Recurving on the road, one can expect several weeks of changes and trials to get spot on.
At the end...it is worthwhile.
Basically one establishes the piont of faint ping at a range of rpm by advancing the dizzy without vac advance under WoT
Then create the curve in the dizzy, droped back 2 or 3 degees.
The vechile is loaded (dyno or hill) and timed up a hill, usually retarding the curve to get optuim times.
A piont to note, idle advance is not important unless u cant get a smooth idle or have hard starting. The advance moving is the important part, hence why when setting timin it should be done at full advance rpm rather than idle.
Vac Advance:
Establish cruise engine vac and off cruise (1/3 to 1/2 throttle) this is the vac range the vac adv unit should be working at.
Generally setting the degs of advance in the vac advance to 3 deg below the ping curve will give close to optimium economy.

You will end up with a cent advance coming off intial adv around 800rpm, pulling fast to around 1800 rpm , rounding off slightly but still climbing to 28 to 36 degs at 2800 to 3300 rpm where it is all in.
The vac advance could be anywhere depending on many factors in the engine like cam profile that effect the working vac range of the engine.
Total vac degs could be anywhere between 5 and 15 degs. (total advance 32 to 52 degs.
Machining of the arm slot, or adding adjustable stops top and bottom of the slot adjusts the working vac range and the deg range of the vac adv unit. Even then one may have to dig thru a pile of units to get one that is suitable to modify.
If there is not enough deg advance in the dizzy to get a good idle/easy start and full advance, one can use manifold rather than ported vac from above the butterflys...I prefer using manfold vac anyway.

A pionts to note,
the carb has to be in good condition and no leaks like around butterfly bushes.
The simplest way to establish if the dizzy is in condition is a timing light with repeatable rpm/advance numbers and no wandering of the advance in the curve and top of the curve at rpms above when the adv is all in.
The are several types of springs, lite heavy and sloted.
Sloted have a long hook, that doesnt engage at low rpm, so the weights swing out quick, then hook up slowing rate.
In most cases a dizzy can be set without adding mass to the weights.
Too light a springs or a light/sloted, at idle will cause the engine to speed up and slow down as it runs out of gas on the idle curuits in the carb.

Its a learning curve, lot of messing around, time consuming, often frustrating and confusing...hence not something the classic car enthusist under takes...Still there is no reason why it cant be done.
And the rewards are very satisfing.

[Forumadmin]

Someone wrote in the Jowettteeer an article on dissie springs. I must look at the index on Jowett.org...........

http://jowett.org/jowettnet/dt/library/ ... _index.htm

................................

Distributors (White) 2002 Feb Page 08

Amazing.
I will scan in for our overseas members.

[Keith Clements]

DISTRIBUTORS (of the electrical kind!)
My distributor was discovered to be in terminal decline and I set about finding a replacement - and here are some of my finings that I pass on for further comments.
Most people recommend a replacement from a Mini - but “which Mini distributor suits the Jowett?â€

[Keith Andrews]

Beware. ?

Rubish

This can be all wrong if pinging occurs prematurely due to some carbon build up on just one cylinder ie oil carbon!

Yes...the engine has to be in good condition ie carb etc, so at most one would have normal carbon build up...this is not enough to cause pemature ping..IF it did the curve would be established ping maybe a little lower or in other words closer to the final curve anyway...so the point is irrelivant.
In Therory a highly carboned engine in effect has a higher compression...this aspect can influnece the final curve within a couple of degrees..in practice the difference is minor and can be adjusted simply by moving the curve up or down a couple of degs (advance/retard the intial) if the engine is de coked.

Keith A. what point tension ounces should the gauge show for the Jav Jup

Tension is not relivent to a car model but relivant to the model and geometry the points of the dizzy used. Any dizzy can be interchanged so long as rotation, shaft, and drive gears ar correct, the latter canbe interchanged with the stock vechlie dizzy if shafts are the same...these can thenbe recurved to suit the engine.
I have not recurved a Jowett Dizzy to date...I have recurved many dizzys HEI and pionts over the yrs, track/offshore and street applications on dyno and street. One of these a Rookie took out the NTH . Sth Isand, National, and Auckland championships in top 3 places in dirt track Street stock class a couple of yrs back.

Like most engines there is nothing exceptional about the jowett engines to make it unique in respect to Tuning.

[Keith Clements]

I have not yet found my treatise on setting up the DM2 for the Marathon rallies and race seasons. But here are a few points from memory.
Bearings and cam were checked to give an even dwell. You need to get within +- 1degree at crank.
The worn end stop was welded up and filed down to give 20 degree max advance.
Springs were adjusted by shortening or stretching to give desired ramp changes on the 'curve'. Ideally I would have bought new springs which subsequently I found are available. The curve is actually two step changes where each spring comes in.
Weights could also be changed but I did not do this.
Car was taken to dyno tuner who checked power output and spark on oscilloscope. You can tell by looking at the trace whether the spark is firing at the correct time. Settled on 21 degree advance.
We tuned the carbs and got nearly 5% more power without standard air filter and hyperbolic input throat. Later replaced with racing air filters.

Never did get around to camshaft changes on the dyno although the car was already on a modified profile cam.

For competition the car is generally either on or off and in the high rev range outside the dissie curve so the curve is not that important. On the road the more accurate curve would help below 2000 revs.

[Keith Andrews]

The timing of the spark is like shooting a deer on the run...
One has to shoot in front..to alow the time of the flash across the compression chamber and max effect at at the appropiate time for max explosion and pressure to push the piston down..
This Piont has several variables, such as how well the the chambers transfer the explosion, the flow rating of the inlet and exhuast runners, the rev range of the cam, the dynamic compression ratio (pressure at piont of explosion, the type of fuel and efficiency of the carberation systems at different rpms...Some of these variables such as fuel types have changed quite dramitically over the yrs with very differeant properties.

As with the deer, the brand of gun used doesnt matter, the accuracy does.
Also as with the killing power a gun, which may vairy to a big or small caliber caliber, shots per sec etc... the same applies to the spark...ie high voltage (HEI), low voltage pionts and MSD (Multiple Spark Discharge)

These are all common on internal combustion engines (not so much desiel) be they a chainsaw, a Briggs and Stratton lawn mower with a magnito or a top top fuel dragster.

As I mentioned in passing above, one can have to identical engines, both to be used in the same applications, but when fine tuned they will have slightly differant tuning parameters for optimal performance.

There are differnces in a track engine to a street engine..
A track engine is held up in the power band and doesnt drop below full advance, and doesnt need vac advance as it is run at engine vaccums below cruise...Hence the advance is fixed at max performace with no curve at all.
A Street engine uses cruise, off cruise, WoT and full range of rpm therefore needs a curve otherwise it will ping at low rpm

Becuse of no requirements of a curve on a track engine it is very quick (1/2 hr) and easy to establish max efficency of the advance on a dyno.
A street engine takes a long time on a dyno (4 to 5 hrs) at many points of throttle, rpm pionts, to set centrifical and vac advance efficiecy.

[Keith Andrews]

I sence an underlaying resentment, I have no intention of going down that track..
But if u wish to share how u curve a dizzy and why fine, There is more than 1 way to skin a cat...As I mentioned above there are 2 methods that Im where of, both have there good pionts, I have just presented the method I prefer...please share/explain how u fine tune a custom curve.
If there is an easier way I would like to know because it is a very time consuming job, like profiling a billet cam.