Lotus Elan

Getting OGU roadworthy again

PostPost by: AHM » Sun Jul 14, 2013 11:39 am

Worth giving it a good clean and oil.

Don't be tempted to fiddle with the springs - They are supposed to be like that!

You will achieve nothing by taking them off and adjustment will make the curve wrong. Yes one of them is supposed to be loose!

Total advance is a function of the static advance + distributor mechanical advance, so if you retard the static you won't get the 35deg if you advance it you will get more.
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PostPost by: billwill » Sun Jul 14, 2013 12:37 pm

Don't worry, I will have a good re-read of the relevant bible:
http://www.vitessesteve.co.uk/PDF/lucastuning.pdf
before I start. :D

>Total advance is a function of the static advance + distributor mechanical advance, so if you retard the static you won't get the 35deg if you advance it you will get more.

Aye, but I think it was still not advancing enough.
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PostPost by: jimj » Sun Jul 14, 2013 4:18 pm

I agree totally with AHM but, more than that, I`d fork out for a good electronic ignition system and a session on a rolling road with experts who`ll set up the timing and the carbs, possibly re-jetting for your new head, then leave well alone. I appreciate that there are those who like to faff rather than drive, and respect to them, but it does seem that those with recurrent problems are those with more knowledge than me. Maybe ignorance is more blissful.
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PostPost by: billwill » Sun Jul 14, 2013 7:37 pm

No real point in taking it in for an expensive rolling road tune up until I am sure all other aspects of getting it back on the road after 4 to 5 years are sorted out and the new head has been "run-in"

I already have a version of Electronic ignition, I've had various ones over the years, but I like to be sure that in the event of a failure of Electronic ignition I can revert to plain simple contact breaker and coil to get me home.


I appreciate that there are those who like to faff rather than drive, and respect to them,


Heh heh, I have covered around 195,000 miles in this Lotus. :D
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PostPost by: billwill » Mon Jul 15, 2013 12:06 am

Now for today's tests.

I set the timing back to 19 degrees at 1000 rpm and then checked some increased speeds.

2000 rpm about 24 degrees
3000 rpm about 29-30 degrees.

I did not try higher rpm except very briefly unmeasured and did not see the advance rising any higher than about 30 degrees. I don't want to run for any significant time at over 3000 rpm until running in is a bit more done and I had no assistant handy to dab the thrrottle & shout out the rpm. I was setting the rpm with the idle rpm screw, which takes significant time to speed up and slow down.

Those figures above match those from the later Lotus Elan Workshop manual after adjusting for the static setting, except that the 24 degrees at 2000 rpm is a bit lowit shoud be nearer 27 degrees.

However as yet I don't know if previous tuners of this engine changed the distributor or its springs.

Afer all the testing, the engine was again too hot to attempt to take the distie out without a scald from the radiator metal so I will leave the inspection until tomorrow (well later today now...) :)
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PostPost by: billwill » Mon Jul 15, 2013 11:43 pm

Well I've now had the distributor out and inspected and oiled it.

Pleased to find that my eyes were not decieving me yesterday, this distie cannot do a dynamic advance of more than 10 degrees, because it has a 10 degree stop cam plate in it. Which is non standard, I think it should have an 18 degree stop cam plate.

Both springs seem to be identical, same number of turns and seem to be the same thickness wire. Neither are loose, I expected one to be loose.

So now the mystery is now WHY is it like that? Was it changed by someone who did not know what he was doing or was it changed by someone who knew EXACTLY what he was doing?

I've been over all my invoices and none specifically mention a new distributor body, but the engine had major overhaul at least 4 times, Each time by highly competent engine men with a racing bent. It was originally supplied by Ian Walker's to Malcolm Ricketts, both of whom know lots & lots about twin cams. So it might have had this distie since the very beginning. Since I bought it it has has a major engine refurb by Vegantune of Spalding, one by Malcom Rickett's favourite engine man and once by Rob Morley while he was engine man at Vegantune Finchley. Later in 2000-2001 after Rob had left them, Vegantune Finchley had the car for quite a long time for some body repairs and did do some other changes, which just might have included a distributor, but I don't know and have only an overal invoice covering all the work, the detailed invoice never arrived.

I'm very puzzled, of course, as to whether or not I should get it converted to a standard advance curve or leave it as is.

In any case it is most unlikely that this is the cause of the hesitation and acceleration hiccups on the Saturday before last, because I must have already driven many miles with this distie as the last time anyone else could have changed it was 2001, about 25,000 miles ago.

So back to puzzling over the carburettors, with the next most likely suspect the accelerator pumps.
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PostPost by: oldelanman » Tue Jul 16, 2013 7:32 am

billwill wrote:Pleased to find that my eyes were not decieving me yesterday, this distie cannot do a dynamic advance of more than 10 degrees, because it has a 10 degree stop cam plate in it. Which is non standard, I think it should have an 18 degree stop cam plate.

Both springs seem to be identical, same number of turns and seem to be the same thickness wire. Neither are loose, I expected one to be loose.


Which distributor do you have ? This is my spare 41189A ..... looks to be 10 deg the same as yours......
Attachments
Distributor 41189A 005.jpg and
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PostPost by: AHM » Tue Jul 16, 2013 12:22 pm

Bill, I just looked in Miles Wilkins book P168/9 - Total advance for 41189A is listed as 26 degrees (it is the 40953 that goes to 36 degrees)
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PostPost by: billwill » Tue Jul 16, 2013 1:11 pm

It is a 41189a, datecode appears to be 868 8th week of 1968 the other number is 2304

Even at 26 degrees total that would mean that the cam should be at least 14 degrees not 10, assuming 12 degrees static.

Interesting that your spare is marked 10 degrees and it does not look ground away just like mine, maybe all new/replacement 41189a were issued with 10 degree cams because you can grind the tag away to create a bigger angle.
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PostPost by: oldelanman » Tue Jul 16, 2013 1:26 pm

billwill wrote:Even at 26 degrees total that would mean that the cam should be at least 14 degrees not 10, assuming 12 degrees static.


I don't think so.......distributor turns at 1/2 engine speed so 10 deg on the distributor shaft is 20 deg on the crankshaft and with 12 deg static advance you have 32 deg in total.
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PostPost by: billwill » Tue Jul 16, 2013 1:53 pm

This is the data from the Lucas Distributor database referenced in another topic.




Service Number 41189a
Model 23D4
rotn CCW
ECM curve
RPM 1 3250
Advance 1 7
RPM2 1000
Advance2 5
RPM3 600
Advance3 1
RPM4
Advance4
No advance below 400
Vacuum code no vacuum
Connection screw
Years 1968-73
Models Lotus
comments Elan_2S, 130S, S4, Sprint, Ford Escort and RS1600


Which I read as no dynamic advance below 400 rpm
1 degree at 600 rpm
5 degrees at 1000 rpm
7 degrees at 3250 rpm

Notice that maximum advance is not specified.

Unfortunately the database table does not clarify whether this is crankshaft RPM or distributor rpm, so they could be wrong by a factor of 2. That would make it 7 degrees at 6500 rpm crankshaft

All suitably confusing to the innocents. :D :D And not matching exactly to Lotus timing instructions of about 19degrees at 1000 RPM (12+5 =17 not 19).
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PostPost by: billwill » Tue Jul 16, 2013 2:36 pm

oldelanman wrote:
billwill wrote:Even at 26 degrees total that would mean that the cam should be at least 14 degrees not 10, assuming 12 degrees static.


I don't think so.......distributor turns at 1/2 engine speed so 10 deg on the distributor shaft is 20 deg on the crankshaft and with 12 deg static advance you have 32 deg in total.


Ah... I had momentarily forgotten that so you are right there. a 10 degree cam allows 20 degrees of crankshaft advance. So the 30 degrees or so that I saw with the timing light is bigger than the 26 degrees that Miles Wilkins shows on page 168 for a 41189a with Big-Valve & dellorto.

Nowt wrong with my distie after all.


And I have remember that Vegantune Spalding did change the distie in 1983 because I had a fire in the engine compartment that damaged the Weber carbs and presumably the 25D4 distie, so they fitted Dellortos and a 23D4. I miss the old unused vacuum mechanism, because its thumb nut made it so easy to adjust the timing.
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PostPost by: billwill » Tue Jul 16, 2013 10:31 pm

Well with the Distributor now exonerated from causing the problem, I now started looking at the fuel system.

I have a combined fuel filter and pressure regulator a Malpassi Filter king, like this:

Image

So I carefully took the bowl off and indeed there was some crud in the bowl, but none of it would have got through the filter into the Dellortos.

However an interesting fact is that the pressure control valve had fallen out of its seating and it and its spring and nylons seating plug were inside the filter !! Poor engineering, the nylon plug is expected to hold the valve in place, but it is just a tight push fit in its cavity, with no positive method of locking it in.

So this means that the Dellortos were being fed with fuel at the full pressure of the electric pump in the boot! This may have been the cause of my acceleration surges, but personally I doubt it, I think the needle valves in the carbs would cope.

Anyway, I've cleaned it up and reassembled it. (I hope I got the parts of the valve back in the right way around). I broke the larger rubber washer seal for the bowl while cleaning it so I've done one with silicone gooo, instant gasket and left it to cure overnight.

I will take her out for a new run real soon to see if the symptoms are still there.

8)
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PostPost by: andyhodg » Wed Jul 17, 2013 10:47 am

Hi Bill

I always though that petrol dissolved silicon sealant? Be careful.

Regards

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PostPost by: billwill » Wed Jul 17, 2013 12:16 pm

andyhodg wrote:Hi Bill

I always though that petrol dissolved silicon sealant? Be careful.

Regards

Andy

Noted... Will buy new rubber washer as soon as possible.


~~~~~~
Woke up this morning with one of those AAAARGH moments, my engineering subconscious overnight has worked out that I assembled the Filter King Regulator valve in the wrong order and I have created a bigger problem for myself that now I have to get that nylon plug back out and I tapped it in with a hammer and there is nothing to grip.

Curses on the stupid non-maintainable design of that valve and a fervent desire that my lathe was still working, because I could then make a new nylon plug if necessary.
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