Distributor 41189 advance curve.

[fatboyoz]

Hi All,
Decided to check the timing on my '68 S4. Prior to doing it I referred to both the Lotus Workshop Manual and LOTUS Twin-cam Engine (Miles Wilkins) tome. My Elan is an 1968 S4 with the standard weber spec' twin-cam and is fitted with a Lucas 41189 distributor.

The car spent the first 19 years of its life in Hong Kong (from where I purchased it in 1987 and has been completely restored) where it did a total of 35,000 mls and, due to the lack of spares and a service agent for the Elan, I presume that it came from Lotus with this distributor fitted even though both of the above books indicate that it would have been fitted with a 40953 distributor.

Upon looking up both static and centrifugal advance for the 41189 in these books I discovered that they are quite different in when the max' advance should occur. I then searched this forum and came upon this discussion from several years ago to see if I could resolve the difference:http://www.lotuselan.net/forums/elan-f15/distributor-question-t2109.html all very interesting, but no definitive answer (that I could see).

So, set 10 degrees static advance and ran the engine up using an engine-bay tachometer for reference. Max' advance of approx' 24 degrees (10 degrees static plus 14 degrees centrifugal) was achieved at approx' 2500rpm (crankshaft speed) increasing (by eye) fairly evenly from approx' 1000rpm. This is as per the the Lotus Service Manual P17 Technical Data. MW's book says: no centrifugal advance between idle and 2000rpm and max' advance not until 5000rpm for the 41189 and that the Service Manual is incorrect.

Comments?
Cheers,
Colin.

[Galwaylotus]

Sometimes we can read too much?

[oldelanman]

I have no idea which data is correct but I would say the number on the outside of the distributor body only indicates the spec when it left the Lucas factory but is no guarantee of what's inside now - it may have been "tuned" over the years. For instance I have a 41189 distributor which has a 10 deg advance cam in it instead of the 7 deg which you would expect - I think it came from a works twin cam Escort. From your results it looks like you have the correct 7 deg advance cam fitted but maybe the advance springs have been changed or become stretched/weak and consequently the advance commences earlier than expected.

Just to add to your confusion there is more information here...... http://www.mgaroadster.co.uk/Technical_Information/lucas.pdf ...... but it shows advance commencing at 800 rpm crankshaft speed!

Regards,

[ppnelan]

There was confusion in the Workshop Manual over distibutor rpm & crankshaft rpm - I believe Miles' book highlights this somewhere. This might be why things don't match up

Matthew

[martinbrowning]

Colin,

Matthew is correct when he says that there was confusion between crank and distributor rpm. (Page 168 of Miles' book). For what it is worth, I would always go with Miles' data where it differs from Lotus.

Martin B

[fatboyoz]

Thanks Guys,
Yes, I am well aware of the conflicting numbers between the two books, hence my last sentence in my original post. Everyone seems to defer to MW's figures. If you have a read of the link that I originally posted, you will see where I am coming from. Here it is again: elan-f15/distributor-question-t2109.html
Seems strange to me that a distributor, that has only done 35000mls, should fail (with stretched springs), to exactly the same numbers as quoted in the Lotus Workshop Manual.
Surely, when timing their cars, people must be aware of what type and number their distributor is and how much max' advance they are achieving?
If so, is anyone else able to post their actual numbers from their 41189 distributor? They can't all be stuffed!!!
Colin.

[twincamman]

I have found there is no advance below 900 RPM . The elan manual says set the static at 18 degrees static, this has not worked for me as it is too advanced and close to timing rattle My 7 manual says 5 degrees to start and I have found 6 degrees at 900 RPM works best for my engines. There are about 6revolutions of the motor cold before it fires up and I like to think there is oil pressure by that time. So try 5 degrees static to start and use a timing light for the other one or two degrees. All the advance should be in at 2500 RPM Twincs are very sensitive to both cam and dynamic timing....Both cars have the centrifugal advance distributors .....and it's total of 24degrees all in at 2500 RPM......



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