I did some plots some time ago on various curves to get a better picture of what does go on


By gtmowog

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that is interesting GT - is it possible to send me the source data?

I'm going to ask a dumb question, just because I'm exactly sure what it is that I want to know...

here goes

is vacuum advance "constant" - meaning for a constant throttle position, at any particular RPM, will the vacuum advance be the same?

for example, if I put my car in 2nd gear and open the throttle a little bit and just let the revs rise without changing the throttle position, will the vacuum stay the same all the way to when the car stops accelerating?

Simon, I'll email you later today.

To answer your question on the Vacuum advance, essentially yes, once you get a bit past idle, the amount of advance given is independant of RPMs, only the amount of Vacuum (or if you like engine load - hint hint) will give you X advance.

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Simon K,
Re your original question.
There are two 23D4 Mk1 S distibutors, No 40819B and 40819H.
40819B is for the first type AEG148 cam and the 40819H is for the later AEG510 cam.
The AEG148 cam was used up to engine No 9FSAY40005. The AEG510 cam was fitted from engine No 9FSAY40006.
The 510 cam has 10/50inlet valve timing compared to the 148 which has 5/45.
The advance curve for the 40819B has slightly less advance, about 1 deg up to 3500 Dist RPM/7000 engine RPM due to 10deg less inlet/exhaust valve timing overlap.
The 29D4/AYG0175 type used on the Mk2 S and Clubman GT? have the same advance curve as the 40819H. The police spec distributors would be different as they have different Lucas service numbers but I don't have any info on these.

Regards
RonR

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68 build Mk1 Cooper S
72 Clubman GT project. Total restoration required

From BLMCA Service Liaison Summary 212 dated October 1970 for SPO41 (MK II S Police Specification):

The first 70 vehicles approximately (from chassis no. 2372) will be fitted with the MK II distributor AYG 0175, incorporating the wide blade contact points from the Mk 1. These distributors can be identified by a white paint spot on the body.
Later vehicles will be fitted with distributor part number AYG 0272, also having the Mk 1 points, plus MG centrifugal advance weights and springs, the advance curve being as MGB.
Timing: 3 degrees BTDC at 500 rpm.

Winabbey,
Thats great info. I've always wondered what the actual difference in the police spec distributors was.
It seems the first 70 cars only had the strong spring type points. The rest had a modified advance curve as well based on the MGB advance curve.
Do you have any parts info re the MGB advance weights and springs or advance curve data?

Regards
RonR

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68 build Mk1 Cooper S
72 Clubman GT project. Total restoration required

Hi Ron.

It's taken me a while to respond because there is some vague and conflicting data in some of the BMC and Lucas publications I'm using (nothing new there ).

According to the Lucas Equipment Specifications for Australian vehicles (1958-1970) the MGB had a 29D4 distributor (part 62941070A). This was fitted with the same points and weights as the MK II S (points - 54419946/GL19 and weights - 62410413). However the springs are different (MGB - 62410961 and MK II S - 62411108). There's no advance curve data in these manuals so I guess you'd need to look in an MGB workshop manual for that.

The later 1971-75 Lucas Equipment Specifications shows the Clubman GT (called "Leyland Cooper Clubman" in the manual) having a 29D4 distributor, part 62941090D (versus A for the MK II S) with the same points, weights and springs as the MK II S. I wonder what the difference is between the A and D models?

Interestingly, the same issue shows a "Leyland Police Mini" (presumably a Clubman GT built to SPO 28 - Police Specification) as having distributor part 62941122B, which lists the same points and weights as the MK II S and Clubman GT (not the Mk 1 points as mentioned in the SLS) but with the MGB springs (62410961).

For the record, the Mk 1's 23D4 distributor is shown as 40819A/H with points - 54413568/GL568, weights - 54413073 and springs - 54414766. So I'm assuming the points fitted to SPO 41 MK II S's were 54413568 although this is not mentioned in any Lucas publication.

If you find any advance curve data for the MGB please post it here.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43