Putting the distributor back

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Stephen Aitken
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Putting the distributor back

Post by Stephen Aitken » Fri Apr 05, 2019 8:52 am

I have an optronic distribution 45D on an 81 GT. I had to remove it as the vac advance failed - lack of vacuum and a new one now fitted.
In terms of putting it back I have the instructions to set the static timing ie use a volt meter and ensure the rotor is pointing to no 1 position etc - I think that’s ok but do I need to crank the pulley to get TDC at the same timeor do I do the timing with a light after the static approach is completed? bit confused here
Any help appreciated
MGB GT LE 1980

Vic Butler
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Re: Putting the distributor back

Post by Vic Butler » Fri Apr 05, 2019 12:59 pm

If the rotor is pointing to number 1 lead then just set the static timing and then give the vehicle a run to see how it performs.
The vacuum advance on rubber bumper B's works only on tickover where it's not needed and on a very light throttle. Peter Burgess advocates disconnecting it altogether.
For my Stage 2 engine I have had a distributor rebuilt to suit it and without vacuum advance. I haven't fitted it yet. The vacuum advance take off point is on the rear HS6 carburettor.
I think the static timing is 10 degrees btdc.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine

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Charles Farran
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Re: Putting the distributor back

Post by Charles Farran » Fri Apr 05, 2019 1:31 pm

Stroboscopic ignition timing on my 1980 MGB per the handbook is 14 degrees B.T.D.C. at 1000 rpm (vacuum advance disconnected ).
Cheers, Charles
1980 Roadster

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Charles Farran
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Re: Putting the distributor back

Post by Charles Farran » Fri Apr 05, 2019 1:55 pm

I have just checked in the Repair Op Manual1978 AKM 4070 that for the UK spec year 1978 ( to European emission control reqs EC 15)where it indicates 10 dggrees B.T.D.C. at 1000 rpm for strobe timing.(No changes indicated in the 1979 supplement ).This seems at odds with the handbook!
I recall using the handbook figure of 14 degrees when fitting a 123 distributor some 6 + years ago & have been pleased with the performance ever since!
It would be interesting to hear other views on what the appropriate setting is - clearly what suits one engine does not suit others of the same spec (mine being as it left the factory).
Cheers, Charles
1980 Roadster

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Charles Farran
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Re: Putting the distributor back

Post by Charles Farran » Fri Apr 05, 2019 2:43 pm

To be more definitive you need to establish the engine serial number - my original engine has the spec 18V 847 H following by the individual block number.
An F per "Barrie' Notes" indicates twin carbs , this in my case is replaced by H which denotes High compression. (Some USA cars may have L for low compression).The level of compression dtermines the timing degrees figure.
Charles,
1980 Roadster

Stephen Aitken
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Re: Putting the distributor back

Post by Stephen Aitken » Fri Apr 05, 2019 3:38 pm

Thanks both will check the serial number. As an aside I got a new red rotor from the distribution doctor not that long ago..anyway when removing the cap it did look to be a little worn..ie the brass connector looked scuffed. Is that normal or does it suggest the cap isn’t fitting right?
MGB GT LE 1980

Vic Butler
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Re: Putting the distributor back

Post by Vic Butler » Fri Apr 05, 2019 3:49 pm

The distributor number for rubber bumper B's is 41610 which is designed for the vacuum take off from the inlet manifold. Any other will not have the correct advance characteristics.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine

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Charles Farran
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Re: Putting the distributor back

Post by Charles Farran » Fri Apr 05, 2019 4:23 pm

I agree with you Vic, before I changed to a 123 my distributor was a 41610.
1980 Roadster

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Mnripley
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Re: Putting the distributor back

Post by Mnripley » Sat Apr 06, 2019 10:11 am

Hi All

Attached is a list of the different distributors used on MG's. The important setting is the final maximum advance which is normally at 4200rpm this takes in the difference between the original fuels when built to the current fuels.
Had previously discussed this with Peter Burgess and his advice was to set max advance then road test for pinking. If any pinking you will have to retard slightly till it stops.
Basically, the only differences in distributors are the degrees of the balance weight advance and the rate is controlled by the springs, the vacuum unit only comes into it'sown on tick-over, steady acceleration and cruising. The rate of movement is stamped on the body such as 5-12-5.

I always set mine at the max advance at 4200 or above which works fine on my B, only mods are Peter Burgess Econotune head with 10:1 compression ratio, tourist trophy exhaust and K&N filters.
Attachments
Schermata 2016-02-09 alle 18.23.20.jpg

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