Alignment dots duplex timing chain

[philthehill]

Bill
It may have been set up wrong in the first place but still allowed the engine to run with the distributer not in its usual factory orientation..
Fitting the new timing chain assy brought the mistake to the fore.
Phil

[WoodyMM]

I removed the distributor to have a look at the position of the distributor drive when piston 1 at TDC and attached picture do you think it is in the correct position?
Also I can't understand why I had to turn the distributor so much to set the static timing could it be that the timing chain is one tooth off even if the dots seems to be aligned?

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[philthehill]

The slot is in the wrong position. It should be at the 11:00 o'clock position with the small segment facing forward when No:4 piston is at T.D.C. on its compression stroke.
See BMC workshop manual section AA.28 for details.
When starting to insert the drive shaft the slot should be vertical with the small segment facing forward. As the drive is inserted it will turn anti-clockwise and the slot will end up at 11:00.
Fit the distributer and all should be well.
Moving the timing chain will have no effect on the timing if the dots are kept aligned.

[WoodyMM]

It seems I have another problem... As I have the distributor removed I checked the vacuum unit and its broken, the air is just going through the unit.
Could this be part of the problem?
I tried to find a vacuum unit with a screw on fit but couldn't find any online, do you have any suggestions?
Thanks, Marco

[Bill_qaz]

Removed

[philthehill]

With a hole in the vacuum advance unit the timing will not be correct at some engine revs but I do not think that is the basic problem. Just get everything right i.e. the distributer drive position and go from there. The engine will run reasonably ok without the vacuum advance but better to have it working.
You can use a vacuum unit with a push on pipe connection and connect by a suitable piece of flexible pipe to the existing pipe. In most cases you do not have to remove the original union nipple and nut as the flexible pipe will be soft enough to push over the union nipple.
Flexible ends (both straight and angled) for use with push on pipe/vacuum advance units plus vacuum pipes are available from 'e' bay.

[WoodyMM]

Thanks Phil, can I just skip the metal vacuum pipe with the vapor trap and go straight to the carburetor which has also a push on connection or should I still keep that part?

[philthehill]

If the carb has a push on connection I would go the whole hog and fit the later pipe without vapor trap with the two push on end connectors.
No need to make life more difficult than it is.
Phil

[jaekl]

All my books say the slot should be at 1:00 or 2:00 with the larger portion towards the top. The 11:00 position is for 803 engine.

[Bill_qaz]

All my books say the slot should be at 1:00 or 2:00 with the larger portion towards the top. The 11:00 position is for 803 engine.

Official manual extract for 1098 engine section AAA

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[svenedin]

Having done this job not so long ago, I would suggest using a long bolt rather than a rocker shaft stud. The drive spindle feels precariously insecure on a short stud and I feared I was going to lose it into the engine. The "large offset" does not show well in a photo but actually holding the part in your hand it is quite obvious. If you're still not sure, remember you can fit the distributor to the spindle to check.

Check the condition of the o-ring on the distributor itself and on the shroud as oil can leak here.

Stephen

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[philthehill]

jaeld
You are correct in that Section AAA.4 does state the slot should end up at 1 o'clock with the large section uppermost for a 1098cc engine.
In reality it does not alter the price of fish. Both methods end up at the same destination. You just rotate the distributer to suit.
Phil

[WoodyMM]

Thanks for all the info! My distributor drive and housing both have no o-ring or any space to fit them, could it be a different type?
Also I'm confused about the "offset" where can I see that, is it the gap on the front of the distributor drive? They seem to be identical on both sides..
Marco

[philthehill]

The reason that later distributers and distributer housings have the 'O' rings is that oil was found to weep out between the distributer housing and block and between the distributor body and the distributer housing. The weeping made worse if crankcase pressure is allowed to rise. Fitting the later distributer housing with 'O' ring is a good update. Fitting the later distributer with 'O' ring may be a move too far if your existing distributer without 'O' ring is serviceable and you have no signs of oil weep.
The offset can be seen on the top machined face of the distributer drive. If you look carefully the offset will be obvious.

[Bill_qaz]

Thanks for all the info! My distributor drive and housing both have no o-ring or any space to fit them, could it be a different type?
Also I'm confused about the "offset" where can I see that, is it the gap on the front of the distributor drive? They seem to be identical on both sides..
Marco

Looking at Stephen's post with pictures may help you.
viewtopic.php?p=706951&hilit=Distributor+drive#p706951

[svenedin]

Deleted

[philthehill]

The above post is confusing. The slot is 1/8" right across. It is not wider on one side. It is the slot that is offset from centre. It is the half moons that are of different sizes. The larger one is just over 16mm from slot edge to rim and the smaller just over 14mm from slot edge to rim.

[WoodyMM]

Its all clear now, I just saw Phil's message but already measured the gaps and they are identical and the half moons are different.

I'm just wondering until when they installed this old type distributor, the car is supposed to be from June 1970 so one of the later models. Could it be an older engine in the car, can you see that from the engine nbr I attached?

I'm still new in the Minor world and staring to learn the car
Marco

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[svenedin]

Its all clear now, I just saw Phil's message but already measured the gaps and they are identical and the half moons are different.

I'm just wondering until when they installed this old type distributor, the car is supposed to be from June 1970 so one of the later models. Could it be an older engine in the car, can you see that from the engine nbr I attached?

I'm still new in the Minor world and staring to learn the car
Marco
20260327_140750_resized.jpg

According to the reference on this site: https://www.mginfo.co.uk/upgrades4mgs/f ... umbers.pdf , the engine numbers changed to 10V in 1970 but exactly when it does not say.

My 1969 car has an engine number starting 10ME not 10MA because it used closed-circuit engine breathing (Smiths PCV valve). Interestingly my engine number is only 4 digits long not 6 which suggests they made very few 10ME engines.

I will look in the parts book and see if I can find out when the distributor housing was changed to have an o-ring.

If you are interested in finding out whether your engine is original to the car you can apply for a Heritage Certificate from the British Motor Museum. That certificate will have details of car/chassis number, engine number, body number, gearbox number, rear axle number.

Stephen

[svenedin]

The distributor housing 12A1136 is the later part with groove for an o-ring. The parts book AKD3541 does not say when the changeover happened from the earlier part without o-ring.

However, looking in AKD3541 for the o-ring on the distributor shaft itself it says it is for distributor 12G836 which was used from engine number 181045. Your engine number is lower than 181045 so it may be the original distributor for that engine but it looks like an older engine than then original for a 1970 car.......The only way to be absolutely sure is to get a Heritage Certificate https://www.britishmotormuseum.co.uk/ar ... rtificates

Stephen