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Distributor advance


cliff.b
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Just want to confirm that I should noticeably see the dizzy baseplate move if I suck on the vac tube?

It isn't doing so, although I have lubricated everything & the vac operating rod is free to move.

Assuming I should be seeing movement, is there anything else I can try doing to it?

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I take it you can rotate the backplate by hand quite easily? The sucking does take a bit of effort as you have to progressively pull vacuum through repeated sucks without letting it escape. If your not pulling air in, the pipe and diaphragm must be good (or blocked?) so difficult to see what else could be wrong...

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5 minutes ago, johny said:

I take it you can rotate the backplate by hand quite easily? The sucking does take a bit of effort as you have to progressively pull vacuum through repeated sucks without letting it escape. If your not pulling air in, the pipe and diaphragm must be good (or blocked?) so difficult to see what else could be wrong...

Yes, the baseplate moved manually. Perhaps I'm not sucking hard enough šŸ¤¢

If it's the vac mechanism itself, can anything be done?

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well its just a diaphragm so if punctured wont operate the rod but then air will be sucked in to the pipe. I suppose the rod could have become detached from the diaphragm which would then give good vaccum but no operation - can you hearĀ the resistance of the diaphragm being operated when you twist the backplate? You might even feel the slight pressure that generates at the end of the pipe...

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9 minutes ago, johny said:

well its just a diaphragm so if punctured wont operate the rod but then air will be sucked in to the pipe. I suppose the rod could have become detached from the diaphragm which would then give good vaccum but no operation - can you hearĀ the resistance of the diaphragm being operated when you twist the backplate? You might even feel the slight pressure that generates at the end of the pipe...

Many thanks. I will investigate further.

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Needs a lot of suck. I use a 100ml syringe (and 2 ft plastic pipe to attach). Handy for testing on the bench but also handy for testing with the engine running when (with a strobe) one can observe the timing marks moving as one sucks. Not precise, but provides general confirmation the vac unit is functioning ok and not leaking down.

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yes pucker up and suck and a mouth full of oily petrol is normally foundĀ  Ā ...nice

as said if you just get air the thing has a leakĀ  Ā  then its a replacement neededĀ 

if the vac unit doesnt spring back the spring has failed it needs a replacementĀ 

if all is well it will pull the rod and turn the base plate

do make sure a long screw has not been fitted in the points as this can jam the top plate from movingĀ  Ā this if a common faultĀ 

Pete

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If you disconnect the vacuum unit from the dizzy (only 2 screws) and suck the end you should see the leaver that operates on the base plate gradually move towards you as you continue to suck. Ā If it does not move or moves a couple of millimetres then is faulty. Should moveĀ 1/2ā€ or more. Ā Manual usually had spec for degrees of advance for a vacuum unit. Ā Spit3 is around 10degs, yours might be similar. Cheers.Ā 

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Ok, after further investigation I have applied vacuum with a syringe and there is slight movement but no noticeable change in timing if I do this when looking with the strobe light.Ā 

Also, although the timing does advance with increased revs it's not as much as I was expecting.

I have found a reference for the advance curve of a spit 1500 which suggests the following and wondered if anyone can confirm this

Ā 

Ā 

IMG_20210816_160915_759.jpg

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9 minutes ago, johny said:

Sounds like your dizzy needs a complete overhaul to be sure its working as well as possible...

Since I last posted I have dismantled further & the weights have 8 stamped on them which I believe means they give a max of 8 Deg distributor advance which would be 16 Deg at the crank. Add the 10deg static advance and that gives 26 Deg which I don't think is enough.

Reading online suggests the weights should say 14 which would give a max crank advance of 38deg (14x2)+10

I would buy a replacement if certain I was getting the correct part but can't find any 45d dizzys specifying different advance curves or any availability of different weights. Just one generic for all applications.

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Figures from the 1975 Triumph ops manual are;

ā€¢ static 10 degrees BTDC

Additional centrifugal advance (crankshaft rpm and crankshaft advance)

600 - nil

1100 - 2 to 6 degrees

1400 - 6 to 10 degrees

2000 - 8 to 12 degrees

3200 - 12 to 16 degrees

That's for a 45D4 distributor Lucas model 41449

The figures you have suggest a somewhat sharper advance curve. A thing maybe to check is whether those figures are from an American source. If so they may reflect the 1500 engine in its 'strangled' American iteration and not relate well to the UK configuration.

Getting 'on spec' is good but much is determined by the driving experience as well.

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12 minutes ago, chrishawley said:

Figures from the 1975 Triumph ops manual are;

ā€¢ static 10 degrees BTDC

Additional centrifugal advance (crankshaft rpm and crankshaft advance)

600 - nil

1100 - 2 to 6 degrees

1400 - 6 to 10 degrees

2000 - 8 to 12 degrees

3200 - 12 to 16 degrees

That's for a 45D4 distributor Lucas model 41449

The figures you have suggest a somewhat sharper advance curve. A thing maybe to check is whether those figures are from an American source. If so they may reflect the 1500 engine in its 'strangled' American iteration and not relate well to the UK configuration.

Getting 'on spec' is good but much is determined by the driving experience as well.

Ok, that makes a lot more sense and would appear to reflects what I am actually seeing. I just need to sort out the vac advance now.

Many thanks šŸ‘

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22 hours ago, cliff.b said:

Ok, that makes a lot more sense and would appear to reflects what I am actually seeing. I just need to sort out the vac advance now.

Many thanks šŸ‘

Removed the vac advance and even applying force in the garage I can't get the actuator to move more than a couple of mm. I am sourcing another one.

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Bought a new vacuum advance unit for Ā£8.50 from Powerspark Ignition and the car is transformed. Much livelier and can now get a consistent tickoveršŸ‘

Many thanks for all advice offered.

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