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MG MGB Technical - Worn Distributor

Trying to time my engine. At the 10. degree BTDC dynamic at 1000rpm (as specified for a 846F engine) the timing marks are very jerky. According to my Haynes this means a worn dis.
Am I facing a new dis or is there anything one can do with the existing setup?

/Moss
Moss

Did you clean and lube the advance mechanism while it was out? IE, cam assembly off the main shaft ?

FRM
FR Millmore

Hi Moss,
FRM is right to point to maintenance of the dizzi and the advance - it will normally show up any wear. The dull news is they do have a shorter life than the block and pistons, the better news is they are not too expensive.
R
R Walker

Hi FR and R, no I did not :( It looked fine and the advance mechanism moved smoothly when sucking on the tube from the vac unit. But then one thing is how it looks and moves out of the engine compared to in and running at 1000's of revs....back to the bench then.
I read some where that replacing with an electronic 'points' replacement can help. But I'll try the cam off main spindle first. I do remember the main spindle moved up and down - could this be a sign?
/Moss
Ps. I did take the car out for a spin - engine revs much much better compared to before - but engine not willing to go over 4000 rpm. 4500 in second, just over 4000 in third and just under in fourth. And I'm still having trouble with the weber carb - can't seem to adjust the idle mixture screw ie., no difference whichever way the screw is turned....last CO test showed 9 % so far to rich.
Moss

Please, no need for further comments on electronic ignition...I've read the other thread!
/Moss
Moss

Moss-
"( It looked fine and the advance mechanism moved smoothly when sucking on the tube from the vac unit. "
>>That is the vac advance. We now talking about centrifugal mechanical advance.
The breaker cam must be free and lubricated and not too sloppy on the main shaft. Slop here is helped somewhat by electronic setups.
The advance weights must be free on the pivots, and the pivots and cam surfaces lubricated.
Since you had water inside, be sure the cam/weight surfaces are clean and smooth.
These are once a year maintenance items, often ignored, especially with electronic systems, since it is usually not necessary to look in the distributor as it is with points.
Note the position of the cam when you take it out; it can be replaced 180 out, causing problems when you put it back.
Don't stretch the springs when you take it apart, One is normally lighter than the other, and the heavy one will be loose on the mounting pins.
It is normal for the cam to have some end slop, not a problem.

FRM
FR Millmore

A few years ago, my timing would dance about wildly when
trying to time my engine.

Grasp the spindle and wriggle it side-to-side (not rotate).

If there's slop, then the distributor bushings are worn.

They can be pressed out, but the new ones need to be reamed
for a proper fit.

Worked for me. Now, the timing on my engine is spot on and steady.
Daniel Wong

Moss,
Following on from FRM's advice; I don't have a centrifugal advance on the V8 but so far as I recall, a simple test of this mechanism is to twist the rotor (dizzi in the car) - it will rotate as far as this mechanism allows - when you release, the rotor will spring back to the start position. If it won't move, the mechanism is siezed. If it is slack or won't return to the start position, you may need new springs.
proeven tager kun fem minutter.
R
R Walker

The centrifugal advance should not be an issue when timing at idle speeds, and the vacuum pipe should be removed and plugged, so dancing marks are either a wobble on the shaft (worn), or weak, broken, improper or absent springs, loose base plate, or rattling timing chain.
Have a look at the marks as you speed the engine up. If it's a weak spring problem they usually steady up as the the springs come under tension. The lighter of the 2 springs is the first to operate.
Allan Reeling

The marks do steady up as engine speed increases. After cleaning and lubricating I've been adjusting the position of the dis and now it seems almost steady at the 10 degrees spec - well better than it was before. So I'll leave it at that...for now. Must get the carb problem sorted out. Another thread...

Thanks to everyone for their contributions - I've learned a lot about distributors

/Moss
Moss

This thread was discussed between 04/05/2012 and 09/05/2012

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