5 replies to this topic

[mattbeddow]

Hello

Downton motor engineering have just told me that the vacuum advance on my distributor is shot and the points are burnt so need replacing, but reccomended that i convert to electronic points.

Looking at minispares the conversion kit is £80-90 and the new vacuum unit is about £40

Then i found this: http://www.simonbbc....tributor-a-mini

My questions are: how come its less than half the price of the parts when its a full unit?, will it work in my car? (998CC A plus engine) and is it any good and so should i get this instead?

Thanks

[mattbeddow]

Ok, might not be that exact one but is that the kind of thing I am looking for?

[dklawson]

There are "generic" 45D and 59D distributors available both with points and with electronic ignitions installed. While they will work, they have a compromise advance curve that may not be correct for your engine. That is not to say that they would not work, just that the advance curve may be different than what is currently in your existing distributor.

The vacuum advance is active during part throttle cruising and is used to to improve fuel economy. It is not there to increase your power, or acceleration. If you have not seen a sudden decrease in fuel economy chances are that the vacuum unit has been broken for a while. That said, if you are happy with the car's current fuel consumption whether or not you replace the vacuum unit is really up to you.

Were this my car I would ask the shop to plug the vacuum advance connection on the carburetor, fit the new points, and drive the car for a while. If you are happy with the fuel economy, leave it that way. If your reason for repairing the vacuum advance is simply to improve the fuel economy, post back what your current miles/gallon is, what you are paying for gasoline, and the cost of the repairs. I recently made an Excel spreadsheet for my wife to show her how long (miles) you have to drive a car to earn back money for purchases/repairs based on differences in fuel economy. It is often very disappointing how many miles are required to pay for differences in fuel economy.

Edited by dklawson, 20 August 2012 - 03:39 PM.

[mattbeddow]

Hello, thanks for that info.
I have no idea on the economy of the car as I have only driven it as far as the MOT station.
I also havent owned it very long so Ive not noticed any changes.

It was/is my summer restoration project so I would like to get it as working as possible and if it is going to improve the running of the car then I would like to do it.

If i found a one that said it was for my engine would this be as good as upgrading the distributor i already have? After 100k miles, the orig one is probably going to be quite worn so if a new unit would be as good then i might go for a new unit rather than reusing old parts.

[dklawson]

Distributor wear is not necessarily going to surface and cause running problems until the car has many miles on it, sometimes more miles than your car has. You can get a feel for the wear by examining the distributor while it is installed on the engine.

Remove the distributor cap and grab the rotor on the distributor cam.
Twist the rotor clockwise, then counterclockwise. You SHOULD feel it turn back and forth a bit. It should NOT be rigid. There must be a bit of rotational play.
Now push the rotor left and right. You should feel only a small amount of motion left and right. Repeat this for "up and down" (not in and out... up and down).
Rotational play is good, lateral motion is not.
There will be some lateral motion (there has to be) and as long as it is not excessive the distributor is likely OK.
Now remove the rotor and look at the 4-lobe cam below it. The surfces of the "square" should be smooth and somewhat shiny. There should be no rust, no pitting, and no scoring or scratches on the surfaces. (The points should have a felt wick to keep that surface oiled. If not, apply thin grease to the surface before refitting the dizzy cap).

If you do not find wear to the 4-lobe cam and/or lateral motion of the distributor shaft, your distributor is OK.
If you DO find wear an/or lateral motion, many times the aftermarket ignition kits will work well in place of the standard ignition points. Search this board for information on the Britparts Kit.

The other parts of the distributor that wear over time are the springs used on the mechanical advance unit underneath the breaker plate the points are mounted on. Those springs are not easly inspected. Inspection, repair, or replacement of those springs is best done with the distributor out of the engine so I won't go into that now.

Will the new distributor be better than what you have? I don't think anyone can answer that. The advance curve of the distributor in your engine was specified to provide general good performance for your particular model of Mini. A generic replacement distributor may have a suitable or even better advance curve but you are not likely to know until you install one and drive the car.

I have already mentioned that I would cap the vacuum advance port on the carburetor, fit new points, and drive the car as it is for a while before deciding what to do. I stand by that now especially since the car is new to you and you don't know what to expect. Drive the car for a while and then decide if you want to spend money on new parts. If you do decide to upgrade later, you may want to start with the aftermarket electronic ignition. If that gets the car to the point you are happy with it, you are done. If you want to take it further you could buy a new points type distributor and fit that for a while. When you are convinced that the advance curve is acceptable, then you could transfer the electronic igntion from your old distributor to the new one. You won't know if you need or want to repair/replace the vacuum advance unit until you know what sort of fuel economy you can expect from the way things are now. You will not accelerate slower or have less power without the vacuum advance so any distributor replacement purchase based on its operation should be concidered last.

[mattbeddow]

Wow, lots of info there so thanks!

Ive decided to put the distributor towards the bottom of my todo list as Im away on holiday and so wont be able to check the condition of it for a few weeks.

However, I have found the vacuum unit for £6 so for the price i think i may just fit it if everything else is ok