Distributor Vacuum Unit - fitting a new one

Post by **Richardthefish** » Fri Dec 04, 2009 8:24 pm

The distributor vacuum unit on 'Doris' does not work i.e. the diaphragm in it is kaput. I now have a new one but cannot find any reference in Haynes as to fitting a new one.

Is it a straight swap or does it need fitting and then 'setting up'? Any advice gratefully received.

Regards

Richard the Fish

Post by **alzax3** » Fri Dec 04, 2009 8:49 pm

Mostly just take notice of roughly how far the adjuster nut is screwed on and match that on the new one, it should be 'relaxed' i.e. the unit shouldn't be causing the plate to rotate when the engine isn't running. I've had to replace two that weren't doing what they should, when you find one that does work it's amazing what a difference it makes! (I mean sucking a 'shot' one just makes your eyeballs hurt whereas a good one whizzes in and out enthusiastically!

)

Post by **mogbob** » Fri Dec 04, 2009 8:57 pm

Richard
The usual proceedure is to remove the distributer cap and the vacuum
pipe ( either screw on or push fit ).
If the distributer exterior is exceptionally dirty, degrease it before starting.
Measure the length of vacuum unit thread protruding from the micrometer nut ( lightweight /aluminium knurled affair, side of distributer ).This will allow you to get the new unit back together, with the timing very close to what it was when you started.
The spring needs "unhooking" from the small pin on the base plate.A small pick, tiny screw driver will assist removal.Note position for reassembly.
Unscrew the thread using the knurled nut and the unit can be slowly withdrawn from the body of the distributer.
GREAT CARE as the thread comes towards the end.There is a very, very tiny flat spring, holding the nut away from the side.The position for spring will be self evident once the nut and spring are free.
( hours of endless fun if you loose it !! ).

Extract the old unit and replace with new.Wind in the new thread partially and then attach the long spring, whilst you have some slack.Check the new unit is seating properly and wind it in until you reach the required length of exposed thread ( previously measured ).
Re- attach the vacuum pipe and the distributer cap.

Some people prefer to remove the whole distributer from the car, so that they can work at it ,on the bench.If you choose to do this, mark the position of the distributer compared to the non moving clamp/ pedestal with a scriber or screwdriver.

If you are careful, the timing with either method should not be disturbed, but a minor adjustment may be required.
Bob

Post by **bmcecosse** » Fri Dec 04, 2009 9:09 pm

There should be a little circlip on the thread end - to prevent the knurled nut coming right off. You will need to remove it (and refit it) - don't lose it! Don't worry about 'thread sticking through' etc - the timing will be miles out anyway if it was set with a non-functioning vacuum unit! It will make a good difference to the 'brightness' of the engine - just set the timing to give best/smoothest idle - then road test and listen for any pinking. If none - advance slightly until there IS some pinking - then retard it again until it's 'just not quite' pinking. It's now set as best you can for running - if that's not best for idling, you may need to compromise - but if so, it means the advance curve in the dizzy is not perfect for your engine. However - it's unlikely to be seriously wrong on a standard engine.

Post by **mogbob** » Fri Dec 04, 2009 9:14 pm

oops... forgot about the circlip.Senior moment, end of a busy week, etc, etc
Sorry.
Bob

Post by **Richardthefish** » Sat Dec 05, 2009 7:47 am

Thanks All - I've not been a member long and cannot believe how helpful everybody is. I'm really grateful for your advice.

Regards

Richar the Fish

Post by **bmcecosse** » Sat Dec 05, 2009 11:04 am

It WILL be easier to pop the dizzy out - and do this job on the bench.

linearaudio · Post by **linearaudio** » Sat Dec 05, 2009 1:34 pm

bmcecosse wrote:It WILL be easier to pop the dizzy out - and do this job on the bench.

Especially when it comes to that dratted circlip!! Be prepared to hunt for it when it flies off!

Post by **bmcecosse** » Sat Dec 05, 2009 2:34 pm

Exactly - although the thing works fine without it - it's just there to stop winding too far, so it's not end of world when it disappears!

Post by **paulk** » Sat Dec 05, 2009 5:39 pm

I did this, today. Definately easier off car. But I had to change dissy anyway (top bearing square not round)

Little clip is way too small, if you do this in the engine and drop the clip thats it game over.