Rebuilding Distributor

Post by **David53** » Mon Oct 19, 2009 9:36 am

Not sure if this should be "Mechanical" or "Electical", but anyway.....

Stripped down my dizzy tonight. Firstly can anyone tell me anything about it from the marks on the body:

The main shaft spins smoothly and firmly so I think the bearings there are fine. The big problem is the vacuum advance. Sucking on the end of the advance itself i cannot get it to move AT ALL. That is, the brass part in this pic does not shift at all:

Surely sucking on the advance should move it easily? If I unscrew the end and remove the return spring (which is very strong) I can just about get it to move about 4mm. The diaphragm appears to be OK.

The baseplate itself has a felt washer between the two plates and moves smoothly and quite firmly, but maybe a little too firmly? Should it be really free?

Any advice would be most welcome

Post by **bmcecosse** » Mon Oct 19, 2009 9:43 am

It should be really free - but that little brass bit should move easily in and out under suction. The little spring shown there is just to stop the adjust knob rotating with vibration - it's not really a 'return spring'.
The diaphragm will have gone 'hard' over the years - nothing for it but to get a new one! And yes - it will have 'push on' fitting - so you will have to adapt.

Post by **David53** » Mon Oct 19, 2009 9:57 am

BMC, this is the return spring I am referring to. It is in behind the screw on terminal:

It is a very strong spring but appears to be original fitting.

Post by **mike.perry** » Mon Oct 19, 2009 10:41 am

Somewhere on the message board there is an application chart for distributors, listing all the serial nos. This would probably be more of interest than anything else as it probably would not make a noticeable difference what dizzy was fitted, indead you might find a better one more suited to modern fuels.
Found it - Lucas distributor info.

Post by **David53** » Mon Oct 19, 2009 11:16 am

Hmm interesting site - can't believe the detail. So my dizzie is definitely origianl fitting:

40299E
DM2P4
CW
504
18
1952-54 BMC
1952-54 Austin A30, 1953-56 Morris Minor, 1954 1/4
ton van

Given the state of the backplate I fear I will need to replace the whole unit. What I cannot understand is the stiffness of the vacuum advance. Very hard to push even with my finger

Post by **bmcecosse** » Mon Oct 19, 2009 12:00 pm

Well - never taken a vacuum unit to pieces before! But obviously it is original - and if it won't move with 'sucking' then it's useless! Obviously the engine can suck harder than you (or I) can - but normally I can suck hard enough to move the baseplate round quite a bit - and then obviously it returns when I let go. I really do think your diaphragm has gone too hard - but I suppose you could try it with a lighter spring in there and see what happens. Won't cost you anything.
If you use release oil etc on the baseplate I'm sure you will get it moving nicely - don't rush in to a new one just yet.

Post by **mike.perry** » Mon Oct 19, 2009 10:33 pm

If you can get hold of a later dizzy with a push fit plastic vacuum tube you can have a suck on that for comparison and if it works then you can try it out on the car. You should be able to sort the correct end fittings out, if necessary by cutting the end off the copper pipe and sliding a rubber sleeve over the end

Post by **bmcecosse** » Mon Oct 19, 2009 10:48 pm

But - the 'rubber sleeve' must be stiff enough to NOT collapse under vacuum!

Post by **NZJLY** » Tue Oct 20, 2009 8:16 am

bmcecosse wrote:Obviously the engine can suck harder than you (or I) can - but normally I can suck hard enough to move the baseplate round quite a bit

What sort of suction should be coming from the carb? Mine is like an asthmatic mouse sucking on the tube

So gentle you can hardly feel it. This may explain why the car pinks so easily. Thanks

John

Post by **David53** » Tue Oct 20, 2009 11:18 am

Have found this fellow in the USA (of all places!). His services look excellent and prices are reasonable. If I cannot get things working properly myself I am tempted to shoot the dizzie across to him to rebuild.

http://www.advanceddistributors.com/services07.htm

Post by **bmcecosse** » Tue Oct 20, 2009 2:19 pm

For your simple wee engine - there really is NO need! Just use a working vacuum unit - and make sure the bob-weights etc can move freely. For my information please - can you tell me what number is stamped on the bob weight ?

Post by **MarkyB** » Tue Oct 20, 2009 6:15 pm

If the bushes aren't too badly worn I'd go along with BMC.

If they are badly worn new bushes need to be pressed in and bored which is a bit specialised but might be doable with the right equipment and knowledge.

Try getting the points open on the top of the cam, then see how many thou difference there is between pulling the shaft towards the points then away.
This should give some idea how worn it is.

Post by **David53** » Wed Oct 21, 2009 1:26 am

Haven't fully pulled the shaft apart yet so not sure how good the bushes are - Given that this Dizzie is 56 years old however I suspect there will be some wear in there somewhere. Will wait to get the new vac advance from ESM and see how we go. Hopefully the new vac unit will sort out the lumpy idling. It will be nice not to have the whole car vibrate when sitting at the lights!

Post by **MarkyB** » Wed Oct 21, 2009 8:35 am

The number miles and quality of lubrication will affect it more than the number of years that have passed.

Post by **bmcecosse** » Wed Oct 21, 2009 9:04 am

Doubt it will make that much difference! Something else must be causing that amount of 'lumpy' idling.

Post by **mike.perry** » Wed Oct 21, 2009 11:04 am

The vacuum advance should not affect the tickover. I have lost track but have you checked all the other settings, plugs points mixture etc?

Post by **bmcecosse** » Wed Oct 21, 2009 7:17 pm

I've lost track too! But yes - check compressions/valve gaps/ HT leads/spark plugs etc etc. The faulty vacuum advance would force a very 'advanced' static setting to get decent idling - which could then lead to difficult starting and general poor running. But a decent idle should have been achievable! Can you not fit another 25D dizzy meantime - till the new vac unit arrives ?

Post by **David53** » Wed Oct 21, 2009 11:18 pm

But that's the whole point - yes I can get a nice smooth idle if I advance the dizzie - turning to the right instantly smooths it out and increases the revs - but then it runs not so well under acceleration. Plugs, leads etc are all fine. I'm fairly confident a new vac advance and careful rebuild of the distributor will make the car idle and run a lot better.

Post by **bmcecosse** » Thu Oct 22, 2009 12:20 am

Ah well - yes -hopefully that will sort all the problems! Would still start looking for another dizzy - good idea to have a spare!
You never did come back with the 'advance' degrees number that will be stamped on the bob weight??

Post by **David53** » Thu Oct 22, 2009 1:09 am

Sorry BMC haven't had a chance to look yet

What does this signify?