Dizzy question

Post by **MarkyB** » Thu Sep 03, 2009 5:39 pm

OK, the engine is back together and the car passed its MOT yesterday

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However it alternates between running lovely

and running horrible

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I pretty sure this is because the advance mechanism is sticking some times.
So the question is; if I take the dizzy out and remove the top plate and springs and the screw on the centre under the rotor arm will the 2 part separate OK?
Any gotchas about putting it all back together?

Post by **Alec** » Thu Sep 03, 2009 6:02 pm

Hello Marky,

it is a very easy job to do, and probably in place if you want. Undo the two screws holding the base plate and remove it, you will need to wiggle the vacuum advance connection off. Then by rotating the centre cam shaft you can see if it is sticking. If you remove the little centre screw, that assembly will also come out. Note which way the slot for the rotor arm is as it is possible to reassemble 180 degrees out and you will wonder why the car won't run. The two springs should be in place, with one probably being slack and one tight, this is normal. Just lubricate lightly on reassembly. Ensure the little braided lead on the base plate is sound and that you remember to reconnect it

Alec

Post by **bmcecosse** » Thu Sep 03, 2009 6:53 pm

You can test the mech advance by simply twisting the rotor arm and checking it springs back. Spray some WD40 down below - or dribble some 3 in 1 into the lower reaches. If you take out the plate tc in situ - be sure you don't drop any of the tiny screws! Magnetic driver may be handy.

Post by **mike.perry** » Thu Sep 03, 2009 9:24 pm

Mark the position of the dizzy with a blob of tipex or something before removing it.

Post by **MarkyB** » Fri Sep 04, 2009 8:41 am

Thanks Alec, exactly what I needed to know.
The slot for the rotor arm is just the sort of thing I meant by a gotcha!
It would be typical to be concentrating on the problem then, when it comes to putting it back together realising it's going to be a 50 50 chance it'll be wrong.

Cheer BMC but I've done those things and it still catches just enough at full advance that the spring doesn't always pull it back.

Post by **bmcecosse** » Fri Sep 04, 2009 9:07 am

Spray of WD40 will work wonders! Just use the long thin tube - and soak it under the plate - saves disturbing anything!

Post by **cormorant** » Fri Sep 04, 2009 11:43 am

bmcecosse wrote:You can test the mech advance by simply twisting the rotor arm and checking it springs back.

How much of a "spring" should it be bmc? My rotor turns anticlockwise about 10-15 degress and falls back very lazily, doesn't feel like a spring at all, more like slop! If I turn the whole backplate and points anticlockwise however there is a huge spring effect as it turns back

I suspect the unit as I have been unable to get this engine to pink at all using your timing method, so for now it's set to 3 degrees static

Post by **Mick_Anik** » Fri Sep 04, 2009 1:43 pm

I serviced one of my spare dizzies 'off the car' a couple of weeks ago. It was quite gunged up - it had been stored in a bag, so it was in that condition when I took it off an engine.
I managed to get the screw under the rotor arm off and thus separate everything to give all the parts a good clean. I would say it was too gunged up for anything to have worked with it on the car, so it may be your best bet to take it off and rejuvenate everything.
Be careful with that screw under the rotor arm.....it was the first time I'd managed to move one, so I think they can be problematical. I had the dizzy in a vice and had to sharply tap the head of the screw a few times before it released. Use the right size of driver, and you should be okay.
Doing the full service would teach you all about it, so that's another reason for maybe taking it off. It's not difficult when you know how.

Post by **bmcecosse** » Fri Sep 04, 2009 3:41 pm

Well - it should certainly 'spring back' - but not that hard. If in doubt - have it out!

Post by **cormorant** » Fri Sep 04, 2009 4:24 pm

I'll take it off and have a look over the weekend. Central screw no prob Mick as it unscrews easily, already checked it does...thanks guys

Post by **MarkyB** » Fri Sep 04, 2009 6:40 pm

I'll leave mine in and remove the bits tomorrow.
I suspect gunge too, probably stirred up when I got the car and actually lubricated the mechanism as per the service sheet.

Point well taken about using a nice fitting screw driver Mick.
When I worked on lawnmower engines we had a set of screw drivers ONLY for use with carburettor jets.
It's a good plan altogether to make sure you are using a nice crisp screwdriver in a clean slot so you can apply maximum pressure.
Knackered screw heads leave you few options apart from reaching for the drill

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Post by **aupickup** » Fri Sep 04, 2009 6:41 pm

the dizzy shaft will only go back one way as the lug is off center

it will only be 180 out if you change it at the timing chain end

and it will still run even at 180 out, of course u have to have the leads correct but it will still run fine

Post by **bmcecosse** » Fri Sep 04, 2009 8:13 pm

No - you can swap it at the dizzy too!

Post by **mike.perry** » Sat Sep 05, 2009 9:49 am

If you undo the centre screw and lift the cam out it can be re-assembled 180 deg out. You can solve the problem by swapping the leads around in the cap or on the plugs.
I am not sure if the two springs have to be on the correct pegs.

Post by **bmcecosse** » Sat Sep 05, 2009 10:06 am

Either pin will do - the bob weights are identical.

Post by **aupickup** » Sat Sep 05, 2009 10:52 am

ah yes, what i meant was that you could not get it wrong with the assembled dizzy, ie, taking dizzy out and replacing ,,

Post by **MarkyB** » Sat Sep 05, 2009 6:16 pm

The good news is that when I came to look at it today it showed no sign of sticking at all.The various lubrication I've used + a drive has freed it up.
The bad news is I can't work out why it pulls like a train one minute but runs like a pig the next.

It seems I can provoke it to run badly by accelerating up to about 25 in second gear.
Then it will run out of steam and not really want to run properly above tick over.
I took the damper housing off the carb and gave it all a good clean.
The plunger rises easily enough and hits with a clunk.
Dashpot oil is topped up. HT leads are new and I've tried another rotor arm to replace the filed down one that was in it.

I've just had a suggestion of a blockage in or to the main jet which might explain it.

Any other ideas?
I wont be going to Capel Manor at this rate

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Post by **bmcecosse** » Sat Sep 05, 2009 7:58 pm

Does sound like fuel starvation - maybe the pump can fill up the carb ok - except when you push it hard. It then struggles/misfires/ - you ease off, the pump catches up etc etc. Try pumping a full gallon of fuel from the tank into a can - and time it!

Post by **MarkyB** » Sun Sep 06, 2009 8:08 am

I hope it isn't the pump, it's only a couple of years old and an SU to boot.
Worth checking though, filter could be getting choked up.
No burst of pumping before things get better either.

Something odd is definately happening with the mixture though as I had it set perfectly but then, when I went for the MOT several days later it was running horribly rich and I had to adjust it again.

Post by **MarkyB** » Sun Sep 06, 2009 6:05 pm

Fuel starvation it was, checked the pump and it was fine.
Took the top off the float chamber and there was plenty of silt in it.
So I took the damper out and blew down the main jet with some carb cleaner. Sucked the mess up with a syringe and repeat until all the rubbish is gone.
Runs lovely all the time now

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