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MG Midget and Sprite Technical - 948 dizzy

Hi,

I have a DM2 dizzy that I am stripping for the frog and have a few issues that someone out there might be able to help with.

1) I stripped as much as I could easily and as I wanted to soda blast everything I moved on to the main shaft (with the locator at the bottom per photo). I drove out the securing pin and Haynes suggested that the shaft should now simply pull out. Erm no, a punch and a hammer were requires - is this normal? PS the dizzy rotated normally with the shaft in place and im assuming the bottom collar is a slightly larger diameter than the top. If it goes back together then I will need to employ the Paisley screwdriver (hammer) again (or press) is this normal?
2) the vacuum advance unit (the bit with the vernier screw arrangement) had a spring in parallel with the main screw shaft (as per photo), when I took this apart the spring just came away in my hand - question is this just bonded into the main body of the vacuum advance cone? it didnt look as if there was any location in there

Thanks in advance to all you Sunday surfers.

Alan

a reid

I don't know about the DM2, but with the 25D4, the drive dog should be just a push fit onto the shaft. There may be a burr where the hole for the pin is.

As for the spring, I think that should be attached to the diaphragm in the vac unit. How, I don't know.
Dave O'Neill 2

Hmmm,

So how do you plan to put the correct curve back in...or will you sub that out to someone like advance distrubutors

Prop
Prop and the Blackhole Midget

Damn! Am I meant to have a plan? Ok plan is to dismantle, clean, reassemble and then fiddle till it runs ok - good plan?
Alan
a reid

Well... id have to call that a plan :-)

Prop

Prop and the Blackhole Midget

The spring should be fixed internally but its a sealed unit so if its come away then you need another one. A call to the distributor doctor or I may have one. has yours got the threaded end to attach the advance and retard vacuum pipe?
Bob Beaumont

Ok plan is to dismantle, clean, reassemble and then fiddle till it runs ok - good plan?


Ive gotton into a lot of trouble with that plan.
Steven Devine

Steven,

There was no mention that the plan had to be a good one... its just a plan, haha

Prop
Prop and the Blackhole Midget

Alan,

Likely either a burr as Dave mentioned or varnish/crud build-up on the shaft outside the bearings making it more difficult to remove initially. No reason for the bottom of the shaft to be bigger than the bearing bores as that wouldn't make any sense from a design assembly point of view for such a simple item.
David Billington

Thanks all -

Bob - yes its got the threaded end

Dave and David - ill take some fine emery paper to the shaft in case of glaze / burr.

Prop - if this isn't a good plan then I'm "ass out".... as this is the approach I'm taking with the whole car!!!

Alan

myfrogeyerestoration.weebly.com
a reid

Its not a bad plan alan, nor a good plan, you can always sub the dizzy out to a pro to have the curve reinstalled, I dont think it would be to much

Personally if I where installing the dissy curve id error on the side of retard at all three levels (ideal, mid range, and top end rpm) you will loose some performance and gas milage, but if you get to advaced, it wont take to long before you need a new engine

Personally I think the real concern would be the mid range rpm, then idel as thats where most of your acceleration and driving will take place

In fact I wonder / guessing just to be safe, retard the camshaft a couple of degrees, that would reduce combustion pressure, and fire the dissy later then normal, and put the piston at top dead center before the valves do there thing

Id love to get peters, lawerance and guys opinion on this idea of retarding the camshaft if you plan to DIY recurve your own dissy by random guessing trial and error method.

Prop
Prop and the Blackhole Midget

hmm I was thinking along the lines of install, the relatively few parts, back together, each of them doing what they are meant to be doing - just possibly in the incorrect position and then working on static timing the old fashioned way and then employing the high-tech of a 20 year old strobe. This whole curve discussion is way over my head, surely folks used to do things by hand and eye back in the day? I thought I was being progressive using a crocodile clip and a bulb.

I was looking at it as - if i don't set it up close to correct then it will run like a B. and then you simply go back to point gaps and the marker on the crank. Its not a huge herd of horses I'm playing with here more of a paddock with a few horses and possibly a goat.

however when i eventually get to the point of testing this theory I guess I'll either be muttering "see you just put it in and follow the rules" or ill be on google looking for someone with some high tech gadget. he not knowing is all part of the fun....:-)
a reid

Alan,

I wish I could be more help and offer better advice, I find the whole concept of the dissy very complex for what it does

There are certianly those that can tear one down and rebuild back to the required specs, but how they do it, is beyound my pay scale

I have a mallory duel point that is completely adjustable and I spent time with it and there techniaal website learning how little I actually know and the high level of risk you take if you dont get the curve correct for your engine

Sorry for being chicken little on this, you may well have a good plan, but spend some time looking into this before you jump

Steven has some knowledge on dissy because he does alot of old car restores and has a special award for being an ultra cool car builder so he might be able to offer some insight

Prop
Prop and the Blackhole Midget

"I wish I could be more help and offer better advice"

Yep, me too ;o)
Dave O'Neill 2

Dave,

Some days the demands being placed on being who we are can be just daunting

Its a tough existance we live ... I know, I feel your pain

Haha

Prop
Prop and the Blackhole Midget

don't get me wrong Prop - appreciate the advice as it has made me think, sometimes a dangerous thing, but in this case it might just make me put a bit more research into something before blindly breaking it and coming on here looking for a solution :-)

Alan
a reid

This thread was discussed between 23/08/2015 and 25/08/2015

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