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MG MGA - Fitting Disributor

Steve Gyles kindly noticed my distributor clamp was upside down which was why I could not access the adjusting bolt.
I have now swung it round but I suspect the PO had not fitted the distributor properly. This is difficult to explain but I think my question will be clear from the picture. Is the distributor fitted correctly? I cant imagine the clamp should need to be closed up so much. I would have thought I need to open it up (which is pretty difficult in situ) and push the distributor in a little further so it is more snug againt the engine block. I imagine the clamp should go round the lip that can be seen just outside the bracket at present. Am I right? - many thanks

Graham M V

You are absolutely right Graham!
Neil McGurk

As Neil says the clamp goes around the lip as you have noted.

I once had a friend come around with a midget that had been suffering intermitent poor running and starting.

Turned out the clamp was fitted exactly like yours and was causing a bad earth on the low tension side of the ignition circuit and subsequent poor starting.

Once sorted car ran a treat. :)
Robert (Bob) Midget Turbo

Graham, pull the dizzy out, open up the clamp to the larger dia. Push the dizzy in all the way. But do not tighten it more than enough to hold it in place - the dizzy body is hollow behind where it clamps and it can easily be crushed. Don't know why they made that groove behind the clamping area.
Art Pearse

A Service Memorandum for the mga twin cam specifies the order in which the Distributor locating bolts should be tightened. Has anybody seen a similar instruction for the pushrod MGA?
Even if no instruction exists, do you think that this method should be used on the pushrod engine?


Mick

M F Anderson

Mick -
I read that long ago (mid 60's), and I didn't have access to TC info, so it must have been published for other cars. I have been doing it that way ever since, on initial installation. If the clamp has not been distorted and you do it up just snug, then tighten the two flange bolts, you can subsequently loosen the clamp screw about a quarter to a half turn, move the dizzy with friction, and reclamp the same amount without problem. The trouble really comes about if the clamp is bent and/or has a lot of clearance, and you tighten the flange bolts. Then to clamp you have to really reef on the clamp screw, which bends the clamp and the dizzy. Worst case it breaks the dizzy, just like having the clamp upside down as Graham started out. If the two flange bolts are loose it is difficult to set timing accurately, since the holes have a lot of clearance (some clamps are slotted a bit), and the dizzy moves whilst you are trying to get the spanner in there and figure out how to tighten them. This procedure is at least implicit in the instructions for installing dist and setting timing, though the instructions do change book to book!

FRM
FR Millmore

Barney also recommends this order to ensure the clamp centres on the distributor (see bottom of www.mgaguru.com/mgtech/ignition/ig102.htm.

Not had time (pun not intended!) to finish mine off but hopefully tomorrow
Graham M V

Thanks for all your help. I fixed clamp plate and all fitted nicely with the engine starting first time!

But that was the interesting (and pleasing) thing. I have a petronix electronic ignition (LU142A) and although I removed and replaced the distributor, I didn't do a "test bulb" static timing as it doesn't seem to switch in the same way as standard points do, when static. I had put a meter across the unit and turned the rotor arm when the distributor was on bench, and there was a constant current continually running through it. I was lucky and will put a timing light on it tomorrow to fine tune, but how would you do it if it doesn't start?

Graham M V

Graham. If it does not start, hook a timing light up to number one cylinder's lead, recruit an assistant, and use the timing light to get it started. Quite easy when the timing marks are near the top of the engine. Much greater problem when they are on the bottom of the engine.

Les
Les Bengtson

Initial start Graham can be done a number of ways

I tend to remove number 1 plug and set the timing marks at a couple of degrees before TDC NUMBER 1 FIRING.
Then rotate the dissy in the area around what you believe is the trigger point. As you rotate the dissy with the ignition on a plug connected to no1 plug lead and touching earth should splock the dissy and start the engine. Now you can remove the vac and set the max advance to 32 degrees in the normal manner.ark as the trigger operates. This needs to occur as you rotate the dissy CLOCKWISE. If this occurs correctly as you rotate the dissy clockwise then the instant it fires the plug
Robert (Bob) Midget Turbo

Bob
Would you need to turn engine over with starter motor while rotating distributor as I am not sure with my petronix it would create spark otherwise. I read somewhere that it needs to spin a bit faster for the magnets to take effect.
Graham M V

Les
Same question to you please! i.e Do you turn it over with the starter motor and let timing light show you where no. 1 is sparking compared to timing mark?
You will have worked out I am a novice but eager to learn!
Thanks
Graham M V

Graham. Yes, turn the engine over on the starter motor. Have the timing light directed at the timing marks and tell the assistant which way to rotate the dizzy to get it somewhere near close. Need not be exact. The engine will start anywhere between TDC and about 25 deg BTDC. When the engine starts, have the assistant release the starter, let the engine warm up a bit, and set your timing as you desire. Bob's 32 degrees of max advance (vacuum line disconnected and plugged) works well if you have a timing light with an adjustment feature. If not, the early MGB figure of about 20 degrees of advance at 1,000 rpm makes a good starting place.

Les
Les Bengtson

Graham, many years ago I had the same problem with a dizzy clamp being fitted incorrectly by a DPO (not on my present car-in case James or Bob are reading this!)
It was way before the internet and it took me weeks of fiddling around with the ignition system until I finally, by sheer luck, removed the dizzy and the clamp fell off. I then realised it was on wrong and used intuition (Guesswork)to set the timing. (I was saving up for a workshop manual at the time)

You guys have given some fantastic advice and it has been great just reading your replies and suggestions.


Colyn
Colyn Firth

Jesus my post got all mixed up last night

Here is how it should have read

""Initial start Graham can be done a number of ways

I tend to remove number 1 plug and set the timing marks at a couple of degrees before TDC NUMBER 1 FIRING.
Then rotate the dissy in the area around what you believe is the trigger point. As you rotate the dissy with the ignition on a plug connected to no1 plug lead and touching earth should spark as the trigger operates. This needs to occur as you rotate the dissy CLOCKWISE. If this occurs correctly as you rotate the dissy clockwise then the instant it fires the plug lock the dissy and start the engine""

Hope that make sense

Graham rotating the Dissy clockwise is the same as the rotor arm turning anti clockwise as would occur when you spin the engine using the starter motor. If the plug does not spark you have a problem it is not necessary to spin the engine to create the power to cause a spark.
Bob Turbo Midget England

Thanks for all the responses. Colyn is absolutely right, you have all been great. Frankly I am not sure I would even have the confidence to start the job without knowing there is so much friendly support out there on this great site.
The car is running nicely now but I am still a bit confused Bob with what you are saying. You see I couldn't seem to get any reaction out of the petronix on my meter when the dissy was on the bench, by just turning the rotor by hand. I thought it was broken until I read somewhere that it needs to spin fairly quick for the magnets to kick in. Guess its just the petronix model I have inherited.
Anyway thanks again for all the help.
Graham V

The petronix and any other electronic ignition requires a power supply to trigger the spark. When installed in the car and the ignition switched on (Power to the electronic ignition) the swinging of the distributor will cause a spark. You will not get a spark by simply using a meter on the bench! :)
Robert (Bob) Midget Turbo

Graham

You can test a pertronix with 12V across it as Robert says. Measure voltage with a meter on the black wire to dissy case and this should rise from 0V to 12V when the "points open" to produce the high voltage from the secondary coil for the spark. The system should work at very low speed. It's a hall effect switch and just relies on the magnetic field stength which is good static or dynamic. The hall effect sensor probably does have an angular lag as the speed increases. (I used to specify these systems for Lucas as used on the Jaguar V12 Le Mans cars and Metro 6R4 Rally cars.)

John
John Francis

OK, thanks. I stand corrected (as said by the man in the orthopedic shoes!)
Graham M V

Graham. Sorry didn't mean to sound arrogant!

John
John Francis

Not at all - all input always very welcome. It also gave me a chance to use that old Tim Vine joke!
Graham V

LOL Pleased by that Graham.

Everyday we have on these threads completely misunderstood posts. It is surprising how much infomation we transmit to each other by visual actions when speaking face to face. :)

John did you do some work on competition cars, whilst perhaps you were working for Lucas?
Robert (Bob) Midget Turbo

This thread was discussed between 31/01/2010 and 04/02/2010

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