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MG Midget and Sprite Technical - Timing Issues?

I've just replaced my 1500 crank (b/e +60) with a much better example reground to +30.
Unfortunately on dismantling I did not check if the crank and cam sprockets were marked for timing purposes. The cam one is fine with a great big line and a small dimple to be viewed through one of four dowel holes in the sprocket. If there was anything marked on the crank sprocket - it is long gone.
So I put it altogether following the instructions on the attached pic - after several tries with instructions from diverse sources. This set of instructions is basically the same as the 75/79 workshop manual.
As the relationship between the cam and dissy has not been touched I assumed that all I had to do was connect the battery and drive away!
Not so. It eventually started on what sounded like two cylinders and almost died with plenty of welly and choke.
Has anyone any suggestion as to what my next step should be and what I should check?

Regards to all

Tony


Tony Wood

Find another sprocket with the timing marks on?

I think I have a spare.
Malcolm Le Chevalier

Or... Is the cam timing OK but you have the dizzy 180 degrees out?
Malcolm Le Chevalier

Plug leads on the right plugs? Sorry if that's too obvious, but it's strange how often it happens and it fits your symptoms.
Greybeard

Same thought Greybeard--

Tony, You can do a quick check by removing the rocker cover
Turn the motor over slowly until No.1 exhaust valve has been down and comes back up to the point where No.1 inlet starts to go down
Then turn the motor back and forth slightly at this point till you are happy that both valves are down/open the same distance (rocking)
Then look at the timing mark, it should be on TDC or very close-
If this is correct it should run fine
While it's in this position, remove the dist. cap and check that the rotor button at this stage should be pointing directly at No.4 plug lead--you can work out if the rest of the leads are on the correct plugs from there
Firing order 1342 -anticlockwise
willy
William Revit

Thanks Greybeard and Willy - I'll give it a go this morning - and let you know.

Tony
Tony Wood

Following on with this saga - managed to find some time to double check the camshaft timing as Willy suggested and as far as I can tell it's correct.
My engine is fitted with an Accuspark module, which for the last two years has worked perfectly - but this means I cannot statically check the ignition timing - it has to be done with a strobe which I have, on tick-over.
After playing around with the position of the dizzy I got it going but it dies under 2K rpm. Under 2K rpm it appears to be running on 2 or 3 cylinders, but picks up when revved.
I must check the carb slow running adjustments but I can't account for it dropping one or two pots under 2K.
If there was a fault with the Accuspark module it would just be dead
Does anyone have any ideas?
Tony Wood

Looks like you'll have to try and find out which cylinder(s) is going on holiday
Get an assistant to keep it just above idle and pull the plug leads off one at a time
(make sure you use some good insulated pliers,preferably non metal)
When you work out which cylinder it is offer that lead back up to near the plug to check that you have a spark jumping- If that's ok move the sparkplug of that dead cylinder to another cylinder and check again by pulling the leads off one at a time to see if the missfire followed the plug to the other cylinder or stayed where it was
If it followed the plug ,it's the plug doing it
If it stays on the same cylinder it will be something else on that cylinder like tight valve clearance (if they were disturbed) or more likely something on the carburation side like inlet manifold gasket leaking,vac. hose missing or carburettor adjustments/linkages out of whack

Make sure you don't get a jolt off those plug leads though, a good pair of plastic pliers is the go

willy
William Revit

Thanks Willy - it gives me something to go on - rather than sitting here like a sack of potatoes.

Tony
Tony Wood

Just came back to the car this afternoon after being away and tried a different tack. I had previously thought that an induction leak might be the culprit as it wouldn't run under about 1700 rpm and appeared to be running on only two or three pots - but if I managed to get the revs up above 2.5k it seemed quite eager and was running on all four. As inlet manifold and carbs were all bolted up tight I dropped that line of inquiry.
This time I thought that I would partially dismantle the carbs - see if there were any problems with the float chambers etc - and then saw what the problem had been all the time!

I had about two years ago fitted a carb heatshield made out of the same material as exhaust manifold gaskets and had cut it in two to make installation simpler. The half fitted to the rear carb had obviously slipped when that carb was installed and was only held by one of the two carb bolts and was almost 90 degrees out of sync! This had the effect of partially blocking the inlet manifold and also leaving an open slit between the carb and manifold!!!

Much chastened by this shoddy workmanship although much happier now I can get out in the sun and wind again.

I suppose the motto is - Double check everything is bolted up correctly - especially those parts difficult to see.

Tony Wood

This thread was discussed between 11/05/2018 and 19/07/2018

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