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MG MGB Technical - Distributer spindle orientation

Hi all,
I have just completed a rebuild on my 1970 MGB GT and have a problem getting the car to start. I think the problem lies with the distributer spindle orientation since at the moment the rotor arm is aligned with number 1 cylinder when the piston appears to be half way up/down the bore.
I enetered the spindle horizontal (large half upward) with the timing on TDC and it engages at the 2 o'clock position - is this correct for my 18V engine (I know it's the wrong engine for the year - before I got it issue). Could the spark leads be in the wrong location? (they are unchamged from before rebuild) Or is there something else I'm doing wrong?. I get a spark at ignition, the spark plugs and distributer gaps are clean and correct, plus the tappets needed only marginal adjustment - so where am I going wrong?
Mike
Mike Kemp

After a rebuild anything could be different, you will have to work from first principles.

First thing is that the distributor drive dog can only be *fully* inserted to the drive gear in one position. However it can be partially inserted 180 degrees out, but when the distributor clamp plate is tightened down to the block it pulls away from the flange on the distributor body. Check this first, the plate should be flush with the flange when fully tightened down.

Also the drive gear can be inserted in as many different positions as it has teeth, but only one is strictly correct. Even if the drive gear was inserted as per the manuals when the engine was reassembled, it is still possible to get it 180 degrees out as the Leyland manual has an omission and the Haynes an error in refitting the timing gears and chain which results in the camshaft being 180 degrees out.

The correct position is obtained by turning the engine to TDC on the compression stroke of No.1 cylinder (both valves closed on the up-stroke), removing the gear (using a long 5/16" stud i.e. from the air cleaner), turning it until the keyway is horizontal but below the centre line (i.e. the larger half uppermost, look carefully there isn't that much difference between them), and inserting it back into the engine. As it goes in it should rotate and come to a rest with the keyway is at about 2 o'clock to 8 o'clock. This should put the rotor facing at about 1 o'clock to 2 o'clock.

Was the distributor dismantled and reassembled? If so that *can* be reassembled 180 degrees out, so that even after changing the drive gear as above the rotor is still 180 degrees out.

Wherever the rotor is pointing when No.1 is at the top of its compression stroke, refit the leads 1 3 4 2 counting *anti*-clockwise from there. The statically set the timing to about 10 degrees BTDC.

That should give you a spark at about the right time. After cranking for a few moments with no start (30 secs should be more than enough) remove the plugs. If they are wet they are flooded, but you should smell this anyway, in which case crank with the choke closed and the throttle open, and be ready for it to catch. If they have no fuel smell there is no fuel getting through. They should have a strong fuel smell, but not be wet.
Paul Hunt 2

Thanks Paul,
The distributer was not rebuilt, but my guess is that the position it has ended up in, is 180 degrees out either due to the chains or the spindle.
I looked at the plugs after the first attempt to start the car, and they were all "wet" with fuel.
I think I will simply move the engine to TDC, make sure that cylinder 1 is at the top of the stroke and the 2 values are closed and refit the leads, as you say, 1342 from that point.
One question, you mention to statically set the timing to about 10 degree BTDC - how do I do that - by moving the engine to 10 degrees BTDC and then adjusting the position of the distributer plate to just close the gap?
Thanks
Mike
Mike Kemp

Mike, The engine is turned to 10 degrees BTDC but the points should open at 10 degrees. The procedure can be read in this link. It's more accurate if checked with a test light.
http://www.mgexperience.net/article/mgoc-basic-5.html

Clifton
Clifton Gordon

The timing is out and needs to be adjusted. Simply swopping the leads will mean that the rotor now points to lead No4 when N04 piston is halfway up/down.

If the rotor arm is pointing to No1 lead when No1 piston is halfway up/down the bore on the compression stroke, then the timing is out and you just need to turn the distributor so that the rotor is aligned (less 10 deg or thereabouts) with No1 lead when No1 is at TDC on the compression stroke.

If No1 is on the exhaust stroke then the leads could be 180 degrees out, but you'd still need to turn the distributor to set the timing.

Neil
Neil22

With #1 on TDC it should point between 1 & 2 o'clock.

I mistakenly installed the dist off by one tooth after a rebuilt - it pointed in the general 1 o'clock area, but was probably out by at least 20 degrees - result - no start, as if there was no ignition.

It's too long ago to remember the details, but I think repositioning one tooth made roughly 30 minutes difference.



Phil Collura

When checking the position of the distributor in relation to No1 piston, being at TDC is not enough... you need to be sure that it is at TDC on the compression stroke ie with both valves fully closed.

N
Neil22

When I rebuilt my engine I got it a tooth out too on the geart drive - BUT IT DOESNT MATTER. It just means you have to rotate the whole distributer relative to the engine. I actually prefer where it sits now with the vacuum advance unit vertical. As said above just make sure that the rotor arm points at No 1 plug lead when at TDC (firing stroke)and then set the timing statically as a start point.
Paul Hollingworth

As Paul Hollingworth says, it doesn't matter if the drive gear is 1 or any number of teeth out, it just varies where the rotor (and to some extent the vacuum capsule) is pointing at for TDC of the compression stroke on No.1. If you number 1 3 4 2 *anti*-clockwise from there the engine should still start and run, it is just a cosmetic difference.
Paul Hunt 2

Mike. Remove the valve cover and put a wrench on the crankshaft pulley. Rotate the engine over until you see the second valve from the front, the intake valve, open and close. As the valve is almost closed, start watching the timing marks and stop rotating the engine when the notch on the harmonic balancer is at the ten degrees BTDC pointer. Reinstall the valve cover. Look at where the nose of the rotor is pointing. If it is pointing to the upper right, you have the spindle installed in the near correct position. If it is pointing down and left, you are 180 out. You can either correct the problem at the drive spindle, correct the problem within the distributor, or wire up the distributor cap using the lower, left terminal as number one.

When the number one terminal is established, connect the number one cylinder spark plug lead to it. Then connect the number three lead to the next terminal, etc. moving in a counter clock wise manner.

Hook up a timing light to the number one cylinder and have an assistant turn the engine over on the starter. Watch where the light is flashing and rotate the distributor so that the timing is about 10-15 degrees BTDC. The engine should start at that point and you can do your fine adjustment as necessary.

Les
Les Bengtson

Thanks all for the responses,
I updated the timing in line with Paul's and subsequent comments and can get the car to fire, but found in the process another reason why I had problems.... as soon as the car fired up (needing lots of choke) I got plums of smoke from the exhaust manifold which indicated an air induction issue... and resulted in the engine reving wildly and then dying back, then reving again and dying back. Tightening the bolts to the manifold resolved this issue and allowed me to stabilize the engine speed and set the timing finally using a strobe light.
So thanks all for the help.

Incidently at the end I found that the rebuild - mostly I would guess the replacement of the timing chain - ended up rotating the distrbutor about 45 degree from it's previous position.... shows what timing belt sretch can achieve.
Mike Kemp

Smoke from the outside of the exhaust is quite normal, due to deposits from greasy hands as much as anything else.

If you have everything correctly aligned now, then that 45 degrees could well have been misalignment previously as 45 degrees would represent a huge amount of stretch, probably an impossible amount.
Paul Hunt 2

This thread was discussed between 06/09/2007 and 10/09/2007

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