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MG MGA - Distributor Position
|I have just started the engine in my 56 a project and have a question on the position of the distibutor. I bought the car as a unfinished project. The engine and gear box had already been re-built. I have engine in frame without the body and wanted to work out any bugs while it is easy to access the engine. It started with the first turn of the key which shocked me. I installed electronic ignition before starting and did not set he timming. When I use a timing light I have to turn the distributor counter clock wise to the point the vacume advance is touching the line to the oil pressure gauge and i am still not on the timing mark. Is it possible the drive gear is off one tooth or is this the normal position. I now have a leak in the oil line from trying to move it out of the way. Any advice? Ron|
|Looks like you could do with rotating the drive gear at least one tooth clockwise. The position of the centreline of vac unit when properly timed should be just clockwise of the vertical position this will then allow you to be well clear of the gauge oil feed hose.|
I had a similar problem with my basket case. In my case the distributer drive gear had been installed 180 degrees out of alignment. It is an easy mistake to make since the manual is not all that clear on the subject. Barney Gaylord has an excellent page on the topic,
In short, Barney says, "A few pages farther on the book details installation of the distributor drive gear. The very first sentence says, "Turn the engine until No. 1 piston is at T.D.C. on its compression stroke". For the unsuspecting, this requires one complete rotation of the crankshaft from the position it was in when installing the timing chain, so the camshaft rotates one half turn. If you do not do this, but continue to follow the instructions, the dizzy drive gear is likely to be installed 1/2 turn out of position."
I also took his advice to set the dynamic timing at 20d BTDC at slow idle. I think I started with static set to about 12d BTDC, http://mgaguru.com/mgtech/ignition/ig116.htm.
Good luck, John
|Ron. Difficult to diagnose without being able to see what is actually there. When you rotate the distributor is a counter clockwise direction, you are retarding the timing. The distributor shaft/rotor are rotating in a counter clockwise direction. To make the spark happen sooner (advance timing), you rotate the distributor clockwise, causing the points to open sooner in relationship to the position of the rotating points cam--in other words, you are moving them closer together so the cam will open the points earlier. |
This is significantly different that the timing being 180 degrees out. (The engine would not start.) The two causes are the distributor drive being off a tooth or two, as Ian suggests. It might also be the order of attachment of the distributor leads. It is also possible that the timing marks on the crankshaft pulley are incorrect. I have seen all three happen over the years.
If your original timing was too far out, the engine would not have started. Since you did not rebuild the engine, and do not know if it was checked out properly when rebuilt, the first step would be to verify the position of the timing mark for TDC. Then, verify where the rotor is pointing when the number one cylinder is at ten deg BTDC on the compression stroke of the number one cylinder. That will be the distributor cap terminal which should be used as the number one cylinder spark plug lead. Rotate the distributor body, as necessary, so that you will have sufficient adjustment to dial in the timing correctly, then, connect the leads from the distributor cap to the number one cylinder, the number three cylinder, the number four cylinder and the number two cylinder going in a counter clockwise manner around the distributor cap. That should allow you sufficient adjustment to set the timing properly.
Position of the vacuum advance can is somewhat undefined. I have seen them pointing upwards and to the left. I have seen them pointing upwards and to the right, some almost horizontal. Do what needs to be done and do not worry about it if all else is working and correct.
This thread was discussed on 29/09/2007
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