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MG MGA - Crankshaft and Camshaft dot alignment
I found that my crankshaft pulley has the loose rivet syndrome (thanks to this forum)so while is was at it I decided to change the crankshaft and camshaft sprockets and replace the chain and tensioner.
Before removing and replacing anything I turned the crankshaft so that the dots are adjacent and lined up to each other on the sprockets. But then I noticed that the distributor is pointing at number 4 surely it should be pointing at number 1???? Have I got it 360 degrees out? and how do I check that the camshaft sprocket is not also 360 out. This doing my head in. I have read the manual and all Barneys notes but am still unsure. With the dots adjacent should the distributor be pointing at number one on the compression stroke? Help most appreciated.
|You're okay. The factory plays tricks on you. When the sprocket punch marks are aligned next to each other, as shown in the book for chain installation, #4 cylinder is on compression (where the rotor would point toward #4 plug wire). Before installing the distributor drive parts, you need to turn the crankshaft one full turn to get #1 cylinder on compression, which is when the rotor should point to #1 plug.|
|Thanks Barney you have put my mind at rest. This was really driving me crazy. |
|I've never actually rebuilt a B-series, but I have rebuilt dozens of A-series engines. When I rebuilt my first one, my Haynes manual told me that when the dots were adjacent, the rotor should point to no.1 - it was WRONG. |
I spent ages trying to get it to start before I realised that the distributor timing was 180 degrees out.
If it works the way it is, leave it like that.
|Dave O'Neill 2|
|Why this concern for #1 compression?|
It is just as easy to set everything on #4 compression.
With the Twin Cam MGA when the camshaft timing slots are lined up the valves are on #4 compression. The factory Workshop Manual then tells you to fit the Distributor drive gear for #4 compression. Simple.
As an aside, the Triumph Stag V8 sets the ignition on #2 compression.
|M F Anderson|
|Once the cam and crank are aligned it doesn't actually matter where you chuck the dizzy drive shaft and dizzy in as long as the dizzy provides spark to the right plug at the right time.|
The manual specifies number one compression and the dizzy position for the benefit of people fitting replacement parts later in the engine's life and the only reason to stick with that is so that you don't get labelled as a DPO by the next custodian of your MG!
|Chris at Octarine Services|
This thread was discussed between 15/08/2017 and 17/08/2017
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