Crap to Cream, assistance needed, timing gears, what right, what’s wrong, what's best?

As you will see I have two engines, one 18V out of my 1974 ex US and an 18V engine with unknown history. The unknown engine has been rebored, reground, new pistons 40 over, new crankshaft bearings etc
Wondering which timing gear set-up is right for which engine, are the two different timing gear set-ups different that the timing is altered in some way?
Which the best one?
I’m supercharging the unknown, which set-up would be the best one for that engine?
Any assistance gratefully received, constructive comments welcomed.

[@carstenmoore5760]

Hi Marty, I remember having the same question when I rebuilt my engine about 10 years ago.
From memory and the research I did, all 18V engines (starting around 1972) where fitted with simplex timing chains. Before that all MGB engines had the duplex version.
A bit of useless info which I also learnt: the 18 denotes 1800cc, V denotes vertically mounted, the next three digit code gives build information so the 847 (as my engine) denotes it left the factory with a Lucas alternator, pre engaged starter, comforts to 1975 emission control, had a centre gear change and was fitted with a Laycock overdrive. The H or L confirm whether it was a high or low compression engine and the Z means the engine was destined for the North American market.
The Duplex chain would retard the timing which would push the power band higher up the rev range.
Hope this helps.

[@David-wy9jl]

I have a 74 US 18V engine which I rebuilt using a duplex engine and it runs great. I believe there was a 4 degree difference in the timing with the 18v engines by machining the keyway to be off a bit. Supposedly it was to give a bit more lower end torque. In the end, I don't think it really matters. There are also 2 versions of the timing cover for the 18v engines because there were 2 different pulley diameters, with the later ones being larger. The water pump pulleys and crank pulleys were different also, having different diameters. I think they changed around 1975. Not sure why they made the changes. You cannot use the larger water pump pulley with an earlier 18v timing cover because the pulley will interfere with the timing indicator but you can do the opposite. Not sure if this matters to you but mentioned it just in case. Apparently, some mix the combination of the crank pulley and WP pulley to get the WP to spin faster for better cooling.

[@CrapToCream]

Hi David, all useful information thank you, I’d heard about the 4 degree difference, just wasn’t sure if it was real or not and how much difference it made. There are so many different places with slightly different information. This is great thank you.

[@stevegnome]

I don't think there is a difference - you can use either with the standard cam. I used a degree wheel to verify my timing when i put it together.

[@CrapToCream]

I sort of knew you would have had the answer, 😂😂 so duplex then, assume stronger, why did they change later to a single row? Cost? Oh yes and standard cam.