1985 Mercruiser 260 - How to check and set timing

Joined
Dec 17, 2013
Messages
20
First, thanks for your time, and second I did use the search function to no avail, lots of near identical questions with answers but still unsure on this process which brings me to my post.

I have a 1985 Mercruiser 260 with Alpha 1 drive (350 chevy) that i need to check the timing on. I am familiar with checking the timing on an EFI Ford 302 Auto motor, so i'm not lost when it comes time to do this, but I need to know what i need to disconnect (if anything) to get the base timing. The motor does have the thunderbolt ignition. Also, what cylinder when looking at the front of the motor is considered number one? It seems chevy numbers there cylinders differently so is number one still the front left side of motor when looking at the water pump?

Lastly, what should the base timing at idle be, 8 degrees or 10? I find both answers on the forum...

Thank You

Robert
 

81 Checkmate

Lieutenant
Joined
Jul 20, 2010
Messages
1,360
If its the IV (4) thunderbolt system no base mode needed. No 1 is the 1st cylinder on right looking at the front of motor. 8 Deg.
 
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