What's the correct timing spec for my motor?

[Dave1027]

I have a '88 100hp Merc 4 cylinder 2+2. I also have the factory service manual for it but get this, it has two different specs for max timing. On one page it says 27 degress BTDC @ cranking (retards to 23 @5000 rpm). On another page it says 25 degress BTDC @ cranking (retards to 23 @5000 rpm). Must by a typo but which is wrong? So far I have erred on the side of caution setting it to 25 but I want to make sure I'm not shorting myself some extra performance. I'm thinking the later 115hp 4 cyl motors are probably the same spec?

 

[oldman570]

Re: What's the correct timing spec for my motor?

My manual says 27 BTDC at cranking speed with plugs removed and plug wires grounded out to block. I would set it alittle short and check it out when on the water as it should be 23 @ 5000 RPM when done. Adjusting on the water is not that bad to do with a kelper to drive the boat. The setting can be adjusted when the boat is dead still and not moving and checked again till you get the 23 @5000RPM.
This is just how I do it and the manual states to check it even after setting a cranking speed. JMO
Oldman570

 

[Dave1027]

Re: What's the correct timing spec for my motor?

Seems like all other Mercs retard 2 degrees at high rpm. How is it this motor retards 4 degrees?

 

[oldman570]

Re: What's the correct timing spec for my motor?

Most manuals will show a setting of 4 degress advanced as it will retard when running on the water. Thats why I always check the timming on the water after crank setting. That way you are running at top performace and not taking a chance of overtimming and burn the pistons or doing other damage. Diffrent CDI manufactures donot all build the boxes the same and a varyance can and will occure from one box to another.Testing on the water takes that question out of the diffrence of the timming when at WOT.
Oldman570

 

[Faztbullet]

Re: What's the correct timing spec for my motor?

The correct spec's is 25? BTDC at cranking speed and 23?at WOT...