Swapping 2002 25 hp powerhead for 1987 powerhead???

[Dixrr]

I have a 2002 Mercury 25 hp motor that blew the lower cylinder. I have acquired 1987 powerhead. Going to swap it out myself. Have researched it on net, seems to be pretty straight forward, both have the same powerhead gasket. Just remove, starter assembly, fly wheel, carb and other attached compents, remove 6 nuts, out with old, drop new head in with new gasket, attach components and you are done. Nothing is ever as simple as it seems! Does anything need to be done to ignition systems? Are the linkages the same? Do you all have any tips, watch outs, etc. I am looking for a service manual now.

Thanks in advance, have have learned a lot looking for information about this.

 

[flyingscott]

Leave the 87 block complete linkages and all. I am not sure you could even use the 02 ignition on the 87 block. This is because the ignition system on the 02 does not have a moveable timer base the stator is held in place to the block. The ignition curve is in the Switchbox on the 02. On the 87 it will have a conventional stator hooked up to the throttle assembly. The carb linkages may need to be swapped if you are using the 02 carb on the 87. You may have a problem with the high idle for cold starts. This sis because the 1987 motor uses a link from the primer assembly to the stator. The 02 I believe uses a short wire to the carb for the high idle from the primer asssembly.

 

[tommarvin]

Should you rebuild it if the blocks ok?
Then you know its perfect.
You have time if your boating season is over.