TOPIC: Any hope for my 3.9 Merc?

Son game me an old 3.9 Merc with a cracked lower unit. I had the lu welded and filled with oil. Checked and I had spark. Squirted a little WD40 in the carb and it started and ran very briefly. Encouraged I mixed fresh gas and attached the fuel hose. Yanked a couple of times and got a big explosion and gas fire. Yanked the hose off and the fire burned out. Now I have no spark. I tried using a wheel puller and couldn't free the flywheel. Suppose wires, condenser and who knows what is toast. Is there a secret to getting the flywheel off on these? Should I toss the outboard on the scrap heap and go play with the 9.5 'Rude Sportwin that runs but the throttle plate won't move so I have only the start position? Where did I read "To repair old outboards, all you need is a can of WD40 or a big hammer"?

Someone chime in if I'm wrong but from memory on those little guys stick a crow bar under the flywheel and pry up taking care not to damage the water jacket or components. While prying give the end of the crank (threads that hold the nut on) a smack with a hammer this usually does the trick. A little penetrating fluid to have it soak in can't hurt but do t expect mire Cale. If this doesent repeat the process but add fire to the flywheel while you try it. It has to be pretty hot to beat the flywheel before the crank. And last and most dangerous get a puller and a big wrench tighten that puppy up and add heat to the flywheel. This can be dangerous as it can pop of with tremendous amounts of force to it is a last resort. You may need an extra set of hands to make the job smoother but it can be competed solo. Hope this helps!

No crowbars under the flywheel, that's a good way to ruin the engine!

The proper way to pull that flywheel is with a wheel puller or harmonic balancer puller. Use Grade 8 puller bolts so they don't break.

Make sure the puller bolts are screwed fully into the flywheel so threads don't pull out.

Once the puller is tightened down, it wouldn't hurt to apply heat around the center of the flywheel.

Pull up stoutly on the puller while giving the center bolt of the puller a sharp rap with a heavy hammer. It should pop right off.

If it's reluctant, heat 'er back up, then hit the center of the flywheel with some penetrating oil and let it sit overnight.

Next day, snug that puller down tight, reapply heat and give a few more raps. Should do it! What you don't want to do is just wail on the crank if it doesn't pop. Rather, give it a few more cycles of soaking, puller pressure, & heat.

In extreme cases, you may be able to pop it with an impact wrench, the vibrations will shock the flywheel and should knock it loose.

I pulled the flywheel off my 120 Looper Johnson and it took me a week of doing that before it popped. And I was tightening the puller with an impact as much as I dare. That flywheel had a very large taper, even larger flywheel nut, and a heck of a lot of tightening force.

The 3.9 certainly won't be as bad as that Johnrude! Sometimes they just need a bit of persuasion, that's all.

HTH & G'luck.......ed

leave the nut without the washer on a few turns to keep it from coming off if it pops and it protects the threads.

Do ou have a picture of the tool? Unfortunately I don't know all the special tools and sometimes find the improper way to get the job done. Thanks for the correction knowlege is power!!