1970 Johnson 20 lower unit bolts stripped

[Soot87]

I have an 1970 Johnson 20 hp that I thought I ruined by stripping the lower unit bolts and someone suggested I try a helicoil thread repair kit on. I was telling my father in law about it low and behold we discovered that one of the lower bolt holes already had a helicoil in it(the only one that didn’t strip). So 3 questions I guess. One has anyone done this themselves and can a novice do it? What size helicoil do I use for that bolt? And if anyone has paid for it about how much did it cost? Thanks for your help.

 

[F_R]

I've personally done umpteen thousands of them (in a manufacturing plant). Yes, a novice can do it, but you need the tools/kit. Available at Auto Zone and others. You use the same size Heli-Coil as the original bolt i.e. a 1/4-20 bolt takes a 1/4-20 Heli-Coil.

I suppose the pro cost depends. It doesn't take long. Lots of shops have a minimum charge. But that is partially offset by not having to buy the tools.

 

[Soot87]

I’ve watched a video and it seems relatively straight forward. Do you have any tips or things that would be helpful before I get started?

 

[F_R]

Depth of hole: As you run the tap in, eventually it will bottom out. That means the first few threads (at the bottom) will be tapered. When you install the Heli-Coil insert, it should not enter those tapered threads. Select insert length accordingly. OR, consider deepening the hole with a drill if that is possible or practical.

Tapping the hole: Try to start it straight as possible.

Insert length: They don't have to be as long as you might think. One diameter in length will give as much holding power as possible.

Inserting tool. I've seen several types and haven't tried them all. My pick of the ones I've used is the one that looks like a screw with a special grind on the end that engages the tang on the insert. Whichever kind you use, it must not push on the tang as you start to thread it into the tapped hole. The screw type I just mentioned will satisfy that requirement.

I dunno, it's all second nature to me.