Broken bolts on 90 hp / Lower unit

[v12mac]

A friend of mine asked me if I could help him with a problem he is having with a 90 hp Johnson 1989? May be a bit newer.<br /><br />While trying to replace the water pump he busted the head off of 2 of the bolts that hold the lower unit on. <br /><br />Does anyone have any tips for drilling these out?<br />Mac

 

[G DANE]

Re: Broken bolts on 90 hp / Lower unit

Hi v12mac<br /><br />Do not start to drill and cut. Get someone that is familiar with TIG or MIG weld to weld a nut or piece of a bolt to the stud. When it has cooled down, 95 % of them are just to screw out. If not weld a bit on it again, then 99.999999 % of them get right out Will not damage aluminium.

 

[R.Johnson]

Re: Broken bolts on 90 hp / Lower unit

Are the bolts broke off flush, or below the surface, or is there enough left to get a lock wrench on? If there is enough left to get a wrench on, use penetrating oil, then heat the area with a propane torch. These bolts are stainless steel! If these broke because of a process called hydrogen imbrittlement, you are going to have one sweet time drilling them out. You could use a carbide drill, but trying to do that freehand will probably break the drill as they won't tolerate any flexing, then your in more trouble. If you have a machine shop in your area with a electric discharge machine they can be burned out. This would require removing the exhaust housing. This is one of those jobs that can be a real headache. Go slow, as this could be costly if anything more goes wrong.

 

[ledgefinder]

Re: Broken bolts on 90 hp / Lower unit

They'll drill out OK, but you want to take it easy & do it right. It will help a lot to have a oxy/acet torch (even one of those $50 hardware store ones). Heat up the area & let it cool a couple times, aiming the torch at the bolt head. Don't overdo it, aluminum melts without warning. While it's still hot, grab the end with a pair of vice grips. If there's not enough end to grab, obviously you have to drill it & re-tap it. Make sure your drill hole starts right in the center by centerpunching a hole first. Then carefully drill out the stud, increasing drill size as you go along. Once your done, retap the hole. <br /><br />This assumes you don't have easy access to a welder to weld a nut onto the stud. You can buy left-handed drill bits for the drilling out job, and the stud may spin right out on its own. I have had zero luck using 'easy-outs' - & don't break one off in the stud or you're drilling work just got a LOT tougher. If you have to go too far (diameter) in drilling to allow good threads, just pop in a Helicoil.

 

[ledgefinder]

Re: Broken bolts on 90 hp / Lower unit

They'll drill out OK, but you want to take it easy & do it right. It will help a lot to have a oxy/acet torch (even one of those $50 hardware store ones). Heat up the area & let it cool a couple times, aiming the torch at the bolt head. Don't overdo it, aluminum melts without warning. While it's still hot, grab the end with a pair of vice grips. If there's not enough end to grab, obviously you have to drill it & re-tap it. Make sure your drill hole starts right in the center by centerpunching a hole first. Then carefully drill out the stud, increasing drill size as you go along. Once your done, retap the hole. <br /><br />This assumes you don't have easy access to a welder to weld a nut onto the stud. You can buy left-handed drill bits for the drilling out job, and the stud may spin right out on its own. I have had zero luck using 'easy-outs' - & don't break one off in the stud or you're drilling work just got a LOT tougher. If you have to go too far (diameter) in drilling to allow good threads, just pop in a Helicoil.

 

[v12mac]

Re: Broken bolts on 90 hp / Lower unit

 

[jim dozier]

Re: Broken bolts on 90 hp / Lower unit

I agree with ledgefinder but I would plan on putting in a helicoil if you have to drill it out. Helicoils are less likely to freeze up subsequently also. If you have to go the drilling route, here's a tip. Start with a small sharp bit and gradually increase the drill size to the final specified by the helicoil kit. A carbide tile cutter bit in a dremel tool is handy for recentering the drill out hole if it starts to wander off center. If the hole gets off center you can delicately bring it over with the tile cutter. Use it only after the hole diameter is bigger than the tile cutter in case it breaks which they will do if you aren't careful.