Broke one bolt on thermostat cover.

[Mark42]

Got the thermostat cover off the 85hp force Monday. Unfortunately, one of the screws twisted the head off leaving about 3/8" of threaded screw sticking out. Tried gripping with vice grips to unscrew but no luck.

Put some liquid wrench penetrating oil on it, and will try again tomorrow.

If it won't come out, will have to drill it out. Any suggestions on drilling out the remains of the screw with the motor on the boat? Never drilled steel stud out of aluminum before. I can envision this becoming a real mess.

 

[BuzzStPoint]

Re: Broke one bolt on thermostat cover.

Do you have access to a welder?

Sometime if you have a bit of the bolt sticking off you can tap a nut on the bolt. Spot weld the inside, Then turn out.

IF not, they make stud removers that will bite into the stud and start to turn out.

After that you're drilling. Hard part here is keeping the drill bit straight.
start with a small drill bit. Drill straight through the bolt, then a larger bit, then even larger. Once you get to the threads, you should be able to pick it out.

I think the big argument here will be using an Easy Out or not..
Let me get that one started..... I say no to Easy outs. rarely ever worked in my cases. Usually broke the easy out.

Others will say a reverse drill bit.. But I have yet to find on in my area. Perhaps a more populated areas have them.

 

[Mark42]

Re: Broke one bolt on thermostat cover.

Thanks for the suggestions, buzzstpoint.

I don't have a welder available. So I will keep at it with heat, penetrating oil, and turning with the vice grip. If it doesn't work, I will do the small bit to large bit routine, then tap new threads. Have two more weeks to get this done, so no real rush.

 

[chuckz]

Re: Broke one bolt on thermostat cover.

Take the cover off that the thermostat is mounted into (I don't remember if it is the head or not). You can then apply penetrating oil from the back of the bolt where the corrosion is. I used a little heat and PB Blaster and I got my screws right out. I replaced the screws with cap head screws so I can get better torque with an allen key.

 

[jason32038]

Re: Broke one bolt on thermostat cover.

Use a right angle grinder to grind the screw down to where it's even with the metal. Center punch screw and drill a small enough hole to where you can beat a flat head tip into it. You can either try a manual impact or use a flat tipped screwdriver with a hexxed shaft so you can grab the shaft with a wrench and turn the screwdriver to get the screw out. If that fails then you'd have to drill and tap it out. This has worked for me for the most part. Only a couple of broken bits.

 

[further]

Re: Broke one bolt on thermostat cover.

+1 for what Jason said. Some heat (not to much), lots of PB blaster, and impact driver did it for me.

 

[Mark42]

Re: Broke one bolt on thermostat cover.

Today I finally got the screw out. Tried the heat, penetrating oil, impact driver, etc for a couple of days, and still no luck.

Picked up two different size "easy outs" and was able to drill right down the middle of the screw. I was surprised how straight and centered the hole was. The first easy out was so thin, I knew right away it was going to snap, so I then drilled the next size, and used the larger easy out. Still not budging, and I was afraid of snapping that one off too. At that point, I just drilled out the hole the size of the tap, then chipped out the remaining screw from the top thread. Then ran the tap in. The tap removed the remaining bit of screw in the threads, and everything seems fine. Also ran the tap in the other three holes to clean them up too.

So, don't be afraid to drill out the screw if it happens to you. I was afraid of not drilling straight by hand, and was going to take the head off to put in the drill press. But a careful eye seems to have worked.

Thanks for all the suggestions.

Now I'm waiting for a new impeller and will find out what condition the water pump is in. I was surprised at how clean the inside of the block looks at the thermostat, but the thermostat itself was pretty corroded. All in all, not bad for a 25 year old motor.