Stubborn bolt feels welded

[Dino89]

Merc 50 2stroke changing impeller hit a stubborn bolt feels welded, undone 3 bolts plus the under the trim tab nut , but the 4th can't get socket on it so having to use 16mm ring spanner it just won't budge , greased all the others and the nut and done them all back up to take pressure off final one ,still won't budge and don't want to round or snap case /sheer bolt ,would heat be to close to seals or any ideas experience removing bolts like this ,will continue spraying wd-40 Everytime I pass it living in hope it will finally move

[Dino89]

this is the bolt in question ,would be one of th two cant get socket on ! tried to do up and undo just cant crack it !

[spartacus]

Get heat on it, and PlusGas. These bolts are tight, but not welded tight. Get a punch and lump hammer and give the head a few glancing blows to break any corrosion. Make sure you have a couple of the other bolts back in for security. If the bolt head breaks, that leg will drop out like a lead weight.

If the impeller was done a couple of seasons ago it should be good. A 16mm ring spanner is fine. If it won't even budge, you can add an extension pipe to it for leverage. That said you do run the risk of shearing it. It could even be cross threaded. You can also hit the spanner with a rubber mallet, but go easy.

When refitting, wire brush the bolts and dry run them in the holes minus the leg, then fit the lower leg and add a very light smear of marine grease on the thread and fit. Don't use the spanner and tighten them finger tight, then torque them.

[Dino89]

Thanks will give it a go ,is plus gas better than wd-40 ? , the impellor has probably never been done imo ,all 3 outboards I have ,have stood for about 8 years without being run 2 are all , done new impellers plugs etc and running fine, this the last on my avon sr4 ,both the other impellers out of the other 2 didn't look to bad to be fair , but figured better to change than risk them breaking up , what torque are these done to ?

[Peter_C]

The chances of getting WD-40 or any penetrating oil to the threads are very low. If it has a split washer and you can shoot into the split that is your best chance. I personally wouldn't even bother.

As mentioned above use a flat punch and hammer, smack the flat sides of the bolt pretty hard in different directions to break the corrosion. Put a box end wrench on it with the open end facing out. If it still won't budge take a larger wrench and hook them end to end. Now remove the bolt. It looks clean and is probably just tight more than anything.

Torque spec is in owners manual, otherwise you can look it up by bolt size.

[paddlers]

If you've got a decent ring spanner on is sometimes a sharp tap to the spanner with a metal hammer can get a result but go easy. I generally tap to tighten first then to loosen . You just need a minute amount of movement and plenty of WD and patience. Fingers crossed.

[Dino89]

Thanks guys got it undone fecking tight though ...used the punch and hammer on sides and 2ft of tube on ring then it was a fraction undo and then do up all the way out and spraying gt85 and wd 40 as I went it did feel close at times to possibly shearing or breaking ring spanner but it's out cleaned threads sprayed internal thread greased bolt and same process back in , it's now turning nicely , will get the bottom end off tomorrow and do impeller all being well .....see what those bolts are like holding the housing definitely don't think this has ever been apart

[Fenlander]

Great result fighting a bolt out without disaster.