TOPIC: Merc '74/7.5 Should I use a Blow Torch?

Got this '74/7.5hp some time ago and looks very good except its totally plugged with that white salt/corrosion thats hard as a rock, tried to remove the bolts with no luck. Any ideas, must I drill the bolts out and retap or use lots of heat but will distroy the paint which I'd rather not do? I tried soaking with WD but no help. Even if I were to remove the bolts and get it apart can I get full access to all the water ports to remove the corrosion? ..fun

Heat the bolts a litte to loosen the corrosion but they are a bugger to get out. If the covers are off you can access the water jackets to clean them,but watch out for the bolts as they are non too strong and easily snapped off. An 3/8 drive air impact wrench at the lowest setting will sometimes work them loose by vibrating them out.

Thanks, I was trying with a socket wrench and knew if I used any more torque I'd snap the bolt, I also tapped the bolt head with a flat-head punch and didn't help. Just incase one does snap off and think some will no matter what, would I drill it out to the threads and retap, if there not stainless think thats all I could do, then helicoil...or not?

How long would you hold the torch to the bolt, 30 seconds or more? guess I cant do much damage by over heating or can I?

You'll probably need to hold the torch on there at least that long. I've had to heat 'em sometimes to the point where the paint is burning or even worse, to get stuck bolts loose.

What you've got to watch for are other parts, such as plastic in the flame's path. Better not to melt plastic or burn up the wiring.

Unless you've got an oxy-acteyl outfit, you probably won't have to worry about melting parts. I have a small Mapp torch and it gets plenty hot! Regular propane will work too, but it's not as hot as the Mapp flame.

After you've done all that stuff and it feels like the bolt's gonna break anyway, it might be better to drill out the bolt head than snapping it off. If you have to, drill the rest of the bolt out of the cover to get it released.

Sometimes you can get the cover off, leaving a stub which can be grabbed hold of with a set of vise grips. With the cover off, heat can be applied more directly.

Worst case, it snaps off at the base; just drill out the bolt completely and install a Heli-Coil.

It's very difficult to only drill out the bolt with a tap drill and try to re-tap to standard size, the stainless left in the hole will foul the tap and tear up what's left of the hole's threads.

Far easier to completely drill out the offending bolt, then it's merely a few minute's work to drill out with Heli-coil tap; screw-in the insert; break & remove the insert tang.

Zap you're done, with a repair that's stronger and much more durable than the original.

To prevent seizing bolts in the future, spread a thin coating of Permatex No. 3 Aviation-type gasket dressing (or equivalent) on the threads. Great for fasteners on water passage covers.

Most everything else (such as lower unit bolts) I use a waterproof marine grease, heck anything in the threads keeps the salt and debris out, but either Permatex or grease do a fantastic job.

It's such a pleasure to get a motor in where all the bolts come out, 'cause the mechanic took just a few seconds extra to coat the fasteners.

Conversely, you can sure cuss out the last guy who worked on it that didn't!

HTH & G'luck with the stuck hardware.........ed

Thats great to hear good instructions. I kept this motor off the bench cause was scared I'd get started and make a mess of the motor then have to haul it to the dump. Much Thanks