Cylinder head and exhaust cover - steps to lesson chance of busting bolts

[WestPoint]

I have an 1986 Evinrude 90HP crossflow that I just changed the thermostats and water pump on, but she still overheats. I'm the original owner - only used in fresh water. I know I should pull the exh. cover and cyl. heads to see what’s up, clean passageways and change the water deflectors. However, I've never done this before and want to lessen the chance of busting bolts.

​I know a lot has been written on things you can do, but I figure there must be some tried and true procedures out there. My plan is to first run the engine up to operating temp (without overheating) and record the temps of each cylinder, find out which is hot, and then do compression tests. While block is still warm, it might be a good time to put penetrating oil on all the bolts. Perhaps also strike each bolt with a brass drift to shock and help the oil work its way in? While I'm waiting for the new gaskets I could oil them over several days- perhaps Kroil or PB Blaster. Should I heat them with a torch as well, or only do that on stubborn ones? If so, how hot is safe? Am I being too cautious – I’ve snapped bolts before, but never on an OMC. My Suzuki DT115- well let’s just say that OMC apparently was much more diligent in putting dressings on bolts to prevent corrosion.

Much thanks, Jim

 

[boobie]

Being it was used in fresh water you shouldn't have to many problems. If you get a stubborn one you might want to try some Mapp gas around it. ATF and Acetone mixed 50:50 make a good penetrating oil.

 

[phillnjack2]

I like the ATF & ACETONE mix sounds pretty good idea, much cheaper than some of the penetrating oils that simply do not work as good as they used to.
in the uk many years ago we had a penetrating oil called plus gas, this was great when bought in liquid form in a tin with a spout.
nowdays we only seem to have the wd40 and its various copy type products that do not penetrate deep enough.
I have used all sorts of oils and concoctions and I must say ATF does seem to creep where other oils do not.
so for me if boobie says it works ill be giving it a try.

phill

 

[JDusza]

The ATF / acetone mix is the way to go.
Tapping with a drift is a good idea, also.
You might also want to try an impact wrench, provided you have the room.
Be careful using heat. You want to heat the area around the bolt to expand the metal around the threads. Heating the bolt will swell the bolt making it tighter...Heat the housing AROUND the bolt.
J

 

[WestPoint]

Thanks everyone- ATF/acetone is a hell of a lot cheaper for sure. One other question- I read somewhere that you should loosen in the opposite order of torque sequence. Makes sense- is that a general guideline for most things?

 

[boobie]

That's the way it should be done but how many people do it today ??

 

[emdsapmgr]

You should also pull the head covers off both heads and have a look inside. That way you don't actually have to pull the head. If you find debris/corrosion/restrictions inside the head, it will also likely be between the exhaust covers, and inside the cooling chamber between the two cylinder banks too.

 

[Bosunsmate]

Also back the bolts off and then back in, alternatively.
If you back them out in one effort you can get stuff sticking in the threads which will tighten up the bolt and can then dehead it.
Careful with an impact wrench, ive never used one on an outboard, ive a big breaker bar to just ease pressure on