I'm thinking about tackling replacing the head gasket in my 75 HP Evinrude but am concerned about the risk of breaking the head bolts trying to remove them. I am not the original owner of the engine, but it doesn't look like the head has ever been removed. I'm not a mechanic or machinist but am a better than average tinkerer. I would appreciate any advice/recommendations on reducing the risk of bolt breakage as well as ways to remove a broken bolt from the block Thanks.
Is the head gasket on your 75hp blown or leaking? 'Cause if not, you wouldn't need to necessarily replace it just because it's old.
If you have a Salty Dog, it's gonna take some persuasion to get the head bolts out without breaking. Even if you have a freshwater motor, it's wise to be cautious when pulling the bolts.
If you find any bolt that doesn't want to move with normal hand pressure on a 3/8" ratchet wrench, it's likely stuck.
The thing to do with a stuck bolt is to give it a good rap on the head with a ball-peen hammer. Followed by a rap with a punch, to each hex-side of the bolt head. This will jar the bolt and help break any corrosion products loose.
Then you must apply heat to the outside of the head, along where the bolt runs. Normally a seized bolt gets stuck in the head itself; in extreme cases the threads stick in the block as well. But typically, you get corrosion products building around the bolt until it's mechanically stuck in the head and won't turn.
You can use a propane torch if it has a decent flame on it. A Mapp torch will give a hotter flame and this'll help, since the block is one big aluminum heat sink!
Just heat back and forth along the outside of the head, while moving the bolt head back and forth a bit with the wrench.
Sooner or later, enough heat is supplied to break the bolt loose. Repeat for the other bolts and you're good.
Note that if you get a particularly stubborn bolt, you may have to drill out the bolt head then work on the stub of the bolt after you get the head off.
Be sure to check the head for straightness, especially if the engine was overheated or the head gasket is blown. You may need to have the head surfaced at a machine shop if it's warped. Or you can re-finish with sandpaper on a piece of glass, but it'll take a while to work it out by hand.
Clean out the head bolt holes and lube them with a few drops of motor oil.
Clean the head bolts as well (a wire brush on a bench grinder works very well). Spread a thin coating of Permatex No. 3 Aviation-type gasket dressing on the bolt and it'll never seize again.
Torque the head & new gasket to specs and you're good to go!
Thanks for the detailed response; it's just what I needed! I have two other questions.
First, you mentioned I might not need to replace the head gasket if it's not leaking. The symptom I have is the engine starts and idles smoothly then starts to run roughly. The fuel level in the carb bowl starts to drop and then the engine dies and will not restart. The fuel pump is working fine. There is a runny, grayish discharge from the lower unit intake port that I assume to be emulsified oil and water. Pulling the plugs shows a light coating of the same substance on each of them. I conclude that water is getting into the combustion chamber and have ruled out any problem with the cooling water intake and discharge tubes. This all started when on a normal run at half throttle, the engine accelerated then died. The only thing I could see wrong was that the gas supply line had burst where it connects to the carb. It was a brand new hose. I replaced it along with a new float and the starboard side low speed needle valve. Following these repairs, the engine started right up but showed the symptoms described above. Is there anything that could cause a gas line to blow? If so, is there a seal other than the head gasket that could be damaged as my compression test seemed to be OK (three cylinders 100 to 110, one at 95.) The hose wasn't just cracked. It was a ragged, diagonal hole that wrapped about half way around the hose.
Second question - do solvents like PB Blast help to loosen frozen bolts in this type of situations? I've used it before on rusty bolts and it seems effective.
Thanks, again, for your info. It's really helpful.
Milky mix on the plugs ain't a good sign! Likely the gasket is blown and the fuel line thing is just incidental to that. Maybe the spring-clamp was a bit loose or there was a nick in the line, who knows!
I haven't found a penetrant to be of much use to bust loose head bolts, heat is more effective. Once you get the bolt moving, the penetrant may be able to get in there and that might help loosen things up a bit more, but just spraying on the outside doesn't usually.
I would try a few bolts with the wrench and if they don't want to come loose, break out the torch.
Definitely recommend getting the head surfaced 'cause there's a reason it's leaking like that.
The motor can take in water from a leaking bottom crank seal, but normally that only affects the bottom cylinder and you say there's water on both plugs.
Another source is a leaking exhaust manifold gasket but I've not seen a lot of trouble with those. Far more from leaking head gaskets than anything else.
I finally got the heads off. I broke one, but got all the rest with a combination of heat, solvents, and wiggling the bolt backwards and forwards. I took the heads and gaskets to my local CarQuest as the manager was an outboard mechanic for 15 years or so. He looked over the gaskets and felt there was no evidence of a gasket leak (ie, evidence of good seal and no high pressure release damage.) So, I'm kind of back where I started in trying to figure out what caused water to get into the cylinders. Could too much pressure on the water cuff I used to supply cooling water have somehow pushed water up the exhaust tube?. I replaced the seal on the exhaust tube simply because I was replacing everything else. I've used the water cuff for cooling on multiple occasions without any problems until this problem occurred. Any ideas?
Did you find any evidence of water in any of the cylinders?
Is the broken bolt stuck in the block?
which bank and bolt location is the broken bolt?
High pressure from a hose can overcome the gaskets on occasion.
I believe this engine has an automatic choke that uses air heated through a heat exchanger inside the exhaust cover. This is between the port and starboard cylinder banks. A bit of a long shot - but the heat exchanger could be leaking cooling water into the choke tube. The covers can be a real bitch to remove without breaking the little 7/16 bolts off. The ones down the center of the cover are most often stuck.
But right now - let's find out more about the broken head bolt..??
The stuck bolt is on the right side of the port bank (cylinders 2 and 4) and is the middle bolt (ie, at narrow part of a figure eight where the #2 cylinder is the top of the eight.) There is about 3/16 inch of the bolt extending above the face of tbe block.
This engine uses the hot water actuated choke, not hot air.
What does water damage look like? The piston walls look smooth and clean, but the pistons won't move. I currently have them soaking in a solution of about 2/3 Marvel Mystery Oil and 1/3 Sea Foam to see if I can free them up.
The engine is stuck? Didn't you just have it running before pulling off the head?
You are very lucky there is part of the bolt sticking up - you have a better chance of getting it out. DO NOT try to remove the bolt with vise grips. Soak the threads daily with Sea Foam or PB blaster for a week or more. Get a nut that is about 5/16 and drill out the threads so it will slip over the shank of the broken bolt. Then Tig weld the nut to the bolt filling the center with red hot metal. Be sure the welder is skilled - as this HAS to be a strong weld bond. Immediately smack the nut with a ball peen hammer half a dozen times while trying to move the nut back and forth - just a few degrees each direction. The heat from the weld will expand the aluminum and help break up the stuck threads. DO NOT force the bolt if it will not move. Just try to budge it back and forth until it starts to move. This almost always works if done correctly.
Yes, I had it running. But, I had to leave it set for about a month before I could move from my summer place to my winter home. Before leaving it, I filled all four cyli ders with fogging oil and worked it through the engine using the manual pull cord before replacing the plugs in the cylinders. I moved the boat home about three weeks again. When I tried to turn it over first with starter then again by hand, it would not budge. I assume the fogging oil must not have done its job or that I didn't use enough it. Since I was going to pull the heads anyway, I figured I could brake the pistons free after I got the head off.
My neighbor is a retired welding instructor so I'll see if he can do the welding for me. In the meantime, do the stuck pistons give you any more insight into what may have happened?
"do the stuck pistons give you any more insight into what may have happened?"
Without being there to actually inspect it - it's just about anyone's guess. So it is my guess that you did indeed have some water in the engine, and that is why it is stuck. Don't forget, that the crankshaft journals and bearings can also possibly be the problem. If they have any rust formation on them - the motor is junk. I certainly hope that is not the case. Tilt the motor so the cylinders are toward the sky, and Spray penetrating oil on the cylinder walls and let it soak in. Get a large socket and breaker bar on the flywheel nut and try to break the motor free. The sooner the better - as if there is rust on the piston rings, you need to get it moving to prevent more damage. If any intake ports are open, spray a bunch of oil down the intake ports - in the hopes of getting some oil on the crank, bearings, and connecting rods.