Head gaskit replacement

[Blizzard]

An old timer was telling me the other day that the head gaskits on outboards should be replaced from time to time. I looked at the gaskits on my 250 hp and they look rusted on the edges.

When should they be replaced? Should they be replaced as part of routine maintenance?

[FishFinder]

I Just did the head gaskets, head cover, inner and outer exhaust gaskets and the anodes in the block behind the heads on my 93 225. The gaskets on the head looked as if they were swelling and some corrosion was starting to be visible. I was (eventually) glad I did this as I found I found a breach were water was coming into the exhaust manifold.. I can’t imagine I would have made through the season without detonation of that cylinder. Bad thing was the bolts were corroded to the point I had several snap off, (4) in total. It was not fun but I was able to drill them out. I would suggest if you’re going to do it, make sure that you soak the bolts with a penetrating oil and take your time and don’t forget to replace the thermostats. When I re-assembled I used a product called “perfect seal” a friend that is an engineer for mercury marine racing division suggested I use it.. They use this at the factory during assembly.. I was able to get it at a local marina without a problem.

[Ken]

FishFinder,
Sounds like you went to a lot of work, but got the job done. I am curious how you drilled out the stainless steel bolts and removed the old threads. Did you have to re-tap and go to bigger bolts. Just curious - I have a fear that someday I will face the same dilemma and would like to know what to do. Thanks.
Ken K

[FishFinder]

Ken,
After the initial shock of what happened I went and got some “stubby” snap on easy-outs. I ended up buying left handed stubby cobalt drill bits. Started by using a punch and center punched the bold, then started with a small LH cobalt drill bit and was VERY careful to ONLY drill through the bolt.. Had to go slow and use a lot of oil while drilling. Tried the "easy-outs".. They did not work, and I am sure if I would had continued I would have broke one of them off too.. I then moved up to the point I where I could get the remainder of the bolt out. This did not save the threads on the hole though, I drilled them out and went up a size tapped them and used helicoils. I have a friend who builds race engines for mercury marine, he tells me they ALWAYS drill out and use helicoils on their race engines as they give significant surface strength over a tapped hole. I also got a set of Metric thread chasers and cleaned out ALL the holes and bought all new head bolts (original yamaha, same size).. (P.S you will use a lot of drill bits, like one per hole… Unless you have a very good sharpener..)

What would I have done different? I was afraid to heat up the bolts, now I would not be so gun shy… I had some of the bolts on the exhaust housing give me fits, would not come loose… I took a round piece of stainless (almost the size of the 10mm bolt head) and placed it on the bolt and hit it with a hammer… Then sprayed it with a product called RustBuster, then heat it from a propane torch, hammer, try it back and forth then the RustBuster.. They all came out without problems. If they still would not come out I think I would cut the heads off so that I would have had the stud to work with. What was absolutely the worst was the that I had the bolts on the lower end of cylinder 6 break, and I had to use a right angle drill to get them out. Every person I talked to told me I would have to pull the powerhead to get that one out.. Sears has the smallest 90 degree drill I could find, and it worked great.

Last for me is I am rebuilding the carbs… I hope to be on the water by next weekend. If you have any questions let me know.

[Ken]

FishFinder,
Great post! Thanks - I will copy and save this one. Some day I may have to do this.
Good luck,
Ken K