Replacing head gasket - 4 questions

[Pete B]

In the past few weeks I've posted several messages re. my efforts to revive an old (1986) Force 35 with low compression in the lower cylinder. Tried several things suggested by folks here (decarb, etc.) to no end, so finally pulled the head. Saw right away that it was a blown head gasket, so am now in the process of putting in a new one. So, here are my questions. First, the service manual and Clymer manual both specify lightly sanding the head with emery cloth to make sure the surface is flat and clean. They also say to remove gasket and sealant residues from the cylinder block with a "suitable solvent". Any suggestions on what to use and how best to do this? Second, right around the inside mating surface on the head, there are a few small nicks. Any idea how to get rid of these? Third, there is absolutely no room to fit a torque wrench over the lower 3 or 4 head bolts because the lower part of the motor casing is in the way. Anyone know how to get the right torque on these bolts without having to remove the whole powerhead? Finally, I am not having any luck finding the emery cloth (120 & 180) specified in the service manual. Seems to me the size of the grit is more important than the backing material, so am wondering if regular old aluminum oxide sandpaper will do or if it is critical to use emery cloth? Suggestions on any of the above would be much appreciated.

 

[kev_79]

Re: Replacing head gasket - 4 questions

Pete, it is crutial that the surface of the head gasket is smooth, but it doesn't have to be like glass. The problem with the scratches is that if you try to take them out, you will sand pits into it, and that would be worse. If they aren't very deep, don't worry about them, the gasket will take care of it. If they are really deep, you can have a machine shop mill the surface, so it will be level, but I would only do this in a severe case. <br /><br />A very fine sand paper would do the trick, but I prefer using steel wool. You can get it at wally world, and it's really cheap. Shouldn't be any sealant on the head gasket, but if their is, I would just use the steel wool. They make gasket removers, but they tend to leave a residue that can get into your water jackets and cylinders, and that can become a bigger job to clean up. <br /><br />As for the torque wrench, sorry man, the cowling will probably have to come off. If you look at it really closely, you will see that it isn't as hard as you might think, just a few bolts. Good luck, and remember to follow the manuals torque and sequencing specifications. Tell us how it goes.

 

[Pete B]

Re: Replacing head gasket - 4 questions

Kev_79:<br /> Thanks much for your advice. I took your advice on the steel wool. Don't know why this didn't occur to me before, but it worked very well getting rid of those rough spots of old gasket material. Anyway, replaced the head gasket last night, following the torque sequence and specs to the letter, and fired it up for the suggested 15 minutes this AM. Retorqued again, then checked the compression with the engine warm. The overall compression dropped a bit, but the difference between the two cylinders was vastly improved. Before changing the head gasket, the compression was 130 (top) and 90 (bottom). This morning it was 115 (top) and a hair over 110 (bottom). Overall sounds to me like it runs smoother too. Is it normal to have a drop in compression with a new head gasket? I plan to check the compression again with a cool motor, since my previous compression checks were with a cool motor, just to see if that might produce a slight increase. Anyway, I wish the overall compression were a bit higher, but I am pleased with the fact that at least the two cylinders match pretty closely.

 

[kev_79]

Re: Replacing head gasket - 4 questions

Pete, a head gasket is a bit like rings. The compression will get better when it gets seated to the surface. A colder engine might have more compression if the air that is coming in is cooler. Cooler air can expand more. In the same respect, the rings when hot expand a bit and create a better seal. I would expect maybe as much as 10 psi at most though. Good Luck. Tell me how it goes.

 

[Pete B]

Re: Replacing head gasket - 4 questions

Kev_79: Once again thanks for your feedback. I figured the compression might come up a bit once I put a few more hours on the motor. If I get another 10psi, that will put me in the 120/125 range, which I suppose isn't really all that bad for an old motor. I think this model is supposed to be in the 125/135 range. At least the compression is nearly identical in the two cylinders and that is a major victory. Just want to keep this sucker going until I can save up for a new merc. Actually though, for all the scorn heaped on Forces on this list, I'm growing kind of fond of this motor. Built like an old Model-T - nothing fancy, just the basics. Anyway, once I get some more hours on the motor I'll check the compression again and will let you know how it goes.

 

[kev_79]

Re: Replacing head gasket - 4 questions

I too was once the proud owner of a force, till some people made fun of me. I told them that it was a great motor, and argued back about it...then, it blew up. Not the motor's fault, due to trashy gas, but I have a merc now and I love it. Personally, if I could I would keep the force to tinker with. It really won't be worth a whole lot, and as always, it's never worth as much to someone else as it is to you. <br /><br />BTW on the compression check, you do have a good hot battery, and the throttle wide open, right?

 

[Pete B]

Re: Replacing head gasket - 4 questions

Kev_79:<br /> Yes, I may just keep the ol' Force around once I've moved on to better things (i.e. a Merc). I've learned an awful lot about outboards in the last month or so, and I'd rather learn those things fiddling around on an old Force than on a new Merc. As you also pointed out, probably not going to get much out of selling it anyway, so might as well hold on to it. Re. comment on the compression check, I actually didn't have the throttle wide open when I checked it yesterday, nor was it wide open on any of the previous checks. I'll do another check with it wide open and see what happens. Just learned one more thing. I'll keep you posted on the results.

 

[Pete B]

Re: Replacing head gasket - 4 questions

Kev_79: Well, I did another compression check this afternoon with the throttle wide open, motor cold, and the two cylinders came out exactly equal - round about 122psi. Given that before I began the whole process of decarbing, etc. two o/b dealers/mechanics told me this motor was blown, this is sweet. Thanks again for all your advice. I'm a complete novice at this outboard stuff, and if it wasn't for folks like you on this list who are willing to share your knowledge and experience I'd still be back at trying to figure out how to do a compression test.

 

[kev_79]

Re: Replacing head gasket - 4 questions

Pete,<br /> I'm glad you figured it out. 122 should run you just fine, especially them being equal. I learned on a force, and I don't think their is a better one to learn on. What you do learn, is how to do it on a simple engine, and then you learn that the other's just have more bells and whistles.<br /><br />This is a great site, and I will forever always come here before I go to a wrench. Between the old wrenchs, enthusiasts, personal experience, etc. on this board, at least you will know what you are walking into before someone tries to take your money. They aren't all like that, but they are out there. When someone gives advice here and it works, it's like charity, it makes you feel kinda fuzzy inside, and that is all we ask for, that you tell us how it goes. I'm not a wrench, and I learned just like you are, and now I'm a boating finatic.<br /><br />For now, run that force hard, keep up the maintenance, because if you don't run it, you can't tear it up; if you don't tear it up, you won't have a justifable reason to tear it apart! <br /><br />FYI: you should be able to rebuild carb, and top end of that engine for less than 300 if you ever have too. Good Luck