Power head off, should I change rings?

I recently purchased a 1957 Johnson 7.5 hp model number AD-11. The last owner indicated the motor ran in February. Did not have a 2 line tank to try to start at that time. After reading this site and others, I decided to do a thourough run through, including head gasket, impeller, carburetor, and new ignition parts.

In changing the impeller, I have the power head off.

Question is should I go ahead and put in new rings at this point? I do not know what the compression numbers were, but I do know that both cylinders had compression.when I started tearing it down.

If I should replace rings, what do I need (other than rings of course), and are there any secrets that will make the job a little easier.

Thanks.

Re: Power head off, should I change rings?

To better answer that, what are your plans for this motor? Get it running and muck about every now and again, or use it lots and keep it forever?

Re: Power head off, should I change rings?

I bought the motor for my son. He is 13 and wants to put it on his aluminum boat. Will probably use it every weekend in the summer and a few times in the winter. Using it on a lake here in Florida.

Re: Power head off, should I change rings?

Hrm . . . tough call then. You may just want to get a head gasket and inspect the top end. If it looks bad, go through it. If not, just let it be. I don't know what you'll pay for parts on that motor, but for reference a ring job on a 80s 15hp was around $200 in parts once I got gasket and seals, rings, and bearings. If it's anything like some of the other older motors those needle bearings are spendy if they need replacing.

Once you peel it apart, be prepared to replace everything that's suspect. No point in putting worn parts back in.

If it were part of a restoration project or something of the like, I'd say do it. If it's just any old motor you're putting on a boat, run it until you can't.

Re: Power head off, should I change rings?

Check the compression. If good (120 or so) forget it in my opinion.

Old axiom, "If it taint broke don't fix it" has a lot of thought in it. Lot of things can be disturbed in an overhaul and yeah you might get it all right, but yeah you might mess something up too....plus the cost.

On an engine of that size, I'd really doubt that you have enough hours on it to warrant ring replacement.

If you want to do something, decarb it and loosen up what rings you do have.

Mark

Re: Power head off, should I change rings?

You will never get 120 psi from that motor. More than 60 psi is fine. I wouldn't rebuild it unless it needs it.

Re: Power head off, should I change rings?

Is there any sign of prior overheating such as burnt paint on the powerhead? That would be reason for going for a rebuild

Otherwise, remove the two intake bypass port covers and take a look at the rings and piston skirts. If the rings are free in the grooves (poke them), and still have the mill marks, and the piston skirts look good, put the covers back on and leave it alone. You can do the same thing on the exhaust side, but certainly will need new gaskets if you take that off.

Before you reinstall that powerhead, be sure to use a new 303355 gasket and 303347 o-ring on the carbon seal. Failure to maintain the integrity of that seal has ruined more motors...

Re: Power head off, should I change rings?

I will open the ports and have a look around. The motor appears in good shape. There was some mild blockage in the water jacket when I pulled the head, and the tops of the pistons look pretty good. I haven't pulled the lower unit yet to see how the impeller looks.

I will change the gaskets, as recommended when I put the powerhead back on. Where is the carbon seal o-ring? Thanks again for all your help.

Re: Power head off, should I change rings?

The o-ring wraps around the drive shaft and seats inside the top end of the carbon seal.

Re: Power head off, should I change rings?

More on the carbon seal: It is at the top end of the drive shaft and funcions as the lower main bearing seal for the powerhead. If it fails, water is sucked up through the main bearing into the crankcase, and it is goodby to all the bearings.

Re: Power head off, should I change rings?

Here is what the seal looks like.

www.myfishingpictures.com/showphoto.php?photo=131819

Like FR says, make sure it is good and installed properly.

Re: Power head off, should I change rings?

Just a side note for Mr. Beaton. When I was a jr., probably 8-10 year old time frame my grandpa had a 10 hp Johnny just like your Avatar. He lived in Rockport, TX. and had a 16' planked, flat bottom skiff. The 10 couldn't plane the heavy hull, even with me ridinig the bow.

He rigged a stick steering hootus (forget everything about it except he had this handle sticking up in front of the middle seat) from which he steered the boat. It had the slide across the front (of the engine) throttle, so that easily stayed put once set.

Moving his weight to midship helped the boat a lot. In the afternoons when the wind would get up, on the way back to the boat basin, we would always have the wind to our backs. The boat would ride up on a crest and then get drawn back into the trough.....very slow going (for a kid ready for some excitement).

One day we were docking in the slip which was much longer than his boat. I stood up on the little front deck and grasp the line crossing the slip for bow mooring. He was looking aft where he was driving the boat and didn't know I was up there. He kept backing up and as I saw that he was driving the boat out from under my feet I was headed for the drink.......This was an emergency situation for me and rather than say the conventional word HELP, I just uttered UOOOOOOGA.....like the sound the old Model T Ford horn made. Don't know why, but that's what came out of my mouth. It worked. He turned around, saw me, and reversed the engine to rescue me.

Mark

Re: Power head off, should I change rings?

Thanks for all the advice. I picked up one of the o-rings and the cork gasket, and the picture helps me to understand how it all goes back together.

I have opened a can of worms, however. In pulling off the large cover on the exhaust side, a couple of the screws were stubborn and broke off. I have to drill and use an easy out tonight to get them out.

In looking inside, everything looks pretty good. the rings are free and there are no gouges or scoring inside the cylinder walls.

I think I'm going to put it all back together and see what happens.

Thanks again.

Re: Power head off, should I change rings?

Excellent example of "if it ain't broke don't fix it"! I'm always scared that will happen when i take off exhaust covers. And quite often it does happen. Even with heat, oil and patience.

That's a nice memory, Mark. Thanks for sharing it. Those motors are two-handers for sure. I can think of a couple times when I could have yelled UOOOOOGA driving mine in choppy water!