1977 25hp Johnson Opinions

[brycebell]

Hello Everyone.

I have a 1977 25hp Johnson. 25RL77H. It overheated a few times a couple years ago and now its time to try and fix it. We checked the compression and i believe were getting around 50-60. Once we took it all apart we saw that the head gasket was blown and a couple others were in pretty rough shape. The cylinders were a little scored on the one ends and the pistons were scored on both sides. My question is if you think to get oversized pistons and rings and rebore it or whats the best way to get this thing running properly again.

Thanks.

 

[F_R]

Re: 1977 25hp Johnson Opinions

Well, that's what it will take. Whether or not you decide to do it is up to you. Consider the condition of the rest of the motor. Clutch dog and gears? General wear and tear of linkages, etc?

The other option is a different motor, or a powerhead swap.

 

[brycebell]

Re: 1977 25hp Johnson Opinions

yeah the rest of the motor isnt in too bad of shape. All the gears are in pretty good condition. I just wanted to see if there was anything else i could do instead of spending all the money on new pistons and everything. Would it be the pistons that would be cause me to loose all that compression or would it have been the blown gasket or a combination of both?

 

[RogersJetboat454]

Re: 1977 25hp Johnson Opinions

yeah the rest of the motor isnt in too bad of shape. All the gears are in pretty good condition. I just wanted to see if there was anything else i could do instead of spending all the money on new pistons and everything. Would it be the pistons that would be cause me to loose all that compression or would it have been the blown gasket or a combination of both?

Blown gasket would most likely be the main culprit with worn/stuck/broken rings possibly contributing. How bad is the scoring in the cylinders? Will the scores catch a fingernail? Post pictures of the damage if you can.

If you choose to go any further with this power head, you will need to figure out how bad the scoring/cylinder conditions are. Light scoring can usually be honed out while remaining in factory tolerances, and then you could use standard size pistons and rings. Heavy scoring will require an overbore of at least the damaged cylinders, and will require over sized pistons and rings. At that point with the extra cash required for a good marine machinist (one who understands how to bore a outboard block) you may be able to find another 25 HP power head or entire motor in better condition.

 

[F_R]

Re: 1977 25hp Johnson Opinions

You yourself said that the gasket was blown. That will do it.

But you also said that it was overheated a few times. A clear warning that the pistons are probably scored.

Next step if you want proceed is to remove the exhaust covers from the side of the powerhead. Then you can see the hot side of the pistons and rings. My bet is that they are scored.

 

[brycebell]

Re: 1977 25hp Johnson Opinions

I will try and post some pictures today after work. This is the first time i have ever worked on a motor so im not to sure how bad the scoring really is. The piston I think is worse than the cylinder. I will let you guys judge for yourself once I put up the pictures and let me know what you think I should do. Thanks.

 

[outlaw241]

Re: 1977 25hp Johnson Opinions

do you know what caused the over heat? if it was mine i would check to make sure the head wasn't warped, if it is warped it's not that hard to get it back flat with some fine grit sand paper & a piece of glass, mirror, or granite, something very flat.an put a new head gasket on it an recheck the compression

 

[brycebell]

Re: 1977 25hp Johnson Opinions

It over heated because the water pump went

 

[1946Zephyr]

Re: 1977 25hp Johnson Opinions

Yea, overheats do most often nuke the pistons. Rings will stick in the grooves and your compression goes bad.

 

[brycebell]

Re: 1977 25hp Johnson Opinions

Here are the pictures of the cylinders and pistons. Your fingernails do not get caught on the groves in the cylinder but you can notice its not smooth. Same thing with the pistons. The rings do not appear to really have any scoring on them. But I am not expert. Tell me what you think about the pictures and what you recommend I do. I am a university student right now and want to keep spending on a minimum.
Thanks.

also, the cylinder head seems to be flat.

 

[F_R]

Re: 1977 25hp Johnson Opinions

You will have to lightly hone the cylinders before you can pass judgement on them. But the pistons and rings are junk.

 

[brycebell]

Re: 1977 25hp Johnson Opinions

So honing them out would just see if the scoring isnt too deep and that they are still the standard size? is honing something i could do on my own or is that something that would need to be taken to a mechanic?

 

[ONERCBOATER]

Re: 1977 25hp Johnson Opinions

at a glance i would agree... pistons/rings toast..... cylinder light honing... will put it back to 85-95% or so acceptable if YOUR doing the work.... not worth it if you have shop do it.

sean

 

[sutor623]

Re: 1977 25hp Johnson Opinions

So honing them out would just see if the scoring isnt too deep and that they are still the standard size? is honing something i could do on my own or is that something that would need to be taken to a mechanic?

You can get a honing tool that attaches to a standard drill. That'll do just fine. Show us some pictures after you hone it

 

[F_R]

Re: 1977 25hp Johnson Opinions

Use a hone in a slow drill or variable speed drill running on slow. Use honing oil. Move the hone in and out as it runs. The result will be a cross-hatch pattern of the honing marks. Don't do it so long as to oversize it.

Wash it with hot soapy water after honing and dry & oil it immediatly.

 

[brycebell]

Re: 1977 25hp Johnson Opinions

Do i want the honing brush or the honing tool that has 3 pads on it?

 

[jmendoza]

Re: 1977 25hp Johnson Opinions

What I see there is the classic aluminum transfer to the cylinder walls below the ports, and very little damage at all to the bore. I would use a Q-Tip dipped in acid to burn off the aluminum before attempting any honing. Since you do not have a proper 2-stroke hone, and the the cheapo 3 shoe spring hones they sell at the auto parts store are not suited to do bores with ports in them, I would just use some 360 wet/dry to put a light cross hatch on the bores in the areas that are scuffed..do not try and remove the minor scratches, just smooth them and get a cross hatch, by hand, use WD-40 as lube. If the rings have no scoring, (they don't appear to have any) you can carefully de-burr the edges of the ring grooves where the seizure was to make sure they are moving freely in the grooves, and lightly smooth the seized areas on the piston skirts with some 220 emery in a 45 degree cross hatch, again, do not try and remove the scratches, just lightly smooth off the roughness and try to remove as little material as possible. After cleaning everything, oil and re-assemble with all new gaskets, and seals.

Now, I only offer this up because I too was once in college, and my 9.9 had a real bad seizure on #1, far worse than yours, with some deep grooves in the cylinder and rings. #2 was seized too, but not as bad. Both has scoring above the ports you could catch your finger nail in, making your engine damage by comparison look minor. I did the proceedure outlined above and ran the engine every season on our local lake from 1982 to 2009, and other than it taking an extra pull or two to start when cold, it ran great.
I have a very old book on rebuilding two strokes that has some good wisdom, and the part of it that applies here is this rule: A seizure will tend to repeat itself if the condition is not corrected, the seized area must be smoothed and dressed down so it is no longer rough, but do not try and remove the scoring. Once again, this is a technique you use if you have no other options, parts not availlable, or cannot afford a full overhaul, it's a stop gap measure.

 

[castires]

Re: 1977 25hp Johnson Opinions

brycebell,

Looks like we're in very similar territory. I'm hoping to get my 35hp disassembled further this evening and see if my rings and pistons are scored. I'm hoping not, but I'm sure they will be.

Good luck with the build. We may need to share tips/secrets to one another.

 

[brycebell]

Re: 1977 25hp Johnson Opinions

Will do castires.

Jmendoza, If I do it your way how well will it run? is it worth taking the risk? What kind of acid would I use?

 

[brycebell]

Re: 1977 25hp Johnson Opinions

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