to rebuild or not rebuild???

[66 joe]

Hello everyone, (first time poster)

Ive got a blown piston on my '95 johnson 112 spl outboard motor.
Motor has about 100 hrs all in saltwater. I took fairly good care or motor, flushed after every use, changed lower gear oil/spark plugs bi-annually. alway used fuel stabilizer for winter storage in the 50-1 mix. Motor was very dependable til last week, when it started running shaky. I thought it was just bad fuel or bad plug so I limped it back to marina and took it home.
I pulled plugs and saw smashed electrode and met bits in one cylinder, which prompted me to do a compr test, that one was bad, 10-15 lbs, all others 110-120. So I pulled the head and saw a hole in piston top exposing the ring. Suprisingly, no visual damage to cyl and other hole is perfect. both cylinders look very good with no scores and only visible cross hatch.
Im gonna try and post pictures, what concerns me is the pitting in the top of the head, and the head gasket was good.
Im a decent garage mechanic, with alot of american v-8 exp, but no outboard exp.

 

[R.Johnson]

Re: to rebuild or not rebuild???

What RPM have you been running your engine, or what does it peak out at?

 

[66 joe]

Re: to rebuild or not rebuild???





I believe the max was about 4-5K. Thanks.

 

[66 joe]

Re: to rebuild or not rebuild???

Im sorry I didnt pay much attn to rpm, what I can say is motor was fairly strong, it pushed a 19.5 center consel fishing boat and would get up on plane fairly quickly, top speed was about 40 mph (according to gps) then it would easily cruise 25-30mph.

I dont know if the picture show enough detail, but the top piston has a hole in it making the ring visible.

If a piston/re-ring, hone (maybe bore) cylinder would work, Id like to go that route. I can probably do alot of dis-assemble and re-assemble work myself and just find a machinist to help me w/ short block. Thats if its all worth it, I dont like the idea of spending 2000+ on power head on a 10+ year old motor.
I do like this motor, but if labor and costs add up too much, Id sooner spend it on a new one.

Thanks,,,,,,,,,,,, Joe

 

[66 joe]

Re: to rebuild or not rebuild???

Im also trying to figure out why piston would fall apart, Im guessing overheat from lean fuel condition??? Im not even sure if my alarm sensor was working. condition of cylinder looks as if block is very good candidate for new cylinders and rings, im just unsure about the pitted top end
thanks, joe

 

[66 joe]

Re: to rebuild or not rebuild???

found 1 new head w/ gaskets would cost approx $200, pistons /rings and bearings,,,, I dont know; Im just wondering if I should try this re-build or not. I was thinking of pulling the powerhead and having machinist check bores and bearing, if all checks ok,, maybe having competent machinist re-assemble power head w/ new parts, saving me alot of labor costs????

 

[Benny1963]

Re: to rebuild or not rebuild???

you need to tear it down and have boat machinist check cyls
if ya can bore one hone three and use new gasket and seal kit
you can get out cheap piston with rings 30$ they have v4 heads on ebay all the time a lot cheaper than that i also have some v4 stuff ,you will have to checlk all bearings use new rings on all cyls .you will need factory manual for tear down and assembly,hole in the piston is usually bad gas .bad timeing
and carb problem ,you will need to be carefull you need to do complete carb builds and make sure link and sink is good.also wot timeing .
i build my motors but have a guy that really good with old school omc stuff tank mine and link and sink saves me trouble at launch trying to time on trailer ,you can static time but it needs to be done under load running to verify .static timeing you will also need to check timeing pointer setup ,
pryor to timeing ,my guy tanks mine makes all adjustment times and sets idle in tank for i hours labor 85$ its worth it if you get the right mech
mine just did mine and man he really did a good job
need anything holla ,by the way im a car guy to that got the boat bug
i have built and 150 crossflow 1983 /johnson 175 1983 /1981 35 evin 7.7 evin
and i am currently looking for older 140 looper to do ,pm me if ya need some parts

 

[Dhadley]

Re: to rebuild or not rebuild???

Most likely the broken ring was from lugging. That's a very typical scenario. Most likely you'll find the other 3 cylinders are out of round and will need to be bored. Not a big deal at all. Most likely .020 will clean everything up. There are lots of good marine machine shops around that can do the machine work and supply any parts you might need. Many will reassemble to any point for you. If you need contact info we can help with that. Strongly suggest not using an automotive machine shop.

What spark plugs are you using?

 

[66 joe]

Re: to rebuild or not rebuild???

Ive been told by 2 marine mechs. that more than likely the other 3 cyls will be out of round as well. 1 is telling me to buy a new power head. The other told me he's been doing marine for 28 yrs and will probably need over-bore. He has full machine shop and I asked if I dis-assemble powerhd and take it to him, will it save me $$. He said about $1000 for parts and re-build of power head, which i though seemed reasonable, heck i may even pay him for re-assembly of whole unit. Thanks everyone, Ive got some work to do, and its nice to know Ill have some support. Joe

 

[66 joe]

Re: to rebuild or not rebuild???

What is "lugging" in outboard????

 

[Dhadley]

Re: to rebuild or not rebuild???

Top rpm not high enough. That causes higher than normal combustion temps (not cooling water temps) and creates carbon on the rings. That carbon, which is a black sticky substance, causes the rings to stick in the groove starting on the side opposite the end gap. The piston loses support and cocks over. Eventually it will shear off the ring. It usually shows up on the starboard side first. The extra combustion heat will cause the cylinders to be out of shape requiring an overbore.

 

[66 joe]

Re: to rebuild or not rebuild???

well my damage was on cyl 1 starboard right????

 

[Dhadley]

Re: to rebuild or not rebuild???

That's normally where it shows up first. When you get it repaired just make sure you target 5800 as the top rpm with an average load.