1977 85hp johnson piston problems

[aintnever]

I just purchased a 1977 85hp Johnson (javelin) from a friend of mine. The story behind the motor is: ran great last year, ran great once this year. About a month ago he took it out and it started making a knocking noise. He killed the motor immediately and rowed back to shore. Once he got it home the flywheel was locked up. he removed the spark plugs and freed the engine. in one cylinder he could never get any compression (simply by putting his finger in sp hole and turning flywheel). He inspected the spark plug from that cylinder and seen that the piston had hit it and closed the gap. I have purchased the boat and motor and need advice as where to start in fixing the motor. I'm a first time boat owner. My friend feels as though all I need to do is replace the piston rings if the piston isnt damaged.

 

[ondarvr]

Re: 1977 85hp johnson piston problems

Most likely its major rebuild time.

If the piston hit the spark plug it means a bearing went out, if it was on the wrist pin you will need a rod too, if it was on the crank then you will most likely need a new crank along with a rod and piston.

What it comes down to is a total rebuild, which can be pricy.

 

[emdsapmgr]

Re: 1977 85hp johnson piston problems

Good advice. You will be able to get a good idea what is going on when you pull both heads and the 4 bypass covers on the sides of each cylinder. You won't see how bad the crank is for sure till you split the crankcase. Keep in mind that his engine is a small bore 92 cubic inch block-the pistons and ringsets are smaller than the 115 and 140 that year.

 

[ezeke]

Re: 1977 85hp johnson piston problems

If you look around, you should be able to find a working 115 powerhead from 1974 through 1977 that will go right on. Rebuilding the 85HP is not economically justified.

If you do decide to rebuild, get the factory manual so that you have step-by-step instructions for the rebuilding process. http://cgi.ebay.com/ebaymotors/1977...Motors_Manuals_Literature&hash=item3a5be2a866

 

[aintnever]

Re: 1977 85hp johnson piston problems

Thank you guys so much for the advice, not great news, but still appreciated.

 

[aintnever]

Re: 1977 85hp johnson piston problems

Well I went out and pulled the heads to inspect the piston in question. Unfortunately this piston has gotten very very hot at some point. It is very pitted and I found small pieces that had chipped off of it. The piston liner/cylinder liner is scarred pretty bad. The good news: no slack in the rod or cam, it is only this one piston, other pistons look good. Anymore advice given this new information.

 

[ondarvr]

Re: 1977 85hp johnson piston problems

There is no cam in that motor.


There a couple of things that may have happened.

1. A ring broke due to carbon build up.

2. The locating pin for the ring came out and the ring broke.

3. A bearing let go.

All the pits you see are from either the ring or bearing pieces getting smashed between the head and piston.

What it comes down to is a complete rebuild or trash it, you don't want to only replace a few parts if you take it apart because it will take a good amount of time and money to just fix the actual damage, that money would be wasted if you skimped on a rebuild and it broke down again soon.

 

[LiLGrady17]

Re: 1977 85hp johnson piston problems

My old 85 hp ran fine on the muffs, but overheated on the water due to no telltale & bad impeller, long story... Piston lost an edge piece about 1/4 inch, and bounced around as ondarvr says, scored piston top, head and wall slightly, then exited the exhaust.. You'll need to evaluate the cylinder scoring carefully, and condition of all the other bolts on the motor. Mine were SW corroded, so some were unrecognizable as bolts..A cheapo repair on this engine could put you in the price range of a newer, running used one, and that's doing the work yourself..

 

[aintnever]

Re: 1977 85hp johnson piston problems

well we tore down the motor a little further and found some wore rings on the other pistons, but no further damage. My little brother works at a mechanic shop and has the ability to machine out the damaged cylinder sleeve and replace it. Sunday we are going to tear down the rest of the motor and assess any other damage. So far the damage was isolated to the one cylinder. Has a lot of carbon build up. My little brother is quite the mechanic and is now determined to help me rebuild. LOL. But we won't sink too much in it before deciding to replace the motor. The boat was purchased as a project anyways. I also have a good lead on a replacement block or powerhead instead of machining the existing one. Overall the good news is my brother and I are getting to spend some good time together.

 

[aintnever]

Re: 1977 85hp johnson piston problems

Got the motor torn completely down today. I found a used powerhead here locally. Decent price, and the shop is ordering me a new piston, bearings, and gasket kit. Had them look at the crank (corkscrew) and they said it was in great shape. Feelin lucky everything working out. Thank you guys for the great advice and help.

 

[aintnever]

Re: 1977 85hp johnson piston problems

well, quick update, found a replacement powerhead. installed the other day. got it to run on the muffs, but when i put it on the water it overheated and i shut it down. the mechanic i bought it off of told me when i bought it to take out the thermostat and only put the big spring and the nipple valve back in, i'm not sure I did it right though, or possibly it could be a bad water pump impeller.

 

[emdsapmgr]

Re: 1977 85hp johnson piston problems

Whenever you overhaul an engine it is best to install new thermostats and a new water impeller. That way you know the new powerhead should run fine right out of the box. I'd put the factory stats back in the engine if it were mine.