72 Johnson needs piston should i junk it?

[ziggy101]

Took the head off my 50hp and the piston that had 10 psi compression is erroded around the primeter in several places to the ring. Cylinder walls look good. I have seen other threads about how hard it is to find parts. I am a rookie, do even know what parts i need or how big a job it is to fix.

Should i sell the parts on ebay and find a new motor?

 

[tashasdaddy]

Re: 72 Johnson needs piston should i junk it?

ziggy, 1st it's an electric shift, which parts are hard to find, especially the solenoids. the carbs, starter, etc will bring some money on ebay.

 

[F_R]

Re: 72 Johnson needs piston should i junk it?

How hard is it to fix? Take a good long look at the powerhead. Can you envision taking it totally apart and getting it back together properly? That is exactly what has to be done. The pistons are the last thing to come out and the first things to go back in.

 

[Silvertip]

Re: 72 Johnson needs piston should i junk it?

If you do decide to rebuild the engine ( I would since the cylinder walls are ok) DO NOT run that engine again until you determine what caused the problem in the first place. Normally it's a lean condition (rebuild the carbs) or a bad water pump, stuck thermostats, clogged cooling system passages, incorrect ignition timing, to name a few. Don't just button it up and fire it up. Rebuild those carbs and do a thorough link&sync. You need a manual for that.

 

[ziggy101]

Re: 72 Johnson needs piston should i junk it?

Silvertip, FR, Tashasdaddy - thanks for the advice. I am starting in on it. First problem is how to get the flywheel nut off. Is it OK to jam a screwdriver between a gear in the flyweel and the lug with the timing arrow to hold the flywheel?

 

[tashasdaddy]

Re: 72 Johnson needs piston should i junk it?

i have a very large screw drive i use, and wedge it in the strongest place i can find. you are suppose to use a large strap wrench.

 

[papasage]

Re: 72 Johnson needs piston should i junk it?

the 72 piston isen`t avaible anymore . you will have to go to a used or use the newer piston with a wrist pen converson berring or use a newer rod and piston . the piston had the top ring to close to thetop . with no led gass they would deterioate . that is the onley thing i could find rong with the motor . the power head of a 1974 has the newer piston in it . maby several years . you would need to check the parts #. that power head canbe put on a newer standard shift foot with some shifting changes .

 

[hoeser]

Re: 72 Johnson needs piston should i junk it?

I find the easiest way to *remove* the flywheel nut is to use an impact gun in reverse. Not such a great idea for putting it back on though. Removing the flywheel afterwards requires a harmonic puller.

 

[ziggy101]

Re: 72 Johnson needs piston should i junk it?

Thanks for the help guys - got the flywheel off, and all the other parts and pieces. Ready to take the head off. Now i have another problems, sounds like a new posting is needed for that. Thanks for the comments on the piston/ring to close to top.

 

[rndn]

Re: 72 Johnson needs piston should i junk it?

Since you have never done anything like this before I have two questions. How do you know what constitutes a good cylinder wall? Do you have the service manual? Without the service manual you will have no idea the proper torque setting for the bolts you will be removing.

 

[ziggy101]

Re: 72 Johnson needs piston should i junk it?

RNDN

i thought i would take the head into a Marina and have them look at the cylinder walls and give me advise on if this needs to be honed, if it needs oversized rings etc. ask them to look at the crank etc.

I have a manual - but it is somewhat generic.

am having trouble getting the power head off.