1972 Johnson 125hp Piston Replacement

[mdgpl73]

Okay, bought a boat with a 125hp Johnson. Model number 125ESL72R. Motor has good compression on all but one cylinder. Only about 24psi. So I took off the head and found chunks missing out of the piston and some metal embedded into the piston and head. I attached images of what I saw. Looking for some input on what you guys think. Worth putting time and effort into it? I have already started to tear it down as i had nothing much going on yesterday. Also if anyone knows how to get the crankcase casting off. I removed all the bolts that i see in the exploded parts diagram. Am I missing something? When tapping it with a rubber mallet I can get about 1/8" gap from the top, but cannot get the bottom to budge at all. I forgot to grab some pics of where Im at on that side. I can snap some tonight. Any advice would be appreciated. Thanks!

Matt

 

[wired247]

Re: 1972 Johnson 125hp Piston Replacement

Did you remove the lower bearing retainer ? It has to come off to split the case.

Your piston damage is pretty typical. 125's are good engines and unless you want to buy a new engine I'd call it worth rebuilding. All of this depends on how much money you have lying around and how handy you are.

New engine= a whole bunchof money and not so handy .
Rebuilding yours= not so much money and a lot more handiness.

Either will accomplish getting from point A to point B.

 

[mdgpl73]

Re: 1972 Johnson 125hp Piston Replacement

Im assuming you are referring to the two bolts on the very bottom with 9/16" heads? I guess that's what I figured they were. Yeah, I got those out.

Plus i got the boat and motor for basically nothing. Paid $300 for both, with trailer. I plan on putting a new piston and rings into the one cylinder. I'm hoping that will be enough to get her going. Am I crazy if I don't do all 4? I'm hesitant on all 4 after seeing multiple negative posts on the electric shift potion of the motor.

 

[wired247]

Re: 1972 Johnson 125hp Piston Replacement

Oh I thought you were trying to split the crank case.

 

[mdgpl73]

Re: 1972 Johnson 125hp Piston Replacement

From what I can see is that the two dowels/alignment pins are the only things holding it together. Do I need to pull those somehow? I dont want to use too much more force and crack the case.

 

[mdgpl73]

Re: 1972 Johnson 125hp Piston Replacement

Yes, I am trying to split the crankcase. From this diagram, the only thing i can think of that is holding

 

[oldcatamount]

Re: 1972 Johnson 125hp Piston Replacement

Those two alignment dowel pins need to come out. Use a "soft", blunt, punch and a mallet. Tap lightly.

 

[tbachelor]

Re: 1972 Johnson 125hp Piston Replacement

Can't see the link?

 

[mdgpl73]

Re: 1972 Johnson 125hp Piston Replacement

I dont know why the Link wont work. I tried it about 5 different ways. Thanks Old Cat! I will punch them out tonight.

Quick question, do they need to punch out towards the head side of the motor or the crank side?

 

[oldcatamount]

Re: 1972 Johnson 125hp Piston Replacement

They're tapered pins. Take a close look at them and tap them from the smaller end.

 

[mdgpl73]

Re: 1972 Johnson 125hp Piston Replacement

Thanks for the advice!! I was able to knock the pins out last night finally. Split the case and removed the failed piston. Piston looks pretty rough, although the cylinder wall feels actually pretty smooth. Hoping I can get away with just cleaning the cylinder up and putting in a new piston and ring set. Anybody have any advice or suggestions? Ordered the parts last night, so just waiting on good ol' USPS, crossing my fingers for Friday.

 

[wired247]

Re: 1972 Johnson 125hp Piston Replacement

Use a ball hone . The spring loaded bar type wont work with the ports in the block.