1972 125hp - compression question

[sheboyganjohn]

I am looking into getting a new project boat. I have found one that fits my needs that has a 72 125hp Evinrude on it. I am going to look at it on Tuesday but from the pictures it looks to be in good shape. It does have a few issues that I have reseached on here and know how to correct: cooling issue which will most likely be a new water pump and stuck in forward with eletrical shift so it will be either a new control box or one of the home made switches that I have seen on here. My qeustion is the compression. I keep seeing in post that as long as it is above 100 and with in 10% it is good. This motor has 105, 110, 125, 125 for compression. I plan on rebuilding all the carbs, new fuel lines, and running a decarb on it. Is the 105 cylinder an issue or will the decarb clear this up. And if it does not clear it up what affect does having a slightly lower cylinder have on the motor. In searching the forums I have never found the reason behind the 10% rule.

 

[tx1961whaler]

Re: 1972 125hp - compression question

stuck in forward with eletrical shift so it will be either a new control box or one of the home made switches that I have seen on here.

I would be more concerned the with the lower end problem than with the compression.

 

[dwyork@hotmail.com]

Re: 1972 125hp - compression question

Run the appropriate mix of Seafoam with fresh gas and it should get your compression where you need it to be. Your biggest concern is going to come from the lower unit...I would have it checked out before you leap into it.

 

[sheboyganjohn]

Re: 1972 125hp - compression question

Thanks for the replies. I wanted to make sure the compression was not that big of an issue bofore I went any further in the process.

I have read over a bunch of posts on this lower unit and will try to test it when I go look at it. I will take the tester and check the reistance on the solinoids if I cannot get it in a tank to run it. My other idea was to bring a jumper wire and jump from the starter to the shift wires turn the motor over (plugs out of course) and see if I can get it to go in neutral and reverse. Of course if I can put it in a tank and run it I wll try the jumper with it running. Does this sound like a good plan?

Not that it matters but I am looking at buying it from a charity group that sells donated cars and boats to raise funds. I have bought from them in the past and even though they are definately projects when you get them, you usually get them at such a good deal it is hard to pass up. The one I am looking at is a 1972 17' open bow with a very good hull, average interior for the age, a very good trailer, and of course the motor for $495. Their inspection process is fairly good so you know where the problems are, they just don't get too deep into the diagnostics.

 

[dwyork@hotmail.com]

Re: 1972 125hp - compression question

It sounds like a good deal if you can do all the work yourself and worse case scenario is that you will have to find another lower unit, but a used replacement for that model is fairly easy to come by and...you are buying from Charity to help raise money for their cause so even if you don't get it operating perfectly at least you will feel good about Giving.

 

[tashasdaddy]

Re: 1972 125hp - compression question

make sure the control works, switches are like hens teeth.

Hydro Electric Shift)
(J. Reeves)

The shifting setup of the lower unit is what's called a "Hydro Electric Shift", which is quite complex consisting of voltage being applied to solenoids in the lower unit which in turn change oil passages via a oil pump that supplies various pressure on a spring loaded shifter dog. The wires leading to the lower unit (at the powerhead) are "Green" and "Blue". The engine must be running or cranking over in order to shift out of forward gear.

You CAN NOT use HI VIS lube in that lower unit. You MUST USE what OMC calls "Premium Blend" lube, commonly called "Type C". (A thinner lube)

In neutral, you need 12v to the "Green" wire.
In reverse, you need 12v to both wires, the "Green" one and the "Blue" one.
In forward, there should be no voltage to either wire. (The spring loaded shifter dog forces the unit into forward gear)

To check the lower unit for proper shifting to make sure you have no trouble there, remove the spark plugs to avoid problems and to allow a higher cranking speed.

This next step eliminates the actual shift switch in case problems may exist there.... Disconnect the blue & green wires at the knife connectors (the rubber insulated boots) leading to the lower unit at the powerhead, then using jumpers, take voltage direct from the starter solenoid to apply voltage to the "Green" wire for neutral, then both wires 'Green" & "Blue" for reverse (Remember the engine must be cranking over in order to shift).
With no voltage applied, the unit should be in forward. No need for a ground jumper... the lower unit's already grounded. You may crank the engine with the key switch or by energizing the starter solenoid with a jumper wire.

 

[emdsapmgr]

Re: 1972 125hp - compression question

Those 125's ran high compression heads. I'd be looking for a recently overhauled engine to have over 130 lbs in each hole. The 125 is probably a solid reading. The 105 and 110 are considered low. I'd run some Engine Tuner through it, as was mentioned and then see what the compression is. If the compression still does not come up, I'd pull the head and side covers on the low cyls and see if there is any piston aluminum transfer/scuffing on the cylinder walls. If not, then run it.

 

[sheboyganjohn]

Re: 1972 125hp - compression question

Thanks for bringing that info up Tashasdaddy, I saw it when I was searching and figured I would have to go back and dig it up. I am not too worried about the switch. I saw some of the posts discussing ways to wire in a home made switch assembly that were very detailed. Doesn't look overly difficult and I have a brother-in-law that is an eletrical geek.

emdsapmgr thanks for the compression info. I will most likely sit on the engine until we thaw out up here. I will then do a full decarb on it and recheck the numbers. Hopefully they will come back up so I don't have to tear into it. I am one of those people that when I start taking things apart I keep finding more things to fix/replace while I am at it so I only have to go in once, which can get expensive in a hurry.

 

[tashasdaddy]

Re: 1972 125hp - compression question

hopefully the controls are connected, using the jump method, you can easily blow the power pack in those motors. if you can get the pos and ground, and use the key to start, you are better off.

 

[dwyork@hotmail.com]

Re: 1972 125hp - compression question

Yeah, Hopefully your controls are good to go...I would avoid the jump method if at all possible.

 

[sheboyganjohn]

Re: 1972 125hp - compression question

Well I was able to get out on Tuesday to check it out. I did not get a chance to start it since I did not get that far. Tested the solinoids and both tested out good, one at 6 ohms and the other at 7.9 ohms. I pulled the drain plug and there was no oil in the LU. I turned the prop a few times and some water leaked out the leading edge of the LU. There was a few scratches there and that is where it was leaking, no visible crack. Anyhow I moved on. With 500 boats on the grounds there were enough other ones to look at. I have some questions on other motors which I will put in a new post. Thanks for the help on this one.