140 Evinrude compresion issues

[FLATS RAT]

Hello,

I have a 140HP 1978 Model is 140843C. This engine was removed from my boat about 6 months ago and has been sitting ever since.
Flashback
Over time,(6 months) it began to become hesitant. I had the carbs rebuilt, that helped a little. Then, slowly it became evident that it had bigger issues as it now would only idle. As soon as you touched the throttle, she would stall out. Rebuild the carbs again, no change. I performed a compression test on it and at the values I was looking at, I just assumed that it would have to be rebuilt. So I pulled it off and stored it. I can?t remember what order the readings were but I do remember the values. 140-122-120-86. I'm not sure what the spec is but I'm sure that is way out. The insides of the cylinder walls are glazed but not scored. (what I can see with a bore scope) There is some carbon build up on the head of the pistons, but nothing I would say is excessive. I feel a fresh set of rings are in order. I was about to perform a rebuild on this engine and thought I should post here before I disassembled it and did something foolish. Any ideas or thoughts would be greatly appreciated.

Thank you in advance for your $.02

a few questions if a rebuild is in order;
Is it safe to.............
use the old pistons if they appear good?
use the original main bearings?

 

[Dhadley]

Re: 140 Evinrude compresion issues

I'd decarb first. Might save a bunch of time, money, effort etc.

 

[fishmen111]

Re: 140 Evinrude compresion issues

Decarb. If you have considerable carbon on the pistons, you may get lucky and simply have stuck rings.

 

[tashasdaddy]

Re: 140 Evinrude compresion issues

Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck

 

[Theoutdoorsman]

Re: 140 Evinrude compresion issues

Take heed to the advice given! These older crossflows are terribly bad about carbon deposit build up. You might not see that much inside the cylinders, but I'd almost be willing to bet that your exhaust housing is packed to the gills with it! I agree in that you most likely have stuck rings. A good decarb would aide in removing the carbon deposits, free up the sticking rings, and likely restore some if not a lot of that lost compression. Definitely make the decarb part of your annual care and maintenance. Good luck and let us know how things turn out for you.............. ALAN

 

[wavrider]

Re: 140 Evinrude compresion issues

Decarb first, and you can also use deep creep sprayed directly into the cylinders after you have warmed the engine up, pull plugs spray deep creep ijtp cylinders and re install spark plugs, use this in conjunction with the sea foam in the gas.

sounds like you may have a head gasket going bad or leaking a little
If you could remember what cylinder it is low on would also help in troubleshooting, you will be suprised what a de carb can do for your rings

 

[FLATS RAT]

Re: 140 Evinrude compresion issues

Thank you all for the quick responses. I will do as you all mentioned. Is it possible to perform this without the engine hanging on the boat? Right now it is sitting on the engine stand. It's going to take some doing, but I'll do the swap if there is no other way. Thank you again!!!

 

[wavrider]

Re: 140 Evinrude compresion issues

If you have a barrel to run the engine in then yes you can do a de carb off the boat.
Make sure the engine stand is strong enough to hold this enngine while idling. do not raise the rpms above 1500

It will burn the carbon off but not as good as a nice wot run on the water.

go ahead and try it and then after check compression, you may need to de carb 2 times to get it all out.

Once you get the engine on the boat and can run it for a good wot run de carb again just to ensure you got it as good as it can get

For now the idling in the barrel will suffice to see if it frees the rings and increases compression.