Why did my 35hp size?

[k650]

Hi all.

First a little background about my engine, it is a Evinrude 35hp -1959 i bought it from the Swedish Navy where the engine have been stored and conserved since 1979. I have in case of changed the impeller, rebuilt the carb, new points and condensers, new coils and new bearings and seals in the gearcase (cause of water in the oil at the time for storing). The engine has been used about 30 hours since new according to the documentation that came along.

Now, yesterday was time for the first test drive in the sea and the engine runed fine and suddenly stopped. Started right away when pulling the rope and i drove back whithout problems. When i came home did i make a compresiontest, and as i feared...bad compression on the lower cylinder. I dont have a clue why the engine sized, the timing was correct and adjusted, the needles on the front of the carb was where the engine was running best, and there did come vapor/water from the exhaust.

Anyone have a idea? Se pics below of cylinder and piston.

 

[orbanp]

Re: Why did my 35hp size?

Did you do a compression test before you started using the engine? Any chance that it was like that before you got it?
That your engine started up right away after the stop might be a clue to that, though you did not say how it was running after that.

It looks like local overheating. My guess would be that when breaking in the engine they ran the crap out of it.

The cylinder should clean up with muriatic acid. After that you will see if it needs further attention. The rings look like they were not damaged. Though that top ring is not at its locating pin, they would not put the ring ends where a port is located. Measure the piston, even that looks reusable after cleaning up.

Good luck, Peter

 

[k650]

Re: Why did my 35hp size?

Hi.

I did a compressiontest before and it was much higher compressionvalues. I am planning to change the rings and hope it will restore the compression.

Regards,
Fredrik

 

[kfa4303]

Re: Why did my 35hp size?

Hi k650. Sorry to hear about the overheat. Was the motor pumping sufficient water while it was on the water? Was the head gasket still intact after the overheat? What fuel/oil mix were you using? A 1959 model OMC should use 24:1, which is about 5.5 US fl. oz. to 1 US gallon of 87 octane gasoline (sorry I don't know the metric conversions right off hand). You should also be using Champion J6C plugs, if at all possible. I agree that with some minor machining the the cylinder is salvageable and replacement pistons are relatively easy to find if need be. Even though it may be a bit of work, repairing this motor should still cost much less than buying a new of equal horsepower. Good luck. Keep us posted on your progress.

 

[orbanp]

Re: Why did my 35hp size?

Hi Fredrik,

Remove the smeared up aluminum from the cylinder wall with hydrochloric (muriatic) acid. You will see after that if you need to touch up the cylinder wall with a light honing. Check the piston to cylinder clearance, the end gap clearance for the new rings if you get those. Also check for the presence of the locating pins for the piston rings.

Good luck, Peter

 

[k650]

Re: Why did my 35hp size?

Hi.

Thanks for your replies

The head gasket was intact what i could see when i dismantled it.

I will as you recommends, clean the cylinder, hone it and change the rings. But i am still concerned why it sized. Can it be a bad thermostat?

Regards.
Fredrik

 

[orbanp]

Re: Why did my 35hp size?

Yes, you should check the thermostat while you are at it.
Also was there any debris found in the cooling passages?
Was the impeller in one piece when you replaced it or was it shredded to pieces? If so, some of those pieces might have ended up in the block.

Still, to me it looks as a preexisting condition. As I mentioned it could have been damaged while breaking the engine in, and it just got worse while you were using it.

Good luck, Peter