1962 Evinrude 18hp- Compression Tests

[GarageBeers]

Good morning! This 18hp has 2x cylinders. I tested compression after a few mins of the engine running to get an accurate "wet test". Top measured 98 psi and bottom measured 90 psi. Gladly they are within 10psi of each other, so I am not too worried. I did rebuild this engine. New pistons, rings, and dingle-ball honed the cylinder walls...they needed it... previous owner slammed this engine harder than a cabin screen door. What could the 8 psi difference be? Did I possibly over-hone 1 cylinder? Pistons are exact same. Spark plugs are exact same. Both combustion chambers in the head looked exact. Layed the block and head on a flat piece of glass with some emery cloth and got them dang near perfect flat and clean. New head gasket. 3x even torque sequence on all bolts. Still only 8 psi difference, so not too bad. Just more so curious if I can get them closer to +/- 5 psi or even 0. More of an OCD thing ha, I know I wont be able to tell the difference operationally

 

[airshot]

Why try to fix what isn't broken ??

 

[GarageBeers]

Why try to fix what isn't broken ??

Haha less of a “repair” thread. Ill still run it stress free. More so curious

 

[LaqueRatt]

Maybe when you run it the rings will seat and the compression will even out.

 

[GarageBeers]

Maybe when you run it the rings will seat and the compression will even out.

Oh good point. Yes rings/pistons have under 30mins so far

 

[thill]

I agree with the above. See how it tests once you break it in for a few hours.

 

[airshot]

Guess I missed the rebuild part ( senior moment), gonna bet things will get much better after ten hours of operation. Make sure you richen up that oil mix a little for breakin....

 

[GarageBeers]

sounds good, thank you @thill and @airshot. Yeah the manual says run 25:1 for first 10 hours and then 50:1 thereafter. Which is a separate topic ha.... "best oil fuel ratio for a 60's outboard"... after breakin with 25:1 i plan to use ethanol free gas with my oil, probably at 50:1

 

[airshot]

Whether you use E fuels or not is a personal preference, just be sure all the hoses in the engine are alcohol approved. More importantly is where you buy your fuel !! Don't be afraid to test the fuel you buy. Many stations do not properly maintain their tanks and filters so folks buy crappy fuel to begin with. Whatever you buy, use a stabilizer in storage like all engine Mfgrs recomend ..
Make sure you have filters on fuel lines. My OB has a filter in the tank, another in the fuel line ( see thru) and another inside the engine before the fuel pump.
I owned a 1964 18 HP Evinrude, bought new by my father, we skied behind it on a 14' mirro. tinney. Great motor !!

 

[GarageBeers]

Whether you use E fuels or not is a personal preference, just be sure all the hoses in the engine are alcohol approved. More importantly is where you buy your fuel !! Don't be afraid to test the fuel you buy. Many stations do not properly maintain their tanks and filters so folks buy crappy fuel to begin with. Whatever you buy, use a stabilizer in storage like all engine Mfgrs recomend ..
Make sure you have filters on fuel lines. My OB has a filter in the tank, another in the fuel line ( see thru) and another inside the engine before the fuel pump.
I owned a 1964 18 HP Evinrude, bought new by my father, we skied behind it on a 14' mirro. tinney. Great motor !!

Yeah good point about fuel source. I wonder what the best way to test that is?

And for remaining fuel left behind throughout the entire system, i like to flush my outboards after each use when brought back home. Figured i would switch over to the TruFuel engineered 40:1 or 50:1 mix during the flush to ensure "healthy" fuel is left behind. No ethanol and can be kept in the lowest quality fuel lines for months without deteriorating. I dont like to disconnect my fuel supply and let the engine kill itself. That means it uses up all the fuel (which contains oil for 2 strokes) which means those final revolutions of the crank and pistons are ran "dry".... unnecessary if i leave engineered fuel or stabilizer in it. Also, i like to start my outboards every so often, which helps prevent rotting lines and gaskets as well, despite whatever fuel source is used

 

[airshot]

Your money, use what ever you want. I have been using E10 fuels since they came out. The only issues ever, were from bad fuel from the station. When I fill a 5 gallon can, about half way thru I put some into a clear container to let sit still and see if any contaminates appear. If so, I go elsewhere.. My neighbor is an old car high performance engine guy. Many SuperBees, Dodge Chargers, Barracuda's etc....Been using E10 in them for over 15 years, not one issue !!

 

[MrGiggles]

Your compression loss could have many causes. Manufacturing tolerances in the pistons (especially if aftermarket), uneven bore wear (typically one bank or one end of the block will run hotter depending on water flow), uneven bottom end wear, etc.

It would be difficult to pinpoint without disassembling and getting some precise measurements, and I don't think it's likely to be an issue long term. Run that sucker.

 

[thill]

Most Evinrudes like 50:1. For a while, some of them had 100:1 labels, but don't fall for it! Run 50:1.

I am not happy at all with TrueFuel. Have had issues with some lawn equipment when using it, as have friends. I will never use it again.

Find a BUSY fuel station, and you shouldn't have any issues with fuel. We have an Exxon at a major intersection near me that also has a fleet fuel side. Always busy, even when they aren't the cheapest around. That is the station close to me that I trust the most.

One thought... Did you rotate your ring splits 180 degrees from each other?

I personally think that once your rings seat into the cylinder, your compression will even out. And remember to vary your engine speed often during break in and even for the first few months, if possible. And don't skip briefly running at WOT after the first hour, so you don't form a ridge at the top of your cylinder.

2-strokes love to be run! I hope it all works out well for you.

 

[thill]

And E-free is not a bad idea, especially for small engines that don't run a lot of fuel through them. So, at $1 more a gallon, if it takes you 3 trips to run through your 6 gallon tank, you are talking $2 a trip. WORTH IT for small engines, in my opinion.

For bigger engines, that may run 6+ gallons every trip, IF you go fishing every month the fuel will never get old and sit for long. On my often used boats I use E10 along with stabilizer. I also replace the fuel hoses and primer bulb anytime they start feeling stiff. Cheap insurance, and I have almost no issues with my engines ever.

 

[LaqueRatt]

I run ethanol because I have no choice. Something to keep in mind for you guys who say never run the stuff. I'd have to drive an hour to get it. I envy you guys who can get it locally.