when is it time to rebuild an engine

[Pescador170]

just had a thouht and i wanted to get your opinion. in a few weeks i will be starting a rebuild on my old girl (1973 170). i would love to repower but do not have the money for an engine so i was just thinking about rebuilding the engine. the engine is a 70HP 1985 evinrude. it still runs good but feels like it lacks some power because to get her on a plane i have to floor the gas. is it worth it?

[JimCt]

Before spending a dime, do a compression check.  Don't recall offhand what the "new" compression spec. is but if you get over 110 PSI on all cylinders and they are within 10% of each other the basic engine is likely fine.  This will limit your "rebuild" work to a thorough tune up.  New factory recommended plugs & wires.  Rebuild the carbs with factory kits, replace the water pump (and housing if needed) and you should be in good shape.  Maybe also a Seafoam treatment to blow out the carbon.

[GoneFission]

I am one of those "if it ain't broke don't fix it" guys, so I agree with Jim.  Check the compression and compare it to specs - outboard compression is widely variable from about 80 PSI up to 150 - depending on model - so make sure you know the specs for your motor.  Also do a good check on the ignition system - old stators and coils are often the source of power loss on older motors.  

If you overhaul the carbs, make sure you get them properly tuned and synchronized - again a source of power loss.  I checked a 3 cylinder outboard for a buddy recently and found one carb was only about 3/4 open at wide open throttle - ran much better when we fixed that!  Some models have variable timing depending on throttle - more advance at lower throttle for a smoother idle - and less advance as the throttle opens to prevent detonation.  You need to make sure you get all those setting right!  

Rebuilding an outboard is not a easy as some folks think.  If you have never worked with needle bearings, reed valves, or 2 stroke ported cylinder bores, you should probably stay away.  Too many outboards wind up actually worse off after a "shadetree" rebuild.  It's more than popping the pistons out and putting in a new set of rings...

Nonetheless, it could be interesting to do an engine overhaul step-by-step on the forum - kind of like some folks have done with boat rebuilds.  An idea?  

[pete]

maybe consider buying a rebuilt powerhead?  

[Pescador170]

thanks for the tips guys, luckily near me there is an evinrude specialist. as soon as i pick up the boat next week i will bring it there and pass these ideas by them
by the way what is this seafoam treatment?

[RickK]

Is a 70 really enough power to get the boat up on plane quickly?  With my 115 I have to get on it to get up on plane quickly otherwise it plows away and finally gets up there, at lower throttle.

[JimCt]

Seafoam is a product that de-carbonizes the engine.

http://www.seafoamsales.com/motorTuneUpTechGas.htm

[John Jones]

Read this decarbon/Sea Foam thread on Florida Sportsman.  The author "Dunk" is an experienced but very opinionated marine surveyor.

NOTE:  Lots of people confuse decarbing with cleaning their carburetor.  NOT.  Decarb is getting the carbon deposits out of the comubstion chamber.  Seized piston rings are a common failure of outboards and caused by carbon deposits.


http://outdoorsbest.zeroforum.com/zerothread?id=2589

[scott_gunn]

I decarbon using the spray foam method once a year.

[Pescador170]

RickK, the 70 does lack the power to get on a plane. in order for me to get it on a plane i have to push it at full throtle then back off once she gets on a plane.  on plane i cruise at about 24mph. i would love to jump up to a 90hp but right now i do not have the money for a new engine. for the time being i am going to follow all of these tips and try to get a little extra power out of the old girl

[RickK]

RickK, the 70 does lack the power to get on a plane. in order for me to get it on a plane i have to push it at full throtle then back off once she gets on a plane.  on plane i cruise at about 24mph.

I wasn't specifically asking about the motor you want to rebuild - I was talking about a 70 in general.  Maybe you were too?  If so, sorry to be confusing.

[RickK]

Read this decarbon/Sea Foam thread on Florida Sportsman.  The author "Dunk" is an experienced but very opinionated marine surveyor.

NOTE:  Lots of people confuse decarbing with cleaning their carburetor.  NOT.  Decarb is getting the carbon deposits out of the comubstion chamber.  Seized piston rings are a common failure of outboards and caused by carbon deposits.


http://outdoorsbest.zeroforum.com/zerothread?id=2589

JJ, have you tried this process?

[John Jones]

I got as far as buying the Seafoam and a 3 gallon tank.  

I'm afraid that carbon is all that's holding my motor together  

[RickK]

You could wait until May, when the skeeters start showing up and then contract your motor out as a fogger?    :)

Another side of what Dunk was saying about pulling the hose off the "in" side of your separator to connect the little tank - every time you pull the hose off, you're going to have to cut off a little bit of that hose before putting it back on.  That means 1) I'd have to pull new hose from the fuel tank because I don't have a lot of spare length in mine already. 2) It wouldn't be too long before everyone would have to replace that hose.

[John Jones]

You should have seen the love bugs out on the bay the other day.  My white boat was black.  We were about ready to pull up and leave the area to get away from them.

If your hose is old you probably should replace it anyway (as I need to do).  The older hoses aren't alcohol proof and can start coming apart inside from the new gas.  Most all gasoline today has some alcohol.

I doubt his 50-60 hours is necessary.  That would be twice a year for me.  You can always splice on a new piece of gas line.