Evinrude 6hp compression low

[seaotter]

Today I bought a 1978 Evinrude 6hp which the seller told me had broken rings - as he was told by a boat shop. So I bought it basically for parts to take apart and learn how they work.

I tested compression at home and got 35 psi on both cylinders. So I removed the cylinder head and saw the head gasket broken in the space between the two cylinders. The cylinder head had not been removed recently nor the exhaust plate so I don't know how anyone knew the rings were broken.

Is it reasonable that the broken head gasket at that spot would give compression at 35 in both cylinders?


Anyway, there is some carbon in there around the top of the cylinders but the cylinder walls do not look scored and I can still see the groves - the little lines sort of like checkering on the cylinder wall.

How do I test if the rings are broken? Or if the pistons are loose due to worn rings? There is a little tiny bit of play in the piston side to side against the cylinder wall. There is also a little bit of play if I try to turn the piston clockwise or counterclockwise.

Do I need feeler gauges or something to measure the gap between piston and cylinder wall?

Can rings be cleaned without removing the pistons? I have no idea what to take apart to remove pistons. Maybe separate the crankcase halves?

I have a feeling all I need is to get a new head gasket and sort of clean up the cylinder head - sanding it or something. At least that would be worth trying before I take the whole thing apart.

I am no mechanic but this looks to be a very interesting new hobby.

Thanks!

 

[boobie]

Re: Evinrude 6hp compression low

Clean up all the surfaces good and install a new head gasket and try to get it running. If you do give it a good de-carb job. Rings may just be carboned up. Check your compression after head gasket replacement. By the way, that was a good little mtr. Hope you get it running.

 

[JB]

Re: Evinrude 6hp compression low

I really doubt that there is anything wrong with your rings. The Tech's diagnosis had a lot more to do with his financial condition than diagnostic skill.

 

[Lion hunter]

Re: Evinrude 6hp compression low

You say your no mechanic but it sounds like you already diagnosed a problem better than someone who proclaims to be. The great thing about internal combustion engines is they all work on the same principle. Introduce fuel, compress it, introduce spark. Knowing those things will get you a long way in troubleshooting. Beyond that every motor has it's own intracacies, and that is where a good manual comes in handy. But 2 strokes are dead simple as far as moving parts go. Keep it up though, it's a fun great hobby.

 

[seaotter]

Re: Evinrude 6hp compression low

I've done a lot of online reading on these outboards in the past month since I bought an old Ted Williams then a different Evinrude - a 4.5 hp.

The thing is, everyone posting about their problems, which makes me paranoid thinking the same things could be wrong with mine.

Yes, I think it is best to put on a new head gasket and see how that works.

Thanks for the comments!

 

[seaotter]

Re: Evinrude 6hp compression low

At one time it overheated because I see the plastic covering on the power pack wiring is melted in a couple places where it contacted the head.

The seller said it was running last summer and I see where it has been greased recently and the plugs don't look worn at all. Probably it was serviced last summer.

I'll try to clean out the channels where the water flows and see what happens.

 

[Lion hunter]

Re: Evinrude 6hp compression low

Don't be paranoid about it. 99% of the people that come on here are trying to fix a problem and not brag about the good. The are a few quirky models of every outboard out there that some stay away from but by and large most that have been around awhile are pretty good motors when taken care of. I stay away from the air cooled lawn mower engine powered ones, but I have had a few and they were even ok. Evinrudes, Johnsons, and most Mercurys have been around long enough that parts are easy to come by and fairly cheap. When you get into the oddball motors they can get expensive to maintain.

OH YEAH!!! Along with the head gasket you might as well rebuild or at least clean the carbs. Use all new hoses as well. And replace the water pump. These are cheap fixes and will save a WORLD of problems later. 90% of the motors I have collected only needed those things to get up and running. People just over look it and don't do the proper maintenance. GOOD LUCK

 

[raczekp1]

Re: Evinrude 6hp compression low

before puting new head gasket do the head flatening.i bet for100% is wraped.
you spend few bucks in auto repair stor for this but its worth.
if it was overheating so the head is wraped

 

[seaotter]

Re: Evinrude 6hp compression low

Well, I decided to keep on digging. (I'm sort of recording my progress and thinking out loud here.)

The water channels around the head had a lot of sand in them. I cleaned that out and took off the thermostat cover. Thermostat was badly corroded.

I also took off the powerhead. One water channel on the carb side was completely plugged with sand. So I cleaned that all up.

Looking up the exhaust outlet on the motor there is not much carbon and at first what I could see of the pistons and rings looked good and clean. After looking again I see faint scoring on the piston near the exhaust ports.

Now I'm thinking the overheat was due to plugged water flow - sand and maybe thermostat stuck.
The overheating was enough to melt the outer wrapping on some powerpack wires and caused the pistons to seize slightly scoring them.

But it did not cause paint to peel nor did the pistons and rings and cylinder get all discolored. Also no signs of carbon blow back along the pistons, as far as I can see looking up the exhaust outlet.

Apparently the head gasket was bad for some time because there is some rust at the top of the cylinder wall in the area between the cylinders where the gasket was broken.

So, the bad part is the motor at least once overheated due to low water cooling and probably seized.

I checked the gear oil. It is very clean - not black at all, but was very low. Had to tip the engine on it's side to get any to run out.

So, I still think the engine was serviced and running till the overheating blew the head gasket so bad it lacked compression to start.

I think I will check the impeller and see what that looks like.

As for the motor itself I am debating whether to open the crank case. On the plus side, I will know exactly what I have by inspecting the pistons and rings and bearings. Cleaning the rings and maybe replacing them and sanding up the piston skirt may be a good idea anyway.

What I am wondering about is the slack in the pistons - they can be slightly turned in a clockwise fashion. So what is loose?
Piston ring in piston?
or bearing where the connecting rod attaches to piston ring?
Or bearing where the connecting rod attaches to crank shaft.

Or is a bit of play there not a problem?

Don't know.

I still think the overheating was on the minor side as these things go.

Best case : replacing a few gaskets and thermostat and it will run.

Worst case : there are some bad bearings in the crankcase, bad ring or piston, and also the overheating ruined some electrical components such as power pack or coils.

 

[seaotter]

Re: Evinrude 6hp compression low

Opened it up some more and found there is a little slack in the needle bearing part where the connecting rod attaches to the crankshaft. I'll have to find out if that is normal or not.

Everything looks real clean, bright and shiny inside the crank case, though. No water ever got in there and no discoloration or scorching as far as I can see.

 

[jrs_diesel]

Re: Evinrude 6hp compression low

I have a 6 HP (72 Johnson) that I'm doing a full rebuild on. My intake area looked spotless too, but my pistons were trashed. I noticed scuffs on my pistons through the exhaust ports too. That and a little corrosion near the head gasket made me open her up.

Was your motor ever a salt water motor? If so, you might want to pull the powerhead and check the lower crankshaft seal. It's an odd spring loaded seal. Real critical one too. On mine the spring had rusted in half, and had leaned out the lower cylinder (fuel mix escaping past bad seal). One of the rings had welded itself to the piston. It's worth a check.

I don't recall how much "play" there is between parts. The service manual specifies the proper tolerances between parts that you would have to measure and verify.

 

[seaotter]

Re: Evinrude 6hp compression low

Thanks for the replies. I've had this motor apart except I didn't open the crankcase. Also had the lower part off.

Today I put it all back together. Just put on a new head gasket and thermostat and cork gasket on crankshaft. Made the other gaskets myself.

Sort of surprised myself that I was able to get it back together.

Decided to see if it would start. After a few pulls the darn thing took off and seemed to run pretty good.

Problem is, water is not getting to the head. I shut the motor down after a few seconds so it would not overheat again.

I think the first overheating did not damage it too much. A little scoring on pistons near the exhaust ports was all I could see.

At least I know most of the parts are ok. Sure felt good to see it run.

Now have to take off the lower unit again to see why no water coming up. Was pretty sure the water pipe was connected. Maybe the impeller key fell out. Oh well.

 

[seaotter]

Re: Evinrude 6hp compression low

Was just reading on another thread - the water in the barrel has to be above the impeller. Pretty sure I had it only above the intake holes. So.. better try adding water to the barrel before I take the lower unit off again!!