9.5 Evinrude Seal/Compression

[ClemsonAlum]

I have a suspicion my upper crankshaft seal is blown or damaged. Also, this motor has low compression, 40 PSI nearly exactly on both cylinders, cold, using a Harbor Freight compression tester.

Edit** just found out my tester is not accurate, need to get another one. Will update thread later when I get an accurate one.**

The low compression may be a separate, but I will give more info below. Any wisdom shared to help me confirm this is appreciated!

Here is some history and pictures.

It is a 1973 Evinrude 9.5. Runs about 12 MPH with 8" x 7 pitch prop on old 1436 Polarcraft, by myself, with battery behind front bench, gas tank as far forward as possible, and about 75 lbs fishing stuff. I built a transom riser to get the Cav plate on plate with bottom of boat. Drafts about 6-8" in back idling. Will not get on plane by myself (may be due to just older motor + my 200 LB butt in the back of the boat).

Today I took off the flywheel to check if the Shear Key got sheared when I hit a log and spun the prop hub the first day I took it out. Oops. Anyway the points were checked and they were good, 0.020 and no corrosion. Looked new.

I lifted up the timing plate to look for tell-tale oilly residue. I think I saw some, but there is so much other 50 year old grease and residue under the cowl due to previous exhaust leak, fuel pump leak, and miscellaneous grease due to all the fittings. You be the judge please (see below).


As for issue #2 Low compression, both cylinders, 40 PSI. Plugs visibly wet. Low speed idle is set per usual instructions. Otherwise it runs pretty good, reliable, just hard starting. Got this motor in October last year and has only gave me trouble once when it flooded idling (think this is separate issue, shellac on the float was gone when I cleaned the carb when I got the motor). Causing float needle to not seat and flood. Or it could have been due to diaphragm in fuel pump breaking. Either way, it hasn't gave up on me much.

The pull start is firm and you get the usual resistance when you turn the motor over.

So I think low compression is due to one of three things. Hopefully I can diagnose without taking the heads off? Maybe with a loan a tool inspection camera from the auto parts store? Any advice appreciated.


1. Blown head gasket between the two cylinders.

2. General wear on piston rings since it is so old and used (I don't think they are stuck since compression is consistent between cylinders?)

3. Related to possible blown upper crankcase seal? I just started learning about these 2 stroke motors, so I may be wrong?

-Kurt
14', 1960 Polar Kraft, '73 9.5 Evinrude

 

[Weldorthemagnificent]

Looks like someone has done coils. Make sure plugs are champion, no others. I am always suspect of low compression readings. Small engines don't always show an accurate reading on an automotive gauge. Usually when there is a low compression event, it is worse on one cylinder. Before ripping anything apart you can do a leak down test. Either buy a test kit or let a small engine guy do it.

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[nccatfisher]

I would be very suspect of a 40 PSI compression reading and it running, and especially running as well or as long as you say it does.

Is that a visible crack on one of the coils?

 

[ClemsonAlum]

Nccatfisher the original psi on these motors was about 70-75 psi, so yeah I am a little hesitant about accuracy on it. I have heard that compression testers can vary in accuracy alot.

-Kurt
14', 1960 Polar Kraft, '73 9.5 Evinrude

 

[ClemsonAlum]

Nccatfisher and yeah there is a crack on one of the coils.

-Kurt
14', 1960 Polar Kraft, '73 9.5 Evinrude

 

[nccatfisher]

Nccatfisher the original psi on these motors was about 70-75 psi, so yeah I am a little hesitant about accuracy on it. I have heard that compression testers can vary in accuracy alot.

-Kurt
14', 1960 Polar Kraft, '73 9.5 Evinrude

I believe if you will check the compression "new" would be considerably higher than 70-75. I had one in the 80's and it had middle to upper 90s when I checked it. Usually 70-75 is what is considered bare minimum to run reliably.

If that coil is cracked it may not be giving you issues yet but it will.

 

[wmk0002]

I have one that ran great at 60 psi. Given the variances in my compression testers, if I retested with my Harbor Freight tester vs my favorite one I would not be surprised to get a 40psi reading.

Mine was about the easiest starting, best idling motor I have ever owned. Only problem I had was a leaking shift rod boot so I had to tear it all down and its still in a box in my shop lol.

 

[ClemsonAlum]

Ok so I just found out the hauge from Harbor Freight I have IS NOT accurate for small engines as it has the schrader valve by the gauge instead of at the end of hose at the spark plug. So I will be returning it....might trade up to their other "Deluxe" one by "Maddox" if it has the valve at the end. It does have a short hose so that should help with accuracy..

Anyways, I would still like input whether anyone thinks the upper crankcase seal is bad or not...I am not 100% sure. I might just take it to a small engine shop as suggested to see of they can do a leak down test on the crankcase.

-Kurt
14', 1960 Polar Kraft, '73 9.5 Evinrude

 

[Pappy]

Let me answer the upper crank seal question.
First off, if the seal were damaged and leaking you would see quite a lot of fuel/oil draining down the outside of the crankcase.
By now if it were severe enough you would also have issues keeping the points sets clean.
Also, the upper seal would affect only the upper cylinder, not both cylinders. The crankshaft has what is known as a labyrinth seal on it that effectively separates the upper cylinder from the lower. this seal is located between cylinders 1 and 2. Crankcases on 2-strokes are not common as they are with 4-stroke engines so the upper seal cannot affect the lower cylinder.
Lastly, if that seal had failed it would have almost no effect on your compression numbers. The compression numbers you are seeing are above the piston ring. The upper seal would have an effect on the crankcase compression which is below or on the crankcase side of the piston rings.

 

[wmk0002]

You can pull the ignition plate and spray soapy water around the crank/seal and pull it over a few times. Look for bubbles like you were checking a prop seal or tire. I'd imagine if it's like any other motor its an easy job to just change it if you want to rule it out while you are under there.

 

[Weldorthemagnificent]

This thread prompted me to dig out the 9.5 I picked up last fall. I poured a couple ounces of seafoam down the carb and rotated the motor around a few times. Let it sit for a day and it started first pull. Smoked like the devil for a few minutes. It had a sneeze that a couple small adjustments on the idle mixture screw smoothed out. Dribbled some more seafoam down the carb and let it run. Now I'm anxiously awaiting the boat ramps to open back up so I can try it on the 12' tinny.
https://youtu.be/cVv_wc89DcE

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[Weldorthemagnificent]

It's a 1969. Not bad for 51 years young!

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[ClemsonAlum]

You can pull the ignition plate and spray soapy water around the crank/seal and pull it over a few times. Look for bubbles like you were checking a prop seal or tire. I'd imagine if it's like any other motor its an easy job to just change it if you want to rule it out while you are under there.

Thanks I will try that.

-Kurt
14', 1960 Polar Kraft, '73 9.5 Evinrude

 

[ClemsonAlum]

Gotcha. Yeah points were squeaky clean as well as the points and such.

-Kurt
14', 1960 Polar Kraft, '73 9.5 Evinrude

 

[ClemsonAlum]

It's a 1969. Not bad for 51 years young!

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She is purring! I have to work on my idle adjustment when I get on the water again. Would not idle lower than about 2000 RPM in the bucket with cowl off without coughing out. I even adjusted the Linkage 1/4"-1/2" past the mark on the timing plate with no effect. Maybe need to clean carb again if that doesn't work?

-Kurt
14', 1960 Polar Kraft, '73 9.5 Evinrude

 

[Weldorthemagnificent]

When it coughs out, do you need to choke it to restart it?

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[ClemsonAlum]

Yeah usually.

-Kurt
14', 1960 Polar Kraft, '73 9.5 Evinrude

 

[Weldorthemagnificent]

Try richening the mixture screw. Turn counterclockwise. I do 1/8 turn increments and wait 15-20 seconds between adjustments for the motor to react to the changes. When I first fired mine up, it started easy enough but had a bad sneeze and I had to keep the throttle on start to keep it running. It took a little over half a turn out on the mixture screw to smooth it out. I was then able to adjust the throttle stop screw in a bit and it idled decent with the throttle on shift. If this doesn't fix it, then you might have to get into the carb and clean some more or out a kit in it.
https://youtu.be/1ShV_pLDSM8

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