1973 65 hp Evinrude: Compression test completed, what does it mean?

[BigJ08]

Did a compression test on the ole' Rude and got the following numbers:
Top Cyl: 97
Middle Cyl: 115
Bottom Cyl: 120

Should I be concerned about the discrepancy with the top cylinder as it is pretty far from the other two numbers? Just checking. Thanks for the help. John.

 

[jay_merrill]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

Generally speaking, a compression value in one cylinder that is more than 10% off of the others, is considered to be an issue worthy of looking into. Additionally, a value of 97 psi is low for that engine. My 1972 Johnson 65hp motor still has values in the 140 psi range.

If your engine were my own, I think that I would immediately replace the head gasket and retest after the work is completed. I recommend that you do the same. While you have the head off, examine the bores for any obvious sign of problems, particularly the top cylinder.

Let us know how you make out.

 

[Daviet]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

You might try and run some sea foam through it. Just a thought.

 

[tashasdaddy]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

i would do a decarb, then if it did not come up, the head gasket.
Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck

 

[BigJ08]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

Well guys, not what I wanted to hear but if it's got to be done, it doesn't look that hard (Glad I invested in that service manual LOL). Guess I'll go ahead and get the parts in the mail. Just flipping through the service manual, it looks like I'll need the head gasket and the gasket for what they call the cylinder head cover. Anything else worth doing while I have it apart? Thanks for all the help.

Also about the decarb, is that just a temporary fix or could that solve my problem? I have used seafoam as an additive before but never heard of it solving compression problems. Thanks. John.

 

[tashasdaddy]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

using it as directed above, it has been known to free up rings, and increase compression. for $10.00 it is well worth a try. i have done it many times on motors i service. seafoam as an additive keeps a clean 2 stroke motor clean, it does not clean a 2 stroke.

here is the head gasket you need, http://www.iboats.com/Sierra_18_296...z.36857--**********.473355568--view_id.173732

 

[jay_merrill]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

I don't disagree with the decarb suggestion, because and as TD said, ten bucks is a pretty inexpensive "fix," if it works. Its also worthwhile, even of you do have to pull the head.

You can also use BRP's "Engine Tuner" in an aerosol can. It does not require mixing with the fuel. My method of using it, is to pull the plugs the night before the main application, so that I can spray some into the cylinders. I then reinstall the plugs and let the motor sit until I am ready to finish the job, the next day. Just spray the product in the carb throats, one at a time until the engine begins to falter. Do that with each carb, one after the other, until you run out of the product. You will then have to run your motor for 30 - 60 minutes, untill all of the liquified carbon is expelled. Your motor will smoke like "a house-a-fire," so be careful where you do this!

The only reason that I went directly to pulling the head, is because 97 psi is a long way off off what this motor should provide. Its also a pretty good jump from the other two cylinders, so the possibility of a leaking head gasket is certainly there.

If I remember correctly, you can pull your head without disturbing the cylinder head cover. I think you will have to pull all of the bolts, because the ones in the cover pass through both it and the head, but as long as you don't disturb the cover and handle it carefully, the gasket/seal will probably remain OK.

The cylinder head bolt torque procedure is simple - just do pattern of circles, moving from the inner circle, to successive outer circles, as you go. I believe this is done in a counter-clockwise direction. Make sure you double check your work on each bolt, then run the engine on the muffs for awhile. Let the motor cool and then recheck the torque values.

 

[BigJ08]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

Guess I'll give it a try then. Better than ordering and waiting on a gasket! Thanks for the link btw, thats about $10 less than I could find it, but I couldn't access the iboats store. I keep ya'll updated .

 

[BigJ08]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

Is there a possibility of me damaging my motor in any way while doing this decarb process? The head gasket honestly seems like an easier fix and it seems like it is more likely than not, the culprit. I say this because the numbers get larger from top to bottom so I'm thinking the gasket is leaking somewhere around the top two cylinders what do you guys think?

 

[jay_merrill]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

You're not going to damage your engine by running a little Seafoam or BRP Engine Tuner through it and that is definately less work than pulling the head. The decarb process is also something that you should do about once a year anyway.

My personal view of your situation is that decarbing probably isn't going to bring the low cylinder up to the 115 - 120 psi range, but I would do it anyway. The other guys are right, in the sense that it is too inexpensive and too easy to do, for you not to give it a shot. Get your internals cleaned up, see what happens and if you still have low compression in the top cylinder, the only thing you are out is ten bucks and a little time.

You can also try checking the torque on the head bolts. Once again, my gut tells me that this isn't your problem, but its a very simple thing to do and doesn't cost anything, so why not?

On the other hand, if you just want to jump to the mechanical view of things, the head gasket for your motor is only about 28 dollars, so you still have a "few bucks and some time" scenario. Once again, try not to disturb the cylinder head cover gasket (another 20 bucks), to keep the cost down.

Let us know what happens. Whether giving or receiving help on these forums, each situation is unique and the learning process goes on. I like to make sure that I follow up on threads, so that I learn whether or not my "guesses" were correct or not. This helps in my own education and thus, helps me to help others in the future.

 

[BigJ08]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

Looks like I won't have time to do it till this weekend so I'll post up some results when I do. Thanks for the help.

 

[BigJ08]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

UPDATE:
I finally go the decarb done and it didn't bring my compression up much, maybe 2-3 on the top cylinder, which is the bad one, the others are basically the same. Gonna go ahead and order the head gasket so I can get it put on this week maybe. For those of you that have done it, how much time should I set aside for the head gasket job? Can I do it in an afternoon? Any special tips or tools that I should acquire? Thanks for the help. John.

 

[14ftgrumman]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

Torque wrench that reads in/lb.

 

[BigJ08]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

UPDATE:
I got the head gasket replaced this afternoon, and it doesn't look good at this point . I removed the head, cleaned the surfaces and torqued the bolts to spec (14-16 ft/lb) when I installed the new gasket. I then let it run for a little while on the muffs and it seemed to run good. I then did a compression test and the bottom two were virtually unchanged and top was up to about 100. I don't really know where to go from here, total rebuild? What do you guys think, because an old saying comes to mind: "sell your boat while it's still running".

 

[Daviet]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

Run it, keep adding seafoam to your gas and use it. From personal experience, compression guages can be finikey, sometimes giving different readings on multiple tries. I don't think the compression difference is worth the bother.

 

[BigJ08]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

Run it, keep adding seafoam to your gas and use it. From personal experience, compression guages can be finikey, sometimes giving different readings on multiple tries. I don't think the compression difference is worth the bother.

I am just imagining getting stranded out somewhere when my motor takes a crap on me though LOL. Idk what to do........

 

[JayM001]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

I don't think you are going to accomplish anything by trying to decarb over and over.

I also don't think you are having problems with a compression gauge. If you were getting erratic readings on all three cylinders, I might buy that, but you are not. You have consistently seen compression values of 97 - 100 psi on the upper cylinder and unchanged values on the middle and lower cylinders - that does not suggest a bad compression gauge. Even if it is not 100% accurate, it is consistent.

Just out of curiosity, did you examine the mating surfaces on the block and head? Any sign on warping of the head or corrosion related pitting on either surface? How about signs of scoring in the piston bore?

 

[papasage]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

i think that motor had a piston problem . the top ring was to close to top of piston .no led gas would deteriorate it . it is no longer available . you can use the newer piston but will have to use a wrist pin bearing kit to use the same rod .
on a previous post you said you didn`t run the gas out before storing . you can`t run all out . there is always a little in the bottom and that is where the high speed jet is . that little bit will dry up quick .a old johnson teck suggest keep it full by pumping the bulb every month .

 

[BigJ08]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

I don't think you are going to accomplish anything by trying to decarb over and over.

I also don't think you are having problems with a compression gauge. If you were getting erratic readings on all three cylinders, I might buy that, but you are not. You have consistently seen compression values of 97 - 100 psi on the upper cylinder and unchanged values on the middle and lower cylinders - that does not suggest a bad compression gauge. Even if it is not 100% accurate, it is consistent.

Just out of curiosity, did you examine the mating surfaces on the block and head? Any sign on warping of the head or corrosion related pitting on either surface? How about signs of scoring in the piston bore?

I agree with your conclusions about seafoam and the guage. I did find some corrosion/pitting on the head around the top cylinder and I'm sure that's what's causing the problem. There was minimal scoring on the top cylinder wall but nothing real serious.

 

[crxess]

Re: 1973 65 hp Evinrude: Compression test completed, what does it mean?

When the head was off, it should have been checked for true.(flatness) It is easy to flat sand and correct minor warp.

Possible the upper cylinder has not been receiving fuel as well s the lower 2 and worn the rings more. Still a usable motor though. If it is not missing at speed and not over laboring, you should still get a few seasons out of it before needing a rebuild.

Did you do a wet compression test?