1978 Evinrude 115 (115893C) Compression Check

[Shorewood Bob]

I just tested the compression on this Evinrude 115hp. First, stone cold and came up with this:

1 - 81
2 - 81
3 - 88
4 - 86

Then got it to run for about 3 minutes with cuffs (having some fuel issues, I believe) and got this:

1 - 80
2 - 80
3 - 90
4 - 88

It seems to be at the limit of acceptable variance (1 & 2 on the starboard side being lower), but I'd like to hear what others have to say before I make a decision to put much time and money into it. Thanks!

 

[whitepointer23]

Thats very low. Is your compression guage correct. I would double check with another guage. It should be over 100 psi. My last johnson 115 was a 1974 and all pots were 120 psi cold. Have you got the throttle wide open . a closed throttle gives low readings. .

 

[whitepointer23]

If you ro have to rebuild the 70's models are supposed to be made of a much better alloy than later models which is a bonus. I think your readings are wrong myself.

 

[Mr Efficiency]

Firstly, make sure you follow workshop manual instructions about disabling ignition components, or you can cause damage even doing compression checks. The figures sound low, and, as you say at the limits of acceptable variance. It is difficult to tune a motor like that properly. But if it does the job as-is, it isn't necessarily a lost cause. It would be expensive to re-build that engine properly, it probably would need re-boring (there is the possibility being that old it has been re-built and re-bored previously, and if it was re-bored 30 thou then, if I remember correctly that is the end of the road, as 30 thou oversize pistons is as big as they made them.) The conrods could be shot, the crank out of spec etc. In short an expensive job, and at the end of it you have a motor that would not be worth much because of it's age, and obsolescent technology. I'd concentrate on getting it to run at a minimum satisfactory level, and just say a prayer for the innards of it.

 

[Shorewood Bob]

I did not have it at WOT... I will retest tomorrow and see how it reads. I remember reading about that but completely overlooked that part. Stay tuned and thanks for all the quick replies. I was a little worried about the low readings, so hopefully the WOT throttle will be more accurate.

 

[Shorewood Bob]

BTW the compression gauge is a new inexpensive Harbor Freight job but I figure it ought to at least give me relative readings.

 

[Shorewood Bob]

And thanks for the encouraging words about the alloy. I have another engine to do the work this summer, so this may be a fun project, or I may just be able to get her going reliably enough to be happy.

 

[Mr Efficiency]

The only person who would recommend a re-build of that old 2-banger would be an outboard mechanic with no work on the books. It does not make economic sense, except in a rare instance where you have something that was either extremely sparingly used, or never saw salt water, or preferably both. And was a very good motor, design wise, which with some reservations, this one was.

 

[Shorewood Bob]

Thanks Mr. Efficiency. I enjoy the work - if there is work to be done. I suspect there will be a good difference doing the compression check at WOT.

 

[whitepointer23]

The only person who would recommend a re-build of that old 2-banger would be an outboard mechanic with no work on the books. It does not make economic sense, except in a rare instance where you have something that was either extremely sparingly used, or never saw salt water, or preferably both. And was a very good motor, design wise, which with some reservations, this one was.

If he is doing the work himself it makes economic sense. Parts are freely available and not that expensive. I wouldn't say that for a blueband merc with steel bolts and propshaft. Those things are better in the scrap bin. You are looking at it from a professional angle and you are correct but for a diy at home its a good project.

 

[Mr Efficiency]

As you say, his PSI figures are probably low because he didn't open the throttle fully, it is probably a good idea to have one of those endoscope thingies to look around inside the bores for scoring, or see how clean it is regarding coke deposits. If the compression is down on one side of the block, I would be a little suspicious that it might have been running hot on that side,(thermostat ?) which can help gum up the rings, from what I have seen. That can reduce compression.

 

[whitepointer23]

As you say, his PSI figures are probably low because he didn't open the throttle fully, it is probably a good idea to have one of those endoscope thingies to look around inside the bores for scoring, or see how clean it is regarding coke deposits. If the compression is down on one side of the block, I would be a little suspicious that it might have been running hot on that side,(thermostat ?) which can help gum up the rings, from what I have seen. That can reduce compression.

Yes I was thinking it may have been cooked but does that normally drop compression in every cylinder or just 1 or 2.

 

[Mr Efficiency]

Engine has one thermostat each side, also there are flow restrictor rubber inserts that can bugger up and adversely affect cooling. It is likely in an engine that old, too. She might have scored the bores a little without seizing, bringing the compression down.

 

[Shorewood Bob]

Well, after retesting with my cheap Harbor Freight tool at WOT it registered 90 across the board, twice, when cold. At least it's balanced. I appreciate the comment about it possibly getting hot and the info about thermostats on each side and the flow restrictor rubber inserts. Those sound like good things to replace in any event. I bet you're right on that's it scored a bit.

I read on another post somewhere that there's a cylinder inspection plate so I'm going in for a manual and take it gradually. First thing is to get good fuel flow from a good tank and line and see if I can get it running better. Right now it will run for a while and then crap out, particularly when adjusting the throttle under power, whether at idle or high rpm.