1977 Evinrude 115 Model 115793S

[mav6759]

I have a 1977 Evinrude 115, it ran very good this summer. I recently last compression in two of the cylinders. I was told that the head gasket or rings or both causes low compression. So I decided to take a chance and try changing the head gasket and rings myself. (done it many times in a car) But please for give me I know nothing about boat motors. I guess my first question is;

1. Is the head gasket and rings (besides the pistons) are the only items that can cause low compression. If not what else to look for while I have it apart.
2. Is the Cylinder head gaskets and head gasket the same or is the head gasket totally separate from the cylinder gasket.

 

[tashasdaddy]

Re: 1977 Evinrude 115 Model 115793S

they are the same, you need to check if each left and right bank of cylinders use the identical gasket, most do. when you look at the cylinder head, the outer cover is the water jacket, which is attached to the cylinder head.
you can see complete diagrams, and parts list, here http://shop2.evinrude.com/ext/index.aspx?s1=bf6ad09c53cead335fcfd8a6471c0f7f

you really need to get and Evinrude service manual for you motor. http://www.outboardbooks.com/

 

[SKEETR]

Re: 1977 Evinrude 115 Model 115793S

Yes, compression is affected by a bad head gasket or bad rings. Definitely check the gasket first and while the head is off inspect the walls of the cylinder for scoring. What are your compression #'s. The process of replacing rings is a complete teardown not at all as simple as a car engine. With an oem manual, some patience and a few 12packs it can be done.

 

[iwombat]

Re: 1977 Evinrude 115 Model 115793S

If the two cylinders that lost compression are on the same side of the motor it's highly likely that you blew a head gasket.

This motor has only one thermostat, so an overheat would effect everything. A lean condition and the resulting burned piston/rings/etc would most likely effect only one cylinder, or in the case of a systematic carb failure the top or bottom pairs.

I suppose the loss of cooling deflectors in one side might coke up some rings and cause them to stick. In that case, you'll see that once the head comes off and a good decarb should fix it.

Bottom line: If the low compression is on one bank, the head gasket should really be all that you need to do.

 

[mav6759]

Re: 1977 Evinrude 115 Model 115793S

Thanks a lot guys, as far as your questions, I have a low compression in on one cylinder on each side of the motor. I saw the cylinder head or head gaskets at West Marine for 9 bucks each. I was thinking I could (as in a car) bring each piston up to the top and pop the rings off and change them. Do I have to brake down the entire engine to do this or do I really need to change the rings. Also, there were sticking of the rings, I sprayed some WD 40 down in the spark plug holds that free it up. Because after I lost compression in the motor, the motor sat for about a month. It seem simple to change the head gasket, I only see 4 bolts on each cylinder head.

mav6759

 

[tashasdaddy]

Re: 1977 Evinrude 115 Model 115793S

looking at the diagram i see 10 bolts on each head. no you can't change rings that way, it is a tear down job.

 

[iwombat]

Re: 1977 Evinrude 115 Model 115793S

Ugh . . . I hate to tell you this, but one on either side is not promising. Before you go spending $$ on head gaskets, pop the heads and take a look.

 

[mav6759]

Re: 1977 Evinrude 115 Model 115793S

Once I have the head off, I know to inspect that head gasket. and the cylinder walls and rings. Is there anything else that I need to look for while I am in there.

1. How would I know if the rings are bad. Are they the same as a car would I find oil in the cylinders.

 

[iwombat]

Re: 1977 Evinrude 115 Model 115793S

Well, let me put it this way.

The rings aren't bad.


If they were, you'd be seeing low compression all the way around.


What you've probably got is a bad carb and either two very carboned up pistons and stuck rings (stuck in the grooves, not to the cylinder) from flooding, or a carb that ran too lean and scoring of the cylinder walls or burned pistons.

If you got lucky, it's an overheat and both heads warped at the same time.


Low compression is both top, or both bottom, right?

 

[ezeke]

Re: 1977 Evinrude 115 Model 115793S

Pull the cylinder heads anyway, it could be rust on the cylinders.

 

[mav6759]

Re: 1977 Evinrude 115 Model 115793S

Now I can believe that there can be rust in the cylinder. because when I first got the motor I had a hard time turning the fly wheel. I sprayed some WD 40 in the spark plug holes and now it spins like a new motor. Then it got stuck again. I sprayed a little more WD 40 and it never stuck again. I can turn it by hand. Could that be rust from sitting and if so do I have to clean the cylinders and how.

 

[ezeke]

Re: 1977 Evinrude 115 Model 115793S

You could be getting water in the cylinders from water in the fuel, from leaking cylinder head gaskets or from blown exhaust gaskets.

The best way to eliminate water in the fuel from reaching the engine is with a full-sized water separating fuel filter.

The exhaust gaskets are a good possibility but because of the number of screws on the covers, replacement can be a bit time consuming.

Changing the cylinder head gaskets is usually fairly quick but you have to have a good torque wrench to do the job properly.

If the compression is fairly good, you can clean the cylinders with fine emery cloth and oil.

In the meantime, buy aerosol fogging oil and keep your cylinders well oiled anytime that the motor is going to be stored .