1975 115 Evinrude Low Compression / Blown piston! Pics! looking for advice

[jammer777]

Hey guys, so ive had a number of threads going here with a number of problems but ultimately i found with a compression test that i have one bad cylinder with about 40 PSI after decarbing the engine a bit, so i pulled off the head yesterday to "hope" that i had a blown head gasket and ultimately found the following located in the pictures in the below link

https://onedrive.live.com/?id=8046A5...4zKWSk&o=OneUp
https://onedrive.live.com/?id=8046A5...4zKWSk&o=OneUp
http://1drv.ms/1JC8Aey


it looks to me like a ring broke, caught on the exhaust port, and blew a chunk of the top of the piston off, heh you can actually see the peice of the ring sticking out, I really don't know when this happened, it could have happened as late as last year, the boat seems to run pretty good otherwise, being down a cylinder an all, there really doesn't seem to be any damage to the cylinder wall in the bad one, there are two very small nicks by the exhaust point but otherwise the walls are perfect,
i guess i have two questions

1. there are two nicks by the exhaust ports on the cylinder wall, looking for some opinions, would you just ignore this damage shown in the picture and put in a new piston and a couple new rings and hope for the best? this engine is 40 years old and i don't really want to put a lot of money into it, which is all about what owning a boat is about i know, and i know i "should look at taking it all apart and getting it all machined and new everything, but hey like i said, i dont really want to do that

2. Can i replace the single piston without totally dismantling the crossflow v4 engine? i don't really see where the crankshaft is, must be behind the intake plate behind the carbs, but has anyone taken one of these engines apart? would i be able to take the connecting rod bolts off and slide the blown piston out all by itself and replace her without total dismantling the engine? not best practice i know, but hey, its 40 years old

thanks guys in advance, appreciate the advice and thoughts as always

 

[Chinewalker]

It is possible to hone and replace the piston with another. You can put as little or as much money into it as you want. You'll be buying some gaskets in any case, the piston (good used would probably work), and new rings all around would be recommended, along with honing the other bores. Of course, this all depends on the damaged cylinder's condition after honing.

On smaller motors, I've gotten away with replacing one piston with a good used piston and used rings. Not sure I'd recommend it here, but I'm sure it could be done.

Not sure what you have and haven't done else wise to the motor, but if needed, carb rebuilds and fresh water pump are good to do while you're into it.

The powerhead should come completely apart for replacement of the piston. An impact drill/wrench can make quick work of it. If you hunker down, you can do it in a weekend. An OEM service manual is HIGHLY recommended.

 

[jammer777]

Thanks for getting back to me Chinewalker, ya ill probably go new piston and rings, but might just stick to one only, i guess i may decide after opening it all up an seeing what it all looks like, ya done the carbs with a full rebuild and water pump, and just odd ball stuff here and there like fuel pump, starter, prop seals, etc etc, i dont have a lot into it, but a bit, ya i may pull her off here before the summer is done to redo it, but its running pretty good right now at the moment, i was pulling kids for the last couple days, ya need to get the service manual, i have the owners manual, but i think the service one your talking about is a lot more in depth

 

[emdsapmgr]

You will want to hone all 4 cyl liners. Get 1 replacement factory piston (don't mix piston brands in an engine) and put in 4 new ringsets. No point in just 1 ringset, then run the possibility that another ringset may fail in the near future. If the powerhead has a lot of hours on it, a modified overhaul like you are planning will get you by. It won't quiet down any piston slap that comes with worn cylinder liners and old pistons. (Piston slap is not necessarily a prelude to any imminent failure.)

 

[crabbydad]

I have the same thing with my 140 hp. I'm in the process of taking it apart. my plan is to bore the cylinder. if it cleans up(already .020 over) I will replace that cylinder and all the rings.