1990 evinrude low compression

[irolmn]

I just bought a 1990 evinrude 90 hp outboard,it was stated to me that one cylinder has low compresion.(from a guys mech.).I was just wondering if I had to do all the pistons and rings or just the one.the other 3 have the same compression,this one is about 40 lbs. less.the motor starts and runs,it is just rough on the bottom end,it seems to come out of it at higher speeds.any help would be great! thanks

 

[irolmn]

Re: 1990 evinrude low compression

I just bought a 1990 evinrude 90 hp outboard,it was stated to me that one cylinder has low compresion.(from a guys mech.).I was just wondering if I had to do all the pistons and rings or just the one.the other 3 have the same compression,this one is about 40 lbs. less.the motor starts and runs,it is just rough on the bottom end,it seems to come out of it at higher speeds.any help would be great! thanks

 

[emdsapmgr]

Re: 1990 evinrude low compression

You need to see what the low compression cylinder and piston look like, then make your decision. If a ring has let go, it may require an overbore and a replacement head. It is acceptable to overbore one cylinder only, with new piston. In any event, you really need to hone the other three cylinders and put new ringsets on those 3 pistons during the overhaul. If you decide to tackle this, you should plan on replacing the impeller and both thermostats prior to startup.

 

[SparkieBoat]

Re: 1990 evinrude low compression

you could also try replacing the head gasket and getting head resurfaced. then do a decarb, also inspect cylinder with head off. could be a partially clogged carb causing a lean condition which will burn a hole in your piston.