Evinrude - 40 HP - 1991 - Cylinder Failure symptoms

[Chris Wilson]

I posted an earlier note (see “Evinrude – 40 HP Powerhead Problems – help!”) regarding this failure and got some nice feedback. However, I have some additional questions about what I am seeing inside the cylinders. In effect, most of the wear (I can move the piston visibly side to side with my finger)and cylinder damage appears to be on the top cylinder only. That is where the cylinder walls are scored and the piston head shows material missing on the edge in the area between the intake and exhaust ports. The coloration is much lighter on the top (looks like it was dryer or hotter – maybe both) than the bottom which looked a lot more normal, or what I might expect a 10 yr old cylinder to look like.<br /><br />I am struggling with what might cause one cylinder to fail so badly and the other not? Since the thermostat is directly above top cylinder (thus where the cooler water would be present) I would expect that overheating would be less likely to show up there vs the bottom. We also changed the impeller last year and have been running on it for quite some time prior to our problem. It is always possible, but water cooling is not first on my suspects list...<br /><br />The VRO is still hooked up and we had tested it earlier in the year using a clear tube filled with oil(but we are seriously considering by-passing it once we get past this issue). But in spite of that, if it did fail after having tested it, I would expect a failure of that unit to at least affect both cylinders. But who knows?<br /><br />I am wondering though, if one carb is not delivering adequate fuel to its cylinder (I assume each carb supports one cylinder – meaning they are isolated from each other some way). I am thinking that if one cylinder is operating and igniting and the other has spark but little or no fuel, I can imagine that I would 1) lose power (which we did) and 2) lose adequate lubrication to that cylinder (which also appears to be the case)<br /><br />I also wonder about ignition failure. Especially, if the timing is off for one cylinder. How that could happen is not clear. However, if it did, I think I would have had bad stuff happen to the piston head but I would still expect the cylinder to be lubricated. Any thought there?<br /><br />In the forum I also have noted references to the negative effects of “too lean” carburetion and it not being good. Can anyone describe what this might mean and what the effect might be inside the cylinders?<br /><br />Any feedback would be greatly appreciated….<br /><br />Thanks – what a great web site

 

[Joe Reeves]

Re: Evinrude - 40 HP - 1991 - Cylinder Failure symptoms

PropHead.... Your problem is due to having the top carburetor fouled somewhat, resulting in a lean running situation. This has a tendency to set up a pre-ignition condition which will curl the top sides of earlier model pistons, melt the tops of aluminum pistons etc etc. Also, obviously, the lean condition would result in improper lubrication, leading to heat from friction.<br /><br />When doing a rebuild, dismantling the carburetors and restroing them to new condition is a must, and personally I'd want a new VRO installed for obvious reasons.<br /><br />The ignition can be checked thoroughly when the engine is reassembled and corrected as neded.

 

[granpafish]

Re: Evinrude - 40 HP - 1991 - Cylinder Failure symptoms

I had a somewhat similar problem witha 93 50 hp evinrude. OMC was not getting the job done in that time frame. It sounds like Bombadier has gotten things straightened out. At any rate check the magnets on the flywheel. One had loosened up and eventually tore up a cylinder. I was not aware of the problem until it was too late. OMC paid for half the bill but it was still a significant hit to me. Last month the same symtoms started up (motor just dying while at cruising speed). I fled. Bought myself a Honda 4 stroke and have to hope that they aren't asleep at the switch. By the way, I had been a faithful Evinrude owner for 30 years. <br /> Good luck Granp***