Detonation of piston 2 weeks after installing new head gasket

[Sal G]

I am at a loss.<br />V4 140 85 VRO Evinrude<br />2 weeks ago:<br />compression 130-140 in 3 cylinders<br />60 in forth- that cylinder had a very slight <br />indication of detonation. Also water leak.<br />Replaced gasket and compression went up to 90+<br />Ran fantastic for the next 2 weeks<br />Noticed sudden change in sound of engine and performancethis past Friday at the end of a days fishing.<br />Today:<br />0 copression on that one cylinder. Opened head and COMPLETE EDGE ALL AROUND PISTON DETERIORATED PARTICLES MESHED ON COVER HEAD WITH SCORING ON CYLINDER WALL. Is this a normal course for detonation- THAT FAST?<br />Someone please explain to me. Engine (as far as I know ) never gave signs of overheating. <br />Always ran 6200 wot, and besides water in cylinder<br />problem has been great!

 

[wilde1j]

Re: Detonation of piston 2 weeks after installing new head gasket

Probably lean fuel/air mixture killed that cylinder, usually caused by crap in the carb. And yes, it can kill a cylinder pretty quick. There isn't any overheating involved.

 

[P.V.]

Re: Detonation of piston 2 weeks after installing new head gasket

60 psi on that cylinder was the indication that something was major wrong two weeks ago. It needed rebuit then as it does now!! Causes of pre-ignition are lean fuel,too much air, too little fuel, timing too far advanced, lugging motor due to too much prop,marginal oiling, marginal cooling.... some or all of the above!

 

[The Marine Doctor]

Re: Detonation of piston 2 weeks after installing new head gasket

I believe that engine was designed to run @ 5250 Rpm's...not 6200 Rpm...I am surprised it has lasted this long.<br /><br />Detonation will occur once you pass the recommended RPM...as the burning fuel does not have enough time to leave the cyl..it will then ignite the incomming fuel before the spark plug has a chance to light it.<br /><br />TMD

 

[walleyehed]

Re: Detonation of piston 2 weeks after installing new head gasket

Sal, buddy, I hate to say it, but you should've quit with noticing the detonation.....that was your warning sign, and you let it go!<br /> When you first noticed the detonation, at that point, you already had contaminated ring lands, and all the needed residual metal to destroy the engine if ran anymore. The sad part is you may have gotten by with replacing one piston.....if you would've stopped before, you may be looking at a total O/H now.<br /> These engines are tough, but you still have to listen to em'....<br />Good luck.

 

[Sal G]

Re: Detonation of piston 2 weeks after installing new head gasket

Thanks to all responded<br />I've learned a great deal and its sad to say that<br />I was completely unaware of the facts you guys stated.<br />Ironically, when I spoke to a service man at a local marine supply co., his response was<br />translated that you can still use the engine<br />and when it happens, it happens!!!!<br />This boat is a 1977 Formula who I purchased from guys who water skiied.<br />God knows that boat was running at 6200 rpm for years!<br />I bought the boat 5 years ago to fish and I occassionally "gave it thr gun" because I felt I didn't run her wot enough. Everyone kept telling me <br />that these outboards love to be run. I thought I was doing the right thing- what I didn't know <br />that 6200 rpms was too high. Live and learn. Thanks <br />guys for all your help.<br /><br />Sal

 

[wilde1j]

Re: Detonation of piston 2 weeks after installing new head gasket

That motor should be propped to run 5800 RPM @ WOT. I have the same motor and the owners manual calls for 5500 to 6000 RPM.

 

[Dhadley]

Re: Detonation of piston 2 weeks after installing new head gasket

Running the motor at 6200 rpm will not cause detonation all by itself. On some V4 looper's the rev limiter is at 6700. Something else is causing the detonation other than just the set up.<br /><br />We routinely run those stock ignitions well over 7000 rpm after by-passing the limiter. <br /><br />You hit the nail on the head when you mentioned that its been running well for 5 years -- capeable of that rpm all the time. Something caused the detonation and its not rpm. Lets look at what happened -- the head gasket was leaking water and that led to the start of the damage. The hardness of the piston was most likely compramised at that point. When you reinstalled the heads you most likely installed new plugs. Did you use the correct Champion plug or another brand?<br /><br />Is your powerhead still a small bore? Or has it been changed to the big bore? If its been changed to the big bore (lots were when they were under warranty) did you use the right gasket?<br /><br />Also look at the center hub magnet on the flywheel to make sure it hasnt moved. <br /><br />Let us know how the project goes! Good luck!