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Old 14 November 2005, 07:15   #11
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Excuse my ignorance - I'm just curious - how does a faulty spark plug and therefore a non firing cylinder result in piston failure.

By my reckoning unless the fuel supply is interrupted there is still fuel and therefore lubricating oil getting into the piston - the fact it is not burning up surely would equate to more lubrication not less.

Or possible could it fail if enough liquid fuel built up in a cylinder that the increased compression its self broke the con rod ?????

Please can a mechanic explain
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Old 14 November 2005, 09:40   #12
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Originally Posted by MarkM
Very sad, but interesting to read about your problems. I'm about to purchase an E-tec 250 for my boat. What size props did you test with the 2 people on board and what size with 4 people? Can you tell me about fuel use and speed?
After all do you still like your engine?
Original prop was a Viper 23. Top speed was 52kn in perfect conditions. On calm water we could cruise at 30 kn and burn 35 l/hour.

Just before the engine broke down we were testing a Mercury Highfive (5 blade prop). It gave us a better acceleration (even on 5 cylinders  ) but Top speed is unknown as the engine broke down while accelerating above 4500 RMP.

I am very happy with the engine. Our problem could have happen on any DI engine. If today I had to buy a new engine, much will depend on how and how fast Evinrude will solve our problem.

Quote:
Originally Posted by roycruse
Excuse my ignorance - I'm just curious - how does a faulty spark plug and therefore a non firing cylinder result in piston failure.

By my reckoning unless the fuel supply is interrupted there is still fuel and therefore lubricating oil getting into the piston - the fact it is not burning up surely would equate to more lubrication not less.

Or possible could it fail if enough liquid fuel built up in a cylinder that the increased compression its self broke the con rod ?????

Please can a mechanic explain
The wear had something to do with the lubricative capacityís of oil and fuel mixture in a cold (non-working) cylinder is not the same as a burned mixture in a warm cylinder. As the fuel and oil accumulates and can only leave the cylinder via the exhaust pipe, is creates wear. But Iím sure someone with more technical knowledge will correct me and explain it a better way.

Paul
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Old 14 November 2005, 10:40   #13
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Paul,
thank you very much. Good figures and it gives me confidence.
Mark
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Old 14 November 2005, 11:12   #14
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Quote:
Originally Posted by roycruse
Excuse my ignorance - I'm just curious - how does a faulty spark plug and therefore a non firing cylinder result in piston failure.

By my reckoning unless the fuel supply is interrupted there is still fuel and therefore lubricating oil getting into the piston - the fact it is not burning up surely would equate to more lubrication not less.

Or possible could it fail if enough liquid fuel built up in a cylinder that the increased compression its self broke the con rod ?????

Please can a mechanic explain
I am puzzled about this too but am inexperienced with 2 stroke behaviour under these conditons.

In a 4 stroke, the non working piston would be a "passenger" but would not essentially be in immediate risk of failure. I have done many racing laps in a high horsepower "V7" without drama in the past.

I have spoken to the guy who lost his Etec 250 they are now citing "injector failure" as a reason.

Now this also resulted in the destruction of one bore and he said it happened instantaneously - no warning, but it caused the entire motor to shut down as a result. This sympton is worryingly close to the spark plug failure in one piston/bore as mentioned in the start of this thread (basically both instances reflect the failure of ignition in one cylinder through spark or fuel.)

I am trying to get hold of the dealers actual tech report and I will post it here for all to see, not for negative reasons but to perhaps help put people's mind at rest or on alert as I know several people about to part with their hard earned.
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