Tuesday, September 22, 2009

A Mechanical Mystery

So Stephanie's already told you about our woes with Lucky. Now it's my turn to provide some technical details.

The short version

Lucky still has a power issue on the port engine. The mechanics don't know why.

The long version

Last we left it, we had replaced the bad injector, everything looked good and we were waiting to replace the secondary fuel filter cover before going out on a sea trial. Friday morning Neil and his new sidekick, Eligh, came and replaced the fuel filter cap and got ready to go. everything was looking good. Fuel consumption was back to normal and no vibration was evident.

We headed down the new river. All the way down, everything looked good. Once I got past the twisty bits, I upped the RPM to 1000. Still no vibration. We headed out the cut onto the Atlantic. Conditions were rougher than the last time, we 2 - 4' waves. Nevertheless, once past the markers, I pointed us into the waves, dropped us down to 600 RPM and waited for Neil's signal.

Last time we went out I ran the throttles up gently, taking maybe 15 seconds to walk both levers to the fully open position. This gave Neil difficulty in matching reading from the engines to each other, as the readings are taken every second. This time we "slammed" the throttles and let the engines wind up to their maximum RPM in their own time. Much to our surprise, the port engine max'd out at 3350 and the starboard was 3530. Not only was the port engine not spinning up to maximum RPM, but the fuel consumption was 25% higher than the starboard. When we throttled back to 600, this increased fuel consumption continued. We repeated the test a few times, going into the waves and with a following sea, walking the throttles and slamming them. The same result in all cases. Lower RPM and higher fuel consumption on the port engine, exactly where we were before the injector was replaced.

We came back in. On the way back I ran at 1000 RPM to maintain around 5 knots heading up river. There was noticeable vibration. A little experimentation confirmed that it was coming from the port engine and not the drive.

Back at the dock, Neil executed one more test. Using the plug in computer, he ran a "run up" test. The computer, by revving up the engine, can some how calculate the maximum compression each cylinder was able to maintain, stated as a percentage of the design pressure. Volvo's specifications require each cylinder to reach 83% of maximum and the difference between the lowest and highest to be no more than 10% for the engine to be acceptable. Number 2 cylinder was 100%, but number 6 - the cylinder that had the bad injector - was only 60%. The others were in the 80's. We also ran the test on the starboard engine and all the cylinders were in the high 90's.

It was late on Friday and none of us had had lunch, so we called it a day with the plan to come back on Monday and look into the cylinders with a boroscope.

Monday came and Junior showed up in the morning to remove all six injectors. They were going to be sent to an injector shop to be tested. Later that day Brent showed up with the boroscope and we had a look. The theory is that if the bad injector had been putting more fuel into the cylinder than it should, the excess fuel would not have burnt and run down the cylinder wall, washing away the oil. This would allow excess wear from the piston to the cylinder wall to occur. This wear is very easy to see. The cylinder walls have a fine crosshatching etched into them. This crosshatching holds the oil and allows the piston rings to seal. excess wear would be evident by the crosshatching being worn, or gone, and there should also be vertical scoring. The cylinder looked fine. In fact, there was no discernible difference between any of the cylinders.

Where does that leave us?

In short, where we were two months ago. A lot had been fixed, but there's still an issue with no obvious cause. Brent thinks there still may be a compression issue with cylinder 6 - maybe a stuck piston ring - but wants to test this "the old fashioned way". So he's going to rig up a pressure tester out of an old injector and we'll try this later in the week. Meanwhile the injectors are being tested and a sample of oil was taken that, after analysis, may show fuel present. This would be another sign of a leaky cylinder. We'll know a little more by the end of the week.

1 comment:

Tokyo Biker Mommy said...

Wow, guys, i had no idea you were facing such adversities. I just caught up with a month or so of your blog and i'm sorry your adventure is not running as planned. But luckily, there is (almost) always a Plan B, Plan C, .... Plan Z.

Take care,