Friday, March 5, 2010

Engine woes in Marina Mazatlan (Feb 5-15), just in time for Carnaval

Apart from a few speed bumps, Tao’s visit in Mazatlan was productive and rewarding. Chris and Dave set to improving the engine situation immediately upon arrival on February 5th. The same day, Chris started the engine for Rafael from Total Yacht Works to troubleshoot. As suspected, the head gasket had blown. Luckily, it had only ruptured along a small segment of the forward and starboard corner of the head, just aft of the manual hand crank on Tao’s Yanmar 2QM20. The critical cooling water pathways were luckily not in this portion, or the crew would have had to deal with water and exhaust spewing into the cabin along with exhaust fumes. From the time when the blowout occurred just outside Bahia Agua Verde to sailing onto the dock in Marina Mazatlan, Yannie chalked up 1 hour of engine run time. Hopefully, this has saved the head and block from further damage.

Chris and Dave removed the head and handed it over to Total Yacht Works for a more complete analysis of the damage extent. Initial reports in the days that followed indicated over 10 thousandths of an inch of head warp from overheating, which is over 2 times the specified limitations in the engine manual. Estrella, Tao, and friends began the search for a used head on the aftermarket, considering the brand new one from Yanmar had a $2,800 price tag, not including the shipping and import taxation. Apparently anything from Asia gets an import tax hike when shipping inbound. Ouch!

Online search efforts failed and repowering options were being considered when reports from Total Yacht Works recanted the initial diagnosis of a badly warped head. In fact, the head was within the specified 4 thousandths of an inch manufacturer limit, BUT another problem had been spotted. Cracks were identified in the seat of one of the exhaust valves. Upon visual inspection, these cracks were hard to see. Stepping back, Chris discussed with Rafael and his father about the root cause of the blown gasket in the first place…overheating. In a raw water cooled engine, sea water passes through passageways in and around the head and block surrounding the pistons where the most heat is produced during engine combustion. Upon visual inspection, a majority of these passageways for cooling were at least partially and some completely clogged. Chris spent half a day clearing these with a scratch awl and anything else sharp that he could fit into the tight spaces. The narrow constrictions which passed water from head to block, and vice versa, had been especially blocked. The overheating alarm never went off, which indicates that the head was unevenly overheated. The areas that were reached by the seawater cooling water were within normal temperature ranges, while the areas that were clogged where likely overheated, eventually resulting in the blown gasket. With raw water passageways cleared, Chris hopes that returned normal water flow in these areas will prevent future over heating of the head once reinstalled. More on the engine repair will follow soon...

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