Yanmar marine engines have a reputation for reliable operation for many years.  We expected few problems with our twin 3GM engines - even when we added the demand to deliver our electricity to their chores.  Our idea what that two reliable engines were easier to maintain than two reliable engines and one generator.

We are still not sure why, but at 4,000 hours both engines failed with broken pistons and other internal damage.

Our first indication of the upcoming failure was hard starting.  One day, after starting the starboard engine, I leaned over to check for oil leaks and was zinged by a "dipstick launching".  The dipstick decided to eject itself from the engine block, race by my face, knock my hat off and embed itself in the roof of the engine compartment.

Stumped me.  Normally excessive oil leakage and the much more serious dipstick launching, are caused by cracked or damaged rings.  The engine pressure pushes into the crankcase and everything in the crankcase is pushed out.  I wasn't ready to admit this was my problem.

I went to a nameless mechanic in Ft. Lauderdale ($50) and another nameless mechanic in Riviera Beach ($500) who both told me I was running the engine to slowly and had built up carbon on my head. (I think they meant the engine's head).  They were sure that if I just ran 100 hours at 3200 rpm the problem would go away. 

Armed with this information $550 less in cash and 5 gallons of Rotella oil to replace what we expected to leak we left for the Virgin Islands.

The problem didn't get better.  I decided to return to Puerto Rico from St. Thomas expecting parts to be a bit easier to find and locate a capable mechanic.

Richard Parent (on left) and his co-mechanic, Tully, agreed to permit me to do as much of the work as I wished - with them hunting up the parts, dealing with the machine shop, and reassembling the engine after completion.  My work and Richard's fair pricing brought in the two complete rebuilds for about $4100 - $400 less than the shop in Riviera Beach wanted to rebuild each engine.

I removed the manifolds and head from the Starboard engine and prepared it for removal from the boat.  The boom derrick made it all possible.  We used the dingy lifting lines clip onto the engine's lift points and ease the engine out of the hatch and on to the waiting dolly. 

In the meantime, Richard had taken the head to the machine shop and come back with the expected news that nothing was wrong with the head.  The machine shop did routine reconditioning for $85 each and sent the heads back in about a day.

This photo tells it all.  Both engines had exactly the same damage.  In both cases, the #3 piston was shattered beyond recognition.  The #2 pistons were cracked or damaged, and the #1 pistons were running the engine. 

Yanmar examined the parts removed from the engines and stated the engines died from overheating.  There were no signs of overheating on the heads, the block, or the bearings. 

The photo on the right gives a hint as to the cause of the failures.  The lower ring is the new ring - just inserted into the cylinder.  The upper ring is the removed ring.  Richard measured the clearance of each of the removed rings that were not broken beyond measure.  Each ring measured over 125/1000" - that's right, there was 1/8 of an inch of clearance.  I believe the plating on the rings might have been incorrectly applied or just worn away more rapidly than planned (the rings are chrome plated to reduce wear).  This would explain why the rings eroded and the cylinders were left relatively undamaged.

In the meantime, Richard put in new bearings, new seals, and new pistons -- effectively a new engine.

Installed, cleaned, air bled, and prayed over, each engine started immediately.  Stay tuned, in another 4,000 hours we will see if they are still running.