The rebuilt engine back in the boat and happily in the Bahamas last March…

The 2004 Yanmar 4LHA-DTE was professionally rebuilt at 960 original hours in the spring of 2020

The Yanmar 4LHA-DTE is considered one of the best 200hp diesel engines ever made! This engine was designed as an industrial engine first, Heavy Duty, sleeve lined cylinders, totally rebuildable, before being marinized. Unlike most other Yanmars that really just last an average of 2500 to 3500 hours and then are replaced, the commercial fishermen using this engine are seeing upwards of 8000-9000 hours before rebuilding! And that’s with the engines predominately being run by them at 3100rpm continuously! 3100rpm is the Max continuous rating for this engine even though it’s WOT (Wide Open Throttle) rating is only 3300rpm. It’s an amazing engine!

Unfortunately, like most down east style boats with inboard engines, this one was also built with only the minimal recommended rise (12”) in the exhaust to turbo riser and as is so often the case with down east boats, this one had taken on a little water through the turbo and into the No.1 exhaust valves which then cracked the engine head. The engine only had 960.7 original hours on it and it ran well (yes even with the severely cracked head!). So I bought the boat Jan 1, 2020 knowing that I was going to have to get the engine rebuilt (I’m too anal to just replace the engine head and hope that all else is well!). I called Mack Boring Co., the East Coast distributor for Yanmar to get their recommendation for a high quality Yanmar rebuilder on the East coast. I was told to contact Specialized Mechanical in Wilmington, NC so that’s what I did. I had Specialized rebuild the engine with all new inner (Yanmar brand) parts, pistons, bearings, piston sleeves, rings, all seals and gaskets, etc. AND had them replace the old cracked head with a new Yanmar factory complete assembled head and finally a new turbo. Of course they took it down to the bare block, inspected in total, cleaned and machined before reassembling with the new parts. Only the block, the main shaft and some of the exterior parts like the alternator, starter and raw water pump were reused after being cleaned and closely inspected. The block was in great shape and should be rebuildable at least a couple more times, easily.

When I wasn’t down at Specialized watching the rebuild, I researched building a proper exhaust system that would minimize the risk of this ever happening again. I emailed with Tony Athens, the well known marine exhaust guru and then came up with a design that not only raised the spill over point in the exhaust from the original minimal 12” to a whopping 25.5”, but I also incorporated a Centek fiberglass Surge Tube into the lower portion of the exhaust system. Surge Tubes are used by offshore Sportfish vessels because they need to be able to back up in any kinds of seas without the risk of flooding the engines. When I had the custom stainless steel exhaust riser welded up, I had the shop incorporate a V clamp flange on the exhaust side to allow the new stainless steel HDI straight mixing “elbow” to be removed for inspection with minimal fuss. Finally for additional engine safety, I installed an exhaust pyrometer just below the mixing elbow with a digital temperature gauge at the helm. The gauge has select-able temperature alarms and continually shows the exhaust water temperature. If the raw water cooling slows or stops and the temperature hit’s my selected, very safe 140F, a 100dB alarm is activated. 

Over $22,000 later I have a virtually new, “bomb-proof” engine that should, with proper maintenance offer it’s owner a minimal of 8000 hrs of trouble free service before needing to be rebuilt again. To put that # into perspective, my first (3 month) trip to the from North Carolina to the Bahamas and back, only logged about 260hrs and only that much because I was leading a group of friends in sailboats part of the time!

The engine was painstakingly broken in for the 1st 100 hours following Yanmars’ recommendations to the T’s. After that I had Josh at Specialized Mechanical adjust the valves at the start of my 3 month Bahamas cruise.  As I said above, that only added 260 more hours to the clock and took me from NC, down the coast to Miami, across to Bimini, the Berries, New Providence, throughout the 360+ islands of the Exuma chain of islands and all of Long Island before heading back through the same islands, across to the U.S. and back to NC. So the engine now has only about <380hrs on the clock. The boat was amazingly comfortable considering my past 41’ sail cat, Kadey Krogen trawler and other boats that I’ve taken to the Bahamas and lived aboard, all of which were much larger and I was much younger! Li’l Dingy did all that I asked of her with calm, comfortable efficiency and I lacked for nothing!

In the trailer getting ready for the trip to Specialized Mechanicals workshop
2 months later, the rebuilt engine being lifted at Specialized Mechanical waiting to get set back into my trailer…YEAH!!!