BMW to Cummins Repower

Peter S. Reich
TEDDY BEAR #15, Shelter Island Heights, NY

We purchased TEDDY BEAR in October 1985. She was a dealer’s boat with 90 hours on the clock and had been in 2 boat shows. Fast forward to July 2008 and 3,150 hours on the original BMW when my brother was pulling into our slip after watching the 4th of July fireworks and there was a loud bang and grinding from the front end of the engine. After determining it was the #1 connecting rod, wrist pin or piston, we began to think about whether to rebuild or repower. Given the age of the BMW and the fact that it was many years out of production, we decided to bite the bullet and repower.

Underway to the yard

I borrowed a friend’s 27’ Boston Whaler and towed TEDDY BEAR from Dering Harbor, Shelter Island, NY to Coecles Harbor Marina & Boatyard located on the other side of the island. I have known the owner, John Needham, since before we purchased the boat. We had collected brochures on about 10 engines, and John and I spent a lot of time and calls researching what would fit. I originally was interested in Yanmar, but the choice model could not be installed in a US documented vessel, according to the distributor, due to emission standards. They recommended a model which didn’t reach rated horsepower until 4,000 rpm which just didn’t make sense for a displacement hull like a LNVT. Most of the other engines were eliminated because they wouldn’t fit without major carpentry which would involve losing some of the galley drawers.

A Cummins ReCon 4BT3.9-M

We settled on ReCon Marine, which is a factory reconditioned Cummins 4BT3.9 155hp with full warranty. We chose the Warner 72 Series with 2.57 ratio. This was the heavier of two gears for this engine. We felt, given the mass of the long shaft, it made good sense to use the heavier gear to overcome the inertia when shifting.

Out with the old

The old BMW D150

Next came removing the old BMW. One of Coecles Harbor’s mechanics came up with a great idea. They cut a hole for a 4” bronze deckplate in the pilothouse sole directly over the BMW’s lifting flange. They carefully put the end of the boom truck through the pilothouse door with a chain through the hole to lift the engine clear of the stringers so it could be slid on planks out the aft doors. Inspection showed that one of the motor mounts had rusted away and the weight of the BMW had been resting on the solid end of an oil line that led back to the cooler. All 6 fuel tanks were also removed. The aft, port tank had developed a leak a few years before so I had isolated and emptied it.

The old fuel tanks and wet muffler

Now that areas of the bilge were seeing light for the first time in a quarter century, the bilge was cleaned, degreased, and epoxy painted. The engine beds had to be extended forward and an FRP drip pan was made for under the engine, something we have always wanted. Bilge water can still flow fore and aft under the pan. A 1-1/2” safety seacock was installed. When closed, a safety seacock has a plug that can be removed to draw bilge water through the engine’s water pump in an emergency. It also makes an easy way to flush the engine with fresh water and add anti-freeze when laying up. Old fuel lines and wiring were removed. This was the opportune time to replace the shaft seal hose. While this was happening on the boat, a lot was happening on the engine back in the shop. The Warner gear was attached and the turbo had to be relocated to the top of the engine. This involved lots of plumbing changes on the engine and a new coolant expansion tank had to be fabricated. That and the plastic overflow tank were installed on the bulkhead just below the hatch in the pilot house sole. The marine gear, new brackets and expansion tank were all painted Cummins white.

In with the new

Dimensions were checked over and over and then the turbo and other components were removed while the engine was physically installed in the boat. We also upgraded from the standard alternator to a Balmar 100 amp. As the systems were all connected to the engine, we had to decide where to locate the muffler and run the exhaust. The old exhaust came off the aft end of the turbo and ran aft down the center-line of the boat. The high point of the old riser was only about 2” above the waterline. John was amazed the engine never flooded in a heavy follow sea. We ended up mounting a Centex muffler between the generator stringers and the exhaust runs across the top of the starboard lockers in the salon. It is located well above the top of the doors and doesn’t take any usable space. It pitches down from the muffler outlet to the new 4” outlet through stern, and the increased height has given us some added comfort knowing it should never flood the engine. We also added a Walker Airsep. All the research and reviews made it seem like a wise thing to do – reduced fuel consumption and a cleaner engine room. The dip stick was relocated to the starboard side and calibrated. An extension tube was added to the oil drain so all engine checks and oil changes can be done from the starboard side of the engine. This was important since the turbo and Airsep are on top, making it impossible to crawl across the top of the engine as I could do when the BMW was cool.

In and all hooked up

Once all the cables, plumbing and wiring harnesses were all connected, it was time for sea trials. The new fuel tanks hadn’t arrived yet, so supply and return lines were run into a 5 gallon jerry jug with fresh diesel. I had a prior commitment and was not able to be aboard when the Cummins rep came. From what I understand, he spent the better part of the day checking over the whole installation which passed with flying colors, thanks to the professionalism of Coecles Harbor’s crew. The rep took dozens of temperature and pressure readings at various rpms. He had the mechanic jam the throttle from idle to full throttle and timed how long it took to reach maximum rpms. John did an amazing job calculating the new prop which is a 24x19x4 LH Nibral. At WOT the engine reached 2,850 rpms which was only 50 over the rated 2,800 rpm’s, but since we had no water or fuel, no fuel tanks, and almost no equipment on board, we figured that was about right.

The new instrument panel

The only recommendation the rep made was to add an engine room blower since they say the ER temperature should never be more than 10 degrees above outside temperature. We never had a blower so we added one above the starboard battery shelf and it discharges below the pilot house door. We added an intake below the port door. Both are screened and have a soft PVC vent aiming down to keep water out and not cut up one’s legs. The blower is on a thermostat and comes on automatically and remains on after engine is shut off.

We decided to replace the 6 fuel tanks with a total (not usable) capacity of 225 gallons with 2 aluminum tanks totaling 150 gallons. Cardboard mock ups were made to check fit and then final dimensions were sent to Luther’s Welding in Bristol, RI, for fabrication. The difference for ¼” instead of 3/16” was only $300 more so we thought that made sense. I picked the tanks up and was extremely pleased with the quality right down to the epoxy coating. I was also surprised how heavy a 75 gallon aluminum tank was! Fueling TEDDY BEAR used to be a real pain with the 4 deck fills and diesel spitting back up through the fills onto the teak or out the vents. Now it is a piece of cake and the pump handle can be held wide open with no problems. We abandoned 2 of the 4 fills by plugging with a wood bung so a nozzle can’t be inserted. If we ever get to replacing the teak deck, we will remove them.

Now for what matters: the operation of the engine. The old BMW was often stubborn starting, even with the cold start lever engaged. I found it needed a full 45 seconds of preheat which seemed like an eternity to me, and especially to the batteries! Once warmed up, we would run at 2,150 which was barely 7.0 knots. Now we make 7.2 knots at 1,900 rpms and 8.0 knots at 2,000 rpms. The throttle is very responsive and the engine feels a lot more powerful. Despite 2 less cylinders, it runs a bit smoother, which surprised me. Starting is instantaneous with no preheating, even after sitting all winter. The difference in starting took a bit to get used to. The BMW started by turning the key to “start” as in a car and stopped by pressing the big black rubber button. After hundreds and hundreds of starts over 25 years, that obviously became second nature. The new Cummins panel starts the engine by pressing the black rubber button and shuts off with the key. I had the fear that I, or one of my other family members, would out of habit press the Start button to try and stop the engine! I cut down a PVC end cap and labeled it “Start” and keep it over the button so it must be lifted off to start and the button can’t be accidentally pressed in the dark. Besides safety, I figure the cap will keep the UV rays from eventually destroying the rubber.

Repowering TEDDY BEAR and replacing the fuel tanks was the best thing we have done to the boat. We have much more confidence in the power plant and she feels like a new boat. The experience with Coecles Harbor Marina (631-749-0700) could not have been better. This was not a simple repower. Their experience and professionalism can’t be beat, and I wholeheartedly recommend them should any Tuggers need to repower or do any other major work. My whole family is looking forward to another 25 years of cruising aboard TEDDY BEAR!

Editor's Note: More pictures of Teddy Bear can be found here.
Reprinted from Tuggers, Spring 2010, Vol. 43.

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