The engine is a Westerbeke 40 (similar to Perkins 4.108), built in 1980, s/n ED 22432U 559349F (decoding this based on Perkins, it's a 4.108 engine, parts list number 22432, madine in the UK, serial number 559349, built in 1979). Cylinder head number 37116500/3. On the block is the code MC25550 PN37112990-1.

Rebuilt the engine March 2006. Had the cylinder head, exhaust manifold, injector pump, injectors, transmission, heat exchanger, and oil heat exchanger rebuilt.

In 2025, I had to pull the engine to rebuild the transmission. With the engine out, I replaced all the hoses, had the heat exchanger, oil cooler, and alternator serviced. Here are the instructions I put together for pulling the engine and leaving it in the cabin.

The drain plug on the oil sump is a 1/2"-14 BSPP thread plus a 13/16" washer (copper or phenolic)

Engine water discharge hose 5/8" ID.

Engine develops 37HP @ 3,000 RPM. Cruising RPM ~2,000. According to Westerbeke, with a 2:1 transmission, the ideal prop size is 18x10 (2 blade) or 18x8 (3 blade). For each 1" reduction in diameter, increase the pitch by 2".

The engine holds 5½ quarts of oil. I'm using Shell Rotella T6 5W-40. The engine burns ½ quart/25 hours at about 1,650 RPM. Changed to this heavier weight oil to minimize engine oil leaks.

In 2001, changed all the hoses, the heat exchanger, and the oil cooler.

I created a cross-reference list between Westerbeke W40 and Perkins 4.108 parts. I've found that the Perkins parts are anywhere from two to 10 times less expensive than the equivalent Westerbeke parts. The cross-reference list is here.

In 2009, added a remote oil filter system to make oil filter changes easier and less messy.

According to the engine manual, the engine itself holds 2.5 gallons of coolant. The remote pressurized expansion tank and overflow reservoir takes about 1 gallon of coolant.

Service Schedule

Rule of thumb: Rebuild the engine when the oil consumption (not leakage) exceeds one quart per eight hours per 100 horsepower.  So, with the 40 HP engine, when the fuel consumption exceeds one quart every 20 hours, then rebuild.

Placed all the engine wires inside flame-retardant split-convoluted (split loom) polyethylene sleeving. The two sizes used were 3/8" and 1/2".

Replacing exhaust hose

Heat the manifold end of the hose with a heat gun being careful not to burn the rubber. Once warm, take a 2" wooden bung (e.g., an emergency seacock plug), put it in the heated end and start hammering it until the top of the bung is 2" below the end of the hose. Turn the hose over and use a broom handle to bang out the bung.

To install the hose, feed one end of the hose down between the engine and engine bed on the port side just aft of the oil filter takeoff. Feed the other end of the hose over the exhaust manifold fitting while putting a bend in the hose near the exhaust manifold. Bending it is the secret to getting it straight on to the fitting. I used a hi-temp RTV (silicone) gasket maker to cover the fitting before slipping on the hose. Once the hose is all the way on the fitting, put on two hose clamps to hold it in place.

Remove the four screws that hold down the Hydro-Hush muffler. Align the hose with the Hydro-Hush and put the hose on the lower (angled) fitting (make sure to first put RTV on the fitting). Then, adjust hose angle to get the Hydro-Hush back to its mounting position and screw it down. Put two hose clamps on this end of the hose.

To create enough room to maneuver the hose between the engine bed and the engine I carved away about 3/8" of material on the top edge. There's a 1/4" stainless steel plate inside the fiberglass that I cut away.

Random Temperature Readings (°F)

Conditions: May 8, 2011, seawater 68°F, air 74°F, 1,600 RPM, in gear, tied to dock.

Water Heater Coolant Plumbing

The engine heats the water in the hot water heater by circulating its coolant through it. The engine takeoff for the coolant is on top of the engine next to the thermostat housing. The return from the hot water heater gets Tee'd into the coolant return line from the heater exchanger to the engine block. To accomplish this, I made a Tee fitting out of copper pipe that gets spliced into the Westerbeke hose 12221

I installed in 2006 an electric fuel pump between the tank and the Racor filter to make it easy to fill the Racor. The pump I used is a Mr. Gasket Micro Electric Fuel Pump model 12S. With the pump off, fuel still flows through it pulled by the engine's fuel pump. The inlet fitting to the pump is a 45° brass flared fitting 1/8 NPTF to 5/16" tube OD (1/2"-20 thread). The outlet is the same size, except a right angle fitting.

The new tank (2006):

Capacity: 50 gallons
Usable: 49 gallons at up to a 20° heel
Weight: 52 lbs. (empty)
0.125" 5052 Aluminum with 0.188" side plates

Deck fill: 2" Sea-dog 351331. Uses an O-ring under the cap (2.0" OD x 1/8" thick, neoprene)
Fuel lines are 1/4" ID with compression fittings

Fuel tank vent: 5/8" hose to a Perko (0509DP4CHR) tank vent fitting (replaced 2016)

Tank designed by me, built by Carter Fabrications in Millersville MD.

Draining all the liquid out of the tank via a siphon, the remaining liquid measured 0.75" from the tank bottom, which I'm guessing is about a quart. The calibration was done pouring one gallon at a time into the tank.

The Plexiglas cover in front of it is 9⅜" x 5⅝" with a 2⅛" hole for the key (full-sized drawing and dimensioned drawing). Replaced 2022.

The cutless bearing sits inside the fiberglass stern tube. Two screws (10:00 and 4:00) are set in the stern tube with stainless threaded inserts. Set screws are used. The screws have putty over the tops of them. The bearing is turned down from 1.5" to 1.40" and then knurled. There are dimples where the set screws go.

I replaced the 3-blade 14"D x 11"P (reconditioned 3/1998 Buedel's #25226, Manufactured 3/1980) prop with a 15"D x 11"P Michigan Prop 3-blade. I also had the yard fair the water entry into the prop by removing the "shoulders" on the deadwood in front of the prop. The reason for this was to get rid of the cavitation and to put more power into the water to fight choppy seas.

The small nut goes against the prop and the large nut behind it.

The easiest way to install the packing:

1. Wrap three turns of TefPack packing around a 1" diameter cylinder. Cut two circles with a diagonal cut from the packing.
2. Take the green Drip-Less Moldable Packing and warm it in your hands. Then, roll it between your fingers into a long "log" that's the same thickness as the TefPack packing.
3. Make two logs of the Drip-Less Moldable Packing, with each being the same length as the TefPack packing.
4. Remove the old packing from the hex spud nut.
5. Insert the first TefPack circle into the nut, carefully noting where the split is in the circle. Push it down into the nut either with a pushing tool or gently tighten the spud nut on the packing gland until the gland touches the TefPack packing material and then back off the hex spud nut.
6. Insert the two circles of the Drip-Less Moldable Packing, taking care to make sure that the splits in the circle do not line up with each other. Again, push it down all the way into the hex spud nut, as above.
7. Insert the last TefPack packing circle into the hex spud nut.
8. Hand-tighten the hex spud nut on to the packing gland.

Changed from using a takeoff on the alternator to using the mechanical take-off on engine (above dip stick). This was done because of interference problems between the electronic tachometer and the Link 2000-R voltage regulator.

Teleflex 82430P electronic tachometer, including hour meter (installed 11/98).
Teleflex 1A96042 sending unit (voltage out)
Teleflex 52776P 0.104" square drive tang

The tachometer has an error with its readings:    True RPM = 84 + 0.858 * Tach reading (4/2000). I determined this with a photo-tach. I corrected the tach calibration by setting different switch settings on the tach (ratio of wrong reading over true reading — 4/2000).

I also had made up a 6" long mechanical drive cable (1998) because of the sending unit was too wide to screw onto the engine. The cable was made at a speedometer shop. On the engine side, the cable has a female 7/8"-18 thread. On the sending unit side, the cable has a male 7/8"-18 thread. Replaced the cable in 2006.

The previous hour meter had 1258 hours on it. (11/98)

Hurth HBW100-2R, Nr: 09-08324, manufactured in 1979, rebuilt 1/2006, 10/2025. To remove the transmission from the engine requires removing the engine! There's not enough space to remove the transmission's spline shaft from the damper plate without moving the engine forward. Here are instructions for moving the engine into the cabin.

Hurth bought by ZF Industries in 1995.

Transmission bolted to the engine with four ⅜"-16 x 1" Grade 5 bolts.

ALL BOLTS ON TRANSMISSION ARE METRIC!

The cable connection to the drive selection lever is metric. It takes both an 8mm and 11mm wrenches.

Gear ratios: Fwd 1.790, Rev 1.860

Holds 12 oz. of ATF fluid. Use ATF A or Dexron II according to the original manual. ZF now publishes a list and the fluid must meet TE-ML 04D. The only one I can find in the list that meets the requirements, is available in the US, and comes in a quart or liter size, is Liqui Moly Marine ATF available at NAPA stores ($14 in 2025).

There is 1.75" clearance between the end of the flange and the compression nut on the stuffing box.

Damper plate had a number on it: 1866 061 001. It's made by Sachs, which is a division of ZF. Alto Products makes another verion, DA-303. The damper plate is secured to the flywheel with five ¼"-20 x ⅞" socket head screws (black oxide) with 3/16" hex drive.