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Old 25-04-2021, 15:57   #1
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Westerbeke Interchange or Substitution

Greetings, CF Community!


I own a 1979 CSY 33 with a Westerbeke 4-91 (also known as a Westerbeke W30). The engine runs well, and it's been reliable. But it's rated at 27HP, which seems a tad underpowered to me. The engine is installed with a v-drive, and I'd like to keep that to avoid the trouble of tearing up the galley to put an engine up there. Is there a suitable substitute (made by Westerbeke or otherwise) that has the same bolt pattern but more power? Anyone know if Westerbekes had a common bolt pattern, or was each model different? Thanks!
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Old 25-04-2021, 22:25   #2
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Re: Westerbeke Interchange or Substitution

Hi Polar...You have to remember that Westerbeke is a marinizing company and not an engine manufacturer. So it is highly likely the trans will not readily bolt up to another engine. That said, the "bell housing" is what adapts the engine to the transmission. That is your issue. My suggestion would be to contact Wersterbeke and ask if they have a bell housing to bolt your transmission to a Westerbeke (Perkins) 4-107. They are 40hp.
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Old 28-04-2021, 10:19   #3
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Re: Westerbeke Interchange or Substitution

Ho, boy. OK. 16,000 lb displacement, 25' LWL. 27 HP should be quite adequate to reach a hull speed of 6.7 knots. More than that is going to be difficult and burn bunches of fuel, whatever size engine you put in it. Is it giving you that 6.7 knots with a clean hull? If not, is the prop wrong or the engine worn out? In short, it's a heavy displacement boat, not a planing boat, and adding more HP does not really mean adding more speed unless you are substantially below hull speed at full power.

If you go to another engine, the bell housing may not be your only problem. Do all the hoses, cables, and electrical connections join the engine in the same places? Are the engine mounts and the stringers right? Will it even fit in the horribly tight space designers leave for the engine?

There are bunches of threads on the forum dealing with switching out Atomic 4s for Pratt & Whitney R-4360 Wasp Majors. No, I'm being flippant. There are bunches of threads regarding the problems that arise when an engine of different design is subbed. The most successful switcher I know of actually built a cardboard engine first to see if it would fit.
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Old 28-04-2021, 11:11   #4
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Re: Westerbeke Interchange or Substitution

I use to often motor north along the California coast with a 2-3 knot current, 15 knot wind with 4 ft. square waves on the nose. It was a 13,000lbs. boat with a 27hp. diesel. Sometimes it would stop me dead and I would have to gain momentum again. I could have used a 40 hp. If you pitch the prop for a 40hp. the boat has a lot more umph to plow through the stuff.

A good example is the 2000 mile motor back to Ca. from Mexico. It would be a hassle with a 25hp. I am of the camp that likes 300-400lbs for one hp.
But if you're not cruising and just need to get in and out of the slip, almost anything will do.
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Old 28-04-2021, 13:24   #5
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Re: Westerbeke Interchange or Substitution

Your BMC 1.5L diesel is an excellent engine and marinization parts are readily available from sources other than Westerbeke. I ran your boat through my program and here are the assumptions I made: 16,000 lb light displacement and 2:1 reduction gear. I calculate that you should attain 6.3 knots in calm water with a clean bottom and a prop sized for you to reach 3000 rpm.

Now your boat is probably heavier and since Westerbeke rated that engine at 25hp @ 2500 rpm they could have limited your revs.

Here's some food for thought. If you can attain 6kts in calm weather and 5 in snotty weather leave well enough alone. But if you can't attain those speeds AND you have the boat properly propped then you should know that that engine is rated for 40hp @ 4000rpm. A good diesel injection engineer can change those settings and fit new injectors. This will not harm the engine in any way but at its age, I wouldn't run her above 3600 all day long. You'll need a new prop too and maybe your shaft will be too small as well. And there is always the risk that your reduction gear isn't rated for that much power.

If you're REALLY after much more hp then I'd suggest sourcing some BMC 1.8L pistons and rings and punching out the bore. The same engine block, connecting rods and stroke but that requires pulling the engine.

Good luck!
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Old 28-04-2021, 13:33   #6
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Re: Westerbeke Interchange or Substitution

These are the go-to guys for BMC B series diesel engine spares https://calcuttboatsshop.com/epages/...d/Categories/2
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Old 30-04-2021, 07:13   #7
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Re: Westerbeke Interchange or Substitution

Quote:
Originally Posted by kenbo View Post
Your BMC 1.5L diesel is an excellent engine and marinization parts are readily available from sources other than Westerbeke. I ran your boat through my program and here are the assumptions I made: 16,000 lb light displacement and 2:1 reduction gear. I calculate that you should attain 6.3 knots in calm water with a clean bottom and a prop sized for you to reach 3000 rpm.

Now your boat is probably heavier and since Westerbeke rated that engine at 25hp @ 2500 rpm they could have limited your revs.

Here's some food for thought. If you can attain 6kts in calm weather and 5 in snotty weather leave well enough alone. But if you can't attain those speeds AND you have the boat properly propped then you should know that that engine is rated for 40hp @ 4000rpm. A good diesel injection engineer can change those settings and fit new injectors. This will not harm the engine in any way but at its age, I wouldn't run her above 3600 all day long. You'll need a new prop too and maybe your shaft will be too small as well. And there is always the risk that your reduction gear isn't rated for that much power.

If you're REALLY after much more hp then I'd suggest sourcing some BMC 1.8L pistons and rings and punching out the bore. The same engine block, connecting rods and stroke but that requires pulling the engine.

Good luck!



So, the experience (mine and others) with this engine so far is that it WILL overheat when pushed above the rated 2500 rpm. It happens slowly, creeping up over an hour or two until the water temp gage is bumping the upper limit. When I keep it at the rated RPM of 2500, it stays at around 195 for hours. And at 2500 rpm, in light chop, I'm doing about 5.2, nowhere near the hull limit. Is that a prop issue, a cooling issue, or an underpowered boat?
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Old 30-04-2021, 09:06   #8
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Re: Westerbeke Interchange or Substitution

Quote:
Originally Posted by Polar Opposite View Post
So, the experience (mine and others) with this engine so far is that it WILL overheat when pushed above the rated 2500 rpm. It happens slowly, creeping up over an hour or two until the water temp gage is bumping the upper limit. When I keep it at the rated RPM of 2500, it stays at around 195 for hours. And at 2500 rpm, in light chop, I'm doing about 5.2, nowhere near the hull limit. Is that a prop issue, a cooling issue, or an underpowered boat?
Let's break it down.

At 2500 rpm the engine produces 25hp. Because of the v-drive and prop bearings, the prop is seeing 23hp. That is enough power to drive your hull to 6kts on a windless, calm day if your bottom is clean and properly propped. The fact that you're reporting only 5.2kts can be a host of issues that I can't diagnose from a distance.

Here's where I'd start to narrow the issues down. Have you checked the accuracy of your alternator-triggered tachometer with an optical tach? How accurate is your speed through the water measurement and SOG is not STW.
The tach accuracy is essential to determine if you have the correct prop. You indicate that you can rev above 2500, so how far can you go above 2500? Perhaps you are underpropped and that would reduce your top speed.

Overheating above 2500 but runs all day at 2500 can mean several things. First to mind is that Westerbeke installed a heat exchanger sufficient only for the caloric load of the engine at 2500 which I doubt since the same heat exchanger was used on the W50. So other items that can reduce the caloric load handling ability of the cooling system to be checked a: When was the last time you serviced the heat exchanger tube stack, raw water impeller, thermostat, and pressure cap? What does the raw water flow through the oil cooler look like? Has it ever been removed and serviced? Another cause of the overheating could be excessive exhaust back pressure which could be caused by exhaust elbow blockage, hose collapse/restriction or poor initial/subsequent installation. Ever perform an exhaust backpressure measurement? Westerbeke has a maximum of 39" H2O or 1.4 PSIG. That's a very low number.

There's a lot to mull over here but at the end of the day, 23hp at the prop is only going to deliver 6kts under ideal conditions. That's should be enough to get you off a lee shore so it comes down to how you use the boat and how much money you want to spend to get those remaining 0.7kts. A professionally done repower could exceed 50% of the value of your boat. BTW you never said what type of v-drive you have which is important info to determine if a bobtail installation is economically feasible.

(PS on edit) You may know this but the BMC 1.5L (4-91) was used in London taxis for years. Its durability and economy are legendary. I'd work on getting that engine running at peak and making sure you have a 2500 rpm max prop fitted.
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Old 30-04-2021, 12:57   #9
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Re: Westerbeke Interchange or Substitution

Wonderful post, kenbo. You really laid it out there.
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Old 30-04-2021, 13:32   #10
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Re: Westerbeke Interchange or Substitution

The same program that I used to see your predicted hull speed also recommends a 17 x 11 3 blade prop. However, I had to make assumptions of a 2:1 reduction and light ship displacement of 16,000 lbs. Both could be wrong.

If you know your reduction ratio and can better estimate your cruising displacement I can put a sharper point on things. Also, are you prop diameter limited? Do you know your current prop diameter and pitch?
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Old 16-06-2021, 08:32   #11
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Re: Westerbeke Interchange or Substitution

Hi Polar et al. If you are looking to adapt to a Perkins /Westerbeke 4-107 we have a complete very good running 4-107 that I removed from our Alden Schooner this winter to repower with a 60 HP VP. The motor was simply too small but has been flawless companion for us over the last 28 years and we would like to find a home for it. It has a Paragon hydraulic gear (2.5:1 LH) that is also in perfect working order.
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