Changing Boat Engine
Keith Putnam, Vashon Island
What Sort of Boat and Engine?
A Tartan 37; the old and new engines were both nominal 40 horse diesels. As with most sailboats, the engine compartment is small and the access is difficult. I’m eighty years old; during the first three weeks I went to the chiropractor six times. He whipped me into such good shape I have not seen him again.
Why Would Anyone do this?
I know some who have changed out even though their existing power system was working fairly well. They just wanted something bigger or newer or more reliable and they thought they could afford it.
I’m part of the crowd that gets pushed into it. My engine was causing me increasing grief; ultimately it started lubricating it’s bearings with salt water and froze up. The engine was probably as old as the boat (34 years) and I understand the hour meter quit working before the last owner took her off for a south pacific cruise. It could be pulled out, rebuilt and reinstalled but that might not cost a lot less than replacement and I probably wouldn’t have faith in the end result. I could do a lot of the replacement work but did not want to tackle rebuilding the engine. So I charged ahead on what turned out to be a three month project, lots of do it yourself plus help from friends and some professional time.
Why not buy a new one like the old one?
Perhaps a good idea; theoretically it would drop into the same space with little modification to other stuff. Friends that did this said it turns out replacements are never quite the same as the original anyway. Besides, the original had been installed at a steeper rake than is recommended which might have contributed to its problems, so I would want a new transmission with angled output. That would require rebuilding the engine beds at the reduced rake and I’d already be into the same problems that came with a new engine.
At any rate, I chose to replace the four cylinder Westerbeke 4-108 with a three cylinder Yanmar 3JH5E. The Yanmar is a little smaller, lighter and suppose to be more efficient. Comes highly recommended. While at it I replace the batteries (seven years into a five year warranty); changing the battery profiles provided more room to service the port side of the engine. I also replaced the control panel, changed to a single lever shift and throttle and added a booster fuel pump that helps with bleeding and can recirculate the fuel through the filters when the engine is not in use.
Out and In
A shore-side hoist set the new engine into my cockpit. All other work was accomplished with the boat afloat in her usual slip. The engine mounts under the cockpit with no hatch above, so it must go forward, then up through the companionway, then aft, tilting this and that way to clear things. Close to 500 pounds going out, nearer 400 going in.
Getting the Westerbeke out was not too bad. I took off the alternator, starter, manifold, transmission and bell housing; a friend helped with the very stubborn head. The remains were smaller and not unmanageably heavy. We hoisted them by running the main halyard down through the companion way. Setting the Yarmar as delivered was harder, a lot heavier all in one assembly. I bought barn door track, we hung it from the boom with supports every two feet, built a little rolling carriage to spread the load, and it worked out quite well.
Engine Sump and Beds
Tartan provides a sturdily built fiberglass combination of sump and beds well glassed into the hull. I saved the sump, cut down the sides of the fiberglass beds and bolted new timber beds to the cut down glass. An alternative would be to build new fiberglass beds but I’m an old wood boat guy and felt more comfortable with wood.
Measuring is a bitch; even after multiple checks and plotting everything on a CAD drawing I was not sure I had it right, but alignment adjustments were well within the range of the Yanmar mounts.
Shafts and Couplings
The combination of slopes and shorter engine/transmission implied a 4” longer shaft. The wheel was mounted close to the strut so the shaft could not be pulled forward as far as needed. I coupled a 4” length of shaft to the engine and coupled the existing and new shafts together with a pair of spider hubs with resilient filler. This adds the advantage of some vibration isolation and allows a little tolerance to alignment. We aligned as carefully as if this tolerance was not available, just something of a safety factor.
Installed
It’s a great feeling when you hit the switch and on a cold day without preheat and the engine fires up on the first stroke! The transmission ratio is not the same as the previous one, but the wheel is a three blade Max-Prop; if necessary the pitch can be adjusted at the next haul-out. So far I doubt that will be necessary. The engine is smoother, quieter and I’m delighted.