Nonetheless, we thought it prudent to size-up the local marine repair talent in Georgetown. But after we arrived, a neighboring cruiser told us that he had waited for an hour-and-a-half at a nearby boatyard without being helped, so that sealed the deal for us. Now don’t misinterpret this to mean that opting to fix our transmission ourselves wasn’t a daunting project. When we mentioned this plan to fellow boaters, the responses ranged from the ‘You’re brave,’ to ‘You’re crazy.’ And who knew what was inside a transmission anyway? Judging from the sample of cruisers we came in touch with, not many. But we were more than willing to jump in and find out.
The experience reminded us of the first time we had to venture into the inner workings of mechanical apparati when the engine on our previous boat blew a head gasket off the coast of Mexico. At the time the event seemed like the end of the world. We made it into the port of Zihuatanejo for repairs. That’s where we encountered another cruiser who helped us get the right perspective on making these kinds of repairs. This fellow, from a South African boat, offered a piece of wisdom that we have since used time and again: "It’s only a Volvo MD2b," he said of our engine in his lilting South African accent, "not a nuclear submarine." Someone had once used a selection of metric wrenches to put the thing together, we figured we could use the same to take it apart.
Expect Setbacks The ability to squeeze into a position that would make a yoga swami scream for mercy, and stay there is high on the list of requirements for working on your own diesel engine. Our first task was to disconnect the coupler from the shaft, which took about an hour. Next we had to get the transmission off the engine, and that took what seemed like an eternity. The heads of four of the six bolts holding the mounting flange to the engine block snapped off in the block despite a generous amount of PB Blaster and gingerly applied force. Sometimes that happens. At least I wasn’t paying someone else to break bolts I could break perfectly well myself. Still, with all the bolts off, the thing was more than a little reluctant to part from the engine. Several more hours passed in which we used a series of wooden wedges, screwdrivers, and chisels to open the seam between the transmission and the engine and separate them, trying not to damage anything else. After digging deep in the persistence department, the transmission finally came off.
Fortunately, we had a technical manual for the transmission, which helped stave off the what-the-heck-are-we-doing feeling that we couldn’t keep at bay. And thankfully, we could still run the engine to charge our batteries, since our transmission and engine are actually separate entities. Some older engines use the engine’s oil to lubricate the transmission. Our transmission, a Hurth 100, has an input shaft, which takes the power from something called a damper plate that is attached to the flywheel and brings this force into the transmission. When the shifter is engaged into either forward or reverse the output shaft spins via a series of clutch plates and provides power to the shaft and prop. I successfully rationalized that the whole arrangement was similar to something I knew pretty well, a two-speed winch, only this thing had a neutral gear.
Stay Calm Should you ever find yourself in the similar role of taking something major apart—say an alternator, engine head, steering system or what have you—the first thing to do is to proceed in a calm and orderly fashion. Label bolts, washers, and other fine parts and keep them in plastic Ziploc bags. Be sure to take notes, and go slowly. If you have to store any of the parts for a prolonged period of time while you wait for replacement parts, take care that they won’t be damaged knocking around inside a lazerette.
In our case we were lucky when it came to diagnosing the problem. With the transmission casing apart, the machined grooves on the end of the input shaft were chewed up. Continuing research revealed that the damper plate on the flywheel would also have to be replaced. The two apparently had gotten into a bit of a brawl that left both destined for the dumpster. We were lucky that the damage seemed confined to the input shaft and the damper plate, the output shaft is a bit more complicated and we might have had to send that back to the manufacturer for repairs. Instead, we discovered that all we would have to do was have a bearing pressed on, then replace the input shaft, some gaskets, and some shims.
Diagnosis But the question remained, why had it this happened? Closer inspection revealed a few clues. Exhibit A was the missing head of a single bolt holding the transmission on the engine that had been broken off by a previous owner. Exhibit B included a thick layer of scale in between the mounting flange. Our boat is a center cockpit design with engine access from the cockpit. The cockpit gets wet from time to time (imagine that) and a leak had dripped down precisely into the seam between the transmission and the engine. The situation is similar to water dripping into a crack in a rock. Eventually enough scale built up to pry the transmission slightly away from the engine, exerting an uneven pressure on the input shaft, until eventually something had to give. The theory we’ve developed is that a previous owner saw what was happening, tried to tighten the transmission onto the engine, broke a bolt, and said ‘forget about it,’ probably reciting the if-it-isn’t-broken-don’t-fix-it mantra. And short of taking the transmission off the engine, there wasn’t much anyone could do about it. If there’s a lesson in this, it’s never underestimate the power of leaks aboard a boat.
Based on where the damaged parts were, we decided the breakdown didn’t stem from a misaligned engine, or else the rear seal on the transmission would have gone and the damage would have been in the output shaft. The nuclear submarine engineer turned cruiser who was anchored next to us thought this theory was hogwash. His take was that the wrong sized damper plate had been installed and the engine managed just enough bite to hang on for 15 years before giving way. We’ll probably never know what actually caused our transmission to fail.
In the heat of the battle, it’s easy to over-tighten bolts to the breaking point. The experience of taking the transmission off the engine helped remind me that this was something we did not want to do, especially since the marine infrastructure we were hoping to find in Georgetown was not exactly what we pictured. Finding a 13-mm fine-thread bolt proved impossible, making each piece we had irreplaceable. When you’re reassembling a fine piece of machined hardware, think of how you tighten the lug nuts when you change a flat. Go slowly and evenly, and if you can borrow a torque wrench from a neighbor and have torque specifications, so much the better.
Replacing the Diesel Engine by Sue & Larry
Surveying a Diesel Engine by Tom Wood
Diesel Maintenance by Mark Matthews
SailNet Store Section: Engine Maintenance Videos
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