Our DIY Boat Engine Rebuild: The First Test Run

We ended the last blog with our Volvo Penta D2-75 engine finally back in Emerald’s engine room. This was a major milestone in our DIY boat engine rebuild following salt water damage. With no previous experience of rebuilding an engine, we’d had many months on a steep learning curve with several soul crushing set backs. But we’d resolved each problem and to have finally reached this point was an incredible feeling.

The next big step was to test run the engine.

Over the last few months people have been asking us when we think we can launch and where we’ll go. At first we expected to be ready by the end of April, then it was May and now it’s August and we’re still battling away. We recently passed the one year anniversary of the engine’s failure and the last time Emerald was floating. So we are very excited about being close to potentially leaving the boatyard. But we try not to think too much about the pleasure of bobbing on the sea again and where we might sail to, because of the things that have unexpectedly gone wrong and set us back. Call it pragmatism, mixed with a touch of paranoia. Whatever it is, the result was a maelstrom of conflicting emotions swirling around inside us.

But before we got to the test run, we had to reconnect all of the ancillary systems. If you want to skip the preparation work, click here to jump to the exciting part where we attempt to start the engine.

Making The Engine Room Watertight

The first job was to fasten down the cockpit floor, with its 28 bolts and a squeeze of sealant for each. This meant Colin contorting himself into awkward positions in the engine room whilst trying not to lean on anything breakable on the engine. I had the easy job – holding each of the bolts in place from above as Colin tightened the nuts on from below.

You might wonder why we would do this because if the engine had to come out again then we’d have to undo all of this work. But, it was necessary to keep the engine room watertight. Afterall, we’d had enough of water getting in to places it shouldn’t go. The weather in Porto Santo is generally settled, but occasional rain showers do come along. They’re rarely heavy, mostly just drizzle, but what does fall onto the cockpit area drains into the floor.

We also needed to secure the floor at the back of the cockpit so that we could put the gas box back to be able to cook our dinners.

hammering in the first cockpit floor bolt with a squeeze of sealant around the head
The first floor bolt going in

The Electrics

With the engine room made watertight, Colin could move on to reconnecting each of the engine’s ancillary systems. First was the wiring loom and the alternator.

The alternator was a pig to reconnect due to poor access to the wires at the back. There are power wires, control wires, wires to our external regulator and to the engine itself. Access was limited due to the changes we’ve made to the exhaust system. He ended up having to take the alternator off to connect the wiring, before refitting the alternator back where it came from.

We were able to test the wiring loom by using the control panel in the cockpit. If something was wrong, we wouldn’t see any readings on the various meters there. The panel also has warning lights for the voltage and oil pressure as well as a glow plug indicator. All 3 lights came on when we turned the start key, as expected. We waited for the glow plug light to go off (meaning they’ve reached the right temperature for starting) and after a few seconds it did. The test was a success.

The engine control panal in the cockpit

The Exhaust

There were two exhaust pipes to connect up. First was the one to the second waterlock, a new addition to the engine room. We’d had to leave this disconnected so that there was space to lower the engine in. Second was connecting the end of the exhaust hose to the engine itself.

The Cooling System

Engines get very hot, so they need a cooling system. In our engine, the raw water and the fresh water systems perform this job. The engine sucks in the raw water via a seacock from the sea. The fresh water circulates within a closed system with an additive in it to stop corrosion.

When the engine is running, the fresh water flows through pipes around it, removing heat to keep it at approx. 90 degrees centigrade. Being a closed system, there is then a need to remove the heat. Otherwise it would just get hotter and hotter until it boiled. This is the raw water system’s job and the transfer takes place within the heat exchanger. The hot, salty water is then expelled out through the exhaust.

The Raw Water Pipework

This job was a simple matter of connecting up the pipe from the raw water uptake system to the engine. We held off from putting in a new impeller until we were ready to do the test. Last year we’d learnt the hard way what happens to impellers when they’re left sitting in unused engines for too long.

The Fresh Water System

After passing through the heat exchanger, there is still plenty of heat remaining within the fresh water cooling system, so we use this to warm our hot water tank. Even just motoring into an anchorage after a sail gives us enough warm water for a nice shower. However, because the hot water tank is above the height of the engine, the reservoir for the fresh water has to be even higher. We have a header tank in the cockpit locker to achieve this.

The result of all this, is that Emerald has a complicated system of coolant water pipes and valves that could rival Spaghetti Junction. Hoses run from the engine up to the hot water tank and back, as well as to the header tank. Each connection is a potential leak point.

When we installed the hot water tank, we also had to change the radiator cap to use a hose connection kit. Rather than just being a simple cap, the kit has a cap with a pipe feeding into it, with a rubber seal underneath.

Emerald’s spaghetti junction of cooling system pipes running between the hot water tank and the engine

The Coolant Water Went In, The Coolant Water Came Straight Back Out

Bear with me, as all of this description is leading up to the next problem with the engine.

With all the coolant pipes reconnected, I positioned myself by the engine ready to look for leaks. As Colin poured water into the header tank above, I could hear soft trickling sounds coming down towards the radiator cap. But, when the water arrived, it immediately began to bubble out of the cap. I called up to stop.

The first problem was to remove the cap itself. Something was preventing it from being pushed down to disengage the lugs that stop it coming off. It took brute force to finally free it.

The second problem was the seal. It looked wrong and when Colin took it off the issue was obvious. Rather than being soft and flexible, it had shrunk and become hard and brittle. Another lesson for us in leaving engine parts in storage for some time in warm places.

At least we hadn’t put any of the poisonous coolant mix in at this point, so we only had fresh water to mop up.

And our luck was in as it was just the seal that needed replacing rather than the whole hose connection kit as the seal cost less than €10, and the kit would be over €250. The Volvo parts dealer in Madeira responded the same day to our query about a replacement seal. They quoted 2-3 days for them to receive it, another day on to us. We had it our hands a week later.

during our DIY boat engine rebuild we discovered the radiator cap seal had perished due to being stored in a warm, dry
The old radiator cap seal on the left, compared with the new one on the right

The Throttle and Gear Linkages

The throttle and gear linkages connect the control levers at the helm to the engine. They run down through the steering binnacle, and exit through a hole below it, in the engine room ceiling. From there, they then wrap around the walls of the engine room and down to the connection points on the engine itself. We keep them out of harms way by cable tying them to points within the engine room.

The biggest issue was feeding them down through the binnacle without the cables snagging on something. One cable fed down first time, the other needed a bit of jiggling to get it on its way.

The black throttle and red gear cables feed out through the steering binnacle, then wrap around the engine room to their respective connection points

The Fuel System

After connecting the fuel in and the fuel return pipes, Colin needed to bleed any air out. There is a small screw on the secondary fuel filter housing, and with this loosened, pressing the priming pump pulls fuel through from the diesel tank. As soon as diesel starts bubbling out of the screw, then any trapped air is expelled up this point. Colin tightened the bleed screw back down.

The fuel pump in silver, the priming pump to the right with the bleed screw above it

The Test Run

On the day of the test there was a bit of setting up to do. Emerald is still on the hard, so we would be unable to pull in sea water to perform the job of raw water cooling. Instead we ran a hose in from a tap outside which we used to fill a big bucket sat next to the engine. Colin disconnected the raw water uptake pipe from its seacock and put the open end into the bucket. With the engine running, it would suck in water and we could use the hose to keep the bucket topped up.

Emerald has a lovely big cockpit, with long benches down either side. Under one is access to a huge locker. The starboard side opens up to give access to the corridor which runs alongside the engine room. This is where Colin would be and with the lid lifted we expected to be able to communicate and hear each other.

We were both jangling with nerves. We tried to focus on the positive of it starting rather than the negatives of what could go wrong. But the problem with that was that we needed to talk through what could go wrong and have a plan for each go wrong scenario.

Filling the big blue bucket with water to act in places of salt water for engine cooling

Diesel Engine Runaway

The worst possibility was that we’d have a diesel engine runaway.

What Is a Diesel Engine Runaway?

This situation occurs when the engine uses an alternative source of fuel other than diesel. An example is oil which could leak into the combustion chamber, perhaps through a bad seal. The engine would then use the oil for its fuel source. It would run faster and faster, until ultimately there is mechanical failure and the engine goes bang.

Terminally bang.

In this situation, turning off the diesel supply would have no effect because the engine has found an alternative fuel source. The way to stop it is to cut off the air supply and we had a bag ready to cover the air intake if necessary.

We got into our respective positions. I was up in the cockpit by the control panel, Colin was below by the engine room. First we had to bleed the fuel through past the injector pump. To do this, the injectors are cracked open and we turn the engine over. This causes the camshaft to turn and engage with the fuel injector. The engine won’t start as the injectors are disconnected, but fuel will flow through to them and push out any trapped air. I turned the start key past the first position to the start position. I did this a few times until Colin was satisfied that enough diesel had pumped through. He then tightened each of the injectors.

The Moment of Truth

For the first test, the plan was that I would start the engine using the key. Colin would then stop it using the stop lever on the engine itself.

I turned the key two clicks and the engine turned over a few times, coughed a couple of times, before firing into life. But we weren’t able to enjoy this moment, as it was revving like crazy, much more than I’d set with the cockpit throttle control. It also wasn’t stopping. As I dashed over to the open cockpit seat to try and talk to Colin, I pushed the throttle back to off. The engine noise didn’t change. I looked down at Colin, but the noise made talking impossible. So, I quickly returned to the control panel and turned the key to off. I held it there for what seemed like an interminable time, but the revs did seem to be slowing. At the same time Colin was closing off the diesel supply. And then, thankfully, Victor went quiet. Between us we had stopped it.

Our hearts were racing. It took a few minutes before we were able to process and review what had happened. The engine had started, this was great! But it had started with far too many revs. Then when Colin had used the stop lever, the engine revs had increased rather than the engine stopping. This was definitely not good. However, we had stopped it before any damage was done.

What Next?

We don’t think we had a runaway because we were able to stop the engine by starving it of diesel. We suspected that the culprit was the engine stop lever because it had done the opposite of what it should. When Colin had moved the lever to the left, instead of stopping the engine like it is supposed to do, the engine had run faster. Also, its range of movement was very limited.

We went to look through the pre-rebuild photos, and noticed something else strange about the stop lever. Instead of it being over to the right, it was pointing straight down. We checked the engine manuals to make sure we hadn’t tied it off in the wrong direction when we refitted the timing case. But no, we had followed all the steps correctly.

The throttle linkage is a tiny lever that connects the throttle control to the fuel injector pump. Its job is to regulate the amount of fuel going into the pump. Our guess is that it and the stop lever were somehow tangled and hindering each others movement. So, before we’d even started the engine, the throttle linkage was being pushed into the wrong position by the stop lever. Hence more revs than what we had set with the throttle control in the cockpit. Then, when Colin pushed the stop lever to turn off the engine, it was pushing the linkage in the wrong direction. This resulted in even more fuel being supplied instead of none at all.

image shows the stop lever in the wrong position on a Volvo Penta D2-75 boat engine
The stop lever is pointing down rather than being positioned to the right

Resolving the Tangle

Colin removed the injector pump in the hope that there would be enough space to get into the timing case and detangle the two levers. But unfortunately, there just wasn’t enough space.

We glumly accepted that the timing case would have to come off for the third time. On the bright side, at least we had a spare gasket kit on board. But the big question was: would we be able to do the work with the engine where it was, or would we have to get it lifted out again?

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Thank you from Nichola & Colin

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