The DIY Restoration of a Small Yacht: Getting in and about the wee engine (#2)

seb-profile-photo-ytSeb, originally from Portsmouth in Hampshire, is the Sales Supervisor for the Gael Force Marine Megastore in Inverness.

He has agreed to write a series of posts following him and the restoration of his 26 foot, 54-year-old fibreglass yacht.

Catch up with his first post if you haven’t read it already.

Estimated reading time: 10 minutes.

BLOG POST #2: First look at the engine – a Yanmar 1GM10.

I must preface this post by stressing that I am no mechanic! Mistakes will inevitably be made and at times more knowledgeable readers will no doubt be left pulling their hair out at my incompetence!

The engine is among the most critical (and expensive) pieces of equipment on a boat, so it would, of course, be prudent to give it a full inspection and test run before any prospective purchase.

In my case the boat was priced very low and had not been on the market for long, so a quick visual inspection and making sure the engine turned over and had compression was enough to satisfy me that I should take the plunge and make an offer on the boat.

The engine in question is a Yanmar 1GM10: an 8hp, single cylinder, raw water-cooled diesel engine.

These small diesel engines are relatively simple beasts, so armed with the Yanmar workshop manual and the excellent ‘Boatowners Mechanical and Electrical Manual’ (a book every boat should have on board), I felt confident enough to service the engine and carry out some basic fault diagnoses.


My aim was simply to get the engine started and give it a basic service including oil & oil filter change, primary and secondary fuel filter change and water pump impeller change.

I will be temporarily removing the engine at some point in the future so a full service will be carried out then. However, for now, I just wanted to make sure it wasn’t a non-runner and also ensure it was properly laid up until I do remove it from the boat.

Fuel Line

Clean fuel is critical to the smooth running and longevity of any diesel engine, so before I even attempted to start the engine I wanted to get rid of the 2-year-old diesel and replace the primary and secondary fuel filters.

The fuel tank is fibre-glassed into the Lazarette and was about a quarter full of diesel. This was not a good sign given that a proper layup would require the tank to be left either full or empty.


I managed to syphon off what I thought was most of the diesel into an old can. After I’d done that, I went down below to catch the ‘last little bit’ in a suitably sized container by taking the hose off the engine.

The fuel hoses were all rock solid with age so there was no chance of pulling it off the hose tail, but given that there was only a tiny remnant of fuel left in the tank, I decided to cut the hose and just go for it.


My puny container was overflowing with fuel in seconds and the mild sense of surprise at the diesel’s rate of flow I experienced soon turned into all-out panic as I scrambled around trying to find more containers.

I tried clamping down on the hose, but it was too hard and it just wouldn’t close up! I jumped up into the cockpit and contorted myself into some unnatural position in the cockpit access hatch to reach the ridiculously inaccessible fuel shut-off valve at the bottom of the tank.

By the end of all of that, I struggled to find something on the boat or myself that wasn’t covered in diesel and there was about 5 litres of the stuff in the bilges.

I’m not sure how I so heavily underestimated the amount of diesel left in the tank, but either way, I still had to get rid of the last bits in the bottom before putting fresh fuel in.

Rather than go through the same nonsense with containers and spilt diesel, I decided to use a Pela Oil Extractor to suck out the remaining diesel from the bottom of the tank. As it got down to the last dregs, an alarming amount of black gungy sediment came up.

I didn’t really have time to give the tank a full flushing out so I just sucked out what I could, put 10 litres of new, clean diesel in and left it overnight for any sediment to settle back to the bottom.

While the fuel shut-off valve was closed, I drained the fuel line and changed the filter element in the Delphi water separator. This was straightforward enough, though it was obviously full of diesel and the entire assembly needed a thorough clean. I also replaced the old fuel hose that I’d cut with a new piece and fastened it with Jubilee clips.

Next up was the secondary fuel filter which is on the engine itself. To cut a long story short, I failed to undo the nut holding the fuel filter assembly in place.

It’s notoriously difficult on these engines and I didn’t want to waste time on it given that I only planned to run the engine for a short test period.  I didn’t want to risk damaging it by trying to undo it without the proper tool either.


The last thing to do on the fuel line was to purge all the air in it by ‘bleeding’ it. On the Yanmar 1GM10, there are three bleed points where you must sequentially open them and pump fuel through until pure diesel with no air bubbles comes out.

Lubrication System

To remove the old oil, I used the Pela Oil Extractor via the dipstick hole and then opened the sump drain nut to drain out the last of it. I poured in some new oil to try and flush out any crud that was sitting in the bottom of the sump.

Removing the oil filter was surprisingly easy – I was able to do it by hand with ease. I then put a little smear of engine oil on the o-ring of the new filter and screwed it on hand tight.


When filling up with oil, a top tip from the Gael Force mechanics is to always fill it to the dipstick rather than putting in the amount specified in the engine’s manual. This is because there will always be some residual oil in the engine so putting in the specified amount will result in overfilling the engine.

I didn’t touch the gearbox oil as I won’t be running the engine in gear for this test. I will change the gear oil before she gets put to use again though.

Cooling System

The Yanmar 1GM10 is raw water cooled, which means that it pumps seawater directly around the engine rather than using it to cool coolant via a heat exchanger. It’s a simple system but it does have some major drawbacks.

Any build-up of deposits on the walls of the cooling system can greatly reduce its cooling efficiency. Additionally, having salt water in direct contact with the engine can result in serious galvanic corrosion if the anodes aren’t replaced regularly.

In a draw on the boat, I found several knackered impellers, which is an obvious clue that there’s some problem with the water pump. All I wanted to do for now was replace the water pump impeller, so I’ll have to monitor that going forward.

At some point in the past, someone had fitted a Speedseal water pump.


As you can see, the water pump is conveniently situated behind the crankshaft v-pulley, so having the Speedseal is great as it means that it can be removed without tools and without the need for replacing a gasket each time.

If the previous owner was having a problem with going through impellers I can see that this would have been a priority upgrade (but not a solution to the problem)!

I took a photo of the old impeller before removing it to make sure I put the new one in with the ‘fins’ in the right direction.


The old Impeller came out with minimal coaxing from my pliers, but I was quite dismayed by the amount of crusty, salty gunk in the water pump. If the engine had been properly serviced that would have been cleaned out.

After doing a sub-standard, rushed job to clean out the water pump housing, the new impeller went in without any issues. I smeared in the glycerine lubrication that it was supplied with before popping it in with the fins bent the correct way. I’ll remove and clean up the water pump more thoroughly when I take the engine off the boat.

With the Speedseal cover plate replaced, it was finally time to get the old girl running.

The yard where the boat is currently lying has no water supply, so to get water to the engine for cooling I had to go to the nearest public amenities and fill up a bucket – far from ideal!

After my jaunt to the loo and with a fresh bucket of water on board, I disconnected the water inlet pipe from the seacock and poured as much water as I could into it to try to reduce the risk of getting an airlock in the cooling system.

The Yanmar 1GM10 has a hand crank and with just a single, tiny cylinder it would surely be no difficulty for me to hand start it… or so I thought.

No matter how much momentum I got spinning the crank handle, as soon as I released the decompression lever it bounced back from the cylinders’ compression. My machismo was severely dented until I read on forums that it is pretty much impossible to hand-start. That’s a disappointment as it means I’ll have to keep two batteries on the boat – one exclusively for starting the engine.

Thankfully the batteries already on the boat had some juice in them (there is no power available in the yard either) so I switched the key and pushed the button and… the engine turned over but made no attempt at firing.

It turns out I’d missed a critical step in the bleeding process. On the final ‘bleed’, between the high-pressure pump and the injector, the throttle must be in the fully open position when pumping fuel through. I did this and tried starting her again.

Amazingly, after two years without use, the little Yanmar spluttered reluctantly into action and quickly settled into a steady idle – she sounded great!

There wasn’t any water being pulled through, however, so I quickly pulled the stop switch and scratched my head. I whipped off the water pump cover and a reasonable amount of water poured out, so it was trying.

After a few more failed attempts at pouring water down the inlet hose to get rid of airlocks, I decided it would be far easier to sort this out when the boat was close to a source of water so I could get a hose onto the engine.

My main concern was that salty deposits had totally clogged up the cooling system but I just didn’t have time to test that theory as the sun was setting on a Sunday evening.

All in all, I’m really happy that I managed to get the engine started and that she sounded sweet without any concerning smoke coming out of the exhaust. The cooling water problem is frustrating but I’m not going to let myself worry about it until I’ve been able to have a more thorough inspection of it.

What have I learned? Try harder not to get diesel everywhere!


My next priority is to get the mast down. If I can get access to the yard’s crane this month that’s what the next blog post will be on. If anyone thinks it can be done without a crane, please advise in the comments section!

If not, I’ll talk about the progress I’m making with gutting the boat – it’s amazing how much ‘stuff’ can be fitted onto a 26-foot boat!

5 thoughts on “The DIY Restoration of a Small Yacht: Getting in and about the wee engine (#2)

  1. Charles McGrory says:

    Hello Seb
    Great to read of your work. I am refitting a Rival 32 which benefits from having a 600 hr Yanmar 20hp. Am learning how to maintain the engine.
    Later I am about to rewire the boat with new circuits. The great benefit here is that all the old wiring is strung out mostly in sight.
    A work in progress is raising the waterline and boot-top which is going reasonably well. I will paint with International Toplac gloss.
    Happy to send you any photos of this work in progress.
    And… have just unloaded the boat and have filled a whole room with what was on the boat. No wonder she was floating low.

  2. Bruno Opperman says:

    Hallo! Can I ask why are going to remove your engine? It seems to me that, as you got the engine started and it runs,If it ain’t broke don’t fix it-or is there a problem with the transmission?
    /propellor shaft/propellor? any how,good luck With your refurbishment-James withers Knows all about me

    • Sebastian Sutherland says:

      Hi Bruno,

      I want to remove it to clean down and repaint the engine compartment. It will also give me a good opportunity to have a much closer look at the engine – access isn’t great on the Invicta 26!

      Thanks for the comment!

  3. h28sealeg says:

    If you are looking for cheaper filters. FRAM PH6811 oil filter fits the 2GM, and FRAM C1191PL probably fits your water separator. I’ve used them both for years. Available at most motor factors.
    Check your thermostat if it’s not drawing water, probably crusted up with salt crystals if it hasn’t been used. Also I had problems drawing from a bucket, any chance of air getting in ( loose jubilee clips or hardened hoses) and mine wouldn’t draw from a bucket. Totally different when it’s in the water and your intake has about a foot of water to provide a head!
    Interesting to see how you progress.
    Some photos of general condition would be nice.
    Have you ever looked at Off Center Harbour website. Some inspirational stuff on there for smaller, older boat owners.

    • Sebastian Sutherland says:

      Thanks for the great advice!

      That’s reassuring to hear that drawing the water from a bucket isn’t easy. Still, I’ll get the thermostat off next time I’m down there to have a look.

      Great tip about the filters too – thanks!

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.