Grampian SailboatsThe Yanmar 8 hp Diesel
The little single-cylinder diesel in many inboard Grampian 26s and other small sailboats of the 1970s and '80s.
In the Grampian 26
Most Grampian 26s were built for an outboard, many in a well. The inboard boats came with a variety of engines over the years: Palmer gasoline engines in the first ones; a Volvo Penta MD1B diesel or an Atomic 4 as factory options in the early 1970s; and later, 8 hp Yanmar diesels. In our Owners Registry, six Grampian 26s list a Yanmar and eleven an Atomic 4 (November 2026).
No record we've found says which Yanmar the factory fitted. Since the Grampian 26 was built until about 1977, an original Yanmar would most likely be a YSE8. A later YSM8, 1GM, or 1GM10 is most likely a replacement.
Read the plate on your engine to know which model you have before you buy parts or a manual: the YSE8, YSM8, and 1GM10 share few parts. Please add your engine's model to your registry entry. Together, owners' entries will show what the factory really fitted.
The 8 hp family
| Model | Built | What it is |
|---|---|---|
| YS8 | Before the mid-1970s | The older horizontal single. Sometimes sold as a YSE8, so check the plate. |
| YSE8 | About 1973 to 1977 | Horizontal single cylinder, raw-water cooled, hand crank or electric start |
| YSB8 | About 1976 to 1978 | A lighter development of the YSE |
| YSM8 | About 1977 to 1981 | The last of the horizontal singles, lighter again |
| 1GM and 1GM10 | From about 1980; the 1GM10 from about 1983 into the 2000s | A compact, upright single cylinder: the common modern replacement |
Sources give slightly different years for each model.
Specifications
| YSE8 | 1GM10 | |
|---|---|---|
| Cylinders | 1, horizontal | 1, upright |
| Bore and stroke | 75 × 75 mm (331 cc) | 75 × 72 mm (318 cc) |
| Power | 8 hp at 3,200 rpm (7 hp continuous) | 9 hp at 3,600 rpm (8 hp continuous at 3,400) |
| Weight | Much heavier than the 1GM10 (figures vary) | About 71 kg (157 lb) without the gearbox, about 76 to 81 kg with it |
| Cooling | Raw water, by a rubber-impeller pump driven by a belt | Raw water, rubber-impeller pump |
| Starting | Electric (12 V) with or without a hand crank, or hand crank only; decompression lever | Electric (12 V) with a hand crank; decompression lever |
| Gearbox | Wet single-plate clutch with a 2:1 or 3:1 reduction | KM2P-1: 2.21, 2.62, or 3.22 to 1 forward |
| Injector pressure | 160 kg/cm² (about 2,275 psi) | 170 kg/cm² (about 2,420 psi) |
| Valve clearance | 0.2 mm, intake and exhaust, cold | 0.2 mm, cold |
| Oil | By temperature, as the manual's chart gives; fill to the dipstick | About 1.3 L; gearbox 0.3 L |
The YSM8 shares the YSE8's 75 × 75 mm cylinder and 8 hp at 3,200 rpm, with a 2:1 reverse gear, and is lighter. The YSE8 and 1GM10 figures here are from Yanmar's own manuals and data sheets; others from dealers are noted in the sources.
The drive coupling and shaft
The engine drives the propeller shaft through a coupling: two flanges bolted face to face, one on the gearbox and one on the shaft. Sizes vary with the model and the boat, so measure the shaft and the flange before ordering a coupling or fitting a different engine, and have the alignment checked whenever the engine or its mounts are changed. Worn or collapsed engine mounts cause vibration and throw the alignment off.
Buying a used one
- Ask for a cold start. A healthy single-cylinder Yanmar starts within a couple of turns. Hard starting, or lots of smoke, means trouble.
- Watch the exhaust for water as soon as it runs: no water means a cooling problem.
- On a sea trial, run at about 80% of full rpm for a while, then at full throttle for ten minutes or so. It should reach its rated rpm without overheating.
- For an older engine, ask for a compression test and an oil analysis. A marine surveyor can do an engine survey for a few hundred dollars.
- Look for rust and salt scale around the cylinder, exhaust elbow, and water passages, especially if the boat has been in salt water. Check the mounts, the belt (on the YSE8), and for oil or fuel leaks.
- Check which model it is (the plate), and whether parts are still available for it. Parts for the 1GM10 are much easier to find than for the YSE8.
- Expect modest power. 8 hp moves a 26-footer well in calm water but struggles against strong wind and waves. A three-blade propeller helps some owners.
Care and common problems
- Cooling: these engines run lake or sea water straight through, so salt and scale build up over time. Check the seacock, strainer, and impeller; replace the impeller every year or two and carry a spare. On the YSE8, check the tension of the belt that drives the water pump.
- Zinc anode: the YSE8's maintenance schedule includes renewing the zinc anode in the cooling system.
- Exhaust elbow: the elbow where cooling water joins the exhaust scales up and corrodes, and a failed elbow can let water into the cylinder. Look at it, and replace it if it's badly corroded.
- Fuel: after any work on the fuel system, bleed the air out of it, or the engine won't start. A weak injector shows in the colour of the exhaust; one at too high a pressure makes the engine knock.
- Hard starting: use the decompression lever to spin the engine up before cranking. Owners advise that if it fires but dies, suspect fuel; if it never fires, suspect compression. During long cranking, close the raw-water seacock so water doesn't fill the exhaust, and open it again as soon as the engine runs.
- Clutch: the gearbox has a wet clutch; slipping is a sign it needs attention.
- Overheating: check for water flow at the exhaust, then the seacock, strainer, impeller, and elbow, and flush the system now and then.
Manuals and data sheets
- Yanmar YSE8 service manual on ManualsLib (free to read)
- Yanmar YSE12 service manual, for the YSE series, on ManualsLib
- Yanmar YSB8 and YSB12 operation manual on ManualsLib, the closest free operation manual for the YSE8
- Yanmar 1GM10 operation manual on ManualsLib
- Yanmar 1GM10 data sheet (PDF)
- Paid copies: the YSE8 and YSE12 operation manual and service manual (eManuals), and Clymer's Yanmar Diesel Inboard Engines, 1980–2009 for the 1GM and 1GM10.
Parts and help
- Yanmar dealers: find one near you with Yanmar's dealer locator (choose Recreational Marine). In Canada, Diesel-Bec of Boisbriand, Quebec, is a Yanmar distributor. In the US, Mack Boring & Parts is the longtime Yanmar marine distributor.
- Parts for the older engines: dealers can still find some YSE and YSM parts by part number. Specialists such as Marineparts.fi (YSE8 parts) and AB Marine Service in the Netherlands carry parts and used engines. Check part numbers against your engine's serial number; sources list different numbers for some parts, like the impeller.
- Forums: owners of these engines share a lot on SailboatOwners.com, the UK's YBW forum, and Australia's Seabreeze.
- Video: how to hand-crank a YSE8 (YouTube).
- Fellow Grampian owners: ask in the registry, and see our Engine FAQ and Grampian 26 FAQ.
Sources
- Yanmar: YSE8 service manual, 1GM10 operation manual, and 1GM10 data sheet
- Grampian 26 reviews: SAILING (2008), Practical Sailor, Canadian Boating, and Wikipedia
- Model years: Marinshopen and Yanmarcenter (Sweden)
- Buying and care: Cruising World on engine surveys, BoatUS on surveys, Sail on overheating, and owners on SailboatOwners.com and YBW