Advanced Search

— Forum Scope —

— Match —

— Forum Options —

Minimum search word length is 3 characters - maximum search word length is 84 characters

Replacing Engine on Skuthen
2nd March 2019
12:01 am
Roger Troup
Forum Posts: 3
sp_UserOfflineSmall Offline

I fear corrosion may have taken its toll on my Yanmar 1gm.

I have only had her for a season and the engine runs very well however the engineer servicing her over winter is adamant she needs an uneconomic amount of work due to corrosion. If I must replace the engine a like for like swap seems to be the obvious least expensive option however that then leads me to question whether I should consider something with a little more power. Money is very tight so my question is does the Yanmar 1gm have sufficient power for a wooden twister? Any advice gratefully received.

2nd March 2019
2:10 pm
Nick Roe
Forum Posts: 16
sp_UserOfflineSmall Offline


The 1GM10 in Brigand started playing up and after quite a bit of thought over a couple of years, we replaced it last year with a 20 HP Beta. The extra power is very noticeable and makes a big difference, so I think that it was a good decision. 

On the other hand, we had lived with the 1GM10 for around 10 years and the engine had been in the boat for about 15 years before we bought her, so clearly the engine sufficed. 

I suppose it depends on your circumstances.  We are based in the Solent, and there are quite strong tides / currents around here, so we found that the engine struggled, particularly if you were trying to punch into the short, steep waves that you get with wind against tide. I also think that our engine was a bit tired, so we were not getting the power that the engine had when new. 

Overall, we felt that it was not worth spending money on the old engine to get it sorted, when even with full power, it was underpowered for the boat. 

I also felt that the engine had some design flaws, and the parts are expensive:

-  the exhaust elbow has a tube in a tube arrangement where the raw water injection is which corrodes through, and then allows water back into the cylinder head. This the corrodes the valve seat so that you get no compression and the engine will not run. We found this problem soon after we bought her and spent £650 for a new cylinder head, £200 for a new exhaust elbow, plus gaskets, etc. So about £1000

-  the water pump shaft seals fail and the shaft corrodes, so it leaks. A replacement shaft is over £100, and a new pump is several hundred. 

I see that you are saying that a like for like would be the least expensive. I think that you will find that there is not much difference in the coat of a new 1GM10 and a Beta. The extra cost would be in making changes to the engine bearers to suit the different engine. ( I should say that we bought a used Beta engine, but decent used engines are like hens teeth, particularly at this time of the year). As you say that the engine runs very well, perhaps worth running it for another season whilst looking out for a replacement?

If you look on the Beta website, there are some photos of a couple of Beta installations in Twisters, including a wooden one. I don’t know where you are based, but the photos are from the Beta ag3nt in Fowey in Cornwall. 

If it is of any interest, I can send some photos of our installation. 

3rd March 2019
12:17 pm
Roger Troup
Forum Posts: 3
sp_UserOfflineSmall Offline

Thanks very much for this Nick,

Skuthen is moored in St Just (Falmouth) and we also have our share of strong tides. As you say although you find the extra power really useful its encouraging that you are not saying you found her woefully under powered with the 1GM

Thanks for the tip on Fowey Harbour Marine Engineers they clearly know what they are doing and as you say have fitted Beta 20's in a couple of Twisters (looks like a very snug fit). Presumably you need a new larger prop as well? Did you notice a big difference in fuel consumption?

Still very conscious of cost as even if I could find a 2nd hand Beta 20 my lack of technical knowledge makes me nervous about risking buying a problem.

But I hear what you are saying on the design faults with the Yanmar, I guess you have to keep a really close eye on exhaust elbow and water pump. 

I think I may be persuading myself to go with the easy solution of a new 1GM but I'm going to give this some serious thought and do some looking around for an affordable Beta 20's. 

Thanks again and if you do have any pics handy (dont go to any trouble) I'd love to see them.

3rd March 2019
12:48 pm
John MacMullen
Forum Posts: 61
sp_UserOfflineSmall Offline

The biggest enemy of engines in leisure craft is corrosion rather than use. I would avoid buying a raw water cooled engine if possible (and I think the Yanmar still is in this category). Much nicer to have the heat exchanger alternative and to have antifreeze/inhibitor circulating around all the busy bits! Our original Albin petrol engine's cylinder head rotted out at 25 years and the block shortly after. Replacement Vetus, bought second hand, was new in '89 so this is it's 30th year. In that time we've replaced the exhaust elbow, serviced the injectors, replaced the water pump shaft and the front bearing seal on the crankshaft. It's probably tempting fate but we are well pleased!


3rd March 2019
2:31 pm
David Hopkins
Forum Posts: 34
sp_UserOfflineSmall Offline

Ive done a bit of thinking about this too. I've currently got a 2Qm15 which must be at least 30years old. Ive decided to keep it for a year or two and then re-engine.


As far as power goes I have more than enough from what is probably a lot less than 15hp so I won't be looking for more. Weight is not really an issue either as all the newer 15s are considerably lighter (15-20%) and no bigger either. It's hard to find a raw water cooled 15 too. So really the only consideration is cost. The unit costs are all in the same ballpark so it's the installation costs that would require thought. 

Engine bed compatibility?

Will it fit my current stern gear?

Will the fuel and water lines require re-routing?

Exhaust, how much will need replacing?( I happen to have the wrong size on my engine. Should be 2inch but it has 40mm with a home made adapter so this is yes for me)

Will the throttle and gear cables require re-routing?

How big is the control panel and where will it go?

If I fit a calorifier where are the engine tappings and where would it go?

There are probably many other considerations but these are what I've thought of. The ancillary costs could end up being more that the engine cost for an engine that doesn't easily fit your current set up.



3rd March 2019
8:21 pm
Nick Roe
Forum Posts: 16
sp_UserOfflineSmall Offline

Hi Roger

We did change the pitch of the prop to suit the new power and revs ( gearbox ratio ), but the diameter remained 12”. 

The 1GM10 used nearly no fuel, and we have noticed a big increase in fuel consumption with the Beta 20. 

The other 1GM10 design problem is with the flexible mount feet which rust and then the flexible rubber detaches. This happened to us, and we replaced them with plastic poly something ones from Australia which were a direct replacement and much better. I would be surprised if you could reuse yours, and they are horribly expensive. 

I agree with a John that raw water cooling is the cause of a lot of issues, and should be avoided if possible (1GM10 is raw water cooled, and Beta is indirect, as are nearly all larger engines now). 

The Beta weight is a bit more - around 105 kg vs 80 kg if I recall, but the 1GM10 is pretty much as light as it is possible to have. 

I agree with David that the engine cost is similar, but the installation cost is much more assuming that you can reuse everything if you just swap like for like. 

The main changes that we had to make were:

- raise the height of the GRP engine bearers ( the transverse spacing is the same for both engines)

- modify the exhaust elbow to miss one of our cockpit drains

- remove the old engine water sea cock, and fit a larger one. 

-  we had to raise the top of our engine box because the engine is a little taller so it would not fit

There was also quite a bit of cost in changes to “minor” items, including new engine exhaust hose and adapters, new morse cable ( old one broken ) , new water siphon and hoses, various pipes, clips, etc

We reused the old shaft after cutting the end off to shorten it. 

The main thing is that it took a lot longer than anticipated, so we missed the start of the season. The main problem was that this was the first time that we had done it, so there was a lot of thinking, planning, pondering. 

If it is of any use to anyone, I made a rough full size 3D model of the engine so that we could play with possible locations. It was good enough to show engine height, bearer heights, etc. It has done its job for me, but I cannot bring myself to throw it away. If it of use, anyone is welcome to have it. 

I have photos of the change if would be of interest.

3rd March 2019
11:18 pm
Justin Butler
Forum Posts: 65
sp_UserOfflineSmall Offline

Hi Roger, all I can usefully add is my experience of my 1gm10.

For; it's a very simple engine. 

       You can hand start when the battery is flat.

       it runs on the smell of an oily rag.

       It has been flawlessly reliable.

       it has never felt under powered (it's an auxiliary after all)

Against; alot of vibration for this type of engine, I think the mounts must be made of jelly. 

                I'd like 30hp.

               A genuine yanmar service kit is £40. That hurts but I don't know how it compares.

I spend two or three hours motoring everytime I put to sea for a day sail,it's fair to say I put it through its paces last season. I can get 4 knots out of it into the wind and tide unless conditions are severe. I think for the reasons above and for the very logical argument you presented at the outset I'd replace like for like if I had to change it. A new 1gm will only need routine servicing for the first 15 years at least. Roquetta is a composite twister of course. Lovely part of the world St Just. I was anchored off restronguet point last summer for a night, an old haunt of mine. Maybe when I'm back there we could scull over to the Pandora?




4th March 2019
9:21 pm
Roger Troup
Forum Posts: 3
sp_UserOfflineSmall Offline

Thanks so much Nick, John, David and Justin, 

Much as Id like an indirectly cooled larger lump I've decided to go for the simplest least expensive route and swap in a new 1GM10

As Justin says it is an auxiliary engine, and as cost is a major factor, as long as I flush out the salt every winter I would hope the raw cooling is manageable. 

In 30 years time I'll upgrade to a BETA 20

I'll buy any of you a pint in the Pandora.


5th March 2019
8:37 pm
Tim Granville
Forum Posts: 11
sp_UserOfflineSmall Offline

I’ve only just come across this thread and I am in pretty well exactly the same position as Roger.  My venerable 1Gm is pushing 30 years old now but is still going.  I had the head off it again this winter and was pleasantly surprised at how little corrosion there was, even around the exhaust valve.  The thing which will ultimately kill mine is the external corrosion over the timing case, caused by a leaking water pump.  At the moment plastic metal is holding things together admirably but it won’t forever.

I too have decided that come the inevitable day I will replace like for like for all the reasons outlined above.  I’ve had the lump out of the boat a couple of times and it’s an easy job so it holds no fears for me.  With regard to performance it’ll push her to hull speed in flat water and my more ‘real world’ measure is that it will push her out of the Deben against the flood.

Marine enterprises in Dorset are advertising s/h 1GMs for £1500-£2000.  Obviously a s/h engine is a gamble but one of them looks, in the pictures, to be immaculate.

6th March 2019
5:51 pm
David Hopkins
Forum Posts: 34
sp_UserOfflineSmall Offline

Hi Tim,

I saw those engines advertised a couple of months ago and for a brief moment considered down powering to the newer of the two. Not sure what the new price is but I think I've seen an advert at £3500. Decided to stick with my current engine for now and had the professionals in Falmouth give her the once over this winter which revealed some interesting findings which have now been rectified.

If anyone wants to know what happens when you use a 1" split coupling on a 25mm shaft:

coupling.jpgImage Enlarger

your hole gets elongated and the bolt bends. 


I don't know how long ago this was fitted but it wasn't the only wrong sized component....................

sp_PlupAttachments Attachments
7th March 2019
7:25 pm
John Tetlow
Forum Posts: 96
sp_UserOfflineSmall Offline

That's nasty David!

I had one of those couplings when I bought my boat but it was the right size for the shaft so no problems there but the R&D coupling it was attached to didn't have enough flexibility for my liking so I replaced it in 2002 with a Centaflex 127 coupling and that has been fine.

DSC_0007-Copy.jpgImage Enlarger

sp_PlupAttachments Attachments
Forum Timezone: Europe/London

Most Users Ever Online: 16

Currently Online:
5 Guest(s)

Currently Browsing this Page:
1 Guest(s)

Top Posters:

Stephen Moorey: 123

John Tetlow: 96

Justin Butler: 65

John MacMullen: 61

David Hopkins: 34

Philip & Cathie Collcutt: 22

Jonathan Mutch: 17

Robert Plunkett: 16

Nick Roe: 16

Calum Kelly: 15

Member Stats:

Guest Posters: 12

Members: 174

Moderators: 3

Admins: 1

Forum Stats:

Groups: 2

Forums: 4

Topics: 184

Posts: 889

Newest Members:

Andrew Gordon, Katie Bond_1, Hugh Birley, STEFAN JAEGER, RICHARD BURNETT, Stephen and Rachael Wyse and Carter, Jim Kellaway, David Lloyd, Nick Ward, harry gregory

Moderators: Katie Bond: 42, Peter Mulville: 63, John MacMullen: 1

Administrators: magus: 0