Yanmar rebuild or replace?

D

dave_gibsea

Well-Known Member
Joined
12 Feb 2002
Messages
270
Location
SW London
Visit site
Hi,

I have a Yanmar 1GM10 which is about 17 years old, hours are unkown but I would guess 50 to 100 per year at most.

The engine starts well and has compression but above half throttle it emits a lot of black smoke and uses a bit of oil (around half a pint in say 10 hours). It doesn't seem to produce all the power it should and the symtoms are the same when the prop and the boat is clean so it's not about foul props.

I am thinking of rebuilding the motor this winter. I have built all sorts of engines from jap motorbikes to classic MG cars but I have never done a diesel. The price of spares looks horrific and I was wondering if anyone has done this and what it cost. Were any special toold needed? I'm thinking of rebore, new piston, valve guides and maybe new main and big-end bearings.

Thanks,

Dave
 
I think PBO , 3-4 years ago, did a full length feature article on a diesel rebuild and compared the costs with a replacement unit. This might be a good thing to get a copy of.
 
OK so diesels have to be pretty robust to take the compression they need. But otherwise, what's so different from an old automotive/agricultural design? I don't think you can presuppose too much about its condition until you have the top off and maybe the piston out. It used to be common to glaze bust motorbikes and fit new rings to pep them up again. That may be all that's needed here too!

Of course, getting the injector and pump serviced is likely to improve things quite markedly - maybe even curing the minor problems altogether.

Best of luck,
Rob.
 
If it has done 100 hours per year for 17 years, that is only 1700 hours. My bigger Yanmar has done about 4700 with no oil used between changes, and no untoward smoke. Unless oil changes have been seriously neglected over the years it should be in very good shape as regards the main and big end bearings. Lightly used engines are often in worse state due to neglect than heavily used ones, but given the low hours it should definitely be worth stripping down and rebuilding.
 
Definitely have a go at rebuilding. Parts may appear expensive, but can be sourced from the US at lower prices. However, remember that a new engine is £2k+ so you have lots of leeway.

They are very simple and easy to move around. If possible lift out of the boat complete with gearbox. The lifting ring is well placed. I used a 2*4 across the companionway plus my mainsheet to lift. It is light enough for 2 people to manhandle it off the boat.

I built a wood cradle to hold it steady on my workmate at home which makes everything easy to get at.

Your symptoms suggest worn rings and/or worn valves. You could take the head off while the engine is in the boat to check out - you may find just a head overhaul will do the trick.

If you do decide to do the works get the official Yanmar manual from a Yanmar dealer. Has everything you need to know. In addition to the "hard engineering" bits, check the exhaust manifold for corrosion of the inner wall. replace the water pump bearings and seals and check the external oil pipes for corrosion and replace if necessary. Replace all the water hoses and the anode, which will give you access to the water jacket to check for deposits. These things are much easier to do when the engine is out.

Good luck.
 
Six years ago I had the mechanic rebuild the Yanmar YSM8. Including a new alternator, rings, big end bearing, welding a cracked cylinder head, etc, it cost $2220. The engine is about 30 years old, hours unknown, the boat was 20 years old.

At a boat show about 3 years ago, a new 1GM engine, cost $7100. So no comparison really with the costs - if it's only wear from age, and not damage, then an inspection could assess the likeliness of a successful rebuild, and the economic figures would follow from that mechanical assessment.

Perfect reliability ever since, apart from the starter battery ev. 3 years.
 
Thanks for the helpful stuff everyone. I should have mentioned that I have had the exhaust elbow off and de-coked the port, I have had the injector serviced and replaced the air filter. I have also re-built the water pump and replaced all the hoses.

Thanks Dave
 
Have you looked into the possibility of it being underpowered for the prop?
From what you've had done it sounds as though there's a chance it could be getting overloaded, although the oil consumption is rather high. Are there any leaks?
 
Check right the way through the exhaust system. The Vetus flexible pipe will delaminte over time and collapse inwards. From the outside it will look fine. The resulting constriction will cause back pressure at higher revs. The result is that the engine doesn't achieve its 'normal' rev range, unburnt fuel gives the dirty horrible exhaust.
 
If the exhaust is OK i would suspect glazed bores. Sounds like the engine has been lightly used, this leads to blocked exhausts and glazed bores. First thing I would do is use this product or its equivalent - www.costeffective.com.au. It is expensive for snake oil but it gives excellent results. Follow the directions with the doses and give the engine a solid work out. Results are noticeable after only a few hours.
 
[ QUOTE ]
Check your exhaust elbow first. That can get clogged and cause some of the symptoms you describe - if you are lucky that may be all that is needed for another couple of years.

[/ QUOTE ]

I second that. If the elbow corrodes its possible for sea water to enter the cylinder head and corrode that too.
 
If you are happy to strip engines down and would find it an interesting winter project, I would go for it. You will save a lot of money
 
You must log in or register to reply here.

Share this page

Top