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farquart

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We have a Yanmar 3GM raw water cooled engine. We noticed last season that we seemed to be losing/burning rather a lot of oil. I have read past posts and have come to the conclusion that we are either using the wrong oil or we have a problem with the rings.
What is the correct oil to use?
I am not a mechanic but can do a basic service, so how easy is it to check the rings and do whatever needs to be done. Is this an expensive job if we had to get a mechanic to the work, bearing in mind we are in France? /forums/images/graemlins/confused.gif
 

farquart

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There is some black smoke when we start up but I thought that was pretty normal. Have noticed a little sooty stuff coming out with cooling water sometimes too. Dont think the oil is leaking into the bilge. The engine is about 15yrs old, we think.
 

steve28

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So long as its a mineral based diesel oil its fine, do not use the synthetic or semi synthetic.
I made this mistake and found myself in the same position. The result was a set of new rings and a skim
 

farquart

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The air filter is fine, havent had the injectors serviced though.

How do we tell if there is something wrong with the rings?

Do I take it we shouldnt be worried about the amount of oil we get through so long as we are using a mineral based one?
 

steve28

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I would just change the oil and keep an eye on the amount you are putting in, the last season mine was in comminsion i went through 4 pints, it didnt produce very much smoke that could be seen in daylight, at night however it could be seen against the sternlight (and it wasnt steam).
A compression test did not reveal any undue readings but when the engine was stripped down it was obvious comparing the new and old oil scrapper rings

i fitted new pistons and rings as it worked out better value


steve
 

pappaecho

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Easiest way to check both valves and rings, and therefore state of the wear in the engine is to get a compression test done - you could combine when changing the injectors. As other posters have indicated dont put synthetic oil into an old engine which was not designed for it.
 

farquart

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Does anyone have a rough idea of how much it would cost to replace the pistons and rings in a Yanmar 3GM?

Also is it easy to do yourself (bearing in mind limited engine knowledge) or would it be a better idea to get a mechanic to do it (also bearing in mind limited funds!)
 

oldharry

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Black or white smoke on start up is normal enough. Only if you get black smoke on load do you need to start worrying about it. It is caused by incorrect fuel/air ratio, but many diesels get more fuel than air when starting up so give a puff of black smoke. If it occurs when the engine is running normally then either the injectors are worn allowing too much fuel in or the air inlet is restricted. White smoke occurs when the engine is not firing properly, and is a mist of unburnt diesel.

If the engine is actually burning oil, you will get blue smoke same as from a worn out car. It is not always easy to tell the difference between white diesel mist, steam from a hot exhaust, and blue oil smoke.

I disagree with Pappaecho, a compression test will tell you very little about the state of your rings and pistons because the intial compression is so high anyway. The quickest way to test for worn rings/bores is to check the level of blowby: this is done very simply by blocking off the crankcase breather, and checking whether the crankcase pressure rises over a 10 second period as you run the engine at fast tickover. The easiest way is to ensure there are no other breathers open, remove the oil filler cap, and block the oil filler off holding a rag firmly over it. Release it after 8 - 10 seconds and if there is a whoosh of air or fumes, then you have ring troubles - or worse! What is happening is that the compression is escaping past the rings into the crankcase, where with no breather it builds up pressure. Take care not to do it too long or you will blow the oil seals out and give yourself a lot more work!

Unless you can do the work yourself, new pistons, rings and a rebore are rarely economically viable because of the labour cost: after all at the end of it you still have an old engine - so what state are the crank and mains in? Is the oil pump still good? Is the injector pump still up to scratch? is the camshaft worn? Are the valves still seating properly? are the valve guides worn....the starter, the alternator, the SW pump, the FW pump, etc etc etc. By the time you have done all that, you will have paid out near the cost of a new engine. Even doing it yourself its not cheap!
 

bonny

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Changing the rings involves a bottom end strip down to undo the big end bearings, and also removal of the cylinder head to extract the pistons & con-rods. Unless you can remove the sump to gain access to the big-end nuts (unlikely) then this involves an engine out job. You would need to be very mechanically confident to to this yourself and since you are asking what's involved then I would recommend that you find a suitably trustworthy friend to help you or employ an engineer.

I have done similar jobs, including re-bores & crankshaft regrinds myself on cars, 4x4's & m/cycles and this cost around £60/cylinder (about 5 years ago) but as I did all the stripdown/assembly myself this was only the parts cost. Labour costs will amount to much more than this and I would expect to be billed for about 2-3 days labour.

Also bear in mind that on strip down your mechanic may also recommend other things are changed, reground or whatever.

About 10 years ago I had an Isuzu Trooper 2.8TD and the gearbox broke. I considered doing it myself but everything looked big & heavy so I entrusted a 4x4 specialist to fix it. They changed the input shaft (£130 part) and billed me £1100 for 48hrs work. It went but whinned like buggery. I finished up doing it myself and putting in a new layshaft aswell (£280 part). To get the layshaft out I had to remove the input shaft thereby doing a bigger stripdown that the garage. I had the vehicle back on the road in 24hrs from start to finish, including getting the part. I challenged them to no avail. How they can justify 48hrs with access to a hoist, specialist tools etc when it took me less than 24hrs on my back crawling under wheel ramps with only slightly above average tools I can only wonder. Since then I'm a confirmed DIYer.

I would get a proper diagnosis done and a few quotes, not easy being in France.
 

Stemar

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Given the cost of parts and labour, (even if you do it yourself, it still costs in time spent getting covered in oil, skinning knuckles, etc instead of sailing) if your engine's running OK and starting OK, may I suggest that, as they say over there, "Il est urgent de ne rien faire"

If the engine's 15 years old, some oil consumption isn't unexpected. Stripping the engine down can reveal a lot of other work that needs to be done - more time, more money. At least consider whther you wouldn't be better off putting cheap oil in for now and saving your pennies for either a complete reconditioning of your engine or its replacement when it is no longer runs & starts OK
 

corncob

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My advise is to remove the exhaust elbow. check to see if the inner exhaust section has vanished? If this is so, sea water will be allowed to slosh around the exhaust manifold corroding the exhaust port and through into the rocker cavity, allowing oil to escape. This is common on old 1 and 2 GM's, not so common on the 3GM You will need to change the cylinder head and manifold. Check the elbow as part of your service shedual. Use 15w40 oil, better still use the official Yanmar oil. The engine was designed to use SAE30 APICC its still available, Comma 30HD springs to mind check around?
 
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