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Old 17-11-2014, 02:27   #1
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Maintenance ambition for Yanmar YSB8


I have a Yanmar YSB8 on my 29 ft sailboat and have just decided that I want to keep it and do everything I can to extend its running life for as long as possible. It was installed in 1976. My question now is where to draw the limit on maintenance...
It got a new cylinder head ten years ago and a new exhaust elbow three years ago.
It is sea water cooled and has always been running in sweet or brackish water.
I live in a climate with long cold winters.
It sits in a sailboat and has probably been used for auxiliary propulsion only and only a few hours every season.
It starts easily every time, in any temperature and runs with a smooth steady rhytm, down to really low rpm.

My inner turmoil on maintenance ambition level can be boiled down to two extremes:
1, Reactive: change oil and filters and winterize properly and then address problems as they come up.
2, Proactive: lift it out and strip it down and follow the work shop manual and check/clean/replace all wearing parts to prevent serious failures that will otherwise inevitably come.

Ideally there is a middle way...

In other words:

is a 40 year old well functioning engine one that should be left alone to do its job undisturbed (save for oil- and filter changes) until it eventually brakes down because of age and for reasons that I can't prevent anyway.


Is a 40 year old well functioning engine building up internal wear problems that should be detected and addressed by inspection before they become serious.

Not an easy one, I know, but interesting and a very central issue for us running old boats on low budgets.


P. Hammar

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Old 17-11-2014, 04:23   #2
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re: Maintenance ambition for Yanmar YSB8

For me it's "if it ain't broke don't fix it". That doesn't mean run it and forget it though.

How many hours on it? How's the oil pressure? Does it reach specified RPM? Is the temp constant within given ambient conditions?

If it's got 4000 well maintained hrs. on it, it might be halfway through its' life. Keep the oil and filters changed, watch the temp (do not let it run hot) and oil pressure, and when she starts getting tired she'll let you know in time to rebuild...

(But keep in mind, it's a 40 year old engine. Check out 'Westerbeke rear seal' thread for some backround about what getting old parts can sometimes be like.)

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Old 17-11-2014, 04:57   #3
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re: Maintenance ambition for Yanmar YSB8

In an ideal world, you pull it, inspect everything for wear, most likely have the cam re-ground, the Crankshaft polished and new bearings fitted and hone the cylinder walls and install new rings, a new oil pump and of course all new seals and gaskets.

Odds are that the crankshaft seals and possibly some others are hard enough now at 40 yrs old, that they are wearing on the steel, maybe could do that for years to come, maybe there is already a groove?
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Old 17-11-2014, 05:09   #4
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re: Maintenance ambition for Yanmar YSB8

Ok so that's one up for the reactive approach.

Oil pressure and temperature is fine, as I said; it runs trouble free. I should imagine it has less than 2000 hours running.

But the over ambitious proactive side of me insists on action and imagines the functions on a diesel should to be logically divided into three groups:
1: Stuff that, unless abused, will carry on quite merrily in it's interior for ever.
2: Stuff that is either fine or broken and that give no notice before breakage.
3: Stuff that inevitably gets worn or dirty and need periodic cleaning/adjustment/replacement in order not to cause major damage.

And local shops are surprisingly well stocked with spare parts for this old engine. Seems to be a classic.

The problem is I don't know which parts fit in which group...
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Old 17-11-2014, 05:47   #5
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re: Maintenance ambition for Yanmar YSB8

One more thing:

The propeller shaft spins when the engine is running in neutral gear, even with the gear lever disconnected. It doesn't spin with much torque, but its enough to drive the boat at half a knot forward in still water, and enough to irritate me...

I have experimented and the only way I can get it to be still is by pressing the gear box clutch towards reverse and find a tiny spot between reverse and forward where the shaft is in fact not moving.

Gear box renovation?
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Old 17-11-2014, 05:59   #6
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re: Maintenance ambition for Yanmar YSB8

a64pilot, I did't read your post before posting my own above.

So that's one hand up for the proactive approach...

It should be added in the equation that I do enjoy working on the engine a lot and will not hesitate to dig into the engine other than for economic reasons and possibly for the risk of ruining well functioning parts by unprofessional handling.
I have understood as much that fuel injector and injector pumps are "hands off" for us enthusiastic amateurs and should be taken to specialists.

A repoweing option is a 10 000 US dollar option. If I can get by on less than 20% of that in a careful and wise renovation that gives me another ten years I'm very happy.
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Old 17-11-2014, 13:25   #7
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re: Maintenance ambition for Yanmar YSB8

Hi P. hammer,
We have a YSM 8 that I'm doing my diesel engine apprenticeship on & can tell you a few Stories. First you have to do all the usual basic diesel things like clean fuel, change oil @ recommended intervals. Parts prices are horrendous. Conrod assembly was $468 US. They dont make crankshafts for them any more. I think the injection pump is actually very simple & I rebuilt mine without too much trouble. The workshop manual is very good but if you look up Bosch PFR type pump on you tube there is a good video showing you how to strip it. I find you can reuse the copper washers if you anneal them. I used a new non-yanmar injector that works fine.
Good idea keeping an eye on the oil pressure as that was the first give-away that our big end bearing was stuffed. Otherwise Id just leave it alone. I am a little suspicious of the metal leaf oil- filter & am going to fit a remote cartridge type filter
I suspect there will be milliuons of chinese Non-marine copies of the Yanmar and I'm trying to chase crossover parts now as our conrod & crank are stuffed. Just welded up the conrod & going to put a phosphor-bronze bush in after machining to get us thru summer ( Not recommended!) It's real easy to get @ the big-end bearing if you want to inspect. If you have any questions you can pm me as we have learnt a bit trying to fix ours on the cheap which we are still doing!
regards Paul
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Old 22-11-2014, 05:57   #8
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re: Maintenance ambition for Yanmar YSB8

I also have a 1980 ysb8. just purchased the boat this year, Mirage 27. engine runs great, no smoke, all temps correct so far. Have run it quite a bit this past summer as "other captain" still getting used to being on the water. starts every time, i change the oil every 50 hours. Its definately a "banger" in all sense of the word. when idling, quite loud but smooths out when at higher revs. can get 6 knots out of the boat at 2850 rpm, 5 ish when into the wind in the harbor. i do however have a small issue can't seem to solve. while running in gear, have significant water generated into bilge, maybe 1 gal per hour. Bilge pump handles well, and i can't seem to find source. prop seal drips at normal 2-3 drips per minute, no issue there. Have laid in cockpit locker with a light while the mate drives and still cant find the source. Looking for ideas?
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Old 22-11-2014, 06:24   #9
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re: Maintenance ambition for Yanmar YSB8

  1. Perform all scheduled maintenance using quality parts.
  2. If used mostly in fresh water, that's great. After extended use in salt water (>1 year) you might want to flush the cooling system with acid to remove scale and salt build-up.
  3. Always allow the engine to fully warm up before shutting down and don't let it idle for an extended period of time.
  4. If the propeller turns in neutral and that bothers you, you could try to rebuild the transmission, but see #5 below.
  5. Resist the temptation to fix what isn't broken. If you do, there's always a good chance you'll make it worse or break something.

... He knows the chart is not the sea.
-- Philip Booth, Chart 1203
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