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Discussion Starter · #1 ·
After being forced to remove engine from boat we've decided to put the effort in to reconditioning our 42 year old single cylinder 8 horse power Yanmar YSM8. She easily gets to hull speed on our Tasman 26 when she's running well; and the alternative is major structural change.

Really the only part that no longer exists for it is the cylinder liner. Ours is pushing tolerance, so the engine is either dead/nearly dead or we need to fabricate a liner. In Australia the cost of that is likely prohibitive, if we can even find someone to do it. Does anyone know different? Has anyone had experience engaging engineers in India to fabricate parts? I'm inclined to believe with a bit of research we could get high quality at a reasonable cost. These guys seem competent and replied quickly asking for drawings Cylinder Liner, Cylinder Liners Manufacturers & Suppliers India Anyone have any good or bad experience?
 

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Are oversizes available? If so, then why not re-bore it?
Take the piston out, turn it upside down, read off the piston manufacturer and check for oversizes.
Take the oversize to your local machine shop and they will re-bore the liner to the manufacturer's piston-to-bore tolerance.
You can re-grind the valves as you re-assemble it.
 

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I'd check with Mack Boring, here in the USA. A few years ago, they were very helpful regarding the rebuilding of my YSM 12, which is essentially the same engine.
The YSM motors are remarkable reliable, but vibrate an incredible amount. In my case, the cost of a rebuild was only a few hundred dollars less than a new Beta Marine 14. I eventually found a nearly new 14 for less than the cost of a rebuild. Operationally, the Beta is worlds better than Thumper. I don't know if it will be viable 40 years from now, but I am sure that it won't be my problem. The engine swap was detailed but easy.
Best of luck.
L
 

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Sometimes, I'm pleasantly surprised by what it costs for a local machinist to make something. Of course, it's always multiples of what the part would cost of mass produced, but I've had parts made that prevented larger replacements, which is the point.

Part of me wonders if a liner is all that hard for them to make. The issue could be getting the exact specs. The oversized bore out is a good thought too.

I guess I can't help but wonder the risk of throwing good money after bad. On a motor that old, you could easily find a new fatal problem, followed by another.

Good luck.
 
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You may be surprised at how many other brands of engines may have the same size piston and liner as the old Yanmar or even a close enough liner that could be turned down a bit or shortened to fit.

Some of the Asian/Oriental companies that make liners may have one in stock that will be a close enough match but won't know unless you send them the specs. A number of folks with the older Isuzu Diesels have been pleasantly surprised when they shopped by liner dimensions rather than engine model and year.
 

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Seems to me that since the engine is out, reboring the the liner should be considered. If that wasn't already done in the last 42 yrs. should be lots of meat in it yet. Micing will tell. Then will the piston need replacing? micing will tell. Is a new Over size available. Then consider ring end gap when going for the new rings. Plastigauge mains and big end to feel good or junk or just new shells. If all is good so far, send out the head for valves and Maybe facing. Pretty standard starting project good luck.
 

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You can get the bearings for that engine but the cylinder sleeve and piston is the problem. no longer available from Yanmar. the cylinder and piston on that engine comes in one size only, no over size pistons. the bore is coated and can not be bored out oversize it was designed to have the sleeve and piston changed as a set. the sleeve is installed with O rings to seal the water jacket to the block. easy to replace if you can find one.
 

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Discussion Starter · #9 ·
Amazing so far, thanks everyone!

I understand/believe it can't be overbored..
@lillia28 great advice. Thanks for finding https://www.trademe.co.nz/motors/boats-marine/parts-accessories/engine-parts/listing-1846074966.htm that's exciting - bought it. Not sure how I missed those in my days of internet research - was assuming it was going to be hard and searching accordingly it seems! Thank you.

I see the Beta 14 has a 'shallow sump' option which might mean it'd fit the shaft (engine is aft under v-berth and cos the YSM8 is flat it's really close to the hull). It'd mean new exhaust system and propellor though at least, if not also some bed and mount mods. It won't be cheaper than the $2k so far spent on reconditioning, hopefully can get the YSM8 thumping along and electric will replace it in some time to come.
@SeaStar58 - I hadn't thought of that. I am about to get far more acquainted with liner schematics than I ever imagined so will keep that option in mind.
 

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Glad to help! For the record, I had to build UP my engine beds to get the Beta at the right angle. I had to add about 1 3/8 inches (35MM) to the top of the beds. So I think it would be the height above the bed, not the sump, that would be the issue. Be that as it may, you are past the point of no return with the YSM-8, so carry on! Some where I have the YSM shop manual in PDF. I got it on line, so it is available somewhere. There is a lot of info on those engines out there, so do a lot of internet searching in your spare time. Yanmar is also an excellent source. I'll look around for the file in the mean time. The biggest hang up I had was finding a wrench for the crank fasteners. The nuts are huge (2?inches [50MM]), and the wrenches had price tags to match, so I sent it to a Yanmar specialist. His price was nearly $5,000, which was way to much. That's about what I paid for the Beta, which is more powerful, smaller, lighter and oh so much quieter and vibration free in comparision.
Let us know how it all turns out. Best of luck.
Lou
 

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Amazing so far, thanks everyone!


@SeaStar58 - I hadn't thought of that. I am about to get far more acquainted with liner schematics than I ever imagined so will keep that option in mind.
In Cuba for example the go to for parts they can't buy new is many times old Russian equipment. They've become pretty adept at keeping vintage motorcycles running where the parts are either unavailable or just too costly by scavenging old parts spec books and junk yards for something close enough.


This may inspire you especially when you get to about 2 min into the video:
 

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The story floating around is that the YS series was designed by Coventry in England as a 2 Cylinder Boxer diesel, originally destined for Landing Craft engines. Yanmar bought the design, cut it in half and produced it as a pleasure boat motor. If you look at the engine block, this story is easy to believe.
Years ago I asked the folks at Mack Boring about the "design" life of the 2 GM and the YSM series. The design life is stated at 3,000 hours, but it was not unusual to see a 2GM running strong at 10,000 hours. The YSM ? "I don't think I ever saw one wear out!" There are lots of good reasons to stay with the YSM.
 
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