Yanmar YSM 8

[Compass790]

Yanmar YSM8 story,
Just wanted to share my experiences with our engine so others can learn from my mistakes. When we bought the yacht ( sailboat) it came with receipts for new piston & rings , also head planed & valves ground. Ran fine on the trial & then we set off on the run home. Oil alarm would fail to turn off occasionally but when we spun the oil filter handle it would stop. Mechanic told us the oil-pressure senders were a common problem he would lend us an oil pressure guage &if it was ok ( over 30 psi ) ignore or disconnect the sender alarm. BIG MISTAKE. Well the oil pressure was just ok but I hadnt mounted a permanent gauge, just tried it for 10 mins.Another BIG Mistake. Used the engine for a few more months ignoring the sender until the knocking got too bad & then pulled apart. Big-end bearing was completely gone & the conrod was worn oval. Next shock was the $630 price for a conrod from the New Zealand agent!
Thanks to the Daily Cruiser a good chap Atoll from Cornwall helped me out posting me a conrod & other parts from his dead YSB 8 which was the same . Swore I wouldnt buy one part from the NZ agent.Had to get the crankshaft ground & machine up some LG2 (gunmetal) bronze big-end bearings. Got an over the phone tutorial from a machinist friend on how to machine myself as I had more time than money. Took me 2 attempts but got there in the end.Had to buy a new oil pump rotor assembly ( from the USA) but that didnt cure the oil pressure problem as the rotor wears down into the case. Luckily Atoll rescued me again with some advice from the local dealer. They machine the case down to tolerance but I just used an oilstone to get it to the clearance specified in the manual. Oil pump working now. Yanmars solution is to buy a new engine case, not in the budget.
Next problem was the fuel supply which showed itself by the engine running slowly & intermittently. Fuel filter was clogged & tank was full of crap. Got more advice from a fuel injection guy who said the lift pump is probably faulty when it still wouldnt go after cleaning tank & replacing filter. Bypassed lift pump with gravity feed & injector still wouldnt spray. Stripped &cleaned injector then got it pop-tested, was ok. Still wouldnt spray so on to the injection pump. Everybody said dont touch it so took it to specialist for testing. They didnt test it I suspect,charged me $100, just pulled it apart & told me i needed a new one for around $600. That was over my budget so they returned me the bits minus a snap ring.Looked on youtube, found a Bosch PFR type injection pump strip down video & decided that it didnt look too hard so had at it with the workshop manual assistance. Figured the only 2 likely bits to be at fault are the plunger assembly and delivery valve. Got them from the USA for $201 & voila the injection pump works. My conclusion is have a go at the injection pump yourself on one of these engines if you have a workshop manual as they arent very difficult & if they are faulty they will try to sell you a new one when you probably only need a plunger assembly & delivery valve.
Bad maintenance caused all these problems. We should have cleaned the fuel system on buying the boat & I had seen metal particles in the oil when changing it so should have stripped the engine straight away. It's tempting to avoid the engine space in the summer on a 26ft yacht but dont put it off! Its real easy to get at the conrod as there is an access plate under the starter motor. Motor is very simple & easy to work on but it's noisy & vibrates a lot but we are going to keep it running as I have a good used block to get parts from.
Probably not many of these engines still alive but i hope somebody finds something useful in this.
Paul

[lockie]

Good on you mate for getting in there and having a go. My experience with a Yanmar 2GM is that 99% of the diesel mechanics see us owners of little old engines as pests. And I guess so long as they can stay busy working on big engines and getting paid accordingly, who could blame them.

It reinforces my view that is if you can't do rigging, glassing, wood, diesel, electrical etc stuff, and aren't willing to learn, you really shouldn't buy a yacht unless you're very well off.

Cheers, Graeme

[Compass790]

Yea too right cobber what you say about the mechanics & small engines. I dont blame them either as at $75 an hour you can quickly run up a big bill & small boat owners dont like it. Not to mention the ripoff yanmar parts prices. Glad I've learnt it now as at least it's a simple engine & not ECU controlled which would leave me in the clutches of the agent.
cheers Paul

[Wotname]

Nice post Compass790

[Compass790]

Thanks, glad you liked it. Hope somebody gets some help from the post as I have from other posts on this forum. Forgot to add anyone with one of these engines can message me if they want any tips on rebuilding.
cheers Paul

[Halifax Sailor]

so how noisy is too noisy? i have a ysb8 circa 1980, well in a 1980 boat but what i find is they stopped making them in 1978. no oil loss, no issues tarting, .6 ltr per hour running at 2800 rpm, has never failed to start. BUT very noisy when running at lower rpms.

[Compass790]

Originally Posted by Halifax Sailor

so how noisy is too noisy? i have a ysb8 circa 1980, well in a 1980 boat but what i find is they stopped making them in 1978. no oil loss, no issues tarting, .6 ltr per hour running at 2800 rpm, has never failed to start. BUT very noisy when running at lower rpms.

Hard for me to say how noisy is too noisy. But its a lot noisier than a twin cylinder.Best thing I can try & do is make a video of mine but I cant promise that I'll be successful as I have computer issues. If there is a hard metallic knocking or screeching sound it could be problematic but ours is pretty noisy at low revs too. If its a good starter compression is probably ok. Does the oil pressure warning alarm go off quickly? If not best to check oil pressure when engine is hot. YSB is the middle version, has a few differences including injection pump & engine case.If anyone in your area has a YS series see if you can listen to theirs .
You may have nothing wrong if it's using that little fuel & no oil but check that oil pressure as ours wasnt using hardly any oil when it wasnt pumping hardly any. Easy to screw a gauge in where pressure sender goes. It's supposed to be between 35-50psi. Will get back to you if I can make a video. I suspect these yanmars will go for a long time if you change engine anodes, oil & fuel filters & keep an eye on the exhaust elbow which can let raw water into the head when it fails.
Hope that helps

[Halifax Sailor]

oil pressure light goes off almost immediately, comes back on after shut down when engine is almost stopped. the knocking is "quite normal" i have been told by several sailors here who have yanmars. BUT, i am trying to decide if i should get the valves checked for clearance. lots of water through the engine judging by what is spewed out of exhaust and shot across the marina, pump throws the water about 20 feet across. I have new engine mounts i will be installing at haul out in the fall, wanted to do this spring, just ran out of time. The ones in now look original, and seem to have some flexibility but am going to change regardless.

[Compass790]

just an update on my original post. LG2 bronze big-end bearings did score the crankshaft as my machinist friend predicted.The material lacks embeddability. It was only meant as a temporary solution to keep us going until i sourced another crankshaft. I have since put a replacement crank ( used) in with tri-metal big end shells & the replacement con-rod. I did get main bearings made out of bearing bronze & we will see how those last. Originals were kelmet metal but too expensive.