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Old 12-06-2019, 14:28   #1
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Yanmar YSM8 handcranking problem

Hello All! I'm currently troubleshooting a Yanmar YSM8 which the boat's owner believed had seized 2-years ago. I have determined that the engine is not seized as I removed the starter and was able to rotate the engine while in neutral using the flywheel/ring gear and an 8-inch screwdriver. However, when attempting to rotate the engine using the hand crank on the front of the engine (no overdrive/chain drive installed on this model), I am unable to rotate the engine. It "feels" like the engine is seized.

I have removed the cylinder side cover and inspected the manual cranking assembly gears, clutch and bearings. All rotate freely and are in pristine condition. While rotating the engine from the flywheel I see the cam gear and PTO idler gear rotate, and cam is operating the high pressure fuel pump. Was thinking that binding was occurring between the cylinder side cover and the gearing so shimmed the cover to simulate a thicker gasket...no joy there.

Am baffled on this one (and that takes a lot to do! ). Anyone with experience on this engine? If so, any suggestions would be greatly appreciated.
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Old 12-06-2019, 18:17   #2
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Re: Yanmar YSM8 handcranking problem

That hand crank has a sprag bearing on it which is prone to give trouble. Did you dismantle the hand cranking mechanism? We have one of these engines & when I dismantled ours the sprag bearing was full of crud which stopped it from working. i suspect all the crud in the engine came from excessive blowby 7 too many short runs by P.O.
Do you have the workshop manual? It shows a view of it in there & it's easy to dismantle & clean. I completely rebuilt our ysm8 & are happy to answer any questions you may have
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Old 12-06-2019, 19:15   #3
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Re: Yanmar YSM8 handcranking problem

Whoops sorry I didnt read your post properly. You say the sprag ( clutch) bearing is working properly & hand crank shaft is rotating ok. I assume it's decompressed when you are trying to rotate it. Hmmm that is a bit of a puzzle. Will try & think of a possible cause & get back to you. It is baffling!
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Old 12-06-2019, 19:41   #4
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Re: Yanmar YSM8 handcranking problem

Compass790, went back over to the boat and removed the front cover (again) and attempted to rotate the engine directly at the camshaft. Wouldn't turn. Still rotates when the ring gear is moved. And yes, the decompression lever is actuated. Am going to pull the head tomorrow to inspect the cylinder liner (injector barrel is also stuck in the head and needs to be overhauled anyway after sitting for 2-years IMHO). Am beginning to suspect cam shaft bearing issues due to angular displacement when the crankshaft is use. That, or (and it's a long shot) a problem with the gearbox clutch assembly has a problem and is creating too much resistance to be able to rotate the engine via the hand crank due to the manual crank's low gear ratio.

And hey! Thanks for giving it some thought!
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Old 12-06-2019, 20:30   #5
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Re: Yanmar YSM8 handcranking problem

Yea was gunna say pull injector anyway just to see if there is any fluid in cylinder. Also the cover that sits under 12v starter with 8? bolts on it that the oil vent comes out of gives access to the big-end & crankshaft if u wanna look in there.
The exhaust elbows are a very bad design in that if they fail they can leak water down on top of exhaust valve & then of course into cylinder. Did the owner tell you if it seized suddenly whilst running or was it left for ages & then it seized?
Gearbox is bulletproof IMO as long as it has oil in it of course. The neutral adjusting screw could need adjusting but it still wouldnt stop you from turning it unless gbox was seized. I 'd be surprised if it's camshaft bearings as our big end & main bearings were destroyed by lubrication failure but the camshaft bearings survived fine as they get splash lubed. I'm still baffled as the camshaft must have been turning before to pump the injection pump.
Anyway getting the head off will be a good start. Saturate that injector with penetrating oil. Let us know what you find
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Old 12-06-2019, 21:50   #6
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Re: Yanmar YSM8 handcranking problem

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Originally Posted by Teknishn View Post
Compass790, went back over to the boat and removed the front cover (again) and attempted to rotate the engine directly at the camshaft. Wouldn't turn. Still rotates when the ring gear is moved. And yes, the decompression lever is actuated. Am going to pull the head tomorrow to inspect the cylinder liner (injector barrel is also stuck in the head and needs to be overhauled anyway after sitting for 2-years IMHO). Am beginning to suspect cam shaft bearing issues due to angular displacement when the crankshaft is use. That, or (and it's a long shot) a problem with the gearbox clutch assembly has a problem and is creating too much resistance to be able to rotate the engine via the hand crank due to the manual crank's low gear ratio.

And hey! Thanks for giving it some thought!
IMO, this is your problem - there is too much resistance to turn the engine over when attempting to do so by the hand crank (or by the camshaft cog).

Using the flywheel ring gear and a long screwdriver gives you much more leverage than trying to rotate the engine by the camshaft cog. This is why it turns using the ring gear but not the camshaft cog.

I doubt the clutch assembly is causing the resistance and I very much doubt the camshaft bearings will be an issue.

I would suspect stuck rings or a stuck valve first.

Clearly you are getting some movement because you can turn the flywheel so everything else that is mechanically connected to that must be moving (i.e. piston, cam, PTO pulley, valves etc) but it isn't turning freely.

Look where water can get first i.e. head (rings & valves) before looking at things that swim in oil (bottom end bearing, cam bearing etc, PTO gears, clutch etc)
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Old 13-06-2019, 15:55   #7
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Re: Yanmar YSM8 handcranking problem

Okay, head has been pulled and the cylinder liner looks to be in good condition. I will concur with Wotname in that it is probably stuck rings as the valves operated smoothly while rotating the engine from the flywheel/ring gear and everything else that "swims in oil" appears to be OK. Asked the boat's owner how far he wanted me to go with this as I was just hired to troubleshoot the engine (I am just semi-retired marine electrician after all). So now have done everything needed in order to pull the engine (nuts and bolts broke loose, prop shaft disconnected, ancillaries removed, etc.) and let him turn it over to someone more mechanically qualified than I.

Now going take my boat out and run up a new headsail I recently purchased, play, and enjoy the sunset with a cocktail.
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Old 13-06-2019, 16:21   #8
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Re: Yanmar YSM8 handcranking problem

Hmm... if the liner looks OK then maybe the rings aren't stuck in the liner. Can you rotate the piston down enough to see the liner wall where the rings sit?

FWIW, it is quite easy to remove the piston without removing the engine assuming some space in the engine area. There is a cover on the crankcase on the opposite side of the head. Remove that and you have access to the big end of the conrod. Remove the conrod cap and the piston can be pushed out (towards the head of course).
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Old 13-06-2019, 16:46   #9
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Re: Yanmar YSM8 handcranking problem

If the rings are stuck, they will free up enough to rotate the engine normally (IMO).

Lubricate the visible section of the liner and then force the piston to rotate towards the head by whatever means - ring gear etc.
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Old 13-06-2019, 16:53   #10
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Re: Yanmar YSM8 handcranking problem

"Now going take my boat out and run up a new headsail I recently purchased, play, and enjoy the sunset with a cocktail."

Many times I felt like doing that when doing the rebuild on our engine

Pity the story ends, was intrigued.
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Old 13-06-2019, 17:12   #11
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Re: Yanmar YSM8 handcranking problem

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Originally Posted by Wotname View Post
Hmm... if the liner looks OK then maybe the rings aren't stuck in the liner. Can you rotate the piston down enough to see the liner wall where the rings sit?

FWIW, it is quite easy to remove the piston without removing the engine assuming some space in the engine area. There is a cover on the crankcase on the opposite side of the head. Remove that and you have access to the big end of the conrod. Remove the conrod cap and the piston can be pushed out (towards the head of course).
(Sigh) Just when I thought my day was done and wanted to go sailing you posted this about the access cover. Would be thinking about it all night and wouldn't get any sleep. On my way back to the boat to do a visual on it (It's not shown in the manual I have). Thanks Wotname! You just might have saved the day!

And yes, once there is access to the conn-rod bolts, pulling out the piston is easy (did this on my own 1GM engine last year).
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Old 13-06-2019, 17:16   #12
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Re: Yanmar YSM8 handcranking problem

^^ that access cover will still be there tomorrow - maybe today is for sailing (and that sundowner) .
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Old 13-06-2019, 17:27   #13
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Re: Yanmar YSM8 handcranking problem

FWIW did tell you about big -end access in post #5
Glad Wotname has shamed you into another go as story was ending with a pile of bolts
it's winter here, good weather for tales on CF
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Old 13-06-2019, 18:28   #14
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Re: Yanmar YSM8 handcranking problem

Quote:
Originally Posted by Compass790 View Post
FWIW did tell you about big -end access in post #5
Glad Wotname has shamed you into another go as story was ending with a pile of bolts
it's winter here, good weather for tales on CF
Might be on the way to a success story here (and I will admit that I misunderstood the big-end access reference early on...language barrier? ). Am ready to pull the piston tomorrow as the boat owner showed up, he lives aboard, and told me to call it quits for the day...pull the piston tomorrow, he wants his boat back for the evening.

Wasn't "shamed" into giving it another go, I got ya. Just learned something new from someone with different knowledge/experience (With many thanks). I am just a marine electrician after all...OK, maybe a bit of a wrench turner too.
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Old 13-06-2019, 18:49   #15
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Re: Yanmar YSM8 handcranking problem

It's lucky we are writing & not talking as I've had a few struggles communicating with my accent in the USA tho we both speak a form of English.
Shamed mitea bin the wrong word, maybe encouraged better. Well good on you for having a go @ it being a sparky. Hope it goes better than some of my attempts at being a domestic or marine sparky.lol. At least the 12v/24v on a boat is less hair raising than the 240v that has bit me a few times.
Hope ya knocked off early enough to get that sail in.
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