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Hey all. I have an old inboard Yanmar SB8 in my Sun 28 that I am having issues with. First off, I am not very familiar with diesel engines and rely a lot on friends, and here, for help. So, the engine has seized. Pulled the head off and looked at the piston. Springs on the head were a bit rusty, but everything else was fine. Tried to manually turn the crank and it doesn't move. At all. Tried the old WD40 down the cylinder with no luck.

My questions are many, but here's a few off the bat.

1 - Should I take it out and overhaul it? Is it that hard to do?

2 - If I replace it, what's a decent engine I could use while considering the dimensions?

Many thanks!
 

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I'd say that a simple, one cylinder, diesel like the SB8 is the perfect engine on which to learn. I'd encourage you to pull it and rebuild it. It's not hard to do, and you will learn a lot. Depending on access to the engine, pulling it out might be the hardest part.
 

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^ This.
 

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Be patient with the WD40 down the cylinder stuff.

Suggest you try some Marvel Mystery Oil into the cylinder now that you've got the head off.
Just a tablespoon or two to soak the rings and their ring grooves.
DO NOT 'force' the crankshaft!!!!!!
If the engine did not seize while running, just keep adding MMO every few days with an attempt to turning the crankshaft nose bolt with a long handled bar and socket - gently 'rocking' the breaker bar back and forth . It will/may take time; but, it usually WILL free up. DONT force the crankshaft to turn as you will inevitably break the piston rings.
 

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It will be MUCH easier to work on out of the boat. Workshop manuals exist. I've got rough PDF's for the 12...

Sent from my GT-P3113 using Tapatalk
 

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It will be MUCH easier to work on out of the boat. Workshop manuals exist. I've got rough PDF's for the 12...

Sent from my GT-P3113 using Tapatalk
I replaced a YSM (same basic engine) in one of my boats - two guys can easily hump it in & out. Could do it by yourself if your boom is strong enough to hold it.
 

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It will be MUCH easier to work on out of the boat. Workshop manuals exist. I've got rough PDF's for the 12...

Sent from my GT-P3113 using Tapatalk
Sorry to hijack this thread, but I saw you post that you have a rough pdf of the Yanmar SB12 shop manual. I'm burning oil, rapidly, and thinking about replacing my valve guides. Willing to email me a copy of the manual? [email protected]

Thank you so much!

Phil Magistro
s/v Tanager, 1978 Bristol 29.9
 

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Sorry to hijack this thread, but I saw you post that you have a rough pdf of the Yanmar SB12 shop manual. I'm burning oil, rapidly, and thinking about replacing my valve guides. Willing to email me a copy of the manual? [email protected]

Thank you so much!

Phil Magistro
s/v Tanager, 1978 Bristol 29.9
Phil,

We also have a B29.9 and have a PDF of the exploded parts manual for the SB12 if you think that would help. Let me know.
 

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RE:
Re: Yanmar SB8 issue/questions
Quote:
Originally Posted by pmagistro View Post
Sorry to hijack this thread, but I saw you post that you have a rough pdf of the Yanmar SB12 shop manual. I'm burning oil, rapidly, and thinking about replacing my valve guides. Willing to email me a copy of the manual? [email protected]

Thank you so much!

Phil Magistro
s/v Tanager, 1978 Bristol 29.9
Phil,
We also have a B29.9 and have a PDF of the exploded parts manual for the SB12 if you think that would help. Let me know.
Here's the link to the manual PDF:

https://www.dropbox.com/s/ud4t67dds6o7jdt/Yanmar YSB12002.pdf?dl=0

cthoops: I could use the parts list PDF as well. Could you post a link?

mark
 

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For what its worth, I just pulled a running (?) YSM 12 from my boat. I also have a YSM 12 head. I'm likely to scrap the engine, so if your interested send me a PM.


lou
 

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I'm putting in a Beta Marine 14. With an 18 gallon fuel tank that gives about 40 hours of endurance. The only way to get that type of endurance with electric is to install a diesel generator, which will need to be between 12 and 15 HP. You end up with a duplicated propulsion system. If you only want to in and out of your slip/mooring electric works well. If you want to do any kind of long distance sailing, using current technology, it is hard to beat internal combustion.
L
 

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I just found my copy of the YSM 8 & 12 manual, if that will help. Drop me a PM with your email and I'll send it along.

Lou
 

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Poor gas down the injector holes until you can see it in the hole, try to keep the level in the cylinder up to the hole for 24 hours. After 24 hours try rocking the crank with a tork bar and socket on the crank pulley bolt(not a screw driver). Gas and most loose nut can and will do or any combination. I freed up 2 6v92TA like this and they are still running like champs. Once you are able to turn the motor by hand 2 full rotation of the crank shaft, then leaving the injector out, use the starter to turn it over. (Get your head away from the injector hole, lol). Once you did this for about 20 sec, reassemble and good to go. Unless the cylinder was at TDC or TDB, the rings and oil going up and down got the rust off the walls. Now before you start it, make sure you change the oil. And then about 30 mins after the engine got hot, change it again so no debris, gas or rust can Remain.
 
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