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superiorvoyager 12-06-2012 04:24 PM

Rebuilding a Yanmar YSM-12 using YSB head
We blew the Yanmar YSM-12 engine in our sailboat last summer and are needing to decide if we rebuild or replace. It needs a new cylinder head, Piston, rings and sleeve as well as crank bearing at the lease. The head looks like it would be the tough part but I have found a YSB-12 that is being sold for parts. Would the head from a YSB-12 work on a YSM? Any suggestions on where to get parts for this? is it even worth rebuilding? Any suggestions/opinions are appreciated.

Rockter 12-07-2012 10:38 AM

Re: Rebuilding a Yanmar YSM-12 using YSB head
superior :

Was it a lubrication failure?
Was the motior under load?

dabnis 12-07-2012 10:46 AM

Re: Rebuilding a Yanmar YSM-12 using YSB head
You might want to check with your Yanmar dealer about the availability of a rebuilt short or long block. I would think if it comes from Yanmar it should be reliable. Also, hope you found the cause of the failure.

Paul T

superiorvoyager 12-08-2012 11:41 PM

Re: Rebuilding a Yanmar YSM-12 using YSB head
Cause of the Failure isn't for sure other than it is an Old motor (mid 70's) that has an unknown number of hours on it and clearly has been overheated at lease once (I know that a year ago the impeller on the water pump when when someone else was using it and although they say they shut it down right away who really knows.) Needless to say the motor has had low copression for years and has just been getting worse with harder and harder starting. I knew this was going to be the final season before a rebuild but she finally just wouldn't even start anymore. When it finally gave up the ghost we found a cracked head bent and sticky Valves, badly scored piston and sleeve, Worn out bearing etc. There could have been any number of reasons for the final failure but that doesn't matter. It needs to be rebuilt or replaced. Yanmar does not carry the heads and my local Yanmar dealer can't get me a rebuilt. I have found a used Head from a YSB as well as a YSE but don't know if they would fit. Not sure what you mean by a "Short Block or Long Block". I assume you mean something other than a YSM which I can get but fitting it into the boat of course can be a lot of work. Rebuilding this motor, if I can get the parts, will probably cost as much as buying another rebuild but avoids the problem of retrofitting the boat for another configuration.

superiorvoyager 12-08-2012 11:52 PM

Re: Rebuilding a Yanmar YSM-12 using YSB head
Looking at the dimensions of the YSM compared to the 2GM they look quite close so it might not be to hard to replace it with that. What have other peoples experiences been with replacing YSMs with other motors. Any suggestions of a close fit. This of Course will not be done by a Yard or dealer as they do not exist here. I'll do it myself with the servics of a mechanic friend.

dabnis 12-09-2012 11:04 AM

Re: Rebuilding a Yanmar YSM-12 using YSB head
Some manufacturers may offer short or long blocks. IIRC, a short block was just the block without the head, the long block was the block and the head, maybe I got it backwards? been a long time ago. Both had all the moving parts replaced with new, or re-built or re-furbished components and required your old block and or head to be returned to them, known as a "core". However, if Yanmar doesn't offer them or re-built engines you may have to find one to re-build on your own. Changing to another Mfr's engine would likely be a complex and difficult job as likely nothing fits.

Paul T

superiorvoyager 12-09-2012 12:04 PM

Re: Rebuilding a Yanmar YSM-12 using YSB head
OK I understand. I have found a few places that will sell you a Re manufactured engine and take your old one. Problem is they don't have the older YSM engines like this and these 1 cylinders have a different block then the newer yanmars. I think the 2GM is close in dimensions and wouldn't take a lot of modification to fit in but not sure if they would take my old YSM-12 for a 2GM. I might be stuck having to drop in a different Yanmar.

superiorvoyager 12-09-2012 06:09 PM

Re: Rebuilding a Yanmar YSM-12 using YSB head
Well I ended up finally finding someone who sells re manufactured YSM-12s and he is only about 9 hours away (in the states mind you but still close by northern standards. )he will take my old core on trade so it is win win.

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