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Discussion Starter · #1 ·
I was looking at another boat yesterday and it is has a Yanmar SB-8 motor. When it was first started it was really loud (banging noise not exhaust loud), and when the throttle was applied at certain times the banging was really loud, then quieted down in different throttle positions. First time ever hearing a diesel boat engine run so I don't know if anything was wrong.

The boat was on boat stands so we only had the motor run for 30 seconds max so I don't know if it would quiet down after it warmed up. It really seemed like the piston was slapping around a lot inside the cylinder wall but what do I know.

I am pretty positive that running the motor even for that 30 seconds was enough to fry the water impeller so i am planning on that first thing if we end up buying the boat.

Any help is appreciated.
Zac
 

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With covers off a single cyl diesel can be appallingly loud. We once installed a brand new Volvo one-lunger in my brother's boat.. when it first fired up I could've sworn the piston was hitting the head, it was such a metallic 'bang'.. but it was 'normal'....
 

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Zac, I've only been up close to a one-banger on one boat, and my reaction was pretty much like yours: Hey, is that engine going to blow?

When in doubt...get a diesel mechanic, or put some money into an escrow account for 90 days to make sure it keeps working, as a "warranty" amount.

Remember that internal combustion engines, all of them, work by creating a series of explosions, and explosions sometimes may seem violent and noisy when they're planned properly.
 

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Discussion Starter · #4 ·
Oh, thank you both for the response. That really sets me at ease because it is exactly how you describe it. I thought the piston was smacking the head but I guess it is just loud. It wasn't scary loud and nothing really seemed to be rattling around so it seems like it is normal.
 

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I have a Yanmar 1GM10 that is a single cylinder. It isn't quiet, but I never thought it was excessively loud either. Sweet little motor. If you go to You Tube and type in "Yanmar SB8 on Sailboat" you can watch and hear one run.
 

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The single cylinder we had made a distinct sound. The old farmers used to talk about the one-cylinder John Deere they called the Poppin' Johnny. Perfect description.

Since there's no other cylinders the one firing really stands out, esp at lower rpms.
 
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