Yanmar 440 RPM

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Ductboy

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I'm looking at a boat with a single 440 Yanmar. The engine has around 450hrs and has had great service. The head was changed out by Mack Boring due to the known casting issue some of these motors had.

My question is this, I went for a quick ride on the boat, and was surprised to see almost 4500 RPM on the tach. I have had several boats with Yanmar 6cyl diesels and have always thought that top rated RPM was around 3300.

The boats propulsion set up is original and within spec.

Is this posibly a tach issue, that it is reading too high?,
 
quote:
Originally posted by Ductboy

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The current Yanmar lineup does indicate max rated power of the 440's at 3300 RPM.

http://yanmar.com/product/marinepleasure/powerBoatPropulsion/library.php

http://yanmar.com/product/marinepleasure/powerBoatPropulsion/catalog/Yanmar-6LY2A-STPdatasheet.pdf

http://yanmar.com/product/marinepleasure/powerBoatPropulsion/catalog/Yanmar-6LY3-STPdatasheet.pdf

If you have access to the crank pulley you could have a reality check with use of an inexpensive photo tach.
http://www.amazon.com/s/?ie=UTF8&ke...vptwo=&hvqmt=b&hvdev=c&ref=pd_sl_2ngnztprjm_b

Are you sure you were not confusing engine hours with Tach RPM? (450 & 4500?)
 
Sandy

Thanks for the reply and the documentation.

The tach was not digital, so no mistaking the hours. I just couldn't believe it when I saw the thing running up that high. Those are WOT numbers I am used to seeing on an outboard!

I have to think that the tach had been wired incorrectly or something. The WOT speed was about correct for the boat and sea conditions, and the motor wasn't screaming to any abnormal degree at that level.
 
Something is wrong with the tach. 3300 is max rated rpm and a properly loaded setup should be able to hit 3400 rpm. The no load, in neutral rpm is 3700 or 4000, I don't remember which but I'm pretty sure it's 3700.

4500 is way off the mark IMO.
 
To rule out the tach, simply use a phototach. Will yield exact results directly from the crank pulley.
 
Like Gary said...use a phototach. I had this same thing happen on a boat I was buying a while back. The tach was reading high by about 500 rpm. There is usually an adjustment hole on rear of tach head. We noted the true rpm and adjusted accordingly. Problem solved.
 
I have done a little more digging and it seems that the alternator was changed out recently with a non Yanmar replacement. I have been told that this is most likely the reason for the tach being incorrect.
 
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