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  #1  
Old 05-19-2008
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Perkins 4.108 shaft rotation

I pulled my Perkins 4.108, and I am replacing with a Yanmar 4JH4E. The Yanmar shaft rotates counter-clockwise when viewed from the stern. I can't remember which way the Perkins rotated! All you Perkins folks, please advise. Also, does a Left Hand rotation mean the same thing as counter-clockwise viewed from stern?

Thanks.
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Old 05-20-2008
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Old 05-20-2008
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Quote:
Originally Posted by jr438234606 View Post
I pulled my Perkins 4.108, and I am replacing with a Yanmar 4JH4E. The Yanmar shaft rotates counter-clockwise when viewed from the stern. I can't remember which way the Perkins rotated! All you Perkins folks, please advise. Also, does a Left Hand rotation mean the same thing as counter-clockwise viewed from stern?

Thanks.
I have a 4 108 from 1980 (there are different versions of the 4 108) though I doubt that they would rotate in different directions.

I have a left hand prop which means my engine rotates...... um...... It's late and I haven't slept much lately. That's what that means.

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Old 05-20-2008
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Rotation

Yes and Yes, check with your local prop shop (the larger the better) and have them do a computer analasis of horsepower and wieght of the boat and desired cruising hull speed to determine if your prop can be used or it just needs to be tweaked. More than likely you will need to have them recondition and repitch your prop. But what do I know, that's just what I would do. Good luck! I am assuming you have an 1 1/4 Shaft?
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Old 05-20-2008
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If the crank rotates clockwise when viewed from the front, it's gonna be counterclockwise when viewed from aft. I think most, if not all, engines run clockwise when viewed from the front of the crank. The transmission determines which way the propshaft turns, think of gears on a shaft, each gear drives the next one in the opposite direction so final direction is determined by number of shafts in that drive path. Just workin' with an old feeble brain here, I'm sure someone will correct me if I've erred, and tell us of every "left handed" engine in the world.
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Old 05-20-2008
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OK, gotta correct myself, standard engines are called left handed because rotation direction is named by viewing the flywheel. Reverse rotation engines (RH) are rare but do exsist. See the link for diagrams.
Determine Engine Rotation GM Marine
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Old 05-20-2008
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  1. Quote:
    Originally Posted by capttb View Post
    OK, gotta correct myself, standard engines are called left handed because rotation direction is named by viewing the flywheel. Reverse rotation engines (RH) are rare but do exsist
Correction! RH is a "standard" rotation engine; prop rotates clockwise as viewed from the stern. The LH is an odd rotation usually one engine on powerboats with twin screws.

Also be aware that some transmissions will reverse the rotation of the shaft relative to the engine rotation; so you need to check either the driveshaft while the engine runs or the prop pitch to determine if the driveshaft is LH or RH.

My boat has a 4-108 with a B-W Velvet Drive (1:1 IIRC). The shaft rotation is RH.
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Old 05-20-2008
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I knew this had the potential for some real confusion, couple quotes on the subject.
Quote:
Rotation is always determined by looking at the flywheel end of an inboard engine. The flywheel of a standard rotation engine turns left, or counter-clockwise, when viewed from the flywheel. The flywheel of a reverse rotation engine turns right, or clockwise, when viewed from the flywheel. Most single engine inboard and I/O boats use a standard rotation (L.H.) counter-clockwise engine.
And to add to the confusion we can think about the starter motor viewed from the pinion gear.
Quote:
Starter motors, when mounted forward of the flywheel, will turn clockwise (R.H.) to start a standard rotation (L.H.) counter-clockwise motor. Starters mounted aft of the flywheel will turn counter-clockwise (L.H.) to start the same engine. Everything is just the opposite when speaking of a reverse rotation (R.H.) clockwise engine.
Source:Boat Engine Rotation
Try reading that last one fast a couple times.

Last edited by capttb; 05-20-2008 at 07:17 PM.
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Old 05-20-2008
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Quote:
Originally Posted by KeelHaulin View Post
Correction! RH is a "standard" rotation engine; prop rotates clockwise as viewed from the stern. The LH is an odd rotation usually one engine on powerboats with twin screws.

Also be aware that some transmissions will reverse the rotation of the shaft relative to the engine rotation; so you need to check either the driveshaft while the engine runs or the prop pitch to determine if the driveshaft is LH or RH.

My boat has a 4-108 with a B-W Velvet Drive (1:1 IIRC). The shaft rotation is RH.
Ok, so, like yours, my Perkins probably also spun clockwise viewed from stern. This would mean that the Yanmar type 4JH4E has an odd, non-standard rotation? The specs say that it spins counter-clockwise when viewed from stern, which would make it just the opposite of the Perkins. I checked Yanmar's products... they apparently don't even offer an engine that rotates clock-wise viewed from stern. The Westerbeke 55C4 also rotates counter clock-wise when viewed from stern.

Could it be that the Perkins is the odd rotation?
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Old 05-20-2008
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I don't think so, current Perkins-Sabre diesels are all "Standard Rotation", LH, counter-clockwise at the flywheel, clockwise at the front, engines.
Perkins Sabre M65 - Specifications - Marine Diesel Engine for Leisure Craft and Commercial Craft Applications
The Perkins-Sabre M65 is the replacement engine for the Perkins 4-108.
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