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Old 17-04-2016, 20:00   #1
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Rotate diesel engine in reverse?

I am trying to remove the prop shaft & coupling from my Perkins 4108. The 30 mm shaft is secured to the coupling with a 1-1/8" nut. I can't free the nut because the shaft rotates when I apply torque. The only way to get significant resistance To shaft rotation is to put my hurth HBW 150 v-drive tranny in reverse. Even then, There is still too much rotation to remove nut with a standard box wrench, but I think an air impact wrench would do the trick. But this will definitely cause the tranny and engine to rotate somewhat in reverse of their normal rotation. Does anyone know if this will cause damage?
thanks for guidance.
Tom
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Old 17-04-2016, 22:39   #2
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Re: Rotate diesel engine in reverse?

monkey wrench or vice grips on shaft and resting on a board for weight distribution. Longish piece of pipe on the spanner on the wrench. penetrating oil on thread. Should work. Check that the washer under the nut hasn't been bent up to lock the nut.
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Old 18-04-2016, 00:19   #3
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Re: Rotate diesel engine in reverse?

Try an alternate solution.

Put the prop back on and place a block of wood between a prop blade and the hull. Then go back inside and try the nut.
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Old 18-04-2016, 00:26   #4
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Re: Rotate diesel engine in reverse?

If you have the starter off, it is often possible to jam a screwdriver into the ring gear on the flywheel to lock up the crank.

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Old 18-04-2016, 00:49   #5
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Re: Rotate diesel engine in reverse?

It shouldn't cause a problem. Before hydraulic transmissions most diesels were made to rotate either way for twin installations. On some engines the only difference is the cam and starter.
If you're near a rental place or bigger auto parts store, they may rent an electric impact wrench. Also Harbor Freight has one for about $50.
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Old 18-04-2016, 09:19   #6
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Re: Rotate diesel engine in reverse?

If it is taking the engine backwards (reverse) just fix a wrench to the nut and tap the starter, (just make sure it doesn't start!) just tap the starter a touch, and you will loosen the nut.

Michael
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Old 18-04-2016, 09:31   #7
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Re: Rotate diesel engine in reverse?

Pipe wrench on the shaft. Be sure to file any marks off before removing the shaft thru the cutlass.
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Old 18-04-2016, 10:02   #8
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Re: Rotate diesel engine in reverse?

I assume you meant the 1 1/8" nut on the "Prop", not the coupling. Coupling's normally have little nuts, Props have the big nuts.

Put a heavy rag on the prop blade, hold it with your hand, and jam it to your shoulder. Then use an air impact wrench. You won't have to hold it with anything else.

An air wrench is much better than an electric impact wrench, which is itself many times better than a hand wrench.

There would be no problems turning the engine in reverse, but you shouldn't subject your transmission gears to the vibrations of an impact wrench.

Put the tranny in neutral, and hit the nut with the wrench. Use a 1/2", or larger, impact wrench, not some puny 3/8 wrench. It'll come off so fast, you'll wonder what the fuss was about.

Cheers, and happy wrenching.

Paul.

PS, use a proper 6 point impact socket. Bronze nuts won't take well to using an impact wrench with a 12 pointer.

You're also going to need a prop puller, and depending on the coupling configuration, you'll need a puller for that too.

And for heaven's sake, don't listen to CaptnMike's suggestion. That's really not safe.

Use any advice at your own risk.

If you're V-drive has a coupling I've never seen before, with a large nut as you describe. Put a pipe wrench on the coupling and use the air wrench as described above.

Good luck.
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Old 18-04-2016, 16:01   #9
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Re: Rotate diesel engine in reverse?

Using the starter motor? I can't stop visualising a wrench though the hull or worse, fingers crushed if the nut doesn't undo. Sailing is all about risk assessment and management- the what ifs.
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Old 18-04-2016, 16:02   #10
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Re: Rotate diesel engine in reverse?

I assume you have ensured whether it is a right or left hand thread and you are not trying to tighten it!
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Old 18-04-2016, 16:39   #11
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Re: Rotate diesel engine in reverse?

Hi ya
Get a 4x4 or similar size of wood, cut to a length that will hold the prop blade at right angles and the ground, place on the side that the prop will turn when you undo the nut, thus locking the prop so you can loosen the nut.
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Old 18-04-2016, 16:59   #12
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Re: Rotate diesel engine in reverse?

If its the shaft nut holding the CI Coupling to the reduction gear box, probably does have a locking devise on the nut, probably a nylock.
You should be able to hold the fwd coupling and use socket, but check nut for correct rotation and any possible locking devise, (tab washer, split pin etc)
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Old 18-04-2016, 17:57   #13
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Re: Rotate diesel engine in reverse?

Quote:
Originally Posted by dlymn View Post
Using the starter motor? I can't stop visualising a wrench though the hull or worse, fingers crushed if the nut doesn't undo. Sailing is all about risk assessment and management- the what ifs.

My error, I had the assumption people were smart enough not to hold the wrench as they bump the starter, but to block it against something suitable such as a block of wood. I guess that is why anything you buy nowadays has the first ten pages warning the operator not to use electrical appliances while standing in a swimming pool etc.
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Old 18-04-2016, 19:58   #14
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Re: Rotate diesel engine in reverse?

Quote:
Originally Posted by Lepke View Post
It shouldn't cause a problem. Before hydraulic transmissions most diesels were made to rotate either way for twin installations. On some engines the only difference is the cam and starter.
If you're near a rental place or bigger auto parts store, they may rent an electric impact wrench. Also Harbor Freight has one for about $50.
No No No! Oil Pump rotation is important too.
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Old 19-04-2016, 07:09   #15
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Re: Rotate diesel engine in reverse?

I have had my 1GM10 Yanmar start in reverse by accident a couple of times, I quickly stopped it then restarted it normally, doesn't seem to have done any harm but only running for couple of seconds. Nonetheless it probably did a hundred or more revolutions before shutting down, therefore the one or two revs that the impact wrench might induce is not likely to cause any issues IMHO.
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