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Old 17-04-2020, 02:42   #16
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Re: Engine Swap

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Originally Posted by mvweebles View Post
Some gears (transmissions) are designed to do just this. Twin engine power boats have counter rotating props - stbd engine has a RH prop, port has a LH prop. Either the crankshaft reverses direction or the transmission does. Years ago, Detroit Diesel made left and right engines - mirror images of one another. These days it's all done via the gear.
BTW - I should have added that not all transmissions operate in reverse the same as forward. Before doing this, you would need to consult the manufacturer. GL brings up a good point about matching the gear to the engine, shaft, and prop.
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Old 17-04-2020, 13:38   #17
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Re: Engine Swap

I know from experience that Detroits will run in either direction if stalled and force reversed. Interesting to watch with the old mesh on oil bath air cleaners.
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Old 19-04-2020, 16:43   #18
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Re: Engine Swap

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Originally Posted by mvweebles View Post
Some gears (transmissions) are designed to do just this....

The one dad looked at wasn’t. Hence the bandsaw impersonation.
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Old 19-04-2020, 16:44   #19
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Re: Engine Swap

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I know from experience that Detroits will run in either direction if stalled and force reversed.

I remember reading somewhere on CF that some older ship engines worked this way.

I think it was in the context of “don’t expect a ship to stop quickly “.

I certainly filed it under “good to know”.
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Old 19-04-2020, 17:23   #20
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Re: Engine Swap

I think a lot of ship engines still work this way. It removes the need for a gearbox!
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Old 19-04-2020, 18:49   #21
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Re: Engine Swap

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Originally Posted by GILow View Post
I remember reading somewhere on CF that some older ship engines worked this way.

I think it was in the context of “don’t expect a ship to stop quickly “.

I certainly filed it under “good to know”.


Virtually all (conventional) ship engines operate this way.

However these huge engines are designed to to this, lube oil is supplied by electric pumps so direction of rotation doesn’t matter. Camshafts slide fore-aft to align different lobes with the exhaust valves and injection pumps...etc.
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Old 19-04-2020, 19:27   #22
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Re: Engine Swap

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Originally Posted by Sailmonkey View Post
Virtually all (conventional) ship engines operate this way.

However these huge engines are designed to to this, lube oil is supplied by electric pumps so direction of rotation doesn’t matter. Camshafts slide fore-aft to align different lobes with the exhaust valves and injection pumps...etc.


I try not to make a habit of getting in front of big ships, but I was kinda hoping the majority of them were NOT using this system. I seem to remember the original poster remarking that it took a number MINUTES to engage reverse.
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Old 19-04-2020, 21:36   #23
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Re: Engine Swap

I have the same shaft alignment issue. My engine is out of the boat for some service and when I reinstall it I want to check the alignment. The articles/videos I've seen involve moving the engine up/down/sideways etc. to align with a shaft that is fixed in position. My question is how do I get the shaft aligned and fixed in the correct position. The shaft is in the boat, and the boat is out of the water. However, is not practicable to remove the shaft and use laser as suggested above.
The shaft is only supported by the cutlass bearing and the gearbox, so when the gearbox is out, the shaft is free to move 2 or 3 inches in any direction. How do I make sure it is properly aligned in the cutlass bearing? Eyeball or ??
How critical is the alignment with the cutlass bearing as compared to the engine/shaft alignment?
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Old 19-04-2020, 22:08   #24
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Re: Engine Swap

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Originally Posted by Sailmonkey View Post
Virtually all (conventional) ship engines operate this way.

However these huge engines are designed to to this, lube oil is supplied by electric pumps so direction of rotation doesn’t matter. Camshafts slide fore-aft to align different lobes with the exhaust valves and injection pumps...etc.
Most of them are two strokes with two oil systems. The lower one is for the crankshaft etc down the bottom end of the engine, and is seldom changed, the upper for piston lubrication and is sacrificial.

There is a sealed push rod under the piston which works in the air pressured plenum. Under the plenum seals are cross head slides to which the crank rods are attached.

They are direct drive to the prop shaft and run at about 700 RPM. With the mass of rotating metal it probably takes a minute or two for them to reduce to reversing speed then get back up to reversing speed.
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Old 19-04-2020, 23:22   #25
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Re: Engine Swap

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Originally Posted by osprey877 View Post
I have the same shaft alignment issue. My engine is out of the boat for some service and when I reinstall it I want to check the alignment. The articles/videos I've seen involve moving the engine up/down/sideways etc. to align with a shaft that is fixed in position. My question is how do I get the shaft aligned and fixed in the correct position. The shaft is in the boat, and the boat is out of the water. However, is not practicable to remove the shaft and use laser as suggested above.

The shaft is only supported by the cutlass bearing and the gearbox, so when the gearbox is out, the shaft is free to move 2 or 3 inches in any direction. How do I make sure it is properly aligned in the cutlass bearing? Eyeball or ??

How critical is the alignment with the cutlass bearing as compared to the engine/shaft alignment?


If your shaft was currently connected, then you can just make a temporary cradle/frame to support it in that position before you disconnect the engine. Make it good enough and you can keep it for next time too.

But yours isn’t, so the simplest way I know of is to put a marker pen through one of the flange holes, “wobble” the shaft through a full circle of movement while drawing a circle on a reference board, find the Center of the circle on the reference board in the usual way, then line the flange hole up with the circle Center.

Not perfect, but should be close

Cutless bearings do like to be reasonably straight, but nothing like the tolerances required for the coupling.
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Old 19-04-2020, 23:49   #26
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Re: Engine Swap

You can use an outward pointing set of dividers to align the gearbox out put shaft with the inside of the prop drive shaft,

I had no room to use any thing else, I did mine over the last two weeks,
This will make the gear box square with the prop shaft,
Up and down on the engine mounts till the four points on the gear box and input shaft are identical,
Top and bottom, and both sides have to be Identical,

If the engine bed is level and square to the prop input shaft, Its just a matter of lifting the engine to suit the height,
Then adjusting the mounts to get it square, Both ways,
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Old 20-04-2020, 19:10   #27
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Re: Engine Swap

Quote:
Originally Posted by RaymondR View Post
Most of them are two strokes with two oil systems. The lower one is for the crankshaft etc down the bottom end of the engine, and is seldom changed, the upper for piston lubrication and is sacrificial.



There is a sealed push rod under the piston which works in the air pressured plenum. Under the plenum seals are cross head slides to which the crank rods are attached.



They are direct drive to the prop shaft and run at about 700 RPM. With the mass of rotating metal it probably takes a minute or two for them to reduce to reversing speed then get back up to reversing speed.


You’re a little fast @ 700 rpm. (Medium speed engines) They’re direct drive @ less than 200 rpm (slow speed engines).

I worked as a ship mechanic apprentice through college, I was usually delegated to rebuilding the stuffing box, measuring the cross head slides, or rolling bearing shells in/out. Hot dirty work, but interesting.
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Old 20-04-2020, 20:49   #28
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Re: Engine Swap

Quote:
Originally Posted by Mr B View Post
You can use an outward pointing set of dividers to align the gearbox out put shaft with the inside of the prop drive shaft,

I had no room to use any thing else, I did mine over the last two weeks,
This will make the gear box square with the prop shaft,
Up and down on the engine mounts till the four points on the gear box and input shaft are identical,
Top and bottom, and both sides have to be Identical,

If the engine bed is level and square to the prop input shaft, Its just a matter of lifting the engine to suit the height,
Then adjusting the mounts to get it square, Both ways,
Quote:
Originally Posted by GILow View Post
If your shaft was currently connected, then you can just make a temporary cradle/frame to support it in that position before you disconnect the engine. Make it good enough and you can keep it for next time too.

But yours isn’t, so the simplest way I know of is to put a marker pen through one of the flange holes, “wobble” the shaft through a full circle of movement while drawing a circle on a reference board, find the Center of the circle on the reference board in the usual way, then line the flange hole up with the circle Center.

Not perfect, but should be close

Cutless bearings do like to be reasonably straight, but nothing like the tolerances required for the coupling.
Thanks. I’ll try your suggestion.
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Old 20-04-2020, 23:04   #29
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Re: Engine Swap

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Originally Posted by Sailmonkey View Post
You’re a little fast @ 700 rpm. (Medium speed engines) They’re direct drive @ less than 200 rpm (slow speed engines).

I worked as a ship mechanic apprentice through college, I was usually delegated to rebuilding the stuffing box, measuring the cross head slides, or rolling bearing shells in/out. Hot dirty work, but interesting.
Don't know where that number came from, "Emma Maersk's" is rated at 109,000 hp at 102 rpm.
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Old 21-04-2020, 06:24   #30
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Re: Engine Swap

A few piccys on mine, I hope you dont have to stand on your head like I did to get it all lined up down the hole in the deck on the transom,

It is very time consuming, As the full weight of the motor and gearbox must be sitting on the engine mounts to line it up,

Turn the prop shaft to get a good reading on the dividers, Left and right side and up and down, Top and bottom,

Cheers, Brian,
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