Twin Screw Engine Rotation...

Engines, Shafts, Steering, Struts, Rudders, etc.
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carl
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Twin Screw Engine Rotation...

Postby carl » Mon Jan 30, 2017 2:45 pm

Here is another string of questions, this time about engine rotation. I have a 1990 32’ Fly Bridge Sedan. It is powered by two 350 Cu. In. Crusader engines with closed loop cooling. Both engines start right up and sound great; however, just like every other part of my boat I will be visiting both engines in the near future. I do understand that one engine is a normal rotation (Left Hand) while the other is a reverse rotation (Right Hand). I have spent very little time with my engines to date since I bought this vessel focusing on the interior. Looking for answers to the following:
1. Does this mean that my propellers will not be identical; I mean will they have been cast with an opposite profile to one another to accommodate the opposing rotation? (I have yet to see my props)
2. How about my transmissions? Are they also rotating in opposite directions?
3. Is one of the distributors different than the other (reverse rotating) or are the spark plug wires on the reverse rotation motor simply arranged on the distributor cap in a different sequence to meet the reverse rotating engines firing order?
4. The alternator?
5. The water pump?
6. Starter motor?
7. Anything else I’m not aware of regarding the differences between the Port and Starboard engines?
Last edited by carl on Thu Feb 09, 2017 6:31 am, edited 2 times in total.
1990 Marinette 32' Sedan Fly Bridge "IKOI"
Twin Crusader 350's (Closed Loop Cooling)
Bow to Stern Full On Restoration in Progress
Chickamauga Lake, Tennessee
A boat is always safe at shore, but that's not what its built for...

honestcharlie56
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Re: Twin Screw Engine Rotation...

Postby honestcharlie56 » Mon Jan 30, 2017 4:04 pm

1. Yes, the props will be mirror images of each other. Exact opposites. Port must spin Counterclockwise when viewed from aft forward and stbd must spin clockwise. This does a number of things such as keeping the props from sucking air, which they are more likely to do if the blades were to pull from the exterior of the boat towards keel. This is why they spin keel outwards.
2. Yes, your transmissions will rotate in opposite directions. Assuming you have Velvet Drive 71C's they are only designed to operate at rated power in the forward gear. If you were to accidentally swap the props, you couldn't just run them "in reverse" to go forward......at least not for long.
3. I'll let a GM guy answer that one. I haven't messed with a counter rotation GM in 7 years!
4. See Above.
5. See Above.
6. Willing to bet this will spin counterclockwise.
7. Not sure.
1990 Marinette 32 Sedan Flybridge "Hubba"
Twin Chrysler 318's

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Busia
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Re: Twin Screw Engine Rotation...

Postby Busia » Mon Jan 30, 2017 7:11 pm

I have 350 crusaders also, send me a message here or if anybody wants to talk about anything---cell is 907-617-7832 home phone is 907-247-2874. The alternators are the same, water pumps are the same. The starter motors are different, and the serpentine fan belts are different. I have the factory manuals, if you need info. The part numbers are Crusader numbers, but slowly getting Chevy and Napa part numbers. Now take pictures and use ShrinkPictures.com to make them work here. We want to see all the work you are doing. Good luck, Ed
BUSIA
located in Ketchikan, Alaska. Gods country
32 foot Marinette express. (no fly bridge)
twin 350 Crusader (Chev 350) engines
1:1 Borg Warner velvet drive transmissions
Closed cooling (antifreeze in the engine)
Proud to be retired IBEW

EWRice
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Re: Twin Screw Engine Rotation...

Postby EWRice » Mon Jan 30, 2017 8:32 pm

The true marine water pumps for the GM engines (and most for that matter) have stainless straight blades instead of the angled blades. This makes them bi-directional. They also have a different seal setup for raw water.

The distributors are identical. The rotor rotation is the same for both engines, but the firing order is different. I will make a recommendation if you still have points style distributors and would like to upgrade to electronic. Crusader sells a conversion kit with all NEW parts: Delco HST distributor, coil and bracket, wire harness, plug wires and instructions. These will fit any flywheel aft, std. deck Chevy small or big block engine. Crusader, Mercruiser, OMC, Chriscraft, etc. Highly recommended. Not that expensive, either.

3 different types of starters, in 2 different rotations available. Prestolite, Delco and various aftermarket PMGR (Permanent Magnet Gear Reduction) starters.

Alternators do not care which direction they spin. There were a few different styles used. There is now a Delco SE (Self Exciting) 10SI available with the correct mounting frame. This is a one wire unit.

If you get into the raw water pump, be aware that the pumps are the same but the hoses are reversed on the opposite rotation engine.
Muskegon Lake
1972 32' Express flybridge
Twin 318s
On board air & prime 920
1963 Thompson Super Sea Lancer
Graymarine 327
1961 Alumacraft 12'
'55 10hp Johnson

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carl
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Re: Twin Screw Engine Rotation...

Postby carl » Tue Jan 31, 2017 2:09 pm

I understand the rotation of a motor comes from the crankshaft. I can see the timing chains spinning the cams and the valve trains and also driving the distributors. I just looked at right hand and left hand rotating engine diagrams on the web and both distributors are rotating in the same direction with different firing orders, I always knew a chevy distributer is driven from the cam gear mesh. So if one engine is rotating clockwise and the other engine is rotating counterclockwise then how in the heck are both distributors rotating in the same direction? Killing me!
Last edited by carl on Thu Feb 09, 2017 1:25 am, edited 1 time in total.
1990 Marinette 32' Sedan Fly Bridge "IKOI"
Twin Crusader 350's (Closed Loop Cooling)
Bow to Stern Full On Restoration in Progress
Chickamauga Lake, Tennessee
A boat is always safe at shore, but that's not what its built for...

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carl
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Re: Twin Screw Engine Rotation...

Postby carl » Tue Jan 31, 2017 2:12 pm

I am starting to assume that the cams and the distributors are different from one engine to the other, perhaps the cams are rotating opposite each other but the gear mesh on the cams and distributors are set to rotate both distributors in the same direction?
1990 Marinette 32' Sedan Fly Bridge "IKOI"
Twin Crusader 350's (Closed Loop Cooling)
Bow to Stern Full On Restoration in Progress
Chickamauga Lake, Tennessee
A boat is always safe at shore, but that's not what its built for...

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carl
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Re: Twin Screw Engine Rotation...

Postby carl » Tue Jan 31, 2017 2:14 pm

I can also understand the need for the two starters to be different from one another right, because they need to rotate the motors in opposite directions to start. Correct?
1990 Marinette 32' Sedan Fly Bridge "IKOI"
Twin Crusader 350's (Closed Loop Cooling)
Bow to Stern Full On Restoration in Progress
Chickamauga Lake, Tennessee
A boat is always safe at shore, but that's not what its built for...

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carl
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Re: Twin Screw Engine Rotation...

Postby carl » Tue Jan 31, 2017 2:19 pm

My Borg-Warner Velvet Drive transmissions must be configured to rotate opposite of one another as well right, with your explanation that they must operate in the forward direction, so this means that Borg-Warner has a clockwise and a counterclockwise rotating transmission, correct?
1990 Marinette 32' Sedan Fly Bridge "IKOI"
Twin Crusader 350's (Closed Loop Cooling)
Bow to Stern Full On Restoration in Progress
Chickamauga Lake, Tennessee
A boat is always safe at shore, but that's not what its built for...

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Busia
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Re: Twin Screw Engine Rotation...

Postby Busia » Tue Jan 31, 2017 2:48 pm

Same transmission, just set up to turn which ever way you want. Some of the accessories on the front of the Crusader engine spin the same way even if the engine rotates the other way. They do this by having an extra idler pully and a longer serpentine belt. It wraps around so it goes around the other direction on some pullies.
BUSIA
located in Ketchikan, Alaska. Gods country
32 foot Marinette express. (no fly bridge)
twin 350 Crusader (Chev 350) engines
1:1 Borg Warner velvet drive transmissions
Closed cooling (antifreeze in the engine)
Proud to be retired IBEW

honestcharlie56
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Posts: 200
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Re: Twin Screw Engine Rotation...

Postby honestcharlie56 » Tue Jan 31, 2017 4:04 pm

Assuming Borg Warner Velvet Drive 71C's check the model number and let us know. But the velvet drives are easy to swap rotation. The front pump can be indexed clockwise or counterclockwise wise to accommodate either rotation engine. As I stated earlier though, there are two clutch packs inside the transmission, one is meant for the rated power and one is meant for reverse. You cannot run the rated power of the transmission through the reverse clutch pack. I have some pictures I can dig up to show you.
1990 Marinette 32 Sedan Flybridge "Hubba"
Twin Chrysler 318's


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