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Twin Screw Engine Rotation...

Posted: Mon Jan 30, 2017 2:45 pm
by carl
BigM

Re: Twin Screw Engine Rotation...

Posted: Mon Jan 30, 2017 4:04 pm
by honestcharlie56
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.

Re: Twin Screw Engine Rotation...

Posted: Mon Jan 30, 2017 7:11 pm
by Busia
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

Re: Twin Screw Engine Rotation...

Posted: Mon Jan 30, 2017 8:32 pm
by EWRice
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.

Re: Twin Screw Engine Rotation...

Posted: Tue Jan 31, 2017 2:09 pm
by carl
BigM

Re: Twin Screw Engine Rotation...

Posted: Tue Jan 31, 2017 2:12 pm
by carl
BigM

Re: Twin Screw Engine Rotation...

Posted: Tue Jan 31, 2017 2:14 pm
by carl
BigM

Re: Twin Screw Engine Rotation...

Posted: Tue Jan 31, 2017 2:19 pm
by carl
BigM

Re: Twin Screw Engine Rotation...

Posted: Tue Jan 31, 2017 2:48 pm
by Busia
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.

Re: Twin Screw Engine Rotation...

Posted: Tue Jan 31, 2017 4:04 pm
by honestcharlie56
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.