Standard Rotation

Bruce Herrington

Bruce Herrington

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Just bought distributors for the twin 7.4 Crusaders, inboard straight shaft coupled to BW Velvet Drives.

Does standard rotation refer to LH? I guess if one doesn't work right, use the other?
 
Yes, but not necessarily on the left side of the boat. Traditionally, automotive engine rotate in a counterclockwise position when viewed from the flywheel looking forward. Thus they are commonly called "left hand" or normal rotation. A right-hand or reverse rotation turns clockwise. Some boat manufacturers, i.e.: Bertram used reverse rotating transmissions on both sides and thus the LH turning engine was on the right side of the boat. I recall that my old Palmer Internationals were installed with the front facing aft and had the transmission mounted to the front of the engine with an exposed flywheel.

You do need to tap the starter and see which way the crank balancer turns. If looking from flywheel to balancer in turns counterclockwise-its LH. By the way, both distributors should turn in the same direction regardless of the direction of the crankshaft. The gear at the bottom of the distributor shaft is reversed for the opposite rotating engine.

If I remember correctly, the distributor shafts on my 454 Mark IVs both turn clockwise when viewed from the flywheel end of the engine. The firing order is different but not the direction of turning.

Gene
 
Same on my crusaders, they use the same distributor even though one is a counter rotation engine.
Had to send back one of the delco voyager kit distributors and get a standard rotation one.
 
Visual aid for Gene's good explanation:
http://www.arcomarine.com/xhtml/tech determine marine starter rotation.pdf
The distributor rotor shafts on those GM engines will tune CW on both the standard LH/CCW and reverse-rotation RH/CW engines .

(If you have the Series 71c, or more likely 72c to handle the 7.4L power, the transmission output rotation may be either same or reverse(like mine) of engine rotation, depending on particular gear ratio, so always go by engine rotation not just prop LH/RH or side of the boat engine is on. )

VTBoater- Did you mean you had to send back one of the standards and get 1 Voyager EST specifically for the RH ...reverse... rotation engine? I had to get a Voyager kit of each type for my old RH/LH engines. Reverse Voyager was pricier( now +$100) . Great distributors & kit.
 
For some reason Crusader must have made some changes through the years, so it seems very dependent on when they were made.
I had ordered one standard and one RH rotation kit, thinking that is what I needed because one engine turns opposite. But the RH motor still had a standard rotation distributor. So I had to send back the RH distributor and get a standard one.
I am liking the way the engines are running now with these installed.
 
I use the same distributor in both my Crusaders. LH and RH rotation... no problem. You can use the same distributor in both the small block and big block Chevy.
 
quote:
Originally posted by VTBoater

For some reason Crusader must have made some changes through the years, so it seems very dependent on when they were made.
I had ordered one standard and one RH rotation kit, thinking that is what I needed because one engine turns opposite. But the RH motor still had a standard rotation distributor. So I had to send back the RH distributor and get a standard one.
I am liking the way the engines are running now with these installed.

Click to expand...


Repeating info above, both LH and RH GM engines' distributor rotors turn CW. Main difference in the LH and RH engines' distributors is they have opposite-cut bevel gears at the bottom to match the different oil pump drive gear.

If the distributors you used on your 2 engines were exactly the same including gear, I would imagine the engines were actually both standard LH CCW-flywheel rotation and they were just hooked up to "full-reversing" transmissions rigged same-input/ opposite-output of each other,( or attached to opposing stern drives.)

But if you meant you originally ordered 1 of the distributors to have the rotor shaft turn CCW, the it sounds like you likely ordered or at least received & sent back a dist. meant for a Ford engine whose distributor rotate opposite of GMs.

Anyway, apparently you ended up with what you needed and are nicely squared away.
 
The hei that I ordered specified standard rotation only, so I called them up and ordered one for non-standard rotation; it only cost $100 more! :-(
Plan to install them this weekend. Really appreciate all the help. Maybe one day I can return the favor. :-)
 
Bruce - I will be a little surprised if you are able to use that non standard rotation distributor, maybe depending on the year.
I had a mechanic do the install of my kits, since I did not know much about engine timing. He verified by flywheel rotation that the engines were turning in opposite directions, so the transmissions are not doing the reversal work.
There must be a reversed gear at the bottom where the distributor meets on some models, mine is one of them.

So if yours are around 1988 vintage, you may run into the same scenario. Pull the distributor caps and crank over and watch the rotor rotation and you will know right away if they are turning in the same direction or opposite directions.
 
The engines originally had points and condensers, so they may be older than '88 models. I know they rotate differently because the raw water pumps are plumbed opposite one another.
 
Yes to both of those on my engines as well, I think mine were the last year before they stopped using the points.
 
Jamie,
I never had twins so I never did much thinking on the subject, but, It seemed to me the cam and dist gear had to be reversed if the engine turned opposite. The cam should have lobes specially ground for opening and closing ramps.

Also, why would a reverse dist cost $100 more when all that needed to be changed was the gear. Boy they try to hook you for everything marine.
 
quote:
Originally posted by VTBoater

Bruce - I will be a little surprised if you are able to use that non standard rotation distributor, maybe depending on the year.
I had a mechanic do the install of my kits, since I did not know much about engine timing. He verified by flywheel rotation that the engines were turning in opposite directions, so the transmissions are not doing the reversal work.
There must be a reversed gear at the bottom where the distributor meets on some models, mine is one of them.

So if yours are around 1988 vintage, you may run into the same scenario. Pull the distributor caps and crank over and watch the rotor rotation and you will know right away if they are turning in the same direction or opposite directions.

Click to expand...


My old GM carbed Crusaders were 1988 too. Again, the rotors turned the same (always CW on both standard LH and reverse LH rotation GM engines.) But the distributors are not the same as the bevel gears are cut different direction. If you used the "same, standard dist.", the bevel gear was changed out or a "standard " distributor for Crusader's GM motors would not go in & engage the oil pump gears on a RH engine. It would not work. Without changing anything , you can't pull the dist. out of your LH engine and make it work on your RH rotation engine.
With some electronic distributors , more than just the bevel gear is different between dist.s for LH and RH engines.
FWIW, My 2003 MPI LH and RH Crusaders still both have CW turning rotors but the standard LH distributor is a stock electronic Delco with cast alu housing but the reverse RH engine's distributor is machined by Crusader out of billet alu ( and has reverse bevel gear of course) according to the factory tech. Both OEM but different.
 
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