switching from rh to lh rotation

rdj59 · Post by **rdj59** » Tue Jan 18, 2011 11:30 pm

Hello, I have a very tired lm318 that is need of a rebuild but like the old addage goes, there's no replacement for displacement. I'm contemplating of switching to a standard rotation chevy 400 that i have. I've been doing alot of reading and i get mixed reviews. I've read a couple that say you can switch the prop to a lh rotation and rotate the trans pump 180 and you'll be good. Others say you need to change the pump and get new gears in the trans. I have a fully dressed inboard 350 that im stealing all the front accesories from and just need the bellhouisng and starter. Current motor tops out at 3200rpm with a 14x7 prop with a lite cup and uses a little more than a quart of 15w40 per 1.5 hours. plus it has low compression, 100 psi and less. Motor has a little more than 3700 hours. Is it possible to just rotate the pump 180 and switch to a lh prop and be good?
Thanks,
Jeramie

prowlersfish · Post by **prowlersfish** » Wed Jan 19, 2011 6:56 am

If your changing the rotation of the engine and you have a Velvet drive , Just rotate the pump and change the prop .

You are putting 350 marine parts on a 400 SB Chevy ?
First do not use the 350 flywheel or balancer. the 400 is balanced differently

Also may sure all cooling system parts are at 100% . they need to be to keep the 400 from running hot .

Paul · Post by **Paul** » Wed Jan 19, 2011 10:43 am

Why not make the Chev a right hand rotation? A new cam shaft and timing gears and you're there. What type of boat? You might also consider using the 350 since it would be simpler to bolt up to the Velvet Drive. As Paul said the 400 is externally balanced which means that it's automotive fly wheel is part of the balancing and would need to stay in place. (unless of course you have the entire rotating assembly re-balanced with a marine fly wheel)

rdj59 · Post by **rdj59** » Wed Jan 19, 2011 10:50 am

So if i rotate the pump so it spins the right way per engine rotation then wont the output of the velvet drive rotate the same direction as engine rotation, requiring the use of a left prop instead of a right hand prop? Sorry if i'm over thinking all this.
Don't worry, i'm using a 400 balancer and a flywheel balanced for a 400. The engine is a pretty stock like boat rebuild. 9:1 comp, 5.7" rods, stock 70 400 heads rebuilt with a mild port job, edlebrock dp intake, holley 600 vac secondary marine carb, 212/218 on 112 deg lobe sep cam and center rise manifolds. Shouldn't overheat and don't worry, i boat in fresh water only, no salt water even close.
Jeramie

jav · Post by **jav** » Wed Jan 19, 2011 1:18 pm

Jeremy-

there's a couple different velvet drive variants. With a 318, you most likely have a 71C. If that's the case, my understanding is that changing the pump can address using the gear with a different rotation engine. HOWEVER - it does get somewhat confusing from here.

The consensus is that the 71C has different strength "forward versus reverse" gears. In other words- using the original engine and original prop lets say the transmission lever was towards the bell housing is the factory location to make the boat move forward. That "shift lever location" would be the high torque drive side of the gear. Reverse can handle bcaking up but it cannot handle driving the boat on plane like the forward direction can.

To be clear- if you trashed your original prop and had another just like it but in the reverse rotation- mounting it and running the gear in reverse to move forward would eventually damage the transmission.

The question then rises as to what is the "forward gear position" when running a differennt rotation engine and swapping the pump? I was always taught the direction of the transmission lever itself determines the higher torque drive setting. So if the lever is towards the bell housing now to move forward, the lever should also be towards the bellhousing after an engine rotation change. In that case- I believe you are correct that ultimately- the boats shaft will be spinning in the opposite direct to what it does now.

I would definitely dig deeper and don't take my word for it as it has been some years. Also- most people opt for the 72C when they they go above around 250HP... that's probably pushing a 71 to it's limits regardless of rotation.

prowlersfish · Post by **prowlersfish** » Wed Jan 19, 2011 1:22 pm

Yes just rotate the pump and change the prop ( my earlier post I said rotate the pump and change the pump not prop ,oops )

There is no "marine flywheel" marine engines use a standard transmission flywheel .

As far as running hot , as I said the cooling system has to be at 100% as a 400 will push the system to its limits , It would not be a bad idea to put a larger raw water pump on it (like one suited for a big block)

I have use the 400 more then once and know how sensitive it is to over heating

prowlersfish · Post by **prowlersfish** » Wed Jan 19, 2011 1:25 pm

A 72c would not be a bad idea at all . and yes the gear lever must be forward ( towards the engine) when going forward , revese can not handle full power

gettaway · Post by **gettaway** » Thu Jan 20, 2011 6:22 pm

this is something I m interested in as well, I have mercruiser 228's (gm 305's) that are counter rotating, I have velvet drive 1.52 :1 71C transmissions. If I replaced the engines with standard and like rotation (both rotating the same direction), I am under the impression that I would need to change the transmissions, one being a reverse gear so the shafts continue to counter rotate.
Is the forum saying that one could reverse the pump in the transmission so it will "pump" and then change on propeller? this would not cause the boat to walk to the side?

clarification would be greatly appreciated

prowlersfish · Post by **prowlersfish** » Thu Jan 20, 2011 6:43 pm

gettaway wrote:this is something I m interested in as well, I have mercruiser 228's (gm 305's) that are counter rotating, I have velvet drive 1.52 :1 71C transmissions. If I replaced the engines with standard and like rotation (both rotating the same direction), I am under the impression that I would need to change the transmissions, one being a reverse gear so the shafts continue to counter rotate.
Is the forum sain that one could reverse the pump in the transmission so it will "pump" and then change on propeller? this would not cause the boat to walk to the side?

clarification would be greatly appreciated

You are correct , you change the pump to match the engine . It your case if you where to install 2 engines that turn the same you would need to replace one transmission with one that could reveses the output direction , the good new is that velvet drive makes a 71/72 gear that will do so in your ratio.

On some other brands of gears like ZF you don't have and forward/reverse so to speak . You have a A position and a B position B reverses the power flow and can handle full power . so you can use that gear for counter rotation . Both my Engines are standard rotation I use ZF220A gears , one in A position the other in B position when going forward .

gettaway · Post by **gettaway** » Thu Jan 20, 2011 6:59 pm

Paul

thanks for the information, I was not aware that Velvet Drive had a 71/72 with the same ratio that was counter rotating, this is good news, I have repower plans in the future and have been trying to figure the cost for the total project. transmissions are a big factor unless replacing with counter rotating engines, my plans are for 130 -150 hp diesels.

20+ knots are not a requirement for me , 12-14 cruise would be ideal with 16-18 top speed

prowlersfish · Post by **prowlersfish** » Thu Jan 20, 2011 10:45 pm

I have not been able to find any listing on a 1.52 gear counter rotaion change , Even thought I am sure they made one , But I could be mistaken ( I will keep looking )
_________________

gettaway · Post by **gettaway** » Fri Jan 21, 2011 6:10 pm

Thanks for the help Paul,

I have been told that I need to go to a 1.91:1 (which counter rotates than engine) and a 2.1:1 (same direction as engine) and these are the closest in ratio for counter rotating velvet drives or I need to go to ZF 65(?) which can handle full power in either direction. this would be a $7,000 change, this would 86 the repower because of cost.
I doubt that my mercruiser 228's with 1000 hours are worth much, even with the transmissions. I hope to be able to find a used pair of transmissions or trade... I am not in a hurry so maybe something will come along