83 Chris Craft engine question

Jeffgrant00

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Well, I recently purchased a 1983 Chris Craft 251 for what I thought was an absolute steal.
It came with a brand new chevy 305 crate engine already sitting in the mounts ready to be plumbed.
The issue is that the new engine is a standard rotation automotive engine with marine hardware installed. From what I have read and learned talking to people I may have bitten off a little more then I care to chew.
My question is, has anyone here changed the rotation on one of these transmissions and how big of a project is it? I cannot find and literature on how to even begin such a project. Would i be better off going a different route and looking for a marine engine to drop in?
 

alldodge

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First question is why do you want to change from standard (left hand) to right hand rotation, is it twin engine?

If it is twin and this is why you want RH motor this will take a cam change. The cam would have to be custom.

Which transmissions are installed?
 

Ned L

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Hmmm, ....... When did "LH" rotation become standard? I understand that automotive and marine have always been opposite each other, but in the marine world "RH" was always the standard, and "LH" was opposite or reverse rotation.

But, yes, to change the rotation you would need to change the cam, the starter, (maybe oil pump?) and the reverse gear (on some gears there is a plate for the internal oil pump that can be turned around to change direction).
 

alldodge

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LH has always been standard and is determined by looking at the flywheel, so looking at the front of the motor it rotates RH or CW

ROTATION.jpg
 

Scott Danforth

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Hmmm, ....... When did "LH" rotation become standard? I understand that automotive and marine have always been opposite each other, but in the marine world "RH" was always the standard, and "LH" was opposite or reverse rotation.
.

it used to be that way for some marine motors....... now its no longer that way. the cost of a RH motor vs simply improving the drives.....

LH rotation is standard for motors


Jeffgrant00 , which trans do you have. do you have a single or twins. if single, the 305 is woefully underpowered in the 251.
 

Broaters

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From the mercruiser manual.

LH is the std for all sterndrive.
check with your propulsion type as suggested in previous answer.
​if you ever need to convert to RH you need a camshaft, cam gear instead of chain and probably starter...

 

CrazyFinn

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The OP's Chris Craft 251 is a straight inboard (NOT a sterndrive), single engine, likely a Paragon transmission. Engine mounted in the middle of the boat. Reverse rotation is how they were built from the factory. His problem is that he bought the boat with a standard rotation engine, and is now trying to figure out what to do with it.

So - either he needs to reverse the rotation of the engine, or the transmission, or find another engine or transmission. Or maybe those transmissions can be run either way with some small changes, and he just needs a new prop. I think - from my earlier research - that the main concern is the oil pump in the transmission. Anybody know the answer?

Cool boat though - I considered buying one before I got my 240.
 
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Scott Danforth

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I personally would drop in a BBC and newer trans, like a Hurth or ZF
 

Jeffgrant00

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Thank you all for the quick responses!
The original engine to the boat was a 305K, on the water jackets the firing order stamp says 1-2-7-5-6-3-4-8 and to my knowledge (((which is limited!!))) Is reverse rotation i think? The transmission is a PM10R made by paragon, the plate is so faded and beat up i can hardly read it. The only numbers on it are 518 off to the far left and then PM10R Z-8249

I am at a complete loss as to what i have and what route to take? The engine is bran new, never even had oil in it but an anchor to me if its spinning the wrong way??!
 

Jeffgrant00

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Would it be more cost effective to change the rotation of the engine or the transmission? This subject has my head spinning,, literally!!!
The boat was completely gutted and i thought that as long as the drive and engine were good I would be in great shape.
 

alldodge

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Would it be more cost effective to change the rotation of the engine or the transmission? This subject has my head spinning,, literally!!!
The boat was completely gutted and i thought that as long as the drive and engine were good I would be in great shape.

If you can find a tranny I would go that route. It will cost to change the motor over, the main benefit is no longer have to find things that are no longer made to repair. You could probably find a used tranny from a rotted hull.
 

Ned L

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Maybe,......... Do you have the prop that came with the boat? One look at that and we can tell you what rotation was in the boat.
 

alldodge

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That is a RH prop, you need a RH engine or change the prop and trans

Posted before I thought about it
 

Jeffgrant00

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Thats what I was afraid of. Well,,,,,, im in the market for either an engine or a tranny & prop if any of you fellas have one for sale

Thank you all again for the help!
 

Ned L

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Yep,... RH prop.

Next question I'll ask is where is the flywheel on the original setup. For years the Chris Craft SBC marine engines were set up fly wheel forward, with the reverse gear driven off the timing chain end of the engine (fan/radiator end in the car).
As new as the early '80's I don't know which way they were building them. Certainly the 50's, 60's and 70's were flywheel forward.
 
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alldodge

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Don't want to discuss buy/sale
Is this a straight shaft, offset or V drive trans. My guess is its straight?
 

Jeffgrant00

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Straight shaft, coupler from the rear of the transmission to the screw shaft.
The flywheel is on the rear of this engine, i cant speak as to where it was on the original because i never saw it. The guy i got it from was pretty excited to see the boat go for minimal money amd now i see why!
 
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