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question about opposite rotating engine

M

Mike29

Contributing Member
Hi folks!
There is a guy at the yard with a Chris-Craft express running twin crusaders. He purchased a new motor to replace a blown one but it is standard rotation and he needs opposite. I read somewhere that you can switch plates in the borg warner units to make them run reverse rotation. Is this true? His new motor has only 10 documented hrs on it and he is talking about tearing it down to put the reverse rotation cam in. Thought I would ask here as it would seem easier to me to have the gear do the job than tear down his new motor.
 
The answers to both questions depend on the age/model of the transmission and the engine. A motor usually needs more than a different cam to run reverse. Most older BW xmssions will not reverse shaft rotation internally. You might be confused with the ability to RUN forward CW or CCW, but it may not always allow CW in with CCW out, etc.
 
[FONT=&quot]Rotating the oil pump in these older trans will only match the pump with input (engine)rotation. The output rotation will be the same as the engine rotation[/FONT].
 
Unfortunately the Chris-Craft express owner approached this purchase without educating himself regarding RH or LH engines.

In order to change a Standard LH rotation engine over to a Reverse RH rotation engine, it will require:


  • a change to the piston wrist pin offset (offset now will be reversed).
  • a change to the camshaft profile.
  • a change to ignition firing order.
  • a change to the distributor "driven" gear (unless the cam is twin gear driven).
  • the distributor now needs to counter a downward shaft thrust (unless the cam is twin gear driven).
  • oil pump remains the same for either cam drive scenario.
  • both front and rear main seals must be RH rotation capable.
  • engine circulating pump housing and impeller must be RH rotation capable (the Marine version usually is).
  • and it would not hurt to index (mark off) the harmonic balancer for REV Rotation ignition timing.

IOW, to do this correctly, there is more required than a simple camshaft change!

He may be better off to sell this engine and build himself a REV RH engine.
Or perhaps install this engine in the Port side, and then over-haul the Port engine to become his fresh Starboard REV RH engine.



.
 
..."a change to the piston wrist pin offset (offset now will be reversed)."

Right on, RIck! It's amazing how many "maraine mechanics" don't know about this. I've argued 'til I'm blue in the face with some, and all for naught.

Jeff
 
fastjeff said:
Right on, Rick! It's amazing how many "maraine mechanics" don't know about this.
Jeff
Click to expand...
Oh I hear ya!

You'd also be surprised at how many do not understand the vertical thrust load on the distributor shaft.
While the shaft and oil pump maintain standard rotation, standard LH rotation places an Up-Lift on the shaft.
This thrust is checked or countered via the two gear to housing surfaces.
Older units used a bronze washer here.

Reverse cut gears (although the shaft rotation is the same) places a down-load on the shaft.
So technically, the RH distributor should have a down-force thrust surface at the upper side.

Mallory (for example only) offers a YLM624AV (standard rotation) and a YLM624BV (reverse rotation).

.
 
Last edited:
Don't forget to add the starter to the list...if the engine uses V-belts up front, you may have to add the alternator's fan to the list as well.
 
True, but many alternators have a fan blade design that works either direction. Ditto the circulating pump on a small blcok Mopar.

Jeff
 
Not to mention that the RH Reverse rotation engines work only in the Southern hemisphere.
If you are lucky, you may get one to work at the Equator. :D
 
Hey guys thanks for the info. Great info as ussual. I was told crusader turned everything around on the cw motor... pistons face with arrows to back of block etc and you guys have brought up stuff that I was not knowledgable about. I will mention it to him. I was thinking when time to repower on my own boat of using the 8.1 crusaders if I can't find a pair of Cummins. I realize now I will need the gears too to spin my props the right way.
 
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