counter rotating engines

[chas285]

I have a 26 foot sedan cruiser wellcraft. Twin inboards 305 chevy mercruisers. I replaced the starboard engine with a converted car engine. I got the rebuilt 305 and changed all the components to the marine version. this is the counterrotated engine. I was told by a teacher of votec that the counterrotated engine pistons have to be turned 180 degrees then put back in. he said that the other way will work but the engine wont last as long. any thoughts? thanks

 

[DJ]

Re: counter rotating engines

chas,<br /><br />Never heard of the pistom rotation issue. The only reason I could see for that would possibly be the valve clearance reliefs in the piston tops.

 

[chas285]

Re: counter rotating engines

He gave the reason, but i forgot what the reason was. I was only thinking of all the work I might have to do to rectify the situation. I will have to ask him next week

 

[snapperbait]

Re: counter rotating engines

Far as I know, OE. and most aftermarket (with the exception of some HP pistons) pistons for SB Chevys have four symetrical valve reliefs, so it does not matter if the pistons go in either way...<br /><br />Please let us know when you find out the vo. tec's reason.. Interesting?

 

[Capt Ken]

Re: counter rotating engines

That one I'd like to hear also. Been doing it for 30 years and chevy pistons don't know what side they're on. Just put the notch toward the front. Even from the factory the notch is toward the front. I wonder if he means to reverse the rods rather than the pistons?

 

[chas285]

Re: counter rotating engines

I just looked at the old engine block and the notches are reversed. On the standard engines they face front. these are flat top pistons so I dont think it has anything to do with the valves.

 

[flashback]

Re: counter rotating engines

I believe the wrist pin is slightly off center to the center line of the piston in an attempt to reduce wear. shoot I can't remember. but I read something on this a long time ago......

 

[ODDD1]

Re: counter rotating engines

Flashback hit the nail on the head...the piston/rods are rotated 180* [notch to the rear] because of wrist pin offset in the piston...the pin is offset to compensate for side thrust of the piston with a 'normal' rotation...reverse the rotation, offset the wrist pin to the other side of the piston.

 

[flashback]

Re: counter rotating engines

Thank you Oddd1, I knew I had that memory somewhere, anyway chas285, if your engine is complete now, I would most likely leave it alone but figure on it not lasting quite as long, only other option is to tear it down and flip the pistons.......good luck.........

 

[chas285]

Re: counter rotating engines

thanks for the info. I lean towards popping the engine out to reverse the pistons even though it means having the guy at the marina lift it out with the crane at a cost of 75 bucks.

 

[chas285]

Re: counter rotating engines

how long do you figure the engine would last ?