full circle crank in rude??

[sasbenson]

Pin weight

Yes indeed!! a lighter pin helps any racing engine providing it doesn't fail. The service piston and pin for the 49inch motor is in serious need of a diet!! You can actually buy a small block chevy racing piston which is lighter!!! Keep in mind though, the engineers designed this engine for a low rpm powerband with max rpm only being 5500. In the past ,We have seen a lot pin/bearing failures in the early engines as a result of a too small (in diameter) pin in combo with these heavy pistons. The later style connecting rod which has a bigger pin and improved beam is much better in this regard and has proven to be a reliable part even at higher rpm levels. This rod BTW, is also common to many 25-35 hp twins. The Mod 50,which was really just a modified service engine (at first!) needed a lighter better piston and a longer rod in order to make any power at higher rpms so they had TRW do the pistons and used the longer "big twin" rod with a .75 pin. Excellent piston (except for the ring package) in my opinion. The rod however, was/is not that great. The method used by OMC to break the cap leaves a very small footprint to hold things together under high stress and they WILL fail at high rpm!!! The best advice I would give to people using this powerhead is not to try and make it into something it isn't( high rpm racing engine) but instead,take advantage of the excellent wide torque band and reliabilty of this engine with your propellers and setup. And maybe a little bigger boat !!!



Benson

[pro350hydro]

Re: Pin weight

Originally posted by sasbenson
Yes indeed!! a lighter pin helps any racing engine providing it doesn't fail. The service piston and pin for the 49inch motor is in serious need of a diet!! You can actually buy a small block chevy racing piston which is lighter!!! Keep in mind though, the engineers designed this engine for a low rpm powerband with max rpm only being 5500. In the past ,We have seen a lot pin/bearing failures in the early engines as a result of a too small (in diameter) pin in combo with these heavy pistons. The later style connecting rod which has a bigger pin and improved beam is much better in this regard and has proven to be a reliable part even at higher rpm levels. This rod BTW, is also common to many 25-35 hp twins. The Mod 50,which was really just a modified service engine (at first!) needed a lighter better piston and a longer rod in order to make any power at higher rpms so they had TRW do the pistons and used the longer "big twin" rod with a .75 pin. Excellent piston (except for the ring package) in my opinion. The rod however, was/is not that great. The method used by OMC to break the cap leaves a very small footprint to hold things together under high stress and they WILL fail at high rpm!!! The best advice I would give to people using this powerhead is not to try and make it into something it isn't( high rpm racing engine) but instead,take advantage of the excellent wide torque band and reliabilty of this engine with your propellers and setup. And maybe a little bigger boat !!!



Benson

Thanks for the detailed post. I'm sure this knowledge will not go unnoticed by all the FE guys around here.

Mike

ps how is project "56"

[sam]

So, Phil's repro pistons might be copies of the TRW piston ... sounds like fun!

[David_L6]

So, Phil's repro pistons might be copies of the TRW piston ... sounds like fun!

Not exactly........ You'd have to have a "Mod 50" cylinder head if he'd had exact copies made.

[bh/]

pistons

David;-is the bright two ring flat top on the left, Phil's '05 batch?
I do not have any down here, so can not compare

[David_L6]

Yes, the shiny two ring piston is from the batch that Phil had made this year.

[Richard K.C. Mo.]

Low rpm moter?

Maybe that's why most say 7's 'bout it for those. Without a lot of mod's i here those will run in the mid/upper 90s, true?
I was told with my weight that i could not run a merc d lower, 249#, but then again i'm loseing all the time, or is it loosing? I fergit.
Richard F.

[David_L6]

Richard I don't know how many RPM's those motors are turning.

Speeds may get into the low 90's on a long course.

I think everyone is still guessing about lower units. Some people are running D Merc units, some Yamato hatchet units, some Konig units (and probably some Konny units), some Bass units. Take your pick and try it. I don't think it's so much the drivers' weight that destroys lower units under those motors - it's the torque those motors produce.