full circle crank in rude??

[form-e one]

would a full circle crank in a v-rude be better or worse.?????....and no i dont run one ....honest..

[fasterboats]

It's alot of work!

I did one where I TIGed 6 steel bands and then filled the voids with epoxy.

I saw this before in some really old alky McCulloch Kart cranks.

It was for a Sled everyone was happy with how it worked
After 1000s of Miles the epoxy lost it's bond (expected) there were tabs to keep the filler captive.

[modifiedoutboard]

Lyle Mason has alot to say about the triple cranks along those lines. He may be at Ocoee and is always willing to talk about tech stuff.

Wish i could be there but! have to work.

Maybe we will see you later in 2004 !

[Dave M]

Like Dad taught me, if you are runnign aloop charged engine, stuff it.

Anthony, use the graphite powder in the epoxy, it will not burn out. We use West System mix in Graphite and it can withstand filler block temps. That is all we use to glue them in. It works well to plug off the botton of the stock exhaust on the Mercs real well. To remove, it is not to bad.

Full circle cranks, I have seen one run, it was not any faster than normal. But then maybe the person, God rest his soul, did not have other things inside to work either. We have never tried t because OMC tolerances are so crappy on balance, we figured it would break the boat in half vibrating.

[David_L6]

Originally posted by Dave M
We have never tried t because OMC tolerances are so crappy on balance, we figured it would break the boat in half vibrating.

LOL :D :D :D

I guess they all vibrate??? The only ones I've driven did.

[bh/]

The mid range low frequency vibration in these triples is as bad as any British 500cc single I was ever on! Where is it coming from? Does varying flywheel weight affect it?
Does a Mod50 shake like this.
The smaller 44" twin does not seem as bad.
:confused:

[pro350hydro]

Originally posted by Dave M
Like Dad taught me, if you are runnign aloop charged engine, stuff it.

You got that right........stuff that ***** ******!

You are the first person I've heard mention that here.

Mike

[sasbenson]

Originally posted by bh/
The mid range low frequency vibration in these triples is as bad as any British 500cc single I was ever on! Where is it coming from? Does varying flywheel weight affect it?
Does a Mod50 shake like this.
The smaller 44" twin does not seem as bad.
:confused:

Without sounding like a "know it all" Maybe I can answer your question and perhaps clear up the mystery of the 3cylinder Shake!!
A three cylinder inline crankshaft assembly with 120 degree spacing on the crankshaft is symmetrical and can be made to run in perfect balance! If all the rotating weights along the shaft all made equal and opposite there is no vibration. The reciprocating forces ,however, are another matter entirely and are the culprit for making this engine shake. The problem with this design is the fact that there are piston "coupling" forces which combine when they move back and forth in their bores and produce forces which the crankshaft counter weights cannot oppose and cancel. You always have two pistons heading in the same direction at any given crank rotation and they produce a strong "rocking" motion along the lenght of the crankshaft you feel as vibration. The Stock rubber mounted mid sections do an excellent job of absorbing these motions and the engine is very smooth on the back of your fishing boat. Take away the rubber mounts and mount it solid on a race boat though and you sure as hell are going to feel these shaking forces!! OK, so what to do?? The only real "CURE" would be a counter balance shaft such as you see in some single cyl M/C engines or inline 4cly 4stroke automotive applications. Not a practical solution for what we do !! Our approach is to reduce the piston weight as much as possible and use a flexplate flywheel which acts somewhat as a vibration damper. Other than that just make sure you build a hell for stout mid to bolt this beast on to!! And, by the way, a 180 degree big twin also has an inherent rocking couple. ask anyone who tinkers with Rotax Twins about the shake factor on those things!! Hope this answers the question.

Steve B

[Dave M]

Originally posted by sasbenson
Without sounding like a "know it all" Maybe I can answer your question and perhaps clear up the mystery of the 3cylinder Shake!!
A three cylinder inline crankshaft assembly with 120 degree spacing on the crankshaft is symmetrical and can be made to run in perfect balance! If all the rotating weights along the shaft all made equal and opposite there is no vibration. The reciprocating forces ,however, are another matter entirely and are the culprit for making this engine shake. The problem with this design is the fact that there are piston "coupling" forces which combine when they move back and forth in their bores and produce forces which the crankshaft counter weights cannot oppose and cancel. You always have two pistons heading in the same direction at any given crank rotation and they produce a strong "rocking" motion along the lenght of the crankshaft you feel as vibration. The Stock rubber mounted mid sections do an excellent job of absorbing these motions and the engine is very smooth on the back of your fishing boat. Take away the rubber mounts and mount it solid on a race boat though and you sure as hell are going to feel these shaking forces!! OK, so what to do?? The only real "CURE" would be a counter balance shaft such as you see in some single cyl M/C engines or inline 4cly 4stroke automotive applications. Not a practical solution for what we do !! Our approach is to reduce the piston weight as much as possible and use a flexplate flywheel which acts somewhat as a vibration damper. Other than that just make sure you build a hell for stout mid to bolt this beast on to!! And, by the way, a 180 degree big twin also has an inherent rocking couple. ask anyone who tinkers with Rotax Twins about the shake factor on those things!! Hope this answers the question.

Steve B

Well said. There is no way to eliminate it completley. A ton of research has been done with this, trust me.

[bh/]

Good explanation there, Doctor Benson, and obvious when u think that with 60deg spacing, two pistons are always going in the same direction. On the old vertical singles if we tried to 100% balance the reciprocating mass with rotating mass;
-you ended up totally out of balance in the horizontal plane. The 'experts' would talk about 55%, or 60% balance factors, attempting to put the out of balance forces into a plane that one could not feel. My XT500 single had a counter balance shaft,
and it 'buzzed' some, but did not 'shake'.
The MOD50 should be a bit better, on solid mounts;
i]the longer rods will lower piston acceleration,
ii]pistons are lighter?,
iii]it uses a flexplate fly wheel.
Good warning about the mounts;
-this one wants to be well tied down!! :eek:

[Mike Schmidt]

Has anyone tried counterweighting the crank by welding on pads like they used to do on the Quincy Loopers?

Michael D-1

[David_L6]

Originally posted by Mike Schmidt
Has anyone tried counterweighting the crank by welding on pads like they used to do on the Quincy Loopers?

Michael D-1

That sounds like a good idea to me if it's possible and legal.

BTW, Quincy padded the cranks on some of the deflectors too.

[sam]

Some of the V-6 drag race guys are tapering the insides of the ends of the wrist pins to reduce reciprocating weight.

On the big bore V-6's this is a lot of weight.

Do you think this could be done with the triples?

[pro350hydro]

Is anyone balancing the stock crank in these motors?

If so, are you noticing a big difference?

I also bet it ain't cheap....

Mike
R-15

[mercguy]

Originally posted by sasbenson
Without sounding like a "know it all" Maybe I can answer your question and perhaps clear up the mystery of the 3cylinder Shake!!
A three cylinder inline crankshaft assembly with 120 degree spacing on the crankshaft is symmetrical and can be made to run in perfect balance! If all the rotating weights along the shaft all made equal and opposite there is no vibration. The reciprocating forces ,however, are another matter entirely and are the culprit for making this engine shake. The problem with this design is the fact that there are piston "coupling" forces which combine when they move back and forth in their bores and produce forces which the crankshaft counter weights cannot oppose and cancel. You always have two pistons heading in the same direction at any given crank rotation and they produce a strong "rocking" motion along the lenght of the crankshaft you feel as vibration. The Stock rubber mounted mid sections do an excellent job of absorbing these motions and the engine is very smooth on the back of your fishing boat. Take away the rubber mounts and mount it solid on a race boat though and you sure as hell are going to feel these shaking forces!! OK, so what to do?? The only real "CURE" would be a counter balance shaft such as you see in some single cyl M/C engines or inline 4cly 4stroke automotive applications. Not a practical solution for what we do !! Our approach is to reduce the piston weight as much as possible and use a flexplate flywheel which acts somewhat as a vibration damper. Other than that just make sure you build a hell for stout mid to bolt this beast on to!! And, by the way, a 180 degree big twin also has an inherent rocking couple. ask anyone who tinkers with Rotax Twins about the shake factor on those things!! Hope this answers the question.

Steve B

Mr. Benson, may I be excused for a second......I just ran outta paper in my notebook!!

[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

[pro350hydro]

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/]

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

[David_L6]

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

[Richard K.C. Mo.]

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.