In Line Crankshaft balance factor,

[FMP]

Hello, I'm new to S&F and what a useful forum. I'm rebuilding a couple of inline F5's, don't joke. Have done all the regular clean up , 5 new Wiseco pistons , equaled all pistons and rods and felt the need to balance the crank. The inside experts that I have listened to have informed me that any in line 3,4,5,6 any make OMC,Merc,Chrysler , all follow the 100% rotating + 0%reciprocating balance formula when the cranks are factory made, or at least that is the goal because the recip. mass forces must be kept in the fore aft direction on the horizontal. The mounts and mass of the complete engine absorb the force best in the manner . Any additional weight % from the recip. will transfer said forced out of the fore aft directions and create an unwanted side to side force to a degree. In reading many threads in the quest for practiced knowledge some insight has been gained from IL 4,6 Merc threads. Reference was made to a 1500xs crank that was lightened and balanced. I have also read that same work done to IL4 Mercs only to create a shaker that doesn't last. Can anyone that has balanced an IL recall the % numbers used. If you lighten one side the other must also be made lighter.

[Mr. Demeanor]

Cant answer your question but when Falicon balanced my V4 crank they needed the entire rotating assembly including flywheel (pistons, rods, bearings, clips, pins, crank, flywheel)

[FMP]

Thank's for the reply. Yes, have done all those things, flywheel as well. The Big end rod weight , bolts , rollers, cages all rotating weight. The small end weight: piston , pin , clips, rings, rollers don't come into the equation on the IL, 100% rotating 0% reciprocating since the small end weight is all reciprocating. The V4 6 8 uses a reciprocating % greater than 0, sometimes as much as 65%. That is why they needed all the small end parts. What I was looking for was a tested % for the IL . I can go with the 0% recip value but was hopefull for an actual practiced number .

[Chaz]

So by saying 100 / 0 % you are in essence saying 100 / 100 , 200 / 200 , or as the Hines people say ... "all in lines - no bobweight needed" .

That is not to say that the crank shouldn't be spun up , it's just that you wont need to take the time to build up a set of weight's first ... ;)



IMPORTANT: Normally, unless an engine is list
ed below, using 50% reciprocating and 100%
rotating will suffice.
Manufacturer
Engine
Type
Engine Size
(CID)
Throw
Angle
Recip. Wt %
Rotating
Wt %
Internal


External
Balance
AJS (M)
1 cyl.
61%
100%

Acura
V6
3.2 L
44%
100%

All In
Lines
NO BOB
WEIGHTS
REQUIRED

Auburn
Speedster
V12
NO BOB
WEIGHTS
REQUIRED

Audi S4 2000
V6
2.7 L
50%
100%

Audi
V6
2.8 L
44-46%
100%

Audi
5 cylinder
50%
100%

Benelli (M)
Symmetrical No
bobweighting

BMW (M)
Opposed twin
(street)
60
%
100%

BMW (M)
Opposed twin
(race)
50%
100%

Briggs & Stratton
1 cyl.
Go Cart
Racing
67%
100%
Use mini
bobweights

[FMP]

With the 100% rotating mass and 0% no reciprocating mass to be used as the correct bob weight . In this case mini bobs since the throw is 1.1395 inch and the weight is 225g. Spinning the crank without bobs and removing weight to static balance it will make it unbalanced once the rest of the rotatating mass is fixed to it i.e the big end mass. If you lighten the crank then the big end would need lightening to achieve the 100% 0% .

[Chaz]

No one ever said anything about static balance , you still need to spin the crank .

It just that inline's do not require you to use a bobweight in the equation .

The set of mini weights has to do with the diameter of the pin , not the length of the stroke .
I made up a set of shims so I could use the std automotive set .... but in the case of your inline "YOU DO NOT NEED ANY BOBWEIGHTS"

Outboard cranks are pretty slim to start with. Only thing you could really do is profile the end weights . I would be more concerned about breaking thru the hardened surface , than any benefit you might find in knocking off maybe a half a pound .
And unless you spun it up before you went to whittlin , you just might take mass away from an area that needs to keep it .

Ohh BTW .....

All In
Lines
NO BOB
WEIGHTS
REQUIRED

[FMP]

Thanks for the input . The 100% rot. + 0% recip. is the mass needed for the bobs in this case. That has been established and confirmed by 2 inside industry experts and one motor sport balance expert. I will give you the names and emails on a private if needed. What I am tring to find is if anybody has added weight to the equation , IL at one time was the only choice so it had to have been done. The hardend surface of one of the cranks that I have has been removed in an attempt by a balancer to spin and balance with out bobs. This may weaken the crank some say. (The pin diameter is what I ment not stroke I missed typed in hurry. Stroke is 2.8760) . The idea is to get to the 100 0 . IL 4Mercs that have been lightened develope a balance issue at high rpm. These cranks when made were done to the 100 % 0% , so I was told . If you spin them with out bobs the big end mass is not accounted for. Shaving them to equal or approach equal mass to the pin side creates the imbalance.

[Chaz]

I am no one that can hold a candle to your three experts ... :nonod:
And all I have at my disposal is an old azz S+W machine .
I have also used a Hines balancer , which was the state of the art for many years before the CWT hit the market place .
Which ever machine you use ,or send your parts to will have (should have) a balance weight chart that came with the machine.
The 6 page chart below , and in your case the third line down is clear in saying that you dont need to waste your time building up a weight set .
Why do you feel that you need to mock up , big half of the rod , bolts , bearing when all they are going to do is cancel each other out in a flat crank .. ?
You could add twice weight and nothing would change .
As far as lighting the crank and balance issues go . Outboard cranks have very little pin overlap , perhaps what they are experiencing is crank flex , especially if there are highly stressed area's that have had the surface heat treating ground thru ...


http://www.hinesindustries.com/documents/reciprocalmass.pdf


http://www.pro-bal.com/tech_info/library/Precision_balancing_of_reciprocating_engines.pdf

[FMP]

We thought the same until I noticed that one of the factory cranks I have , which has never ben out of the power head until I pulled it, has factory installed heavy metal in the counters. I mean the factory drilled and added weight to the already shaved counters . I have listened to the many opinions and how things should be. I contacted the guys who did the R&D for this ph , him and his goto guy who was also the OMC guru for many years (but at a different date) pondered it for a few minutes and remembered what they had done. The end result is that in order to get it right the above formula has to be followed. I also threw it to another 3rd man,who after while with a pencil said that is correct. The first guy said "use the big end weight only", the second guy said "you are correct ... elementary". When they did the crank they couldn't touch the smallend mass the size of the counters wouldn't permit it and was no need. The 72* spacing and 15234 firing order produces a .449 unbalanced moment factor, compared to 3.464 for a 60* V6 120*crank, 1.414 for a 4cyl IL and 1.732 3cyl IL. according to the SAE paper. The paper also says" Each cyl is equally counterweighted with 100% rotating balance being trimmed by end counterweight orientation". We will have it on the balancer this week with bobs and sneak up on the number they used from the factory. If you change the 0% number you introduce unwanted side to side forces that transfer to the transom and not the mounts and mass of the engine. All 3,4,5,6 IL OMC, Chrysler Merc, Tohatsu vertical crank, horizontal cyl require this formula. The 100%50% works for horizontal crank, vertical cyl. and a different mounting system. The guys said " if you follow this % life is golden"

[Chaz]

After you have balanced the crank , do yourself a favor and leave it in the machine . Unbolt the bobweights and give it a spin . I'm interested in what you find ... :thumbsup:

The reason I mentioned that static balanced was not enough is because rotational is only parameter , the end to end gyro wobble is why the factory put a slug or two of heavy metal in the untouched crank .

:D 5 cylinder's are as common as a ....>

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTOieTJE6qhFxSThA3qlEvHlR4Wyl55l1kPhvu2FOSbitREsv3P0w:upload.wikimedia.org/wikipedia/commons/1/18/3_dollar_bill_Jefferson_County_Bank.jpg :D

[FMP]

I have two of these ph , the first is an original F5 big bore , the second is a Merc produced big bore replacement ph dated 2000. The original crank has the added weight in all counters , the Merc doesn't ( they really didn't fit the thing together as well as the original, end gap was at 0.005 and harsh ports). We spun the Merc one, it's the one that now has been shaved to get it to what the balance guy thought was correct with out bobs ( removed heat treat surface) . The amount that came off was enough to raise the flag that the crank was made to the above % so we thought and the adventure began.
You might be surprised that these ph can still be bought NEW from Merc dealers on the cheap .

[powerabout]

On a 2 , 4 and 6 the pistons going up are opposed by the ones going down
On a 3, and (5) there will be an uneven number of pistons going in one direction
On the 3 cyl crank they look to be zero balanced with counter weights on each throw, I guess this is all you can do?

[Chaz]

Not true . a three cyl has a pin every 120* ( or every third of rotation )


Power , have you had a chance to go watch the process done in person yet ... ?

[powerabout]

Yes they are 120 apart but that means 2 are going up when 1 is going down and then that changes to a different pair and so on.
I have seen a few 4 strokes balanced but never a 2 stroke but sounds like its the same.

[Chaz]

Well , yes ..... and ahhhh , No :D

Some of the better software out there that deals with rod ratio to camshaft profile ( and yes 2 strokes mirror port profiles to that of a cam shaft events ) will show that piston speed is higher ( moves farther) in 10* ( 5* before and 5*after) while the crank pin is at a right angle 90* to the cyl center line than it does in ( 40*) the 20* before and 20* after top or bottom dead center .
What does that mean to you ... ?
Cut a triangle out of a piece of paper . Pretend each point has a rod and piston hooked to it pointing straight up . Rotate it , you will see one out to each side haulin azz in different directions , while the third is moving lazily around the top or bottom , nullifying the thrust vector of your two against one theory .. ;)

And I am glad you have seen a crank being balanced in person .. I was afraid we were losing you in " Balancing 101 " :thumbsup: :thumbsup: :thumbsup:

[powerabout]

Thanks Chaz
yes I have a good grasp of rod stroke ratio/piston acceleration/tdc dwell time/skirt thrust etc as 3 cyl OMC we have a choice of rods and hence it also changes your port time/angle relationship
saying that, I never thought about the balancing issue with rod ratio.
Unique to the 3 cyl crank is counterweights on each pin. Can or should we change the counterweight size to suit the new rod piston weight or length but will that be via the balancer or only via software or can a balancer run via a software program?

"while the third is moving lazily around the top or bottom , nullifying the thrust vector of your two against one theory .. http://www.screamandfly.com/images/smilies/wink.gif"
now that was enlightening!!

[FMP]

Update
So we spun the thing without , with at 100%+ 0%, and 100%+50%. And wouldn't you know we got three different sets of numbers. The strange thing is where and how much weight it's calling for to be removed. If this crank was made as indicated by the experts someone missed the number. According to the guys who should know the 100 , 0 factor should have had us in the ball park. The 100 , 50 even worse. Something was done in the design of this piece that has been over looked and has a few heads being scratched. Both of these cranks have similar values to correct, so it's not a one off error. It may have been done for strengh or high speed harmonics. It will be resolved soon.