Engine Balance

[Jim_Pat]

Can anyone tell me if there is anything I should know or do when balancing a Johnson V6 225 (open deck). The only thing I have seen so far is I will have to make smaller bob weights. We have only done 4 cycles in our shop.


Thanks

[Markus]

If you mean that you are going to balance it like you balance a cross plane V8, there is really only one thing you should know:

It is impossible.

[Capt.Insane-o]

Make sure the crank is straight. You can balance a motor until you are blue in the face, but if the crank is'nt straight..

[Jim_Pat]

If you mean that you are going to balance it like you balance a cross plane V8, there is really only one thing you should know:

It is impossible.
Markus, not sure what you mean by cross plane v8?

[6Killer]

Make sure the crank is straight..

...........+1

[m3mm0s rib]

If you mean that you are going to balance it like you balance a cross plane V8, there is really only one thing you should know:

It is impossible. exactly :thumbsup:

[Markus]

Markus, not sure what you mean by cross plane v8?

Here is a good explanation:

http://en.wikipedia.org/wiki/Crossplane

[rev.ronnie]

Can anyone tell me if there is anything I should know or do when balancing a Johnson V6 225 (open deck). The only thing I have seen so far is I will have to make smaller bob weights. We have only done 4 cycles in our shop.


Thanks

I balance a lot of V6 automotive cranks and they have different mass percentages depending on engine/model etc.

Here is a mass percentage list. I have been using Hines' figures for over 20 years with no problems. I actually have a Hines balancing machine and have used the info right from my manual.

This list has outboard motors listed, particularly Yamaha. I believe they are the same configuration as OMC. I would balance the crank first, then install the flywheel and make any further corrections on the flywheel itself. This way you are using the crank as an "arbor" to true the flywheel as well.

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

I do not understand why this would be "impossible" to balance. What is the difference between a 45 or 60 degree automotive crank to a two stroke of the same bank angle? The operating rpm may be higher and thus the different mass percentage.

I guess I would like to know the reason that it is "impossible" rather than just a closed statement.

[Markus]

I do not understand why this would be "impossible" to balance. What is the difference between a 45 or 60 degree automotive crank to a two stroke of the same bank angle? The operating rpm may be higher and thus the different mass percentage.

I guess I would like to know the reason that it is "impossible" rather than just a closed statement.

Unlike a cross-plane V8, a V6 is inherently inbalanced.

Here is a description without equations. http://www.autozine.org/technical_school/engine/smooth1.htm

[powerabout]

a 2 stroke fires every time the piston is at tdc hence the force on a piston going down is always larger then the force of it going up.
On a 4 stroke you send the piston up and down once without it firing.
So how much weight are you going to use to balance the power stroke of a 2 stroke?

[rev.ronnie]

I balance V6 automotive cranks all the time. Actually, our 4.3 GM engines are quite legendary for their smoothness. After balancing , your dash no longer shakes at idle. In fact I just did one for a guy who heard similar tales of not being able to balance them...he has sent me 3 emails thanking me for how well his engine runs. I have done several 3.8 Buicks for Stock Eliminators who run them in excess of 8000 rpm with great results too.

Its all in correct mass percentages and accurate balancing. I don't think cylinder firing forces have that much effect on dynamic balance. Some engines, in fact, are balanced fully assembled and the whole rotating assembly is spun and corrected. Pontiac used to do this with their v8 engines. It was an impressive sight. That's why the counterweights were drilled at an angle from each end...the drilling machine had to clear the main cap.

[lokinutz]

I balance a lot of V6 automotive cranks and they have different mass

Have you ever balanced an OMC v6 looper crankshaft though?
I ask this because I have read a lot of info on people trying to balance them, only turning them to junk. There is a reason they are not "balanced" from the factory.
These stock cranks turn 8k without problems, and can make over 400hp without being touched.

I think another question to the OP, is, Why do you want to "balance" your crank. There really is no reason to mess with it. Polish the journals and flywheel snout and run it.

[rev.ronnie]

Have you ever balanced an OMC v6 looper crankshaft though?
I ask this because I have read a lot of info on people trying to balance them, only turning them to junk. There is a reason they are not "balanced" from the factory.
These stock cranks turn 8k without problems, and can make over 400hp without being touched.

I think another question to the OP, is, Why do you want to "balance" your crank. There really is no reason to mess with it. Polish the journals and flywheel snout and run it.

Oh, no I've never done one. That's why I am watching this. I want to see what the procedure is, or how it checks out on the machine with a certain mass percentage represented. The biggest problem I see is that they are not a split pin engine. It would really throw a wrench in the gears.

If that thing gives you a real whacked out reading on the machine, I would not attemp to change it, I agree. It's probably not the correct set up.

I gave up trying to balance my inline 3 for the same reason. I was not believing what I was seeing on the correction necessary.

[Jim_Pat]

Thanks for all the info, I will bypass the balance and proceed from here.

[lokinutz]

Now, if you want to balance the rods, for both overall weight and end weight, and make sure pistons (including pins, bearings, rings, clips) all match, then you would be spending some time in the right place. A balanced (reciprocating parts) engine will run pretty darn smooth. If you start looking at the weights of these stock OMC pieces, you can easily get a combined weight of over 100 grams difference between a light rod and light piston matched up compared to a heavy rod and heavy piston.

[Instigator]

Heres one for you.

When OMC went from the early era, heavy rods to the late era, light rods they did not change cranks or any form of balancing to my knowledge.

The difference in weight between early/heavy and late/light is 100 grams per. Times six.
Now turn it 5K let alone 8+. I have done this multiple times on both w/zero issues but not sure I understand it.

[JohnR]

Could it be that as long as all of the piston/rod assemblies are early or all are light they balance each outer out?

[lokinutz]

Could it be that as long as all of the piston/rod assemblies are early or all are light they balance each outer out?
You would think this to be the case, but I have seen early big rods have as much as 70 g difference. I am sure others have seen more. These were run together on same crank in same engine for about 20 years until I got my grubby hands on them.

[mike1]

I don't chime in much I was reading this dicussion and was wondering if maybe the primary and secondary compression act like shock absorbers for any imbalance and since the powerstrokes are more continuous than a fourstroke maybe that's helps the balance as well...I don't know just a guess...

[Chaz]

I balance a lot of V6 automotive cranks and they have different mass percentages depending on engine/model etc.

Here is a mass percentage list. I have been using Hines' figures for over 20 years with no problems. I actually have a Hines balancing machine and have used the info right from my manual.

This list has outboard motors listed, particularly Yamaha. I believe they are the same configuration as OMC. I would balance the crank first, then install the flywheel and make any further corrections on the flywheel itself. This way you are using the crank as an "arbor" to true the flywheel as well.

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

I do not understand why this would be "impossible" to balance. What is the difference between a 45 or 60 degree automotive crank to a two stroke of the same bank angle? The operating rpm may be higher and thus the different mass percentage.

I guess I would like to know the reason that it is "impossible" rather than just a closed statement.

Rev,
The biggest reason they are impossible , is because they don't own a machine. ;)

Just like was mentioned, about the loads put on the piston durring the explosion ... err ... firing stroke. easy to see lots of wifes tales make up people minds for them . If they actually opened their minds thought about it , it would become pretty clear that unless the motor is detonating , that the push on the piston crown on the power stroke keeps every thing loaded nice and tight . pretty mild when compaired o a 4 stroke aproaching TDC after the power stroke with the ex valve open. More pins are pulled out of pistons, rod caps and bolts broken at this point .. than at any other event. I know turbo guys who make 3000 hp who have told me that their motors are actually more reliable because the slight back pressure on the ex side actually cushions the whip at the end of the ex stroke ..
Back to crank spinnin ... :D
A 60* bent 6 has it's own set of problems and cures built in. The short answer is to spin it between 350 and 500 rpm at 52% and dont look back.
Because of it's primary aplitude of balance, you will find that you can then remove all the bob weights and spin it and it will still 0 out, or be pretty close. Put the machine on FORCE ( rockin coupling) and you will see the end to end has went out of sync ... most outboards Ive seen, need one slug in the counter on the flywheel end to get the secondary plane happy .
Your spot on about using the balanced crank as an arbor. I made an arbor out of a short stick of 2" stress proof to do my 3.0 wheels ... but the absolute best way is to do it as a unit .... wouldnt even hurt to hang the drive and prop shafts in the V- blocks ... but then my wife tells me that not a lot of guys out there really care to get it any closer than a mass produced part .. and in the end ... that's just what they'll have .. :thumbsup:

[powerabout]

ever looked at a single cylinder racing 2 stroke and seem what they have done?

[Forkin' Crazy]

Heres one for you.

When OMC went from the early era, heavy rods to the late era, light rods they did not change cranks or any form of balancing to my knowledge.

The difference in weight between early/heavy and late/light is 100 grams per. Times six.
Now turn it 5K let alone 8+. I have done this multiple times on both w/zero issues but not sure I understand it.

I was waiting on some one to bring this up. Maybe that's why the upper bearing retainer screws come loose.

[powerabout]

thats my take , the balance has less to do with the reciprocating weight more to do with the size of the bang at an rpm and the rotating weight ( on an even fire engine that is)
What does Jay say, every lightened crank on a merc he ever saw broke.
We all lighten pistons and rods though dont we

[powerabout]

Heres one for you.

When OMC went from the early era, heavy rods to the late era, light rods they did not change cranks or any form of balancing to my knowledge.

The difference in weight between early/heavy and late/light is 100 grams per. Times six.
Now turn it 5K let alone 8+. I have done this multiple times on both w/zero issues but not sure I understand it.

guys also put 31M rods ( old 40hp ) into omc 49 3 cyl and then they rev harder no issues Factory did this in the MOD 50 49ci.
they are like 20mm longer not sure of the weight difference.
same crank in all. 31M run all day at 9000rprm ( with flexplate)

[Chaz]

What does Jay say, every lightened crank on a merc he ever saw broke.
We all lighten pistons and rods though dont we

From what I read, he never seemed to be able to say one without including the other ... but .... You do understand that "balancing" and "lightening" are seperate procedures, dont you ... ?

As far as lightened cranks breaking. Outboard motor cranks have an extremely hard external "skin" aprox .080 deep. Below that they are no harder than any other casting. Machine away the skin and fail to re heat treat the crank to it previous condition and it stands to reason it's going to be trouble.

[powerabout]

From what I read, he never seemed to be able to say one without including the other ... but .... You do understand that "balancing" and "lightening" are seperate procedures, dont you ... ?

As far as lightened cranks breaking. Outboard motor cranks have an extremely hard external "skin" aprox .080 deep. Below that they are no harder than any other casting. Machine away the skin and fail to re heat treat the crank to it previous condition and it stands to reason it's going to be trouble.


yes and yes
but outboard cranks are forged or are some still cast?

[Instigator]

yes and yes
but outboard cranks are forged or are some still cast?

Have heard that's the issue. As Chaz says, that outer skin is really nasty hard. Weld won't stick and why welded up stroker cranks all come apart.