Engine balancing

[xb-60]

Originally Posted by blykins

Step by step.....

The Balancing Process from Coast High Performance - YouTube

Just got to it Brent. Like they say, a picture's worth a thousand words. So it seems that a non-race engine, up to 6500rpm max, external balance is sufficient. So how many - what percentage - of these engines would you internally balance? And what's a typical added cost to a motor for blueprinting/balancing?
Cheers,
Glen

[xb-60]

Originally Posted by Jerry Clayton

http://www.scatcrankshafts.com/scatt...k_the_Nose.pdf

After you have watched that video, check out number 5 of this page---in the video look at all the holes he drilled into the counter weights to try to balance the assy with external weighed flywheel and dampner--In Scat's tech section in very plain language talk about how much to drill and this guy evidently didn't read it--

So, what - would that crank go out as a balanced crank, or would it be a scrapper, Jerry?
Cheers,
Glen

[xb-60]

Originally Posted by blykins

Haha....the wolves are out tonight....

Remember guys, this is a very fundamental thread on balancing. We're not teaching him to be a machinist.

Yep, thanks. Keep it relatively fundamental. I like to understand the concepts, but the wolves make for interesting reading as well, and the 'oversight committee' might just make it better/safer for us sheep as well...

[xb-60]

Originally Posted by blykins

You win some, you lose some....

This thread should be looking at the forest though....not the trees...

I get your point. The forest looks OK

[xb-60]

Originally Posted by CHANMADD

Most engines have an imbalance at 1400_2000 rpm. This is harmonic imbalance.The harmonic balancer helps to absorb that frequency. Most harmonic balancer have arubber ring sandwiched berween two parts. This type of balancer should be balanced with the crank. A fluid filled type balancer cannot be spun balanced because the fluid moves around. The 28 oz thing is like balancing a wheel and on one side there is a big hole drilled , so that before you stick it on the machine you know that you drilled out 28oz, so that exactly opposite at the same circumference you attach a 28oz weight to get the balance close before spin balancing on the machine.
A single cylinder motor would have all the components meticulously polished ,shaped etc.
A blueprint is making sure that all the components match exactly the designers specs.
A multicylinder blueprint is making sure that all the cylinders and all related components are exactly the same, down to 0.002 of a gram. When they are all same the harmonics will be minimized and then spin balancing will require less addition or removal of metal. This is what makes motors live.
Look at the pulley on a good timiing chain set...it should have some balancing drill marks.
So....yes balance everything if you can..it can only make things smoother
John

John - if you drill a hole on one side and then add material exactly opposite, would that not make the imbalance worse?
Cheers,
Glen

[blykins]

Originally Posted by xb-60

So how many - what percentage - of these engines would you internally balance? And what's a typical added cost to a motor for blueprinting/balancing?
Cheers,
Glen

If I'm building the engine from the ground up, it will usually get internally balanced.

Blueprinting has nothing to do with balancing, it's part of the mock-up and assembly process.

A balance job will start at around $200 and can easily go past $400-500 if a lot of heavy metal needs to be added. The last Scat forged 351C rotating assembly that I did required 6 pieces of heavy metal, even with an I-beam rod and a Diamond piston. That added a huge amount to the balancing bill...

[xb-60]

Originally Posted by blykins

If I'm building the engine from the ground up, it will usually get internally balanced.

Blueprinting has nothing to do with balancing, it's part of the mock-up and assembly process.

A balance job will start at around $200 and can easily go past $400-500 if a lot of heavy metal needs to be added. The last Scat forged 351C rotating assembly that I did required 6 pieces of heavy metal, even with an I-beam rod and a Diamond piston. That added a huge amount to the balancing bill...

That sort of cost sounds reasonable to me.
Doesn't blueprinting involve selecting components, or adjusting components (as was seen in that You-Tube video, where the conrods were being ground) so that they are the same weight?
Cheers,
Glen

[blykins]

To me, that's part of the balancing process.

The pistons/rings/bearings/rods, etc. should be selected before hand as part of the engine qualification process.

Blueprinting to some just means checking the parts out. It's really a lot more involved than that...coming up with a plan, figuring out what clearances/dimensions you need, then making everything fit that plan.

[Jerry Clayton]

If a customer showed up here with those parts, I would send him on his way--that crank is scrap and the balance guy would be looking for work doing something else---

[CHANMADD]

K

Originally Posted by xb-60

John - if you drill a hole on one side and then add material exactly opposite, would that not make the imbalance worse?
Cheers,
Glen

yes...:I was typing on the move......little brain phart right there....but I trust you understood what I meant.

[CHANMADD]

The crank in the video became scrap because too much material was removed. If parts selection and balancing had been done it would not have required such extreme drilling.

[xb-60]

Originally Posted by CHANMADD

K

yes...:I was typing on the move......little brain phart right there....but I trust you understood what I meant.

phart understood