Cranks

[Fingers]

Quoted from Gale,
"As to Vibration dampers with neutral balance, we designed a 2 piece assembly that allows us to drive accessories, like a dry sump or blower drive off the front. We make 2 different size inertial rings and tune each differently as to viscosity and clearance to tune to stroke length, bob weight mass and maximum rpm. The inertial ring assemblies bolt to our drive hubs which are zero counterweight or are matched to the various standard Dmax counterweight masses. We own Automotive Balancing Service, started in 1953, it is the first and the oldest automotive balancing shop in the United States. Today, we use the shop only for development and our own internal engine production needs, but we know balancing! We therefor know that the position of the counterweight is incorrect in most of the hot rod Dmax balancers being sold today, that leads to crank failure. We measure crank twist front to rear with the engine running at a wide spectrum of speeds and loads…we don’t guess at this. I seek a maximum of +/- 1/8 degree crank twist
We have made very high output with properly inspected stock cranks and proper attention to the damper design."

This quote has bothered me for a while.

First, the dampener does not prevent twist. Runaway twist from harmonics maybe, but not the actual twisting moment on the crank. Degrees of twist is actually the wrong metric for the effectiveness of a dampener.

The rotational movement of the crank on any reciprocating engine is not smooth. Far from it. It will speed up, slow down, even reverse direction for short moments as it rotates through a revolution. The purpose of the flywheel and dampener is to try and smooth out these variations. With the Dampener also acting as a harmonic absorber.

Diesels are notoriously variable and bad enough to have dual mass flywheels used in their manual transmission applications.

So the real metric would be more like % speed variation or something like that.

Now, the crank itself must be able to handle the twisting moments applied to it. THAT would make sense in Degrees from end to end.

 

[Slowmax]

Is an ati safe to buy for an lb7?

 

[jkholder09]

Is an ati safe to buy for an lb7?

I use them and have been very satisfied. They fit really tight

from mobile

 

[Fingers]

I'm just getting my feet wet with the new software, but so far, it looks like those uncommon failures on the Flywheel side of the cranks are probably from hard shifts.

Interesting.

 

[duramaxnokaoi]

Quick question. Is anyone cryo treating any parts of their rotating assembly? If so, has anyone broke a cryo-treated crank?

 

[duramaxnokaoi]

Also, to rule out block distortion under load, has anyone broke a girdled crank?

 

[juddski88]

Also, to rule out block distortion under load, has anyone broke a girdled crank?

your answer has already been posted in this thread.

 

[Mikey]

I'm just getting my feet wet with the new software, but so far, it looks like those uncommon failures on the Flywheel side of the cranks are probably from hard shifts.

Interesting.

I bet a lock box doesn't help either. In terms of harmonics and not power to the wheels. The converter has some dampening I imagine, but that all goes away when all locked up

 

[Stingpuller]

Nice Fingers

I have always wondered on the same lines as you are seeing. That's why I have been saying mine "should" have broken 10 times over. A sudden lockup at full power I think is hard on the crank. With the power some are making when it goes to lockup something has to give. Good info! Thanks John

 

[RPM Motorsports]

When were you pulling lockup? We had 100+ passes on the Chevelle, and didn't start having engine issues until we started pulling lockup right out of the gate, now that I think about it. #4 bearing was flattened and squished around the main both times.

 

[Fingers]

The model I am using for the crank is far from perfectly faithful to the actual crank. The throw thickness is accurate as are the bearing journals. Its the finer details I am lacking right now.

I am learning how to add a dampening force now. Cool stuff. It better be for the price.

 

[Fingers]

A small update.

One of the features of the new software is the ability to create bearings. That is, constrain a surface in one direction. So I can model the mains on the crank and support it like it is supported in real life.

With this feature, I found some interesting things, and some a little confusing.

Let me put out a teaser. When you load up one end of the crank, the OTHER end is where the forces concentrate if the other end is fixed. (or has a lot of inertia)

 

[SmokeShow]

What do you mean by "load up"? Load applied perpendicular to the axis of rotation, load applied parallel to the rotation axis (push/pull front to back) or rotational force (torque) ??

 

[Fingers]

Apply a force to the rod journal similar to the what a rod would provide.

 

[Dave c]

You get a lateral(bending load),and a torsonal(twisting load)

 

[Fingers]

The bearing simulation supports the crank in the lateral, while allowing axial and torsion.

 

[Dave c]

The bearing simulation supports the crank in the lateral, while allowing axial and torsion.

To the point of bearing clearance reduction, and or block and cap flex correct?

 

[SmokeShow]

I would guess it assumes the "bearing" doesn't crush or move?

You say the force concentration shows up at opposite end of crank from which the force is applied? Is this a steady state (analyzes one frame in time) or dynamic analysis (takes into account the actual movement & "records" some parameter(s) like stress, strain, deflection, movement, twist, etc? Is force concentration on oppopposite side of crank as applied load or same? i.e. crank is bowing (forces on same sides) or teetering (forces on opposing sides) about some axis?

 

[Mikey]

Nothing here makes one stand out more than another except the rhetoric. IMO

Ideally, you would match the balancer to the built motor. Most of us can not afford that.

Or do a zero balance and put the zero balance flywheel and damper on?
But then again more expensive, but going that far into a build would make it a drop in the bucket. You don't see any high performance gas engines externally balanced do you?

 

[Fingers]

Zero balance what? Talking harmonic dampeners here. What are YOU talking about.