R975 help

[Perry Kitson]

I have posed a question on the HMVF site, but have not had any replies, so I will try here.
The spline cut on the crankshaft and in the flywheel are such that they can only be assembled in one location, and it happens to be at the top of the throw on the crankshaft. What are the possibilities that the flywheel/clutch is balanced (or un-balanced) to aid in the balancing of the rotating group in the motor? I am about to have the flywheel/clutch assembly precision balanced, and if it happens to be heavy at the high side, or 180 degree's from it, then one would presume the former to be true. But the next question would be how much weight is correct. When you have an assembly that is at least 175 pounds spinning up to 2,600 RPM, balancing would be very important for bearing life. Any thoughts or comments?

Perry

[Andrew]

From experience in automotive, if the flywheel only goes on in one position, then I would bet money it is balanced to the crank/flywheel position. If you have the assembly custom balanced, there will be no issue as they will either add or remove from the flywheel and or crank to zero it. I don't know those engines, but it will be one of 2 balancing types, one internal, where the crank is balanced and the flywheel is neutral, the other external, where the flywheel is balanced for the internal parts. you cannot switch flywheels from internal to external balanced engines without re balancing the whole assembly

did that make sence?

Andrew

[45jim]

Perry, I'll have to check the manual (I think I lent it to you in the past) on the radial to see if there's anything unique there, but the balance for all reciprocating engines is a basic two-step process. Individual components are "statically" balanced and then the assembly is "dynamically" balanced.

I can't help feeling you already know more than I here, but a flywheel is almost always located by keyway, dowel, bolt pattern or splines so that it indexes in only one position. Low rpm engines may be exempt from this, however.

Most production engines are not dynamically balanced and merely assembled from parts that have been statically balanced and/or sorted by weight so that the engine builder can select parts to achieve a "close enough" balance. I can't say that applies to aircraft engines, I just have no experience there except with the RR meteor.

As an aside, I wonder who would be able to balance a crank like that in London, the bob weight to replace all those pistons, pins and rods would be significant and it would have to be spaced out equal to the stroke, not the type of parts you see in your local engine shop used to balancing short stroke V8's.

The only item I think you would have to be cautious of is the pressure plate, these are often not indexed and the machinist would have to mark this alignment for you after balancing.

Really I'm surprised your not doing it yourself with an electric drill, some chewing gum and a dial gauge suspended from the tailgate of your pickup. I am always amazed with what you accomplish in that garage of yours.

[45jim]

To be more clear, I don't think its advisable to balance just the flywheel/clutch assembly statically or dynamically until you can establish the balance factor. I would have to agree that the flywheel is either "neutral" or contributes to the overall balance of the assembly.

[Andrew]

When you have it balanced, they will take everything that moves into consideration, you should have no worries at all.

I have had many engines balanced, never once had a problem

[45jim]

Perry, the manual gives no information on balancing of components or assemblies at all. The only specifications are "run-out" at different levels of assembly of the crank and when the crank is mounted on "V" blocks or in the actual crankcase. There is some wording of "by selection" in the build up and I think this refers to the engine builder picking from a stock of rods, pins and crank sections. This must mean there is another manual or document that gives the refinishing tolerance for each component.

You are welcome to add the manual to your collection anytime if you would think it helpful.

[Perry Kitson]

I have the ordanance rebuild manual for the R975 C4. It does not mention any balancing procedures or checks at all.
The crank has all surfaces machined and polished, with no signs of balancing. The master rod is considerably heavier than the articulated rods, which adds to the dilemma.
I still need to know if the flywheel/clutch assembly is "neutral" before I proceed.

Perry

[Perry Kitson]

Andrew,

Yes, makes sense. There is a large floating counterweight on the crankshaft, but once the engine is running, centrifugal force will keep it at the end of it's range. Being a single throw crank, I am concerned if I balance the flywheel assembly and it is supposed to be weighted, I will be doing more harm than good.

Jim,
I am having everything dynamically balanced. I have machined up a mandrel to mount the flywheel on, and will first spin up the flywheel and fan, then add the pressure plate, and will have it spun up again after the clutch plates and intermediate plate is in to be sure.

Perry