With as many corners being cut and trimmed in manufacturing nowdays, a slightly oversized generator head is not a bad idea.  you get better phase imbalance performance and cooler running of the generator gear.

I use an oil reservoir used on hydraulic systems. Available in many sizes.
They are available in many shops and have the fill/drain ports already in place.

>> click picture to enlarge <<

Quote from: hwew on March 16, 2020, 01:08:49 PM

to help reduce stress caused by spinning loads that have high inertia.

This makes no sense to me at all.
The whole concept of CS listers is a large, heavy flywheel and slow speed. Some people put extra flywheels on to reduce flicker. If does not matter if it's the flywheel or rotating mass of the load, they have high inertia as do all of the traditional type generators like you want to use.  Never heard of anyone saying they cause " additional stress" ?  Additional to what exactly over any other load??
Any additional weight/mass causes additional stress.

Never heard of anyone complaining about inertia on a generator before. It's the lack of it that gives problems. Your partly right. It’s also dependent how fast an engine is able to respond to a load. Some generators have aluminum flywheels and they do just fine. Some Fairbanks Morse generators with  Wisconsin engines had aluminum flywheels.  That's what gives reactive power and why heavy engines with large flywheels like listers are so well thought of. It is in fact the best thing you can have on a generator.  It's what STOPS them bogging down when heavy loads are dumped on them and voltage sag which the engine then tends to over fuel on when the governor gives it everything to get the revs back up.
And trust me, These engines WILL over fuel when bogged down.  That's what causes stress not rotating mass!

I also strongly question the idea of using 2 head gaskets to reduce compression. Did I say I was going to use two head gaskets? I’m sorry I was not detail enough. I was referring to a head gasket a couple of a thousands thicker if needed to get piston to head clearance correct. I’ve found some engines with not enough clearance. With the Clones it’s probably best to check clearance to make sure it’s within spec.  That is widely known in engineering/ mechanical circles to be hackery and a very bad practice. No idea why you would want to reduce compression on a diesel? Would only make for harder starting for one thing and have great potential for poorer combustion... particularly if you were thinking of burning veg, Bio or WMO.  They are all harder to light off and the more compression the better.

Also Gaskets are meant for sealing, not adding length to Cylinders. need to add or delete cylinder length by gasket size to get piston to head clearance correct.

If you want to reduce the speed of an engine then you have to derate the power as well. What engine are you intending to run? Your correct, yes you have to derate the engine to operate at a lower speed.
An ST 10 is an over sized generator for a 178 to a 186 so you would want to be more concerned about limiting the load on the head to stop  stressing the engine rather than the rotating mass. Did you read that I’m hoping to get 2400 watts continuous to 3600  watts surge? 
In any case if you are belt driving the head there is an amount of slip and cushioning in the belt so really not sure what you are concerned about?? Read about my concerns in the very beginning of my post. We all know the Chinese clones have a history of failure in one from or another. Is it too much to make sure the engines tolerances are within spec? One thing I try to avoid is guessing.

Weren't you all Gung ho about some Briggs twin a while back on a generator and thought that was the best thing sliced bread? Does this have anything to do about this topic? What brought this up?
Seem to remember you wouldn't permit a less than glowing comment about it. It must of been some negative comment that someone wrote. Some people can be too abrasive and disrespectful when posting comments about a persons topic. Such behavior is frowned upon.
What happened to that thing?? Don’t need it. Gave it to my brother to help him start his ST-7.5 generator project. It’s coming along fine.

Good catch hwew. I personally have only seen numbers in the 18 - 20 range.
(Except for the advanced computer controlled variable timing automotive diesel engines. VW, BMW, Merc)