The original oil change intervals set for Lister CS engines were determined back in the 1940's era.
Oils of that vintage may not have been of the same quality and molecular blend as today's oils.
So I'm wondering if we can extend the recommended interval from 250 hrs to something longer?

Reasoning:
1] Most of the newer listeroid variants have roller bearings instead of sleeve bearings on the crank.
This reduces frictional shear at the bearings and makes for a cooler running bearing. Less demand on the oil.

2] Low temperature requirements. The sump is far from the cylinder head & cylinder and the oil is not circulated up to the head where it can gain heat so the whole oil system runs at a fairly low temperature of something like 130f.
Heat breakdown is probably not existent.

3] Today's good quality oils have superior molecular chains and bonds with great fluid film strength properties and oxidation resistance.

I realize that many users simply buy the cheapest basic oil they can find and then change every 250 hrs or less.
That's fine too. But what are your thoughts on longer duration intervals?
I am in the process of adding a small 12 volt gear pump and an inline automotive filter to my Roid again.
The pump will be on a timer relay which runs the filter system on a 50% duty cycle of 10 minutes on...10 minutes off when ever the engine is running.
So the oil should be kept fairly clean.
I was thinking of extending the oil change interval to 500 hrs.

Anyone experimented with longer oil change intervals ?

Without question it's easier on the starter to decompress. But not necessary on some engines. Very necessary on others

https://www.youtube.com/watch?v=XV0swraaikg
Depends on the engine.

Cranking of the engine at 6:15 minute mark
https://www.youtube.com/watch?v=phjoeEld8ac

A big 195 start without decompression. My 195 was able to easily do this also.
https://www.youtube.com/watch?v=DVJelEpPtoE

I wonder if these generic fuel system solenoids would work for your decompression actuation.
They are fast acting and have a fairly good pull strength.
That way you don't have to use PWM signaling to drive a servo on the Arduino. Just use a digital pin to drive a solid state relay.
https://www.ebay.com/itm/1502-12C2U1B2S1A-Fuel-cutoff-solenoid-12V-Kubota-D1402-D1403-D1005-D1105/392399233893?hash=item5b5cd12365:g:KxIAAOSwKgZdY5wN

As I understand it, the over-speeding of an electric motor can certainly provide power BUT the run capacitors (ratings) must be tuned to the specific load for best power quality and performance. Once your system drifts away from the load "sweet spot" the capacitors no longer match the motor output. If you keep a constant load AND tune the capacitors you may be ok.
As glort stated, the name plate data may not reflect output capability.
I recently read an article where an electrical engineer was able to get 3kw from a 5kw motor when tuning the capacitors for a similar project.
He optimized his system for 2500 watts output.
If the load was dropped below 1800 watts the power factor went out the window. Very poor.

The power company adjusts thier massive capacitors on the fly at the power station to match loads, that's why Mains power is always optimized.

saba,

Interesting project. I am currently building the same thing using a Changfa 175. A physically smaller system than yours.
The Yanmar should run quite smooth since these engine types have internal counterbalance shafts.
Having an enclosure for the system will certainly help you get control of mechanical noise.

I have not yet found a robust throttle servo to drive with my Arduino controller. I have several plastic units from ebay (with metal gears) but I fear they may not be reliable enough. What unit do you use?

Veggie

... I'm thinking of 3 large automotive mufflers in a row. Something like 2-1/2" inlet/outlet sizes.
Anyone tried that? I wonder about the back pressure.

I'm looking for ideas to make a listeroid exhaust super quiet for residential use without having to dig a hole in the ground and bury everything.
Other houses are within 150 ft of the engine location.
I want to run the unit for 4 hrs per day without upsetting the neighbors.
Has anyone built a silent exhaust system for their Lister/roid?

Regarding restrictions on rain water collection, that's certainly not the situation here in west coast Canada, but I do have friends down in California where it can be a quite different story. At their remote location, rain water collection is illegal. They still do it via underground cisterns so no-one has noticed. They also have a creek with a very small dam which was used for their water supply. 2 years ago, a large rainfall washed out the 100 year old dam, now they are prohibited from rebuilding.
No legal dam, nor legal rainwater collection. The water table is so far down that it is not economically feasible to drill a well.

Hugh, California is so messed up it's beyond funny. It's totally ridiculous.
BTW ... a 500 ft Well, thats quite deep. Must cost a fortune to drill. Makes me appreciate my 125 ft Well with a static level at 25 ft. 

cheers,
Veggie