Rehoning the cylinder: What grain size?

[Tobias Claren]

I am replacing piston rings, piston and cylinder head gasket of a 4-stroke Peugeot Kisbee 50cc.
The fuel consumption was around 65mpg (3.6l/100km), although this scooter (China 4-stroke, not fuel-injected like the newer Kisbee) should manage 112mpg (2.1l/100km).
Also, the scooter started relatively easily with a kickstarter, but not with an electric starter (it has a new strong lithium battery with 100A cold start energy instead of the usual 50A for lead). The compression was 165PSI (11bar), although 190psi would be more normal for China 4-strokes. Due to the longer stroke of the 139QMB-E engine from Peugeot compared to the standard 139QMB engine, the compression should possibly even be slightly higher.

Hence the idea of fitting new piston rings and cylinder head gasket, and possibly regrinding the valves.
The running surface of the cylinder looks scratch-free, but is smoother and shinier compared to an end piece (where the piston does not reach, you can see the new condition from the factory):

That's why I want to go through it with a honing brush.

I have 3 grit levels flexible ball honing brushes (41mm for 39mm cylinders).
120, 180 and 240.
Should I go in and out with all three stages, e.g. 15 times from each side, or should I only use the 180, for example?
It's been years since I bought the brushes because of some expert or "experts" on a forum.
But now I've also seen videos on YouTube where, for example, only a 180 brush was used.

Which oil available in the household should I use?
Buying special "honing oil" and setting up a pump for circulation is probably overkill for this simple manual surface improvement.
However, I have a 12V oil suction pump for used oil ;-).
Will a few sprays of WD40 (or the cheaper stuff) be enough, or should I use some of the scooter's engine oil.
I could heat it in the microwave to make it more fluid.
Or some rapeseed oil from the kitchen.

What is the best course (grit level or grit levels) of action, especially for 50cc 4-stroke scooters (if that is relevant)?

Thanks.

[GrumpyUnk]

OPINION only.
I would go with the slightest hone that gave me a surface finish that looked good. I understand the angled grooves are designed to allow the cylinder wall to hold a bit of oil, and as long as they are visible oil will (i think) be held. New rings are designed to seat quickly, and should(again, I think) do so even with the lightest hone you do.
I have read of using kerosene as the lube, light weight and would flush/carry away the byproducts of honing.
I think about any light lube should work. I do not think it is terribly important, but I do think you want at least a slight bit of lube on the walls.
I would go with the WD40 and see how it performed. If you are a bit fearful of not providing sufficient lubrication, use some clean motor oil. 10W30 or 15W40 should be fine at room temperature. Just need a slight bit, as if you had a squirting oil can and squirted a splash at the top of the cylinder all the way around. You could splash onto a paper towel and wipe the cylinder wall with the wetted paper towel and should have a good oil slick on the wall after.
I have used dingleball hones and those equipped with 4 rectangular stones. The former must be chosen by size. The latter must have the tension adjusted as you like.
There is a group that indicated no need to hone a cylinder before installing new rings. On a MOPAR web site. Apparently they have results that back up the claim. Another does not use lube on rings at first startup. I am not in that group as I would lube the rings, the grooves and twirl them around to get lube all over the rings top and bottom surfaces, with a bit on the wall facing surface. Car & truck engines, used to lube the rings LIBERALLY as generally things were tight when it was time to attempt the first start. As the pistons were installed, the force necessary to rotate the crankshaft grew with each piston install.
tom

[Tobias Claren]

What do you mean by "slightest"?
The lowest grit, i.e. 120 (not 180 or 240), or the finest grit (240)?
Not 180?
Or 120, 180 and then 240?

[jackrides]

For best results use the honing lube that the Ball Research recommends. Thy likely also will recommend the grit size to use for your ring material and size. Also follow their washing recommendations following honing. Look atthei photomicrographs of results using their products and methods. Been a fan since early 1970s.

[GrumpyUnk]

"Slightest" in my mind was the least abrasive, having the slightest effect on the cylinder wall. Highest number abrasive would be the least aggressive or abrasive.
tom