Engine of Bandit 250 What is the cause of the sound rattle-rattle?

I checked a cylinder head,
However, it did not have the abnormality.
I exposed all the parts from the upper-waist of the engine.

Forgive.Please forgive me; Bandit

The oil of this seemed to be changed frequently.
A piston does not have the terrible damage.

This motorcycle is run around 25,000 kilos.
It that I think is suitable for the mileage.

The lower photograph is a state of the heads.
When I bought it, the rubber packing in the cab deteriorated.
It absorbed gasoline from the different course.
The mixed gases of this were very rich and were ill-conditioned.
However, the sedimentation of its carbon is not terrible.
I ran for a while after I overhauled a cab. It might be removed by the result.

One of the cylinder has little carbon and burns..
If it is the motorcycle of the cab, it is not strange.
There was not the sedimentation of the carbon in the exhaust port. A normal state.
This motorcycle ran the long mileage on rich gas.
When the valve seat that I think sandwiches the carbon. I intend to do grinding.

The lower photograph is a state of the cylinder inside-surface.
I think that there is much brightness.
Its state is not bad.

I thought about the cause of the abnormal noise.

I took one piston off the engine among them for trial. I put it in a cylinder. It had a gap of 0.5mm. I was able to make a sound rattle-rattle.

I measured the cylinder using a cylinder boa gauge. As for it, 0.02mm - 0.03mm diameter got wide. It was worn gently. The human being cannot confirm it by the naked eye.

I see the gap of the piston ring from the top.

I understand that this engine sucks in oil.

The cause is either abrasion of the cylinder or abrasion of the cylinder + piston.

I ordered a new piston, and I compared it. This piston was not worn that much.

I removed a cylinder sleeve from a block. Outer diameter was φ 55.10mm for some reason.
I think normal press-fitting margin is about φ55.03mm- 55.06.
Possibly it may be such a thing.
This has too big Press-fitting margin.
Residual stress is let loose by a secular variation.
The inside diameter becomes slightly big.

Cylinders are not usually worn so a lot.
It does not decrease by 100,000 kilos even if I measure the cylinder of the car which ran. The con rod metal is the same, too.
During a run, the engine inside gets wet with abundant oil. The parts float to the oil slick.
It virtually gets a slimy eel by hand.
In the case of this engine, quantity of abrasion on the piston side is usual.
This engine ran with rich gas for a long time.
This was exposed to combustion gases with much HC (hydrocarbon).
The cast iron sleeve is weak chemically. It had priority over a piston and would be worn.
I have seen very worn sleeve of SR400.
Possibly that might run a long mileage by rich gas, too.

At first where will the performance of the engine having good mixed gases deteriorate from?
I think ,valve face and valve seat .
Valves are always high temperature and dry while driving.
The lubricant has only the carbon which is a by-product of the combustion.
During a run, the valve turns little by little. seat & face sharpen each other.
However, when big carbon comes, there becomes dented, and sealing up worsens.

Therefore I want to do the grinding of the valve.