As a result of measuring the inner diameter of the cylinder, it was 0.02 mm ~ 0.03 mm widened, so boring is necessary.
But, oversize piston is abolished both one over and two over.
Put the oversized and a little can Bore up.
I can expect a little power up, but the dream collapsed fleetingly.

Although I examine the diversion of other car models, Bandit is impossible because the bore is the biggest.

So I have no choice but to make sleeves.
I decided to remove the sleeve.Even boring is troublesome.

I will pull it out with a manual hydraulic press.
When was removed, the block side was scratched.
This is all right if I scrape it off in Leutor.

This is a removed sleeve.

The escape of the intake valve is dug in the upper part.

First of all, I took off only 1 cylinder, and I measured dimensions and drew a drawing.
In this way ↓.

Those who are suffering from bad condition on board Bandit 250, are free to use this drawing without permission.
The outer diameter is mating tolerance becomes m7, but if it is m7 it will be φ55.011 to φ55.041.
The actual measurement here was φ55.100, but in this case the fitting tolerance is u6 or u7.It is a bit too tight.So I changed it without permission.

And,
· No escape of valves.
· The inner diameter is 1 mm smaller.
(Press fit into the cylinder block and boring to finish it to φ49.00.)
· Since the brim comes out of the block, it needs a surface research.
Please pay attention to this.
(Even if there is a problem, I will not take responsibility.)

As usual, I ordered the Dense Bar.I bought 60φ.
So brim will remain cast.

I am able to use it which was rolling at the edge of the factory.

Next time, I will cut out 4 sleeves with my hands.

There was no abnormality around camshaft, so I decomposed everything on the waist.

The oil seems to have been replaced frequently.So the piston is not so seriously damaged.
I think this distance is reasonable because this car is about 25000 kilometers driving.

The state of the head.
When I bought it, the rubber packing inside the carburetor was deteriorating.And it was sucking gasoline from a strange place.
It was very thick, and a condition was bad.But, the deposition of carbon is not so bad.
Because I ran a little after I overhauled a carburetor, It may have removed it.
There is one cylinder with less carbon and burnt.Well, a carburetor car is such a thing.
There was not the sedimentation of much carbon in the exhaust port either.It is a normal condition.

This had much mileage and ran a long distance with having thick air-fuel mixture.
Therefore, I think that the valve sheet is bitten by the carbon and it is rough.
So, I think I will do the adjusting.

The state of the cylinder is such a feeling.
I think that there are many oily looks.
It is not so bad.

I considered the cause of the noise.
As a test, I removed one piston from the engine and inserted it.Then, it moved around 0.5 mm of rattling to the left and right.
When I measured the cylinder with the cylinder bore gauge, the diameter was spread from 0.02 mm to 0.03 mm.
It was gradually worn out,so I do not understand it judging from an eye either.
I can see the piston ring gaps from above.It will suck the oil.

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

Later I ordered a new piston and compared it.And it turned out that the piston was not so abrasion.
Later, I removed the cylinder sleeve from the block, but the outside diameter was φ55.10.
For normal press fitting, I think that it is about φ55.03 to 55.06.
Possibly press fit charges are too big and may influence that residual stress is let loose by a secular variation, and the inside diameter spreads a little.

Cylinders do not usually decrease so much.

Even if I measure the cylinder of a car that ran for about 100,000 kilometers, it has not decreased so much.The connecting rod metal metal does not often decrease in the same way, too.
During running, the inside of the engine has become gooey with abundant oil, so the parts are floating on the oil film.
My image feeling like grasping the slimy eel.
I think that quantity of abrasion of the piston side is a fact when I say with this engine.

The combustion chamber was operating for a long time with the carburetor setting in a different state.
Therefore, it was eating combustion gas with a lot of HC (hydrocarbon).As a result, a chemical weak cast iron sleeve may have worn over the piston in preference.
I have watched the sleeve which the inside diameter spread through very much in SR400.
Perhaps that might have been running a long distance with a different carburetor setting.

Then, where does the performance of the engine properly setting carburetor deteriorate from?
I think that it is desolation of valve face and valve seat.

The valve contact surface is always hot and dry during operation.
When it comes to lubricants, there is only carbon which is a byproduct of combustion.
The valve always rotates little by little during operation and the seat and the face fit the sharpen together.
But, when large carbon particles or the like comes in, it gets dented and the sealing becomes worse.

Therefore I want to do the grinding of the valve.