If after engine overhalling in cylander bore the oilring size in cylander bore uper middle ander lower size is different...this is not good or it is not a problem plz answer me thank u

To be honest for the work involved it would be easier to just swap out the 1600cc engine for a complete 1800cc engine. Engine cc can be set by different things. Piston bore, piston stroke, connecting rod length and so on. 1800cc pistons might simply be the wrong size for the cylinder bore.

no
not a chance as engines use standard size pistons
so an engine from 20 different manufacturers will use a 3" piston and so on for different bore sizes
however all engine manufacturers have a logo or brand cast into the block and you can identify the manufacturer from that

There is one intake manifold, there are two head cylanders. To remove the intake manifold follow this.............https://www.youtube.com/watch?v=ZqDQ2_lNXng

ENGINE 2 stroke single cylinder direct reed valve crankcase induction Liquid cooled 125 cc engine Cylinder size 124 8 cc Bore and stroke 54 x 54 5 mm 200 cc engine Cylinder size 175 3 cc Bore and stroke 64 x 54 5 mm 250 cc engine Cylinder size 247 7 cc Bore and stroke 72 5 x 60 mm 280 cc engine Cylinder size 272 2 cc Bore and stroke 76 x 60 mm 300 cc engine Cylinder size 294 1 cc Bore and stroke 79 x 60 mm I Cant put periods or commas so bare with me

Remove Engine From Vehicle,
Strip Engine And Wash Clean,
Take Engine Block ,Conrods,Cylinder Head To Machine Shop Ask Them To Check all Sizes For Wear Etc If Worn Beyond Usefull Limits Purchace New Liners And Pistons And Have Them Fit It For You,
Some Times The Bore Changes Shape I.E. Bore Is Oval If So They Do Supply Oversize Chrome Linners So That the Block Can Be Borred Round Before Fitthing New Linners!
Check Crank Shaft And Cam Shaft ,
Cylinder Head Should Be Presure Tested And Vave Guides Checked, Valves Should Be Checked For Wear Seating And Lapped Back In
Injector pump Service And Injectors Serviced
Get Full Overhall Gasket Set New Set Mains and Big End Bearings ,
You Should now Be ready To Re Assemble Your New engine!
Good Luck!

Not really sure about the 5% variance unless you measured cylinder bore. The problem could be in the ring material which could be yet a third metal. Every metal has its own expansion rate. Perhaps the rings were okay for the diameter of the bore, but were they too thin for the grooves in the rings?

Even new engines like the new 600HP Mustang can have bore distortion. The cylinder walls go eliptical when heated. Operating temperature can have a small role, but really you are probably talking about 20 degrees to bring it into a normal range?

You might try using a high temperature Laser thermometer on your exhaust manifolds. This would show if 1 particular cylinder is running hotter. Exhaust manifold shape, tight cylinder bore, etc. but at least you would get the right side or cylinder to start looking for the problem on.

I hope my solution is helpful.

take it back to who eve t=did the overhaul or check spark plugs spark plug cables, disrtibutor box

check the voltage at battery engine off, it should be at least 12.6 volts. with engine running should be 14.1 to 14.7, if running voltage is way lower then above. alt or the belt needs attention. if battery voltage when off is lower then 12 volts replace battery. good-day !

There are two different engine sizes at Pontiac Transport. You can find it reading the 8th digit of the Vehicle Identification Number. This is the engine code.
6-231 (3.8L, VIN "L")
6-191 (3.1L, VIN "D")
To buy the motor go to the Internet @:
http://www.car-part.com/
Select the Year, Make, and Model of your car.
1993, Pontiac, Transport.
Select Engine. Select the size of Engine.
I found some engines, Engine Size 3.8L, for $750.

Middle cylinder on firewall side of engine. Front is 1-3-5, firewall side is 2-4-6 from front of engine.