PISTON

   An oil-cooled piston crown, made of heat-resistant chrome– molybdenum steel, is rigidly bolted to the piston rod to allow distortionfree transmission of the firing pressure. The piston has four ring grooves which are hard chrome plated on both upper and lower surfaces of the grooves. A cast iron piston skirt (with bronze sliding bands on the large bore engines) is bolted to the underside of the piston crown.   

1. Piston Alignment?  (MITRA) 
Place the piston inside the liner without piston rings and take the clearance between the piston and the liner.Piston is aligned in fore-aft direction by the guide strips, which are bolted onto the inner side of the guide shoes. Alignment can be changed by changing the shims between the guide strip and guideshoe.
Align piston by changing the shims in the guide strip of the xhead guide shoe. 
2. Oros piston profile benifit  (Bhoumick)  
The piston crown is redesigned in the shape of a small mountain to provide more space around the fuel valve nozzles. This increases the concentration of combustion air around the nozzles and less impingement of direct fuel on the piston increasing its thermal load. OROS name is derived from Greek which means small mountain. Oros piston along with a high top land has claimed to reduce the piston temperature by 90degrees without changing anything in the lube oil properties. 
3. What is top-high land? And why? In which type of mc engine 
Top land is the annular area around the piston and above the uppermost ring.
In order to protect the piston rings from the thermal load from combustion the height of the piston topland was increased (Figure 1). The resulting increased buffer volume between the piston crown and the cylinder wall improves conditions for the rings and allows longer times-betweenoverhauls. The high topland was first introduced in the mid1990s, the positive service experience leading to its use for all new engine types.
it's a development of mc- c engine. 
THE following figure shows an OROS piston with a high top land on the B-side.
 

4.Use of APR(Anti-Polishing Ring) and where is it fitted?(BND) what is topland piston   (Battu)   
anti polishing ring draw diagram, Purpose, material(Bhowmick)
Material steel

Piston cleaning (PC) ring is incorporated in the top of the cylinder liner, the PC-ring has a slightly smaller inner diameter than the liner and hence scrapes off ash and carbon deposits built up on the piston topland. Without such a ring, contact between the topland and the liner wall could wipe off the injected cylinder oil, preventing the lubricant from performing its optimized role. In some cases, deposit formation on the topland could cause bore polishing of the liner wall, contributing to deterioration of the cylinder condition. Introducing the PC-ring eliminates contact between deposits on the topland and the liner, promoting an enhanced cylinder condition and lube oil performance. It also produces a sudden compressive effect on the ring belt which forces lube oil away from the combustion area assisting with reduction in lube oil. 

5. Piston ring - function , working diagram and material(Chakraverty)
Function -  
seal the combustion chamber;
Improving heat transfer from the piston to the cylinder wall; 
Regulating engine oil consumption by scraping oil from the cylinder walls back to the sump.

Types of Piston Rings
i)  Compression Ring - provides a gas seal
ii) Scraper or Oil Control ring – Distributes oil on the cylinder liner preventing the oil passing upwards into the combustion chamber. These rings are normally found on trunk piston engines.

Material
Rings of a pearlitic grey cast iron. A further extension of maintenance intervals can be secured by plasma (ceramic) coating or chrome plating the surface of the uppermost piston ring. Chrome plated rings should not be used if the liner is chrome coated. Rings of vermicular iron have also proved promising. Alu-coating of the sliding surface of piston rings was introduced to ensure safe running-in. The aluminium-bronze alloy coating, a type of bearing material, has proved effective in protecting ring and liner surfaces during the running-in period. Alu-coated rings make it possible to load up a completely new engine on the testbed within only five hours, fostering time and fuel savings; running-in can also be performed with reduced cylinder lubrication. The lifetime of the coating is 1000– 2000 hours, depending on such factors as the cylinder oil feed rate and surface roughness of the liner. The technical explanation is that no scuffing occurs with the combination of aluminium bronze/grey cast iron as the wear components in the cylinder. 
7.    Advantage of CPR ring (Battu) 

The relief grooves ensures optimum pr drop across the top ring.
Relief groves ensure a uniform distribution of thermal load whereby the load is reduced on liner n ring. This reduced wear of liner n ring.  

decreases the l.o consumption

decreases the blowpast, suffing. 

Note The CPR has a double lapped joint which ensure for proper seal n avoid blowpast even after wear.

8.Piston ring clearances how to take of old rings. Different types of butt clearances (Mukopadyay)

Put the ring in the least worn groove and check the axial clearances.
Axial clearance – so that ring can expand n free to slide in n out.
If too large  -  ring will FLUTTER n possible ring breakage, it may also twist n bend in the groove.
If too small -  Ring will stick in the groove. This will result in poor sealing and possible blow by which will burn away the oil and cause scuffing. Insufficient gas pressure behind the ring will affect sealing. 

BUTT CLEARANCE
Take the butt clearance with piston and ring inserted in the liner.

Butt clearance – 0.5% of the cyl dia for moderate ratings & 1% for higher ratings

Too large Butt Clearance   - Excessive localized blow by leading to overheating, burning lo film n excessive wear 

Too small Butt Clearance -             As the ring expands the butt will come together. This will exert a large radial pressure on the liner breaking down the oil film and increasing scuffing wear. Ring seizure may occur. 

RADIAL CLEARANCE

Put the ring in the least worn groove and check the axial clearances.

Take the butt clearance with piston and ring inserted in the liner.

Butt clearance – 0.5% of the cyl dia for moderate ratings & 1% for higher ratings

 

Types of butt-

i)             Butt joint means ring gap is vertical- robust joint for top rings

ii)            Scarfed means ring gap is diagonal    Better gas seal

iii)           Double Lap Joint means S-seal 

 

Too small Groove Clearance

• Ring will stick in the groove. This will result in poor sealing and possible blow by which will burn away the oil and cause scuffing. Insufficient gas pressure behind the ring will affect sealing.

Too large Groove Clearance

• Ring flutter and possible breakage

9.    Grey CI,WHITE CI,NODULAR CI all properties ,whr used(BND) 

10. Iovx or some type of piston in detail?(BND) 
11. What to do if there is not enough space to remove piston with piston rod. How to remove the studs?
Remove the cylinder cover studs using stud setter. Then use the tilting tool on the piston rod.