Why are liners useful for pistons and how do they protect the engine?

[monty37]

in what way are liners useful for piston,do they act as a protective covering?can
they be of many types?

 

[brewnog]

They contain the piston, they act as part of the combustion chamber, they provide a wear surface, they help to lubricate the piston, they seal the combustion chamber, they insulate the combustion chamber, they cool the combustion chamber, they are replacable, they seal the water system, they minimise oil consumption, they maintain compression ratio...

There are a few types, the main differences being wet or dry (depending on whether they interface with the water jacket). They're made of a range of materials, frequently centrifugally-cast iron.

 

[Ranger Mike]

you talking about replacement liners for an IC engine block (case)?

 

[monty37]

when we calculate the bore diameter ,does it include the liner?
is that no calculated excluding the liner thickness?

 

[Ranger Mike]

in our engine ( 2L Ford Cosworth) the liners must be bored. The liners are not finished. So you bore to apporpriate diameter for the pareticual piston plus desired clearence
prety sure this is the universal situation for liners

 

[brewnog]

Bore diameter, as far as performance/combustion calculations are concerned, includes the liner in its finished state. Obviously if you're asked what diameter the bore in the crankcase is, it's without the liner.

 

[monty37]

i read that in olden days ,cars never had these liners,hence re-boring
had to be done but nowadays ,replacing the liner would suffice.
But replacing the liner would result in different dimensions,the piston
would also have to be changed then?

 

[Ranger Mike]

partly correct
early engines were super heavy,,in the 1950s lighter weight engine block ( cases) were introduced but were still pretty heavy..no liners , just lots of Detroit iron. these blocks could be bored out 0.125" with no impact on longevity. With the introduction of the compact car..i.e. Ford Falcon, Plymouth Valiant, Dodge Dart, Chevy 2, et all..the big block big cubic inch engine would not easily fit and front end weight was too great so a light weight thin wall engine block was introduced...Buick had a compact little V6, Chrysler had the 273 cid, Ford 260 Cid and could bored to .060" max before the thin wall construction would cause problems. I am perrty sure that even these engines can be sleeved ( liners inserted) if need be but this causes probelms in effectively transmitting cylinder heat to the engine oil to carry away the excess heat.
In my race class we must maintain the stock CID so we have to sleeve the block once wear sets in..Taper and out of roundness...we still have to bore the sleeves ( liners) to proper dimension..we use forged pistons so we can use the same pistons once proper bore is established..if we were not restricted to the stock CID we could bore the cylinder and use a piston 0.030" oversize and pikcup a cube or tow on displacement..either way..it is expensive..but that's racing!

 

[brewnog]

i read that in olden days ,cars never had these liners,hence re-boring
had to be done but nowadays ,replacing the liner would suffice.
But replacing the liner would result in different dimensions,the piston
would also have to be changed then?

If an engine is fitted with liners, wear shouldn't occur on the bore in the cylinder block, so replacing the liner can be done instead of a rebore. If the piston isn't worn very much, and you're replacing the liners with those of the same unworn bore of the originals, you may get away with just replacing the rings, but if you do decide to re-use your pistons you should conduct dimensional checks. The piston skirts may be worn (leading to high oil consumption and rapid wear) but the ring grooves may also have opened up, which could cause ring failure and subsequent catastophic engine failure.

 

[pantaz]

Cylinder liners also permit the use of light-weight materials for the engine block, such as magnesium or polymers.

 

[monty37]

do we have dry and wet liners?

 

[brewnog]

do we have dry and wet liners?

Sure. Dry don't touch water (like a 'sleeve' in the cylinder block), wet do (surrounded by a water jacket for cooling).

 

[monty37]

we were asked to calculate ovality and taper ,for a cylinder to find
out the reboring dimension,that did not have liner,since it was an old
model,,do we calculate all this for vehicles nowadays?

 

[brewnog]

I don't understand, do you want to rebore a worn engine? Best to use standard overbore sizes in that case after measuring the bores up. If you're replacing liners (and piston assemblies) you generally maintain the standard bore.

 

[Ranger Mike]

typically, a dial bore gage is used to measure out-of-roundness of the cylinder bore. this is a device with a hardened gage point at one end and a floating gage point at the other contact end that is mechanically linked to the dial indicator. a master ring is used to zero the gage. depending upon the gage , the measurement range may be .010" to .050" travel.
Readings are take at a level just below the top of the cylinder. several reading at thisdiameter are taken to determine out-of-roundness. bay taking more readings at different depths from the top of the cylinder, a condition of cylindricity can be estimated. Taper caused by piston wear is one factor used to determine re-bore. Taper causes piston ring flutter. the ring starts to open up whne traveling up towards Top Dead Center and then closes as it returnes to the non tapered portion of the cylinder liner..this stresses the ring and permits blow by ( combustion chamber contaminates the crankcase with spend fule/air mixture). this is degrades the lubrication properties of the engine oil dramatically)