Piston & Related parts FAQ - I'm the one that's asking!

[shiroitenshi]

I have some question about terms I've learnt while trawling the net.

1. What are those coatings on the pistons? I know they're to reduce friction, but what stuff are they? I read about ceramic / molybenum
2. What are 'gapless piston rings'? What makes them different from normal rings?

3. Some pistons have wrist pins located up to the point the edges actually sit on the piston rings (on engines with longer rods than stock). Wouldn't this cause some oil from the sump to leak into the combustion chamber?

4. Why are pistons round? Why not oval?
Thanks for any answers contributed.

 

[hattech-v]

yaloooo... why automototive engineer not making the piston in square.. kekekke...
btw, its molybdenum...n i oso duno wth is that... haha
ceramic.... ceramic tiles i know laa...

 

[minivan]

molybdemun ... yeah its to reduce friction. Its actually a chemical element. Chemical freaks would know better what it is...

ceramics... usually used in high temp, so i guess its for withstanding high extreme temps...

gapless piston rings... well as the name implies. Its a piston ring design that reduces the gap which robs the engine of power. piston rings with gaps allow gases to go into the crank case, oil sumps shortening lubricant life, etc...

piston pins Q... not sure...

why pistons are round... also not sure... i've never asked myself this... interesting...

 

[J101]

heres a good writeup on pistons.

http://www.motorcycleproject.com/motorcycle/text/cows-pistons.html

 

[xxxx]

I have some question about terms I've learnt while trawling the net.

1. What are those coatings on the pistons? I know they're to reduce friction, but what stuff are they? I read about ceramic / molybenum
2. What are 'gapless piston rings'? What makes them different from normal rings?

3. Some pistons have wrist pins located up to the point the edges actually sit on the piston rings (on engines with longer rods than stock). Wouldn't this cause some oil from the sump to leak into the combustion chamber?

4. Why are pistons round? Why not oval?
Thanks for any answers contributed.

1. its MOLYBDENUM. read as molibdenum. this is one of the basic elements from the 118 elements in the periodic table. so, it can't be used on it's own.tat's why it's mixed with other elements as a strong composition.

"Molybdenum is a silvery-white, hard, transition metal. Scheele discovered it in 1778. It was often confused with graphite and lead ore. Molybdenum is used in alloys, electrodes and catalysts."

2. gapless rings -

- this has a special second compression ring that has a special way of butting the ends of the ring together so there is no gap.
-this ring gives excellent static leak-down numbers.

a choice among engine builders in US but honda stock rings are preferred due to their high quality and construction features.

4. this is no stupid question as ppl take the round shape for granted n never asked why.

 

[shiroitenshi]

Thanks for all the info.. still much to learn... (>.>)

 

[hattech-v]

asking about piston, can b18cr engine use b16b pct piston?

 

[shiroitenshi]

asking about piston, can b18cr engine use b16b pct piston?

Is the bore size same? I'm thinking it's not... and that antifriction coating does expand (I think, not sure) so even very close tolerances are a no no.. (again.. I just think, no sure answer)

 

[hattech-v]

bore size is same. 81mm

 

[shiroitenshi]

bore size is same. 81mm

The thing is, from what I talked to friend/mechanic. Those decimal points after milimetre also count, since the pistons (or rather the coating) expand with heat and depending on the coating, the rate of expansion is different.. I don't visit honda-tech much (too much crap and information), but perhaps someone there has tried that combo before.. why don't you try asking?

Or.. why don't you try out and let us now.. if your engine seize, then it's a no-no.. hehe.