Modern pistons/rings

[ronan]

I was looking at a piston out of a modern (less than 10 years old) motorcycle engine the other day. The rings amazed me as there was only 2 a compression ring on top, which had t be less than 2mm thick, and the oil control ring which was not much more in thickness than the top ring.

I am used to old brit stuff with rings nearly 1/4" thick . Are all automotive pistons gone like this with thin rings now ?

 

[123hotchef]

i reakon mate thats why nothing lasts now days

 

[ronan]

i reakon mate thats why nothing lasts now days

Some modern engines last daft mileages though, are they the ones using the older technology ? A mechanic did tell me that if you let a modern engine overheat the rings are knackered as they are so light, they warp and twist and no longer seal the bores.

 

[123hotchef]

not sure really mate I know what u mean though things are enginnered so fine now a little mishap can upset major things

 

[Chris Stevens]

1mm compression rings and 2.5mm oil control are pretty much the norm nowadays. Modern rings are far more effective than old style, and I would say if a motor gets hot enough to cook the rings, you are likely to have far more serious problems than distorted rings, and will need to do a full rebuild anyway.

 

[123hotchef]

probably cracked the head right

 

[ronan]

1mm compression rings and 2.5mm oil control are pretty much the norm nowadays. Modern rings are far more effective than old style, and I would say if a motor gets hot enough to cook the rings, you are likely to have far more serious problems than distorted rings, and will need to do a full rebuild anyway.

I had seen thin rings before, but usually on special stuff for competition and racing. Didn't know it was being used on run of the mill engines.

 

[anto44]

thin rings are a lot better than the old massively thick ones, way less friction and wear on the bores. them old thick rings would have the bores worn to nothing in no length. I've seen loads of 1mm rings cover over a million miles and the bores and rings still be within tolerance

 

[ronan]

thin rings are a lot better than the old massively thick ones, way less friction and wear on the bores. them old thick rings would have the bores worn to nothing in no length. I've seen loads of 1mm rings cover over a million miles and the bores and rings still be within tolerance

Good to know Anto.

 

[anto44]

main weakspot these days is the switch from steel blocks to aluminium blocks. this isn't really a problem if press in steel liners are used but most companies are just using a nikasil coating on aluminium bores which in a lot of cases just isn't up to the job. I've stripped a lot of engines with low compression and the rings are still ok but its the nikasil coating has gone in spots. its the same thing with compressors I'd only buy one with either steel barrels or steel liners, coated aluminium bores are just not as hard wearing

 

[Chris Stevens]

I work on bike engines with Nikasil cylinders, and plated cylinders are far more resistant to wear than anything with spun iron liners. Other than cheap soooters, pit bikes etc, pretty much all bike engines today are plated. The motors I do are off-road, and as long as air cleaner is serviced, the piston will wear out a long while before there is any trace of wear on cylinders. I would guess failures on car engines are not directly related to anything to do with the coating itself (which is far harder than cast iron), but more to do with reducing production costs to a level where long term reliability is affected?

 

[slim_boy_fat]

.....engines with Nikasil cylinders.....

BMW made a backside of their 6 & 8 cyl engines in some models in the 90s and had to replace loads of engines at the time - the wear was down to the introduction of low-sulphur fuels iirc.

 

[The_Yellow_Ardvark]

main weakspot these days is the switch from steel blocks to aluminium blocks. this isn't really a problem if press in steel liners are used but most companies are just using a nikasil coating on aluminium bores which in a lot of cases just isn't up to the job. I've stripped a lot of engines with low compression and the rings are still ok but its the nikasil coating has gone in spots. its the same thing with compressors I'd only buy one with either steel barrels or steel liners, coated aluminium bores are just not as hard wearing

I have seen the small engines we use to power the water pump, for pressure testing dry and wet risers, worn out after less than 200 hours use.

As you say the linings are shot and worn out. On one of them you could see the wear, as dark grey patches on the wall.
Simple test, bit of fuel on top of the piston, wind it down and watch it run away as the piston reached the wear patch.

 

[123hotchef]

new liners are cheap though right?

 

[dobbslc]

Jaguar had the same trouble with their engines a while ago with the plating rotting off due to low sulphur fuel.

 

[barracuda816]

Jaguar had the same trouble with their engines a while ago with the plating rotting off due to low sulphur fuel.

As Chris says, Nikasil coating is harder than steel. The problems that BMW and JAG had was the sulphur content was too high, it attacks the lining. Modern fuel has lower sulphur content so is fine.

 

[slim_boy_fat]

As Chris says, Nikasil coating is harder than steel. The problems that BMW and JAG had was the sulphur content was too high, it attacks the lining. Modern fuel has lower sulphur content so is fine.

Ah, I got it back to front.