ET: Engine (Twin) Ring Orientation

[bmetcalf]

This has some thoughts on ring orientation and gap:

https://www.speedwaymotors.com/the-...all-guide-clocking-and-gap-orientation/120102

If I have enough years left to ride enough to need new pistons, I'll have to watch it again.

 

[erik]

One important thing I learned was that the ring gap of the lower ring should be wider as on the upper ring! This is for letting out the gas under pressure between the rings because if the pressure stays on there will be more leakage of the upper ring.Carillo made this explanation for their pistons.Erik P.S. Maybe others can explain it better?

 

[Speedtwin]

Erik
You hit the nail right on the head.

 

[Elanman39]

I worked at Lotus Cars for many years and at one time I was involved in a series of dynamometer tests run to determine if there was any basis to the various recommendations made for ring gap positions as the production line were fed up with various experts telling them they were doing it wrong.... We performed an extensive series of detailed tests and could find no measurable effect of different ring alignments on blow-by flow rates or oil consumption. We did prove that the rings rotate, but not all at the same rate or even direction on any one piston, so any alignment achieved on build was soon lost unless the rings were staked as on a 2 stroke. Ring gaps were found to be critical, the tighter the better as long as they were not so tight that they closed up due to differential expansion of piston and bore and made the ring scuff. As with all things the law of diminishing returns applied and we found that any gap of less than 0.002" per inch of bore diameter offered an insignificant benefit on a water cooled engine with Nikasil coated aluminium wet liners.
!! edited to add a 0 to the hopelessly wrong ring gap figure @!!

 

[vibrac]

I worked at Lotus Cars for many years and at one time I was involved in a series of dynamometer tests run to determine if there was any basis to the various recommendations made for ring gap positions as the production line were fed up with various experts telling them they were doing it wrong.... We performed an extensive series of detailed tests and could find no measurable effect of different ring alignments on blow-by flow rates or oil consumption. We did prove that the rings rotate, but not all at the same rate or even direction on any one piston, so any alignment achieved on build was soon lost unless the rings were staked as on a 2 stroke. Ring gaps were found to be critical, the tighter the better as long as they were not so tight that they closed up due to differential expansion of piston and bore and made the ring scuff. As with all things the law of diminishing returns applied and we found that any gap of less than 0.002" per inch of bore diameter offered an insignificant benefit on a water cooled engine with Nikasil coated aluminium wet liners.
!! edited to add a 0 to the hopelessly wrong ring gap figure @!!

Always thought positioning rings was twaddle never found a bike to have them correctly aligned when taking apart...
I have never used ring compressors on a Vincent either, I prop up the piston on the crankcase hole on 2 aluminium flats use a third aluminium flat 'poker' and the flat of my hand tap tap on the barrel top. On occasion on other bikes I have fitted the piston in the barrel on the bench and then fitted the gudgeon (wrist) pin to the rod through the captive piston (I just did that on my 1926 SV Douglas)

 

[greg brillus]

I just use a 25mm wide thin strip of alloy long enough to wrap around the piston with a 10 mm gap, the ends of this flat strip bent at right angles and these tabs about 10 mm long each.......you can easily compress the rings .....ease the barrel over the piston enough to cover the rings, then simply feed the alloy strip out between the barrel liner and the hold down studs.......used it hundreds of times on 84 and 92 mm pistons .......best simple installation tool ever......

 

[fogrider]

Some 5 decades ago, I bought some new Hepolite pistons, collecting them from their works in Bradford. A guy in a white lab-coat explained why the rings were positioned in a certain way ( on assembly ). It related to the compression ring gaps being spaced at 120 degrees apart and ensuring they were towards the thrust face, with the oil ring gap on the non thrust face.
Don't remember the techno about it, but I've done it ever since, after all, they designed 'em !
As Elanman said, no difference once running a while, but it seemed to be the right thing to do on assembly.
Perhaps modern materials and closer tolerances make the advice irrelevant ?
Regards all.....