pistons/rings ...design and quality

[sean brady scooters]

i,m not quite sure myself JIMS,but i would suggest the keystone type...mainly cos the design of these reduces sticking rings ,and because malossi use these on the 166 kits... which are cast and revvy:D

[goldeneye]

keystone rings(RIENECKER RINGS) are for use in engines with high combustion temps, diesels for example.the shape of the ring , and indeed the groove,causes ring side clearance to constantly change, which resists the formation of carbon deposits,and thus ring sticking , but can cause flutter on an overly ported two stroke. barrel faced rings,provide positive , and constant sealing function, they assist the bedding in of an engine , because of the small contact area ( remember, 2.5 mil ring, 1mm contact area) RIDGE DODGERS, have a small step in the top face , and are ideal for engines where a re-bore is not considered essential. TAPER FACED rings have a positive oil control, and a slight taper (1-3 degrees) machined onto the face, not suitable for most two strokes. internally stepped, or the opposite, reverse twist rings, can be used to scrape, or control the oil in the bore, NAPIER SCRAPER rings are more commonly found on four strokes, to scrape the oil off the bore, but i have succesfully fitted an "upsidedown napier" to a standard GP 200 stage four , to better oil retention in the bore. total success. PLAIN RECTANGULAR, as its name suggests , is the cheapest, but if chrome inlaid, can be very good for most applications. piston ring ends /gaps can also be specifically made. the usual combination is the "peg joint", whereby a ring sits over ring pegs. an internal pin joint reduces the gap and blow past. an internal peg , with a "HOOK JOINT" or "SCARF" joint , would be cosiderably better, but only on big bores. coatings can range from, chromium , molybdenum, nitriding,plasma moly coating, phosphating, CKS (chromium ceramic coating). graphite, tin,and copper can be used as periferal coatings to aid bedding in. an Asso chrome inlaid barrel ground piston ring will be more than suitable for most cast iron barrel applications. of course , steel wire rings are stronger due to the material used. but dont dis cast iron rings, their is more to cast iron rings than the £3.99 cheapo stuff you get. anyone driving a volvo, ford, vw, porsche, jag, riding a ducati , honda, aprillia, etc. you more than likely have cast iron rings in your engine! its like saying " that horse is slow, so all horses are slow" it just depends on what ring you choose for the job. next week, ALFIN INSERTS, ALTERNATING LOADS, AUSTENITIC CAST IRON, and AXIAL MOVEMENT..................

[J1MS]

Thanks for the Info. I was told that the Keystone were a good efective way of sealing a bore but they were not as efective at elevated revs and the barrel faced rings ith paralell sides were more suited to revs. But is there any mention as regards a cast iron two stroke barrel. I have a few old two stroke tuning books and some rough notes that mention most if not all ring types and section but ther is no mention of what surface they are best suited to only what some rings can't be run on.

[Andy Pickering]

If I wasnt confused before I sure as hell am now...

[goldeneye]

jims, what do you mean , mention? i wasnt reading from a book mate. i was just speaking out loud. it was my job for ten years, so some stuff sort of sticks, narworramean marra?

[red ghost]

Hi Sean,
I understand what you're saying, but how dose that relate with the exhaust port width being a percentage of the bore size?

on a 200/66mm bore ,a 42mm wide exhaust is roughly 65% of bore...
.66 x 65 =42.9mm

70% would be .66 x 70 = 46.2mm

So how do you work out the port width for different rings?

[sean brady scooters]

Hi Sean,
I understand what you're saying, but how dose that relate with the exhaust port width being a percentage of the bore size?

on a 200/66mm bore ,a 42mm wide exhaust is roughly 65% of bore...
.66 x 65 =42.9mm

70% would be .66 x 70 = 46.2mm

So how do you work out the port width for different rings?

ahhh
this is where things can get quite tricky...
as SO CALLED "safe widths " depend on the shape of the port itself....
but basically,and i really do mean basically......
the thinner the rings are ,and the better quality that they are,and deeper section...the better they are at coping with greater widths and higher revs....

[soullad]

Has anyone tried wosner pistons? I`d be greatfull for any info

Just fitted one to my long stroke TS engine, a 70mm reed valve version. (basically a KX 250 type copy)Already wall coated for running in as Mark says. The Germans rave about 'em, top quality and after having seen them in the flesh I agree.
Happen to spend a few hours with Guy Topper the other week and he was about to try one out in a Rapido conversion. Not only did he say he was impressed at the quality but also the price - £50 from ebay !!!

[156 D]

......just some information i have just read from one of my old books...

3 mm ring flutters at an acceleration of 40,000 ft/sec squared
1.5 mm 80,000
1 mm 140,000

....for a 198cc engine.....

6000 rpm maximum acceleration is 58,700 ft/sec squared
7000 rpm 80,000
8000 rpm 104,000
9000 rpm 132,000
This shows quite clearly that you cannot race on road pistons, as the rings are just too fat.

Exhaust ports have traditionally come in all shapes and sizes. The best shape
for power is an oval, or at least something between a square and an oval. The
edges should be chamfered for 10 thou over 50 thou or slightly more, so give
the rings an easier time. The maximum width is governed by the ring size and
the quality of the components. Using thin rings in a good quality piston, the
maximum size is about 70% of bore diameter, but for first tune use 60% or 65%
as the maximum.


......"goldeneye".....in the `60`s i was lucky enough to own two MK1 Lotus Cortina`s and in the early `70`s a MK2 Cortina Lotus......the earlier ones were rebored at about 40,000mls and the reason was they used cast iron rings, which are too soft and wear very quickly, the wear rate was so, that at the 40,000mls the engine was just smoking like a two stroke with no torque or pulling power....the later engine was fine as they had corrected the problem........i doubt very much that modern production cars use pure cast iron rings because of there high mileages especially Volvo...i know some mechanics with 450,000 on there Volvo`s engines.......

[Andy Pickering]

Your making me feel guilty now Sean... ..I might just order a mahle. do you fancy keeping it there and doing the neccesary changes..

1 X Asso piston winging its way to you from Rayspeed as we speak on there rural santa sleigh Sean.. use the standard piston to stir your coffee. I now fully understand the reasons for using a quality piston married to a quality tune, thanks for the thread Sean..