[Edit 23 Nov 2011]
Very basically, YES, I used the 2000-2003 RM125 single ring pistons from Wossner, but you really should machine the heads to give a squish of about 0.8mm. The deck height of these pistons is 0.6mm less than the standard Honda pistons with a different dome angle as well.
I will do a blog "page" about this giving better detail in due course as I can see that this is quite a popular blog entry from the blogger stats. I have set blogger "pages" to appear as tabs at the top of this blog.
Note: I have only done 300km on the engine to date including 3 x 15 minute track sessions.
Also see 2TRaceLabs section on fitting RM125 pistons
[/Edit]
I want to use RM125 pistons in my NSR because I have heard that they fit and that they are about 40 grams lighter per piston. I hate second hand information so am going to suss this out for myself as best I can before spending any money.
NSR250R piston:
Bore 54mm
Gudgeon pin diameter 15mm
Deck Height 22mm (top of gudgeon pin to piston crown edge) [Edit] Later measured to be 22.5 - 22.6
Dome height 2mm
Length 62mm
2 rings, ring pegs 20mm apart either side of rear boost port.
Weight of Honda Piston, circlips, gudgeon pin and small end bearing: 195 grams.
And for what it's worth, the conrods weigh 156 grams
RM125 2000-2003
Bore 54mm
RM125 2004 -
Dome height 0mm (Flat topped)
So, that's the numbers.
The RM125 piston has a 5mm shorter skirt. So the concern here is that at TDC, the RM125 piston may not be fully blocking off the exhaust port. I just checked this and the RM125 piston does block the exhaust port fully at TDC.
So, it appears (on paper) that both the 89-99 and 00-03 RM125 pistons will fit and work OK in the NSR250.
The 89-99 RM125 piston has 2 rings with ring pegs in the same position as the NSR piston.
So this would seem a no-brainer. It will work fine.
The 00-03 RM125 piston has 1 ring with the ring peg centralised at the rear of the piston.
This may at first sound bad as the ring ends could catch on the rear boost port. However, it is not as bad as you might think.
The rear boost port is only about 18mm wide, so there is only 9mm of each ring end sticking out from the edge of the port. It is hard to calculate exactly how much the ring ends will "stick out" into the rear boost port, but it will almost certainly be a negligible amount. There are many instances out there where the ring peg is smack bang in the middle of the boost port. I really need to give some examples to make my case. [ I will work on that, watch this space]
Also, as the piston slides down the bore, the ring (at the exhaust port) gets pushed back into perfect alignment with the cylinder, causing the ring ends to symmetrically merge closely on the pin peg at the centre rear (intake) side of the bore.
In the case of the 2 ring piston, the merging of the ring ends as the piston slides down the bore is not so symmetrical about the ring pegs (they are offset from the centre by 10mm). This situation is more likely to result in damage to the ring pegs and could potentially, over time, knock the ring pegs out if they are not firmly attached. This is a small point and can realistically be ignored.
I can't help but lean slightly towards the performance oriented side of things here, and opt for the lighter, less frictional, 1 ring piston. This is a choice that most road oriented riders probably wouldn't take, but hey, that's fine. For me its going to be the single ring 00-03 RM125 pistons and rings. Also, I will go for cast pistons rather than forged. This is because, as a general rule of thumb, cast pistons are lighter. I would like to try out some Wossner pistons, just because they "look cool" and seem to be pretty good, but they are not cast and will be therefore be slightly on the heavy side I suspect.
I can get some cast pistons from Pro-X.
RM125 2000-2003 Pro-X.
Kit No. Diameter
01.3220.A 53.94
01.3220.B 53.95
01.3220.C 53.96
01.3220.D 53.97
The NSR250 has 3 barrel sizes with 3 matching piston sizes:
A barrel <--> B piston
B barrel <--> Blank piston (no mark)
C barrel <--> D piston
Pro-X list 4 sizes for the NSR125 piston: 53.96, 53.97, 53.98, 53.99. Hmm,.. the size ranges do not overlap all that well.
OK, so I need to look into the piston sizes in more detail to find the correct size for my "A" barrels.
I am pretty sure that the "A" barrel has the largest bore. So am probably after a piston with 53.97 or greater nominal diameter, but I need to get it sorted.
Note: the 2 pistons that came out of my "A" barrels are in very good condition and measure 53.60 ± .02mm at the piston crown (front to back and side to side). This doesn't help much.
Also see some future posts:
1) Wossner Pistons that I bought
2) The text at the bottom of this future post
Some Links:
The 7th post by Matt@TYGA in this thread is of particular interest. But bear in mind that this guy sells Honda piston kits.
Very basically, YES, I used the 2000-2003 RM125 single ring pistons from Wossner, but you really should machine the heads to give a squish of about 0.8mm. The deck height of these pistons is 0.6mm less than the standard Honda pistons with a different dome angle as well.
I will do a blog "page" about this giving better detail in due course as I can see that this is quite a popular blog entry from the blogger stats. I have set blogger "pages" to appear as tabs at the top of this blog.
Note: I have only done 300km on the engine to date including 3 x 15 minute track sessions.
Also see 2TRaceLabs section on fitting RM125 pistons
[/Edit]
I want to use RM125 pistons in my NSR because I have heard that they fit and that they are about 40 grams lighter per piston. I hate second hand information so am going to suss this out for myself as best I can before spending any money.
NSR250R piston:
Bore 54mm
Gudgeon pin diameter 15mm
Deck Height 22mm (top of gudgeon pin to piston crown edge) [Edit] Later measured to be 22.5 - 22.6
Dome height 2mm
Length 62mm
2 rings, ring pegs 20mm apart either side of rear boost port.
Weight of Honda Piston, circlips, gudgeon pin and small end bearing: 195 grams.
And for what it's worth, the conrods weigh 156 grams
RM125 2000-2003
Bore 54mm
Gudgeon pin diameter 15mm
Deck Height 22mm (top of gudgeon pin to piston crown edge)
Dome height 2mm
Length 57mm
1 ring, centre pegged at rear boost port
Weight of Pro-X RM125 Piston, circlips, gudgeon pin and small end bearing: ??? grams.
Weight of Pro-X RM125 Piston, circlips, gudgeon pin and small end bearing: ??? grams.
RM125 1989 - 1999
Bore 54mm
Gudgeon pin diameter 15mm
Deck Height 22mm (top of gudgeon pin to piston crown edge)
Dome height 2mm
Length 57mm
2 rings, ring pegs 20mm apart either side of rear boost port.RM125 2004 -
Dome height 0mm (Flat topped)
So, that's the numbers.
The RM125 piston has a 5mm shorter skirt. So the concern here is that at TDC, the RM125 piston may not be fully blocking off the exhaust port. I just checked this and the RM125 piston does block the exhaust port fully at TDC.
So, it appears (on paper) that both the 89-99 and 00-03 RM125 pistons will fit and work OK in the NSR250.
The 89-99 RM125 piston has 2 rings with ring pegs in the same position as the NSR piston.
So this would seem a no-brainer. It will work fine.
The 00-03 RM125 piston has 1 ring with the ring peg centralised at the rear of the piston.
This may at first sound bad as the ring ends could catch on the rear boost port. However, it is not as bad as you might think.
The rear boost port is only about 18mm wide, so there is only 9mm of each ring end sticking out from the edge of the port. It is hard to calculate exactly how much the ring ends will "stick out" into the rear boost port, but it will almost certainly be a negligible amount. There are many instances out there where the ring peg is smack bang in the middle of the boost port. I really need to give some examples to make my case. [ I will work on that, watch this space]
Also, as the piston slides down the bore, the ring (at the exhaust port) gets pushed back into perfect alignment with the cylinder, causing the ring ends to symmetrically merge closely on the pin peg at the centre rear (intake) side of the bore.
In the case of the 2 ring piston, the merging of the ring ends as the piston slides down the bore is not so symmetrical about the ring pegs (they are offset from the centre by 10mm). This situation is more likely to result in damage to the ring pegs and could potentially, over time, knock the ring pegs out if they are not firmly attached. This is a small point and can realistically be ignored.
I can't help but lean slightly towards the performance oriented side of things here, and opt for the lighter, less frictional, 1 ring piston. This is a choice that most road oriented riders probably wouldn't take, but hey, that's fine. For me its going to be the single ring 00-03 RM125 pistons and rings. Also, I will go for cast pistons rather than forged. This is because, as a general rule of thumb, cast pistons are lighter. I would like to try out some Wossner pistons, just because they "look cool" and seem to be pretty good, but they are not cast and will be therefore be slightly on the heavy side I suspect.
I can get some cast pistons from Pro-X.
RM125 2000-2003 Pro-X.
Kit No. Diameter
01.3220.A 53.94
01.3220.B 53.95
01.3220.C 53.96
01.3220.D 53.97
The NSR250 has 3 barrel sizes with 3 matching piston sizes:
A barrel <--> B piston
B barrel <--> Blank piston (no mark)
C barrel <--> D piston
Pro-X list 4 sizes for the NSR125 piston: 53.96, 53.97, 53.98, 53.99. Hmm,.. the size ranges do not overlap all that well.
OK, so I need to look into the piston sizes in more detail to find the correct size for my "A" barrels.
I am pretty sure that the "A" barrel has the largest bore. So am probably after a piston with 53.97 or greater nominal diameter, but I need to get it sorted.
Note: the 2 pistons that came out of my "A" barrels are in very good condition and measure 53.60 ± .02mm at the piston crown (front to back and side to side). This doesn't help much.
Also see some future posts:
1) Wossner Pistons that I bought
2) The text at the bottom of this future post
Some Links:
The 7th post by Matt@TYGA in this thread is of particular interest. But bear in mind that this guy sells Honda piston kits.
Nice info.
ReplyDeleteThank you very much.
Can you tell me where can I get the crankshaft bearings ? TIA Pablo from Buenos Aires, Argentina
ReplyDeleteEL PROBLEMA ES QUE LOS COJINETES DEL CIGUEÑAL ESTAN AGARRADOS A LA TORTA DEL MEDIO , Y SON MUY FINAS COMO PARA CORTAR,TORNEAR Y PONER UN COJINETE NUEVO COMO SE HACE EN LOS RD 400 O BANSHEE , LO QUE PODES HACER ES RECTIFICAR HASTA 2 DECIMAS EL CIGUEÑAL Y HASTA 2 DECIAS EL OJO DE BIELA Y PONER FIDEOS +0.2 HAY UNOS QUE SON IGUALES DE LARGO SON DE CAJA DE AUTO NO SE CUAL . ESPERO QUE TE SIRVA SOY DE LANUS , BUENOS AIRES . SALUDOS
DeleteSo, are the single ring RM125 1990 - 1999 pistons (641M05400 is the Wiseco part number, not that I'm recommending Wiseco pistons) the correct height or are they too short without barrel mods?
ReplyDeleteRumour on the forums has always been that the RM piston is too short.
For info the NX5 RS kit piston runs it's ring peg straight over the boost port.
You can get main bearings from Mixalisen.
ReplyDeleteGo into the forums at nsr-world.com and send him a PM. He lives in Greece.
See this thread: http://nsr250.net/forums/viewtopic.php?t=5142
I haven't properly physically checked the two types of possible RM125 pistons. But from looking up the specs, as you can see, they should fit. But "should" is a nasty word. (Should = Might not). I will almost certainly find out for sure in due course, but don't hold your breath.
ReplyDeleteThe NSR piston is actually really hard to measure as it has a rolled edge, it's certainly over 22mm to where it would be if it were a hard edge like the RM125 ones are.
ReplyDeleteI've got a single ring Prox 2000-2003 RM125 piston here and a stock mc21 unit, the skirt height is several mm but is irrelevent, it'll make no measurable difference.
Piston pin - top of crown height on the RM unit is 24.70.
The NSR is 24.90.
It's with a set of verniers right in and rhrough the pin hole as far as they'll go, so it's not an accurate measument itself (as the verniers themselves have width so don't sit right at the top of the round piston pin hole) but as a comparision it's good.
The Prox 2000-2003 RM125 single ring piston is close enough to the NSR unit that you could use it and set the squish with gaskets, though you will probably have to buy some thin gasket paper.
Maybe as low as 0.2 or 0.3.
For info, the Honda RS250 kit piston is a good 1mm shorter than the NSR piston from pin to crown.
ReplyDeleteHi, have you tried the rm pistons yet ? I am desperately trying to repair an mc16, i have a broken skirt and the barrels are gone, I read that the mc18 barrels work fine without mods, but as for the pistons, which will work the best, i was trying to get info on the cr125 (2003) pistons but, but i cant get the small bearing dimensions on the con rod of the nsr.the cr125 is 15*19*17.2. Can you help me please. I have had this bike 11 yrs sitting in my room, i livein the caribbean where resources are very limited. Thankyou.
ReplyDeleteYep, the Prox RM125 piston does work though it dropped it's ring peg within 50 miles and wrecked my barrel, so...use with caution.
ReplyDeleteHi there - where is the barrel size marked on the barrel?
ReplyDeleteAnyone else have any more information on the RM125 pistons? Wossner or Wiseco, are either more reliable to not drop their ring peg???
ReplyDeleteWas never a huge fan of Pro-x.