Reed block photos

Well mainly in response to a comment by "2TRaceLab" a couple of posts back, I have included some additional pictures of the reed blocks.
The standard fibre reeds measure 0.55mm thick. The carbon fibre V-Force reeds measure 0.50mm thick.

Note that on the Lower RH side, the gas mixture flows through the crankshaft. The last picture shows the crankcase has deflectors immediately downstream of the reeds to help direct flow in between the crank wheels.
On the Upper LH side, the gas mixture flows towards the crankshaft and then up into the transfer ports.
The 3rd to last picture shows that immediately after the reeds, the crankcase has a small deflector at the bottom of the intake path directing airflow up.

I have no idea if there are any real significant differences here.
However, for the Upper LH side, it seems to me that having no reed petal backstops will help flow into the transfers where I have flowed the case. Other than that, I suspect that there is probably not much in it.
Of course the V-force reeds have 4 petals per reed as opposed to the standard reed blocks 2 petals per reed.
I leave it up to the reader to draw whatever conclusions they can. Back to back Dyno tests are the only real way to get answers I suspect.

V-Force and standard reed blocks with no stuffers or petals

Standard reed block with stuffer blu-tacked in place

V-Force reed block with flowed stuffer

Downstream of reeds. Upper LH side with crank

Upstream of reeds. Upper LH side with crank.

Downstream of reeds. Lower RH side with crank.

Upstream of reeds. Lower RH side with crank

Do RM125 pistons work in the NSR250?

[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

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.

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. 

NSR250 conrods available

I can now get NSR250 conrods made at €160.00 plus freight.
They are Honda 250 GP spec! They will fit the road going NSR250R perfectly.
19mm diameter small end
32mm diameter big end
104 mm between centres.

If anyone is interested just leave a comment or reply to my post at Diff'rent Strokers

MotoTassinari Reed Blocks

I recently took delivery of a pair of MotoTassinari V-Force 3 ( V301A ) reed blocks. (AG602C stuffers) from The Two Stroke Shop.

They are actually designed for the '87 - '00 & '02 CR125, but are a really good fit on the NSR. Just needs a bit of tweaking with the Dremel.

They look like they will flow way better. Especially where I flowed the LH Top crankcase volume.

And they don't block the rear transfer port on the LH Top cylinder as much as the standard reed block either.

Supposed to give a much crisper throttle response with about an extra 2 HP (per cylinder!!) across a broad rev range. Bloody sales talk.

No reed petal backstop on new reeds

The first step is to cut off the existing stuffers on the Reed Block back plate. I just sliced them off with a knife. The kit supplies a couple of washers and nuts. You are supposed to use them to space the reed blocks from the backing/stuffer plate, giving a slot to run the hacksaw through.

The washer/spacer provided creates gap for hacksaw

Now I used a Dremel to match up the original intake shape with the new V-Force stuffers. The V-Force stuffers are made to suit a CR125, so it just needs a bit of a tweak to get everything flush.

Bottom lip

Upper lip

New stuffer ground smooth and flush

Other side also ground smooth and flush

Also, as you can see in the pix below, the rear transfer port of the upper left cylinder is no longer blocked by the standard reed block.

Rear transfer port partially blocked by standard reed block

Almost no blockage of port with new reeds

No reed petal backstops to hinder flow out to side transfers

I do not know how much these new reed blocks are going to cost me, but probably around NZ$500 !! for the pair. Not cheap.

Now a few days later. I have been using a small file to smooth off some small edges on the red cages. At the factory the reed petals must be cut with an abrasive water jet cutter ot similar: one side of the petals is a bit rough on the edges, so I used a bit of 600 grit paper to smooth it off. Hopefully this will make them seal a bit better. Spent about 2 hours filing and sanding just to get them perfect.

 Also, in order to get the central reed petals out, you have to prise the 2 central "sticks" out sideways. This is not very obvious and is not mentioned in any of the paperwork.