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Showing posts from March, 2012

Essential Tools: Feeler Gauge

A simple, yet very important tool for measuring thickness, whether it is for clearance or gap between two points or parts. A feeler gauge with 25 blades in increments up to 1mm, is sufficient for most applications on a two stroke bike.  Some applications that first comes to mind :  Connecting rod lateral playPiston ring gappingSpark plug gapping

DIY Gudgeon Pin Puller

Here's a diy gudgeon pin puller that will work on 15mm pins and up. 
Bill of materials:  M8 threaded rod  M8 nuts x2 Plastic or metal pipe  Metal washer 
Some notes on the construction :  The pipe should have the same or bigger length to the pin that is going to be removed, it should also have an ID bigger than the pin. A soft metal like copper or aluminum will work fine as will a plastic/ pvc pipe. I used stainless steel sheet rolled on a slip roll machine and just covered one side to protect the piston skirt.  Make sure that the LH nut (see pic) will clear both pin and piston bearing or the puller will be jammed. The washer should have the same or bigger OD of the pipe been used and the ID should foul with the M8 nut.

Instructions:  Self explanatory really, see the picture of the whole mechanism bolted on an old piston.  Insert the rod and one m8 nut through the pin, circlips should be already removed.  Then insert from the other side of the piston the pipe, the washer and the secon…

electronic stuff

Busy at the racelab,  modifying a RZV500R YPVS control box for Sandro (US) and a Tzr125 box for Nick(UK), repairing a PgmIII for Jamie(AU), a PgmII for myself and fabricating a Battery Eliminator for Massimo(US).  Still some work left for a Crm250 AR ecu for Ruan(MY). 
I find it very encouraging that more and more people are trusting my services and I try to keep up to their expectations. I'm also quite proud that I have -almost- resurrected two motorcycles that were in bad shape up to proper racers, out of funds solely based on my two stroke services-products.  This might not sound like a lot, though is still important to me and I try to impart some of the knowledge that I gain through the process.  Keep the two strokes alive & ride safe.

Piston Preparation

Pistons nowadays are coming out of the factory ready to be installed. Though, there are still some things that can be done to improve reliability and here are a few of them. Following examples & photos are for Honda nsr250 pistons but most principles apply on all two stroke bikes. 
a) Oil holes.  If you are going to fit the pistons on a cylinder with a bridged exhaust port, you might want to consider adding a couple oil holes on the exhaust side if they are not already there by the factory.  Diameter of the oil holes is dependent to exhaust bridge width but most of the time 1mm holes will be adequate.  Dykem or a permanent pen becomes handy here again. Paint the exhaust side of the piston and temporarily install it on the engine. You should be able to mark the piston from the exhaust outlet by using a machinist scriber and this will reveal the available space to drill the oil holes.  b) Ring grooves preparation.  Exhaust side ring grooves should be filed with a triangular file or o…

Franz's Rd350

Big cheers to Franz(DE) for sharing a couple photos of his beloved Rd350 bike.



Nsr250 Boost port

Here are a few pics of some work that I've just finished on a couple Nsr250 mc21/28 cylinders along with some notes on crankcase and cylinder flowing.
There were some issues while taking a view of the cylinder temporarily installed to the crankcase.  Sharp edges on exhaust port side are not looking that great and making a small radius in there will do no harm. Biggest issue that really catches the eye, is the mismatch between the crankcases and the boost port of the cylinder.  It helps a lot to mark the area that you are going to work on. Proper stuff is machinist's blue or red dye such as Dykem but if the area is small, a permanent red marker will work just fine. 
Now that you have painted the area of the cylinder, use a machinist's metal scriber to make a constant and pronounced outline. After this, you will end up with a nice and contrasting background to create your art...  
For working on aluminum, double cut carbide burrs are the way to go but feel free to improvise…

Engine tip: Primary Gear Installation

Crankshaft primary gear can be easily installed -or removed-, with the use of a soft metal alloy piece, such as copper or aluminum. A 2mm copper sheet jammed against the primary gears will lock them in place and allow you to screw the crankshaft primary drive bolt.
Soft alloys will not damage the heat treated primary gears but be cautious that if the sheet thickness is insufficient, it may slip across the gears and damage the crankshaft seal or other components.

SEEL Tz250 5KE Ignition Curve

An ignition curve that I decrypted a few months back and I had completely forgot it's existence.
It is out of a TZ250 5KE project that SEEL Racetec had prepared for Kurz GP racing team.

Bike features were,
one-off ramair box,
one-off crank,
one-off cylinders, featuring Rs250 NXA porting layout
one-off titanium exhausts etc

It's interesting to observe the similarities-differences  of the two selectable ignition maps and how they compare to stock RS-TZ250 ignition curves. Nevermind the notes written in Greek language... LOL.

Mc18 cylinder port layout

And one last port layout, still with only the port heights... the almighty mc18 cylinder.  


Transfer port duration is a little bit on the low side but exhaust duration is bigger than mc21/28 cylinders.  Out of all Nsr250 cylinders, it looks like the Mc18 will rev just a little bit better.

Mc21 "SP" cylinder port layout

Second layout, this time from a Nsr250 Mc21/28 SP cylinder. 

Just about the same as the "R" cylinder but bigger exhaust duration. Taller than an "R" cylinder as well as it has a total height of 86.5mm.

Mc21 "R" cylinder port layout

It's about time to take some rough measurements and a layout of my nsr250 cylinders, so as to see what needs to be done and make a plan.

I have a pair of mc21 and one mc18 cylinders, so let's see what they will reveal...

First layout is out of an "R" cylinder,  as there is an "H" marking on the lower LH side.

I estimate the deck height to be about 0.6-0.8mm, haven't measured it yet.  Exhaust timing of "R" cylinder looks to be a bit on the conservative side as are the tranfer ports.  Total cylinder height is 86.2mm while most references speak for a height of 86.3mm, so it seems like it has been lapped 0.1mm. 
There are serious mismatches, especially on the width of main transfer ports, I haven't measured them precisely yet but they are in the region of 1.5-2mm. 
Let's go on...

Nsr250, Dry Clutch Tip

The pressure plate of a dry clutch gets worn really quick and as a consequence clutch slipping and hard gear changes might occur. I noticed that Nsr250 shares the same pressure plate for both wet and dry clutches. Only difference between the two is the alloy been used during construction, this has no real importance except that the dry clutch pressure plate has better corrosion resistance.

The wet clutch pressure plate can be used by only changing the center bearing with a sealed type one (KOYO 6001 RS type). Photo shows the suitable bearing already installed in place. All wet pressure plates from mc16 up to mc28 models can be used...