Two Stroke Racelab

Crankcase Flowing

2012-02-11T21:26:00.002+02:00

It helps a bit to have the crankcases of your two stroke engine reworked. Removing castings burrs and making some radius on sharp edges is the general consensus.
Other than the above, it helps a lot to temporarily install the crankshaft and reed valve in place, as these parts will reveal some more work needed.

It is not hard science but needs a bit of experience with a few different crankcases so you can have a broader and more complete view of what needs to be done. Key words are "flow" and "direction". These are the most important aspects when reworking a crankcase. Removing rough casting burrs will aid flow, reshaping the paths of flow will aid for better cylinder filling.

While you are there, matching the mating surfaces among crankcase halves and barrels, is a good idea.

Here are a couple pics of pre-post state of a Nsr250 Mc21/28 crankcase that I just finished working on.

First photo is where the LH cylinder bolts on. I may have exaggerated a little bit on opening up the area to the transfer ports though this is what "racelab" stands for... lol

Second photo shows flow to the RH cylinder, notice the casting burrs on the left side of the pic. Both "pools" were filled up with epoxy putty and I then redrilled the oil holes for the bearings. Final finishing were done with #120 grit sandpaper.

Battery Eliminators

2012-02-08T00:22:00.004+02:00

Made a bunch of Battery Eliminators in red color, all are already gone but I'm going to make some more soon.

Battery Eliminator is essentially a low ESR computer grade capacitor that takes the place of a traditional battery. Highly recommended for track bikes and available through the online store.

Red Bull Yamaha YZR500

2012-02-07T01:29:00.000+02:00

V4 499cc engine, aluminum alloy frame, twin spar design fabricated from a combination of pressings and matched segments welded together. Close firing order aka Big Bang, Keihin carbs, Ohlins suspension, over 180ps and a weight of about 130Kgr.

MotoGP rules specifically state that GP bikes should be light and powerful prototypes as to differentiate them from Superbikes?

Electronic Gremlins

2012-02-05T13:54:00.002+02:00

Quite busy for the last few days at the racelab, repairing and modifying cdi and ypvs control units for Bernd(TH), George (GR), Marcus(UK), Andrea (IT) and Keith (NZ).

Thanks to all people for trusting my services.

Kawasaki GP250 X-09 racer

2012-02-04T21:15:00.000+02:00

Expansion Chamber Porn

2012-02-02T00:21:00.003+02:00

...nice titanium exhausts.

Photo courtesy of tozecanaveira.com.

Crankcase headaches...

2012-01-29T01:45:00.000+02:00

I'm missing the days when I knew shit about two strokes... things were pretty much easier and less time consuming. I didn't had the knowledge to go any further though, so I reckon that's a good thing in my book.

I will do a write up on CCSpecialty porting tools real soon.
Big cheers to Vaggelis(GR) aka 1/2 Racing that lend me some of his tools. A young guy that knows more about porting work than old-aged tuners here in Greece.
Nsr250 crankcases in the background...

Dzus Fasteners

2012-01-26T23:40:00.000+02:00

Quarter turn fasteners are essential for track/ racing bikes and save a lot of time and effort. Dzus bolts are the most commonly used fasteners and come in a variety of types (spring, slip-on, riveted etc) to cover any application needed.

Position of the Dzus spring plates should be right behind the back panel or just slid over it if your stud doesn't have the sufficient length needed.

Mark the position and drill 3mm holes for the rivets and about an 11mm hole for the flared spring plate. On the front fering panel, use a nylon washer after you've inserted the stud as this will keep the stud in place when the panel is removed from the bike.

NX5 Ohlins rear shock on a Nsr250

2012-01-21T00:31:00.000+02:00

Spyros aka Bismarck came for a coffee today, bringing along a couple aluminum spacers for the mc28 project. We fitted the Ohlins Rs250 rear shock and it seems like I finally have a rolling chassis.

Both ends of the Ohlins rear shock should be modified to suit the mc28 frame-proarm. Upper fitting needs to be machined as length is too large to fit the nsr frame and mounting hole should be enlarged. For the lower fitting, we used an eyelet type, kindly donated by KRT aka Kalogiros Racing Team and a couple spacers to suit the nsr shock linkage.

Even then, there are a few minor issues as the upper part of the Ohlins rear shock has contact with the aluminum spacer of the subframe bolt and the LH rearset will not clear the proarm due to the added length of the Ohlins shock. Also, rear brake hose needs to be relocated. Most of the issues already corrected... a rolling chassis at last!

Ethos Tornado

2012-01-14T22:52:00.001+02:00

I came across a set of Nsr250 mc28 expansion chambers made by Ethos, so I couldn't resist taking some measurements.

*Stingers have an ID of 21.5mm and are 400mm long.

Below photo of the pipes mounted on a Nsr250 plus a couple more, can be found at Jamie's Nsr site. Browse the links while you are there as it has tons of interesting info.

Nsr250 swingarms: Proarm Vs Gullarm

2012-01-05T18:42:00.001+02:00

Ok, I might getting a little bit anal here but I had both swingarms side by side while trying to stay open-minded and consider both of them for my nsr250. So, I couldn't resist comparing them...

First of, the eternal debate about the weight of both swingarms.

A complete Nsr250 mc28 Proarm measures about 9.800Kgr and an almost complete mc21 swingarm measures about 8.500Kgr.

So, mc21 swingarm is 1.300Kgr lighter but to make things clear, these measurements are really rough.

As you can see from the photo, the mc28 proarm is complete while my mc21 swingarm has quite a few parts missing. Also, I haven't measured mc21 wheel bearings and all 4 metal spacers as these are part of the wheel while on the proarm these are integral parts of the hub-axle assy (hence included on the above measurement).

Overall, I believe that both swingarms weight really close with the mc21 maybe ending up being just a bit lighter.

I really like the robust looks of the gullarm design and tyga-performance sells a kit with all rear spacers made out of aluminum that looks to be a very good upgrade for a little bit more weight saving.

On the other hand, the proarm has a unique design. It's heavier component is the rear axle as it's constructed out of mild steel (about 3.5Kgr just this one alone!). I think that Rs250 nx5 rear axle has really close dimensions and might be a straight swap, with hopefully less weight. If anyone knows for sure, please let me know.

I also like that the proarm has no silent blocks at all and changing the rear tyre is a joy, as you do not have to chase spacers while you remove the wheel and retightening the chain is not necessary.

Overal, I'm a person that likes innovations and open-minded motorcycle design, so the proarm will most probably end up as my choice but both swingarms are really nice and selection between the two is really down to personal taste rather than specs.

Steering Head Bearings

2011-12-29T15:45:00.000+02:00

A nice modification on the steering stem of most motorcycles, is to replace the stock ball bearings with taper roller bearings. E.g check the lower part of the photo below with the Nsr250 steering head bearings. Bearing assy consist of a cup and a cone ball bearing with the balls held in place by a suitable cage. Even though this method was even used on later racers, they are considered old-fashioned.

On the other hand, taper roller bearings give excellent results and a smooth steering (less head shaking) as they kind of act as a soft steering damper. Only drawback is that installation procedure takes a little bit more time as alignment isn't as easy as using the stock ball bearings.

Nsr250 ball bearings, stock and taper roller on top.

Part numbers are Koyo 32006JR (lower bearing) & NTN 4T-CR-0574(top bearing).

Hellenic Road Racing - The Old Days

2011-12-27T18:53:00.004+02:00

A Facebook group about old era Hellenic-Road-Racing.
Pass by and have a look at the pics... Cheers!

MC16 port layout

2011-12-25T03:19:00.000+02:00

A cylinder port map out of a Nsr250 mc16 model. Timings are very racy and quite similar to early Rs125 nf4 cylinders but port lengths are narrower. This cylinder will seriously benefit from slightly bigger transfer timings while keeping the exhaust port as it is.

Total length of the cylinder is 86.3mm and it's a straight swap to all Nsr250 crankcases. Water jackets could have been bigger so upgrading your cooling system would be a good idea.

I really like the straight roofs of the exhaust ports...

*Numbers are in mm increments.

Oil Blank Plugs for Nsr250

2011-12-20T19:16:00.002+02:00

Spyros(GR) aka Bismarck, made some quick and dirty blank plugs for a Nsr250 mc21/28 crankcase.
Oil pump plug on the left, GPS plug on the right

... looks sweet.

2Τ Oil PreMix Chart

2011-12-16T13:50:00.000+02:00

My favorite oil measuring tube is made by a UK based company called Apico. A really nice graduated tube with a detachable base and a lid to keep the inside clean and leak-free.

Crm250 AR PGM units

2011-12-08T14:16:00.001+02:00

I haven't posted any pics of PGM units lately, so here is a couple of AR units for Des(UK) and Andy(UK). Repaired, tested and ready to be posted back.

PowerJet Kits are now SOLD OUT!

2011-12-07T14:23:00.001+02:00

Adjustable power jet kits are now sold out.

Big thanks to everyone for your interest so far, more two stroke stuff are around the corner!

Blitzkrieg Tools

2011-12-03T22:27:00.001+02:00

...or how to remove the Nsr250 mc28 swingarm axle in a couple minutes without having the proper tools.

I used a -not anymore- 32mm socket for the castle nut and a BR9ECM spark plug with a lock nut for the pivot bolt. To construct such precision and special tools, you will have to make use of some other delicate tools such as an angle grinder and a file. Believe or not, no CNC machines were involved during all the steps of this construction... LOL

Tz250 5KE Kit cylinder port timings

2011-11-22T18:48:00.001+02:00

Quick layout out of a Tz250 5KE kit cylinder ('01 model).

Layout is for general view purposes only,

actual dimensions do not include port chamfering, cylinder radius etc., so they are quite accurate.

Main and auxiliary transfer ports are staggered as per the layout.

Height of the auxiliary exhaust ports is 10mm and width is 13.5mm.
Main & auxiliary transfer ports have a width of 22mm & 21.2mm respectively.
Boost port has a height of 13.4mm and a width of 16.7mm.
Exhaust diameter at the flange is oval shaped at 37x39mm and distance from the piston is 53mm.
Total height of the cylinder is 79mm, front and rear stud hole centres at about 96mm.

Small tribute to my Tzr250 engine

2011-11-20T20:17:00.004+02:00

Well, I'm parting out my 1kt engine on evilbay and I've been comparing some old pics with recent ones. Many memories keep coming through...

This is how about it all started.

And some of the mods I've done:

Rough marking at the very beginning while trying to flow the crankcases and open up new passages from the reed valves directly to the transfer ports.

Ported cylinders, from memory the timings were about 198 degrees for exhaust duration and about 130 degrees for the transfer ports. All passages were flowed and port angles were altered. Two auxiliary exhaust ports have been opened up that had a timing of about 202 degrees and the exhaust valves were modified to work in conjunction with the new ports.

Lightened flywheel that eventually decided to crack after a few years.

Reprofiled cylinder heads. Higher compression and I've converted the stock hemi-spherical design to the TZ250 taper profile.

In the mean while, I have tried quite a few carbs on this bike and every pair worked great.

I believe that the worst pair I ever had on this bike, was the stock Mikuni 28mm carbs.

Then fitted a pair of Rgv250 vj21 32mm carbs, very simple and straight forward conversion, way better than stock but still not that great.

Next pair was again from a Rgv250, this time 34mm Mikuni carbs. Very good results but still kept looking for more... and eventually ended up with a pair of Lectron 36mm.

This was one of the biggest improvements I've made to this bike. Excellent results from the very beginning and unbelievable throttle response.

A Lectron carb, due to it's unique design allows for up to 45 degrees positioning to the manifolds that allows for a completely straight inlet to the reed valves.

This way, a common carb would have flooded badly due to the existence of a pilot jet (Lectron carbs use only the needle as a fuel metering device). So, I made a couple billet aluminum manifolds to accommodate the bigger carbs.

Lectron carbs were modified as well. I've grind the stock power jets and fitted handmade ones that are externally adjustable.

And the last serious modification and also my favorite one, was the fabrication of expansion chambers.

Even though most of the things were surrounded by a low budget theme, tons of rewarding experience has been gained through this project which would have been impossible otherwise. Lots of mistakes as well, but as mr. Phelps once said "The man who makes no mistakes does not usually make anything".

Have fun, keep the two strokes alive and kicking.

The last of the Mohicans?

2011-11-16T00:24:00.002+02:00

Marco Simoncelli's Gilera RSA250.

More info at sportrider.com

OSSA

2011-11-11T19:01:00.006+02:00

The Spanish company Orpheo Sincronic Sociedad Anónima aka OSSA is coming back with a brand new 2 stroke enduro model to accompany the trial TR280i bike.

Some of the revolutionary engineering concepts and/ or tricky specs :

a) The crankcase in one piece with a cassette type transmission unit and a reed intake directly into the crankcase. Cylinder is reversed and the expansion chamber exits at the rear while the Ohlins suspension shock has been moved towards the right side of the bike to make space for the exhaust.

The ignition is an EFI Kokusan battery-less system that also controls the electronic exhaust valve and the innovative dual injection system. One injector is located at the crankcase and one at the combustion chamber. Pre-mix only at 1:100 ratio.

The perimeter frame of the Tr280i has been formed out of chrome molybdenum and cast aluminum parts and this might be incorporated on the enduro models as well. The usual suspects for the rest of the parts like a Marzocchy front end, Ohlins rear shock and Brembo calipers.

Where should have been the ordinary fuel tank is now a casing that involves the air filter box while the fuel tank is below that. The electric starter is

innovative as well, as it does not utilize gears and has a simple and minimal design that contributes to the lightness of the whole bike that will be below 100Kg.

For more info:
www.ossamotor.es
www.ossaworld.com

Modified YPVS Control Box

2011-11-02T23:48:00.002+02:00

It's been a while since I last posted a pic of a modified ypvs control box, so heres one that I just modified for Thierry(FR). This control box is for early Rd350 bikes hence the dip switches can only be positioned on the reverse side of the housing.

Reprogramming the timing of the exhausts valves is now done via the 12 dip switches on the panel. A chart with stock and suggested timings is included and I have described a few of them in previous related posts.

Velcro tape is there to keep the switches clean and from being accidentally repositioned.

Adjustable Power jet Kits

2011-11-01T12:26:00.002+02:00

I suspect that the power jet kits will be out of stock in a few weeks. Spend a whole day fabricating some delayed orders as I had run out of silicon hoses. Polishing the whole bunch was major pita!