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Showing posts from November, 2011

Tz250 5KE Kit cylinder port timings

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

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 e

The last of the Mohicans?

Marco Simoncelli's Gilera RSA250.    More info at


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 fr

Modified YPVS Control Box

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

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!