Two Stroke Racelab

Leak Down tester kits for the Yamaha TZR250 1KT - 2MA & TDR250 bikes, can now be purchased via my  online store. The leak-down tester is an essential tool for any high performance two stroke engine. This kit is installed in place of your carburetor and by pressurizing the engine cases you can check for any air leakage due to worn mating surfaces, erratic torque values due to aged parts, worn crankshaft seals etc. It is a necessary evil that it will help prevent catastrophic damage to your engine and keep performance up. A very valuable tool for a two stroke engine, handmade with care. Directions of use:  Testing can take place after a newly assembled engine to verify that everything is leak free, on a bike you just bought and you need to check crank seals condition etc. Place the tool in the carb manifold, seal the cylinder head with a normal spark plug and seal the exhaust flange with the included CNC exhaust blank plug. Pump the en...

A few months back I made a custom leak down tester for Jason(UK) and here are some photos that I received and wanted to share. Jason owns a Banshee motor with Athena 421cc cylinders and used to have constant seizures on LH cylinder and needed to verify that there is no air leakage on crankcases, oil seals etc. Hi Nick, You did me a special leak down tester for my 421cc Athena Banshee last October. Your kit fitted perfectly and I had zero leakage - actually gaining a bit of pressure after 7 minutes due to a little air bleeding back from the second cylinder through the labyrinth seal after I had taken the pressure a little over 5psi and then used the needle valve to set it to 5psi exactly. Thanks again - I am delighted. Jason      And here is Jason's bike. 

And here is the final part on using a wet clutch basket for a FCC dry clutch conversion. I installed the clutch basket on the lathe and just did a simple "boring" operation. The FCC basket had a clearance of about 0.5mm with the backplate, so this was not really a critical job and it was easy to aim for a tighter clearance as well.  And here is the result after the boring job... The backplate is now a nice and tight fit and everything looks good. I've also used the cushions from the WET clutch basket as they fit perfectly. I don't see why Honda may have used separate rubber cushions for a dry clutch. One thing to note though is that due to exposure to high heat and no lubrication, they become very stiff and fragile while the wet clutch cushions have normally a more prolonged life. I didn't bother with making or buying new rivets as well. I just used a tap to thread the existing holes. Just out of memory, I believe it was a M5 tap that I us...

I repaired a TZ250 YPVS controller today that belongs to Dale(UK). It's from a 1987 TZ250T model and I came across another one unknown YPVS setting that I'm sharing below. This setting doesn't seem to do a lot and it's more like an "on-off" switch for the exhaust valves, as it starts opening the valves at 7.500rpm and it completes movement at about 8.000rpm. And here are a few photos from Dale's bike. Cheers.

I repaired and modified a YPVS controller for Juraj(HR) the other day and found another one unknown YPVS curve that I'm sharing below.  Lovely bike by the way. I'm sure it can serve as a good commuter and for off road use as well.

The HRC piston bearings for the 14mm piston pins are long gone. There are a couple alternatives in the bearing market but they are very unreliable so you will have to reuse the ones you have or search for a NOS part.  There is one very good alternative though. It's the below Yamaha little end bearing that is originally oriented for smaller capacity two stroke bikes. I've used these bearings myself with no ill effects and I found them to be very reliable and can withstand high revs without problems at all. The part number is 93310-21403.  Cheers.

Another one rare PGM unit that needed repair and belongs to Deon(OZ). It is an SPL unit for Honda Rs250 NF5, most probably for the latest 1992 model. I'm not sure what SPL stands for but I've came across a few racing parts marked with these letters and all seemed to be NF5 or NF4 parts. They seem to be special parts, similar to KIT parts for later models.

Here are some photos while dismantling the wet clutch basket. The rivets were drilled as to remove the retainer plate. The rubber cushions seem to be in very good condition, they will become handy later... Here is the wet clutch basket after removing the cushions and the primary gear. Now back to the dry clutch basket. The retainer plate was removed and a real mess was revealed. The cushions were highly damaged and this must have helped for causing the cracks on the basket. Here you can better see one of the cranks on the basket. It goes deep and very close to the mounting points for the rubber cushions and the rivets. The two clutch baskets, side by side. The modification looks pretty straightforward and to use the wet basket on a dry clutch, only a simple lathe boring operation is needed. To be continued...

Just a photo of a very rare Mugen PGM unit that belongs to Richard(UK). It had some Rc Valve issues but it is now repaired and posted back.

Greetings to all. I haven't been blogging a lot lately due to a lot of work and loss of ideas... so, it's a nice opportunity to present some work from fellow Martin.  Martin is based in Devon, UK and I believe he is contributing and helping on 2T forums for more than a decade. I used to read all of his helpful info on tuning Tzr-Tdr250 bikes and I've learned a lot from him.  He is well known for his tuning work on many Yamaha bikes but I believe the most commendable point are his hydroformed ex pansion chambers for TZR and RD bikes ., You can find Martin at "mjseventyseven AT gmail.com" and of course via the tdr250 forum . Some of his work... Tdr250 Pipes   Tzr250 1KT - 2MA Pipes   RD350LC/YPVS pipes (available to give either 9500rpm or 10,200rpm peak power).