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Unread 09-04-2012, 05:04 PM
FriscoMotorWerks's Avatar
FriscoMotorWerks FriscoMotorWerks is offline
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Bat 2 MJ-Works 250RR Racer

Marrten Janssens' 250 racer as seen on The Kneeslider

Originally Posted by THE KNEESLIDER
Maarten Janssens, a 20 year old industrial engineering student from Belgium, got the motorcycle bug very early, courtesy of his enthusiast dad, who had Maarten riding a little scooter at the tender age of 4. By the time he was 18 he was riding in the Belgian national enduro championship and he got the idea he might like to build a racer from his KTM 250cc 2 stroke enduro bike. Of course, thinking and doing are two different things, but Maarten is a doer so, over the Christmas holiday in 2009, he began drawing his plans, by Easter break 2010, he started building, just finishing in March of this year.

He has the advantage of having a pretty well equipped shop at home, lathe, milling machine and several welding posts, but tools dont build on their own, someone has to learn how to use them and then put in the time. It looks like these were well used.

Beginning by creating his design on the computer, he TIG welded the entire frame and swingarm from steel. The gas tank plus front and rear subframes are aluminum. The front subframe holds the radiators and battery. Front forks and caliper are Suzuki 750 SRAD, seat comes from a Honda RSW 125 and the fairing is modified Aprilia RS125. Rear shock is Yamaha R1, wheels are Aprilia on both ends.

The KTM 250cc engine work began by lightening the flywheel by 540 grams and removing 300 grams from the outer clutch hub. He polished the exhaust ports and custom made the exhaust. Maarten says the power kicks in at 9000rpm and runs to about 12500, hes getting about 70 hp at the crank.

Wheelbase is 53.5 inches, fuel capacity is 4.2 gallons and dry weight is a mere 209 pounds!

He still has a little engine sorting to do but the build looks great. Not bad for a 20 year old student, in fact, its not bad for anyone, period. Going from idea to racer, from computer design to finished bike, its a big leap from the idea (the easy part) and the person who gets to work, gets his hands dirty and makes it happen (the hard part). Id be willing to bet Maarten has a great future ahead. Nice work!
Attached Images
File Type: jpg mjworks-250rr.jpg (66.3 KB, 22 views)
File Type: jpg mjworks-250rr-design.jpg (38.8 KB, 22 views)
File Type: jpg mjworks-250rr-2.jpg (47.5 KB, 21 views)
File Type: jpg mjworks-250rr-front-subframe.jpg (49.7 KB, 22 views)
File Type: jpg mjworks-250rr-4.jpg (64.5 KB, 22 views)
File Type: jpg mjworks-250rr-maarten.jpg (66.6 KB, 22 views)

Last edited by ToraTora : 09-05-2012 at 10:31 PM.
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Unread 09-05-2012, 09:17 AM
Four_Ari's Avatar
Four_Ari Four_Ari is offline
Join Date: Oct 2005
Posts: 1,140

Do you think that frame can hold the amount of stress and torque that the engine is putting out? I know that the Ricky Corey put a 250 in an RS50 frame with some support and I believe that it just couldn't hold it. there is a thread about it on the bats i'm to lazy to find it. It was called the Monster

The bike looks sweet and which i had the skills to make something like that.

Welcome to the BATS Forum!
2002 Aprilia RS 50 (Black and Gray)
2003 Derbi Super CR85
2009 Aprilia SR 50
2002 Aprilia RS 50 (Black and Red)

2003 Derbi SM
2009 Yamaha WR250x
2010 GY6 150 CC Honda Ruckus
2010 Honda Ruckus
2006 Aprilia RS 125 Still in the BATS family

Two strokes are The Devil. They will kill you in a second. Even a 125 two stroke is An Evil Beast. Save yourselves, Run!!! Deny the Two Stoke Demon!!!
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Unread 09-05-2012, 09:51 AM
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FriscoMotorWerks FriscoMotorWerks is offline
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The frames rigidness is questionable. I dislike the main top tube, it's goofy looking and just looks unsafe. I prefer a twin spar design. Cool concept none the less.

I couldn't find that RS you were talking about.. Definitely interested in viewing that thread.

Last edited by FriscoMotorWerks : 09-05-2012 at 09:52 AM. Reason: grammer
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Unread 09-05-2012, 10:31 PM
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ToraTora ToraTora is offline
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Join Date: Nov 2006
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I read about this some time ago, and yes the frame can take the stress. The question is will it have detrimental flexing coming out of corners where a bike gets multiple force vectors, it from what I've read it does so quite admirably.
Now: '00 Derbi GPR 75, '87 Puch Monza Barcelona, '05 Wicked GPR, '95 Pika Mito, '07 Bol d'Or
Then: 1974 XR-75, DS-100, IT-175, MB-5(x2), CB400, CB750F, 750 Paso
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