Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: burn1986 on July 26, 2010, 02:37:07 PM
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If you modify a 125, I have heard that just boring the cylinder, replating, and getting a larger piston is not enough since the bigger piston will create more work on the engine. Does having a stroker crank/ motor take care of this? Is this the reason the Athena YZ144 is not as fast as the KTM 150? What about the pipe? Should you get different pipe since the original is made for the 125?
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Eric Gorr has some good info on his site. Even if you go with someone else you can read and learn more about it.
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The KTM is entirely set up to be a 144-not just a bore/stroke job on a 125.That's the difference.
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When I built my RM144. I kept the stock crank. I did machine the cases so I was certain there was enough skirt clearance (A must on CR 144 builds)
I also filled cases for volume and ported cylinder. I did NOT mill the head or clyinder due to clearance. Instead, I went back to my old school days and played different thickness's of base gaskets. I ran a fairly thin one. Once the motor was where I was I wanted it, I clayed the piston and measure the clearance. If I raced up north or cooler weather, I would switch to a thicker base gasket. Just remember that if you run a thin base gasket you may run into detonation issues on pump gas. I always ran 50% C12 and 50% 93 pump gas.
I did require top end jobs on a regular basis. I also went through clutches like crazy. However, I rode a lot of tracks with deep loam so it was hard on all the 2 strokes.
I can honestly say, I LOVED that way the RM ran when it was all done. It was a 250F killer. HAHA ;D
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yeah the ktm is built to be a 144. the pipe is the same as a 125 though. the ktm has some excellent engineering. the air tract from the filter to the carb is built straighter for better / greater flow. more air equals more power....
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If you modify a 125, I have heard that just boring the cylinder, replating, and getting a larger piston is not enough since the bigger piston will create more work on the engine. Does having a stroker crank/ motor take care of this? Is this the reason the Athena YZ144 is not as fast as the KTM 150? What about the pipe? Should you get different pipe since the original is made for the 125?
My 04 cr125 is 2mm overborred,with 2mm longer crank, 1mm taken out of the head, so it,s 1mm up and 1mm down if that makes any sense. HGS makes 144 pipes for YZ,KX maybe more makes, I havn,t been on there website for along time. I custom fit a HGS BUD racing pipe for a 03 KX125 onto my 04 cr125. There,s nothing cut out for the crank, on my cases. There,s engine builders that off center overbore, a stroker crank puts more pressure on the exhaust port bridge, not a good thing for a honda. I have to drill 3 lube holes on the piston,lined up with the exhaust bridge, I didn,t want it overborred. I would rather have a ported cylinder and run a stock size 54mm SRS piston, with the stroker crank.
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If you modify a 125, I have heard that just boring the cylinder, replating, and getting a larger piston is not enough since the bigger piston will create more work on the engine. Does having a stroker crank/ motor take care of this? Is this the reason the Athena YZ144 is not as fast as the KTM 150? What about the pipe? Should you get different pipe since the original is made for the 125?
My 04 cr125 is 2mm overborred,with 2mm longer crank, 1mm taken out of the head, so it,s 1mm up and 1mm down if that makes any sense. HGS makes 144 pipes for YZ,KX maybe more makes, I havn,t been on there website for along time. I custom fit a HGS BUD racing pipe for a 03 KX125 onto my 04 cr125. There,s nothing cut out for the crank, on my cases. There,s engine builders that off center overbore, a stroker crank puts more pressure on the exhaust port bridge, not a good thing for a honda. I have to drill 3 lube holes on the piston,lined up with the exhaust bridge, I didn,t want it overborred. I would rather have a ported cylinder and run a stock size 54mm SRS piston, with the stroker crank.
The reason you your cases are not "cut" or machined out for clearance is because your bike a 134 @ +2mm. It is required to machine the cases to build a 144 out of a CR. If you dont, the skirt will hit and well, the rest is history.
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Yeah I know about that Redrider611, hell I didn,t even want the overborre, just the stoker crank and some more porting. The shop has your creditcard # and they go to town. The shop called me when I was in Cali. trucking 80 days straight, when I found out they ran the bill up and overborred it. It,s bad enough that I,m in and out of Cali. for weeks, and now I have a 1,700 dollar bill for work that I don,t even need. A stoker crank carries the power further, just overborring the motors are flat on top, short shift motor.
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That's illegal, a shop cannot do work without your approval. You could have disputed that. If all you wanted was the crank and porting, that's all you should have paid for. I used to be a motorcycle mechanic, heck if we couldn't produce the old parts, the customer didn't have to pay even.
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Yeah COOP I told him that, and I told him that I every incoming call when I,m in the truck is recorded, because of the corruption in the trucking industy. He blamed the plater for the 1st exhaust port bridge break, he said the chamfering was done wrong, he,s the engine builder and can,t tell it,s done wrong. The plater did a crap job, welding and plating, it broke the bridge again. So last year was 3 months of bs, heat cycles and 2 minutes of riding by my storage,I never made it to a track, and more than 10 k in dedt. After that I never wanted to see a bike again, to top it off there wasn,t nothing for a driver job. I had to get on with a mega co., and run the railyards of Chicago, 6 driving test, 2 drug test,1 is where they cut hair from 5 parts of your head, 6 day orientation, 2 days of rail yard training,supposed to be 4 or 5 days. I had 19 break downs in the 1st 60 days, I stop counting after that, after 8 months I drove 9 different trucks,freightliner junk,broke down all the time. I knew the country was doing bad, in orientation there,s owner operators with 6 trucks, he laid the drivers off and parked the trucks,alot of 25 yr. exp. teamsters, now working for peanuts.
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Sorry about the last post. I sent the cylinder to Millenium Technologies in Plymouth Wi., I heard they do great work, and it,s true. They built the bridge up-thicker,chamfered all the ports,resessed the bridge, it should be bullet proof. If anyones having plating problems,check them out, they do work for team Suzuki, and 2-st. roadracers, so I,ll have to ride it and see.
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Wow, that's a lot of stuff into a 125/ 144. Would a Stroked 125 with a port job run like a 144? Would it run better than a 144?
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Wow, that's a lot of stuff into a 125/ 144. Would a Stroked 125 with a port job run like a 144? Would it run better than a 144?
Yes.
From my understanding the KTM 150 (144) is just a stroked and bored 125... Cases and everything else are off a 125 (same with the pipe, CDI, etc...). So honestly, people saying it is a purpose built 144 isn't too correct.
Big bores give you the low end power but don't rev like the stock 125, stroked 125s give you the revs at the sake of low end a big bore only gives you, bored and stroked give you the best of both worlds (this is true in 2 strokes as it is in 4 strokes).
A stroked 144 with porting would be just like the KTM, which is already a Mid - Top bike (it has more low end than the 125 it replaced but not much more). This is why the GYTR and Athena kits and some other 144 kits for the Yamaha/CRs/KXs/RMs don't have similar power outputs the KTM has (big bore only kits).
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Wow, that's a lot of stuff into a 125/ 144. Would a Stroked 125 with a port job run like a 144? Would it run better than a 144?
On a ported motor with a stoker crank,the powerband would carry further, more mid also,that,s what my engine guy told me.
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The ktm 150 IS purpose built, and yes its pipe is different.
The athena 144 kit is horrible as delivered. It's merely their 125 offering bored out.
A quick glance reveals that the ports are untouched after boring, the boost port is very easy to spot this even if you dont know much about porting.
There is a lot that goes into what stroke should be run...etc. But at the end of the day, a well built purely bored 144 can run awesome.
The athena kit, modified, can eclipse the 40hp mark fairly easily.