Long rod kits?

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11/16/2017 10:04 AM

We were drinking beers in the shop and started talk good old days and In the 90’s everyone long rodded 125’s. Is that still worth it or are 125’s good enough now a days?? My buddies tc125 seems like it has way more motor than my old 01cr 125. Just curious

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11/16/2017 11:30 AM

The thread title was my nickname in college

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2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600

11/16/2017 12:40 PM

Acidreamer wrote:

The thread title was my nickname in college

Hahaha! I knew someone was going there!

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11/17/2017 10:08 PM
Edited Date/Time: 11/17/2017 10:09 PM

im not an engine builder but i did hang out with some. the issue comes down to not very many people being able to build the crank. a long rod includes pulling it all apart and balancing it and sourcing parts from other bikes.

from what I have seen and been told is that a long rod is a very viable option for making power, in fact 144's used to be built this way for the old school boy classes, much like building a super mini. you had a 125 and then a hot rodded 125 bike. this build would allow for a more square bore instead of a huge piston.

but it would still be a killer engine. I remember seeing a mag test of Michael Byrnes 2003 cr125. It had a special spacer under the cylinder to accommodate the long rod and it had strong bottom power that the stocker lacked sorely

here is a picture of Prestons 2002 cr125 you can clearly see the plate

https://dirtbikemagazine.com/wp-content/uploads/2017/07/DSC_0132-copy.jpg

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"If you feel in control, you're not going fast enough" ~Mario Andretti

11/17/2017 10:12 PM

check this article of steve lamsons throwback 2007 cr125. it used a ryan mills 2004 motor which was a composite of engine pieces
http://www.motorcycle-usa.com/2007/05/article/behind-steve-lamsons-retro-cr125/

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"If you feel in control, you're not going fast enough" ~Mario Andretti

11/18/2017 8:31 AM

Idk about 125’s being done but the 93-95 YZ250’s is what comes to mind in regards to Long Rod kits. The question is are the amount of Shops familiar with these mods a dying breed? Lost art?
Maybe just natural progression towards new tech...

Ghost

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11/18/2017 12:21 PM
Edited Date/Time: 11/18/2017 12:31 PM

125SX and TC already have long rods. CR had 4mm shorter rod. 104mm vs 100mm if I remember right. Putting a longer rod to CR can cause serious vibration and short crank bearing life. As a riding buddy who made this mod noticed. Can of worms so to speak. Right crank balancing helps. And btw, long rod kit and long stroke kit are two different things.

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11/18/2017 1:15 PM

I mostly remember the Suzuki dudes doing them.

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11/18/2017 6:24 PM

mwssquad827 wrote:

I mostly remember the Suzuki dudes doing them.

ya suzuki was known for these. thats what they did in the 04 up bikes. i think they ran something like a 104 105? but to mod a short crank motor for it you cant just replace and run it. You need to have the crank torn down and balanced/rebuilt. Not many people do this or even have the tooling for it anymore.

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"If you feel in control, you're not going fast enough" ~Mario Andretti

11/18/2017 10:14 PM
Edited Date/Time: 11/18/2017 10:19 PM

VHM makes YZ long rod crank kit with 3mm longer rod. It comes with piston that has piston pin 3mm higher so no spacer plate needed. Who knows how many these kits kids have since it can't be spotted outside wink . www.vhm.nl www.vhm.nl/docs/upgradekits2017.pdf

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11/18/2017 10:20 PM

Phillip_Lamb wrote:

ya suzuki was known for these. thats what they did in the 04 up bikes. i think they ran something like a 104 105? but to mod a short crank motor for it you cant just replace and run it. You need to have the crank torn down and balanced/rebuilt. Not many people do this or even have the tooling for it anymore.

Is balancing a crank with a longer rod different than balancing a crank with an oem replacement rod?

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11/19/2017 6:03 AM

125mx.fi wrote:

125SX and TC already have long rods. CR had 4mm shorter rod. 104mm vs 100mm if I remember right. Putting a longer rod to CR can cause serious vibration and short crank bearing life. As a riding buddy who made this mod noticed. Can of worms so to speak. Right crank balancing helps. And btw, long rod kit and long stroke kit are two different things.

Yes, I think some have mixed up long rod and long stroke. A long rod by itself does not change the displacement, but it does change the angle that it pushes on the crank pin. It can also change the dwell it which it passes by the transfer ports which changes the time they are exposed.

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Take it to the limit, one more time!

11/21/2017 10:15 AM

mwssquad827 wrote:

We were drinking beers in the shop and started talk good old days and In the 90’s everyone long rodded 125’s. Is that still worth it or are 125’s good enough now a days?? My buddies tc125 seems like it has way more motor than my old 01cr 125. Just curious

The KTM and Husky 150s have a longer stroke. Pretty sure that's achieved with a longer rod. I've been reading quite a bit about a longer rod YZ125 and that combo works really well, by all reports.

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KTM250SX YZ125 YZ85 PW80 ZX6 FZX700

11/21/2017 10:56 AM

YZed250 wrote:

The KTM and Husky 150s have a longer stroke. Pretty sure that's achieved with a longer rod. I've been reading quite a bit about a longer rod YZ125 and that combo works really well, by all reports.

I don't think they have a longer stroke. At least not compared to the 125 counterparts. In fact, I'm pretty sure they both use the same rod.

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11/21/2017 11:53 AM
Edited Date/Time: 11/21/2017 11:53 AM

Both KTM 150 and 125 have a 54.5mm stroke. The 150s have a larger bore size.

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Take it to the limit, one more time!

11/21/2017 3:38 PM

mx317 wrote:

Both KTM 150 and 125 have a 54.5mm stroke. The 150s have a larger bore size.

I believe you are mostly correct. I see a 0.3 mm difference in stroke on the newer bikes, which might be due to pin placement in the crank or piston.
There was a 4mm difference in stroke on the pre-2016 125 and 150sx bikes.

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KTM250SX YZ125 YZ85 PW80 ZX6 FZX700

11/21/2017 7:03 PM

mwssquad827 wrote:

We were drinking beers in the shop and started talk good old days and In the 90’s everyone long rodded 125’s. Is that still worth it or are 125’s good enough now a days?? My buddies tc125 seems like it has way more motor than my old 01cr 125. Just curious

YZed250 wrote:

The KTM and Husky 150s have a longer stroke. Pretty sure that's achieved with a longer rod. I've been reading quite a bit about a longer rod YZ125 and that combo works really well, by all reports.

Some long stroke engines might have a longer rod, but that’s not what makes the longer stroke. A long rod doesn’t change stroke, because even though it goes higher at TDC, it also doesn’t go as far down at BDC. Net is the same stroke, but slightly longer dwell at TDC and BDC as well as a slightly straighter angle as it goes through the stroke. This also equates to less side load on the piston if memory serves.

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11/21/2017 9:57 PM

mwssquad827 wrote:

We were drinking beers in the shop and started talk good old days and In the 90’s everyone long rodded 125’s. Is that still worth it or are 125’s good enough now a days?? My buddies tc125 seems like it has way more motor than my old 01cr 125. Just curious

YZed250 wrote:

The KTM and Husky 150s have a longer stroke. Pretty sure that's achieved with a longer rod. I've been reading quite a bit about a longer rod YZ125 and that combo works really well, by all reports.

I think you need to do a bit more reading about long rod kits. A long rod does not change the stroke. The newest generation KTM 125 and 150 both have a 54.5mm stroke. Pin placement on the piston also has no effect on the stroke. The only way to change stroke is to change the position of the crank pin.

https://www.dirtrider.com/2018-ktm-125-sx

https://www.dirtrider.com/2018-ktm-150-sx

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Tomac and/or Anderson for 2020.....

5/29/2019 6:29 PM
Edited Date/Time: 5/29/2019 6:34 PM

125mx.fi wrote:

VHM makes YZ long rod crank kit with 3mm longer rod. It comes with piston that has piston pin 3mm higher so no spacer plate needed. Who knows how many these kits kids have since it can't be spotted outside wink . www.vhm.nl www.vhm.nl/docs/upgradekits2017.pdf

My 2016 YZ125 has the whole VHM kit, crank w/ long rod, the special billet piston and the VHM head (w/ mx insert). VHM sells the HGS pipes, but I use a factory fatty. I don't know how much diff the crank and rod make but the bike runs very strong. Oddly enough, I bought the bike from the 2nd owner, and he had no idea what was inside the motor...I didn't either until I opened it up. w00t

And yes, the length of the rod has no bearing on the length of the stroke. My bike is still 125cc and the stroke is still 54mm. the long rod is used to straighten angles only.

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