Long rod kits?

mwssquad827
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mwssquad827
Edited Date/Time 11/17/2017 10:08pm
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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Acidreamer
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Acidreamer 11/16/2017 11:30am
11/16/2017 11:30am
The thread title was my nickname in college
mwssquad827
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mwssquad827 11/16/2017 12:40pm
11/16/2017 12:40pm
Acidreamer wrote:
The thread title was my nickname in college
Hahaha! I knew someone was going there!
Phillip_Lamb
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Phillip_Lamb 11/17/2017 10:08pm
11/17/2017 10:08pm Edited Date/Time 11/17/2017 10:09pm
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.j…

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Ghostrider145 11/18/2017 8:31am
11/18/2017 8:31am
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
125mx.fi
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125mx.fi 11/18/2017 12:21pm
11/18/2017 12:21pm Edited Date/Time 11/18/2017 12:31pm
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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Phillip_Lamb 11/18/2017 6:24pm
11/18/2017 6:24pm
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.
125mx.fi
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125mx.fi 11/18/2017 10:14pm
11/18/2017 10:14pm Edited Date/Time 11/18/2017 10:19pm
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
Micahdogg
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Micahdogg 11/18/2017 10:20pm
11/18/2017 10:20pm
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...
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?
mx317
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mx317 11/19/2017 6:03am
11/19/2017 6:03am
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...
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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YZed250
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YZed250 11/21/2017 10:15am
11/21/2017 10:15am
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...
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.
Micahdogg
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Micahdogg 11/21/2017 10:56am
11/21/2017 10:56am
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...
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.
mx317
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mx317 11/21/2017 11:53am
11/21/2017 11:53am Edited Date/Time 11/21/2017 11:53am
Both KTM 150 and 125 have a 54.5mm stroke. The 150s have a larger bore size.
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YZed250 11/21/2017 3:38pm
11/21/2017 3:38pm
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.
omalley
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omalley 11/21/2017 7:03pm
11/21/2017 7:03pm
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...
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...
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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BobPA
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BobPA 11/21/2017 9:57pm
11/21/2017 9:57pm
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...
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...
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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ss-racing 5/29/2019 6:29pm
5/29/2019 6:29pm Edited Date/Time 5/29/2019 6:34pm
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...
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. Woohoo

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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