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Enduro Engine - 2 stroke Cylinder, Piston, Tranny, Bearings, Clutch, Pipes & Silencers, etc.

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Old 08-30-2019, 03:58 AM
sigurdr sigurdr is offline
Join Date: Oct 2018
Posts: 1
Question 09-15 EC 125 conrod replacement


My son has a '13 Fantic TZ125 which is powered by an EC 125 engine.

As a part of rebuilding the engine, I purchased a Prox conrod kit for the engine.
Handed the new conrod and crank to a specialist shop for replacement and balancing.

Got the crank back, pulled together the engine, fitted piston and cylinder and tried to turn the engine - without success. Turns out that the new conrod hits the crankcase on its way down on the exhaust side, due to a different/ fatter shape around the big end. See attached image.

The original Vesrah conrod has a slimmer shape and the crankcase has a grove on the exhaust side allowing the conrod to clear the crankcase.

After investigating a bit, I found out that I had received a Prox 03.6220 kit, that is listed by Prox as a kit for KTM SX/EXC 125 and Husqvarna TC 125.

Prox does not list any conrod kit for EC 125.

After contacting the store where I bought the conrod, I got the following explanation:
- GasGas has ended cooperation with Vesrah, and are now delivering the Prox 03.6220 kit as conrod kit for the EC 125
- The problem affects only some bikes due to differences in production of crankcases
- The solution is to trim the crankcase allowing the Prox conrod to pass

Has anyone else experienced this? Should I accept this as a solution?
Have tried to search the Internet for any info on this topic without success.

Sigurd Ringbakken
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File Type: jpg IMG_0881.jpg (114.4 KB, 20 views)

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Old 08-30-2019, 05:18 AM
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Gasser Nate Gasser Nate is online now
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Never heard of that before. Whilst not ideal gassy crankcases are extremely thick in most places. It would have been nice if they told you that before you had it assembled again. Are all the other dimensions correct?
Back on a gassy! 2018 EC300! 🤘
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Old 08-30-2019, 05:20 AM
fred99999au fred99999au is offline
Join Date: May 2018
Posts: 72

If it were me, it looks like there was plenty of meat in the case, I'd give it clearance and a fudge factor.
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Old 10-06-2019, 08:02 AM
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Zman Zman is offline
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Originally Posted by fred99999au View Post
If it were me, it looks like there was plenty of meat in the case, I'd give it clearance and a fudge factor.
I agree you should clearance the cases. The best was it is to split the cases apart again, unless you can come up with some way to keep the grinding debris out of the crank and conrod bearings.

Thank you for the heads up. I need to do the bottom end on a GG125 soon so this info is very good to know going into the project.
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