Hi everyone,
I have found myself in a bit of a predicament over the replacement of my gas gas ec 125 my 2002 cylinder, I will show the various issues as well as i can, it's probably going to be a long post and I hope my english will be sufficiently understandable, excuse me if not, it isn't my first language.
Recently I wanted to change the piston on my bike in anticipation of the summer, I had stacked up around 100 hours between my riding and what the previous owner told me he had done, might be a bit more as i am quite uncertain of his word at this point, looking back it would have been wiser to change it immediately after buying.
Immediately prior to taking it apart the bike didn't present any issue and ran alright, although as soon as i looked at the cylinder I could tell it wasn't salvageable. There's a small detachment of the chromium plating on the exhaust bridge ("traversino di scarico") which would be repairable, the main issue is the actual bridge being completely broken in half. (not sure if that's it's proper name but here's the picture).
Also the piston has some light scoring probably due to metal chips from it.
I attached the youtube link as it isn't clearly visible with pictures, the top part of the bridge between the valves is basically dangling around, kept in place just by the valves.
I showed the cylinder to a couple mechanics and called the ex gasgas (now rieju) dealer, whom had different takes on it.
The first mechanic said the valves probably wore down, and reducing their size they started vibrating in their seats ultimately breaking off the exhaust bridge, he recommended a new cylinder and valves. He also said to buy an original cylinder because he thinks athena (which makes a 125 cylinder-piston-valves-head kit) isn't a great project overall, he knew someone who worked there, how they operated and he couldn't recommend it.
I then called the dealer, which said that the valves, being steel, were unlikely to be the issue and wear down to that point, he also said that on this particular bike which he personally owned 2 of, and worked on many others, the cylinder design isn't so reliable when not changing the piston for so many hours. He said that the exhaust bridge is cast too thin: when the piston wears down and starts rocking in the bore, the mechanical stress causes the exhaust bridge to break and later seize and lock up. It would seem that i caught it before it locking up and destroying my rod. He also said that an original cylinder would still be the better choice (if I change the piston before the 60/70 hour mark) because the athena makes less power and has a tendency to break the valves.
With this information i proceeded to order a new cylinder-piston-gaskets original kit from said dealer (which is also the main reseller of anything gas gas in my area, never had any issues with him, I can trust him), unfortunately the cylinder kit is for 01-11 models so the piston has a flat top, which means I had to buy a flat top head, since my 2002 domed head obviously couldn't work.
Today my new cylinder arrived, it is advertised as original part and on the box it has S3 written, so I guess they are the ones who supply original parts and took over production since ktm bought gasgas, but I don't know much about it, maybe some of you can enlighten me.
My idea was to take the original broken cylinder and the new one to the mechanic and have him clean out the valve mechanism, put them in the new one and check the tolerances, to understand if I need to buy new valves or not.
The issue is that this new cylinder has a some porosity on the plating (picture below) which really worries me, my uneducated guess (I took a reduced version of "Manufacturing technologies and machines" at uni, where I studied casting processes) is that those holes shouldn't be there; but maybe I'm being a bit over dramatic.
In addition to those porosity holes poking through the plating (which to me mean a lack of quality control on S3's part) the thin bridge, poor casting quality and weak design of the exhaust bridge are evident.
Today I'm going to the mechanic to ask what he thinks about it and what I should do, if you and he tell me that I'm being overly cautious and I can run it with no issues then I will, the holes seems to be at the end of the rings travel, maybe even over.
Otherwise if using this cylinder isn't recommended I'm going to have to send it to get refunded or changed for another one.
The whole point of this thread is: given the lack of quality of the original design, of the S3 casting (allegedly), of the athena kits (allegedly), would I be better off fitting a yz 125 cylinder (not sure what year) instead?
I asked about yzs specifically because I saw threads of other CCs and model years about it, the design look similar, maybe even another brand or a tm (I know gasgas used tm engines until 96 or something like that).
In my head a yz cylinder would be more reliable and have a better engineering behind it, the main issues are probably going to be crankcase fitting, gaskets and water passages, valve linkage, exhaust header size, gasgas exhaust geometry, squish and piston travel.
I'd rather not have to split the cases and change the rod, certainly I'd need to buy a whole valve assembly and head, probably some porting needs to be done on the cases.
A broken cylinder to test all these things would probably be my first step.
Does anyone have any experience doing something similar or any information that could help my case?
Thank you in advance to anyone willing to read all of this and kindly giving his perspective.
I have found myself in a bit of a predicament over the replacement of my gas gas ec 125 my 2002 cylinder, I will show the various issues as well as i can, it's probably going to be a long post and I hope my english will be sufficiently understandable, excuse me if not, it isn't my first language.
Recently I wanted to change the piston on my bike in anticipation of the summer, I had stacked up around 100 hours between my riding and what the previous owner told me he had done, might be a bit more as i am quite uncertain of his word at this point, looking back it would have been wiser to change it immediately after buying.
Immediately prior to taking it apart the bike didn't present any issue and ran alright, although as soon as i looked at the cylinder I could tell it wasn't salvageable. There's a small detachment of the chromium plating on the exhaust bridge ("traversino di scarico") which would be repairable, the main issue is the actual bridge being completely broken in half. (not sure if that's it's proper name but here's the picture).
Also the piston has some light scoring probably due to metal chips from it.
I attached the youtube link as it isn't clearly visible with pictures, the top part of the bridge between the valves is basically dangling around, kept in place just by the valves.
I showed the cylinder to a couple mechanics and called the ex gasgas (now rieju) dealer, whom had different takes on it.
The first mechanic said the valves probably wore down, and reducing their size they started vibrating in their seats ultimately breaking off the exhaust bridge, he recommended a new cylinder and valves. He also said to buy an original cylinder because he thinks athena (which makes a 125 cylinder-piston-valves-head kit) isn't a great project overall, he knew someone who worked there, how they operated and he couldn't recommend it.
I then called the dealer, which said that the valves, being steel, were unlikely to be the issue and wear down to that point, he also said that on this particular bike which he personally owned 2 of, and worked on many others, the cylinder design isn't so reliable when not changing the piston for so many hours. He said that the exhaust bridge is cast too thin: when the piston wears down and starts rocking in the bore, the mechanical stress causes the exhaust bridge to break and later seize and lock up. It would seem that i caught it before it locking up and destroying my rod. He also said that an original cylinder would still be the better choice (if I change the piston before the 60/70 hour mark) because the athena makes less power and has a tendency to break the valves.
With this information i proceeded to order a new cylinder-piston-gaskets original kit from said dealer (which is also the main reseller of anything gas gas in my area, never had any issues with him, I can trust him), unfortunately the cylinder kit is for 01-11 models so the piston has a flat top, which means I had to buy a flat top head, since my 2002 domed head obviously couldn't work.
Today my new cylinder arrived, it is advertised as original part and on the box it has S3 written, so I guess they are the ones who supply original parts and took over production since ktm bought gasgas, but I don't know much about it, maybe some of you can enlighten me.
My idea was to take the original broken cylinder and the new one to the mechanic and have him clean out the valve mechanism, put them in the new one and check the tolerances, to understand if I need to buy new valves or not.
The issue is that this new cylinder has a some porosity on the plating (picture below) which really worries me, my uneducated guess (I took a reduced version of "Manufacturing technologies and machines" at uni, where I studied casting processes) is that those holes shouldn't be there; but maybe I'm being a bit over dramatic.
In addition to those porosity holes poking through the plating (which to me mean a lack of quality control on S3's part) the thin bridge, poor casting quality and weak design of the exhaust bridge are evident.
Today I'm going to the mechanic to ask what he thinks about it and what I should do, if you and he tell me that I'm being overly cautious and I can run it with no issues then I will, the holes seems to be at the end of the rings travel, maybe even over.
Otherwise if using this cylinder isn't recommended I'm going to have to send it to get refunded or changed for another one.
The whole point of this thread is: given the lack of quality of the original design, of the S3 casting (allegedly), of the athena kits (allegedly), would I be better off fitting a yz 125 cylinder (not sure what year) instead?
I asked about yzs specifically because I saw threads of other CCs and model years about it, the design look similar, maybe even another brand or a tm (I know gasgas used tm engines until 96 or something like that).
In my head a yz cylinder would be more reliable and have a better engineering behind it, the main issues are probably going to be crankcase fitting, gaskets and water passages, valve linkage, exhaust header size, gasgas exhaust geometry, squish and piston travel.
I'd rather not have to split the cases and change the rod, certainly I'd need to buy a whole valve assembly and head, probably some porting needs to be done on the cases.
A broken cylinder to test all these things would probably be my first step.
Does anyone have any experience doing something similar or any information that could help my case?
Thank you in advance to anyone willing to read all of this and kindly giving his perspective.
