piston NX250 2

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doyar
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Registriert: Do Apr 02, 2020 11:13 pm

piston NX250

Beitrag von doyar »

Hello. I am new here, so please don't yell at me if I put this post in a wrong place. But my concern - connecting rod/ conrod - is quite near the piston, so I thaught: YOLO, lets's risk :roll: My point is: I am facing the need of replacing the following original parts in the "F" version MD25, 239 ccm: conrod + cylinder rings set. Cylinder itself is okay. The cylinder bolt is available. My big questions are: 1) is it possible at all to buy those parts to this particular smaller capacity engine, or should I put in on the museum shelf and start looking for the 'normal' MD21, 249 ccm one? 2) if any parts are available somewhere somehow - are they not Chinese? 3) if only the Chineese are available, are they worth considering, or is it typical self-cheating? Mind you, I earn for living in Polish zlotys, so 3 Euros buy me a 2 course lunch, so money is not that unimportant :lol:
Guys, I will appreciate any portion of your knowledge and wisedom, please.
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scrambler
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Registriert: Fr Sep 14, 2012 8:50 am

Re: China Kolben NX250

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Hi,
the 239ccm pistons are also sold out and used ones are hard to find. I have one in my barn but I have to check it first.
Concerning the Chinese pistons, they are all for the 249ccm version, so they won’t fit your 239cc cylinder. And I doubt that there is a Chinese piston which is identical to the original piston. Not to mention the (unkown) quality.
It all comes down to of how much you can do yourself (or some of your friends). I know that there are some very good motor repair shops in Poland – maybe you know someone who can bore and re-coat the cylinder. In that case you may consider a larger piston from a CBR900, for instance viewtopic.php?f=4&t=161&start=20.
sauve qui peut
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doyar
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Registriert: Do Apr 02, 2020 11:13 pm

Re: China Kolben NX250

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Thank you Scrambler. But with all the respect, I am not looking for the piston, but for the set of rings and for the conrod...
Maybe I should have placed my questions in the conrod focused thread. Cheers!
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scrambler
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Re: China Kolben NX250

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doyar hat geschrieben: So Apr 05, 2020 12:24 am Thank you Scrambler. But with all the respect, I am not looking for the piston, but for the set of rings
Ok, I got that wrong. The 239cc piston rings are also sold out and nowhere to find. How come that the rings are damaged and the piston is ok? Usually its the other way around.
Anyway – since new rings aren’t available maybe a VFR or CBR900 piston would be an option?
sauve qui peut
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doyar
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Registriert: Do Apr 02, 2020 11:13 pm

Re: China Kolben NX250

Beitrag von doyar »

If all the piston rings for both the versions are out of stock... Well, I will have to take a closer look at this whole VFR/ CBR thing. Are there the brave souls who already paved this way or rather volunteers are welcomed? :)
scrambler hat geschrieben: Mo Apr 06, 2020 8:57 am How come that the rings are damaged and the piston is ok? Usually its the other way around.
Thanks for that remark, I will take all the stuff to the Engine Magician to measure and tell. You know, I am an optimistic person, I just looked at the damn thing and judged from what I saw: piston okay, piston rings to be replaced.
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doyar
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Registriert: Do Apr 02, 2020 11:13 pm

piston NX250 2

Beitrag von doyar »


Thanks. But this engine costs more than I had spent byuing my bike. So "this option is currently unavailable", I have to deal with alternative methods.
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doyar
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Registriert: Do Apr 02, 2020 11:13 pm

Re: China Kolben NX250

Beitrag von doyar »

Alternative methods will not end 'cheaper'! Disassemble a new connecting rod including the crankshaft and replace the bearings, new gasket set - you are at the price the engine should cost!
it doesn't count like that... My engine had already been sandblasted and painted. It is now disassambled. I already have a brand new piston bolt (or pivot) and sealers.
IF repairing the conrod is possible by a bronze bushing and IF new piston rings set is possible to be replaced (I am chcecking possibilities, chances are for 80€ they can be reproduced) and IF the piston itself is OK, then I could end up much much lower total cost. Of course, there are plenty of IF-s and as for the main rule you are right: shortcut usually takes longer, but that is the fun in it! Cheers.
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doyar
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Registriert: Do Apr 02, 2020 11:13 pm

Re: China Kolben NX250

Beitrag von doyar »

Hello Friends,
it has been quite a while, but I am back with my report. So:
1) I had the conrod replaced by the specialist to the China-made one, as described here: viewtopic.php?f=4&t=294&p=16259#p16259
2) I had my piston rings replaced for the custom-made ones as described here: viewtopic.php?f=14&t=1806&p=16251#p16251; the engine refused to start :( so I made a complaint, they took it easy and free of charge and custom-made the rings again, this time with minimum clearance allowed, and...
2) I had my engine disassembled and assembled for the 2nd time, and this time it fired! Wow, what a feeling! The bloody thing works! Hallelujah!
3) I finished the bike, passed the technical inspection, registered and insured the bike and started to commute and try its offroad abilities (or mine rather),
4) I spotted some issues that would need some attention and regulation, but postponed it for the upcoming autumn-winter,
In this post: viewtopic.php?f=1&t=1775&p=18015#p18015 I put some pictures of my finished project and even some of my first painful experiences offroading ;)
Thanks for all the support and comments, also the critical ones :D
Cheers!
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scrambler
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Re: China Kolben NX250

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Thanks for the update - always nice to get a feedback of how things worked out ;) .

About the conrod mods - was that made by a metall shop who is doing that for a living? If so it would be nice to have his email/homepage - since the crankshaft is somewhat of a weak point it's alway good to have more than one option.
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doyar
Beiträge: 30
Registriert: Do Apr 02, 2020 11:13 pm

Re: China Kolben NX250

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Sure! The guy who had changed the conrod is one of the dying spicies of "Good 'Auld Boys" with his own workshop in the very center of my city of Lodz, Poland. The shop name is' Jarmot': http://www.jarmot.obraz.com.pl/
Anyone of this Forum who would like to have their engine repaired anyhow by the man - feel free to ask me for assistance, I would gladly help. I will look for the bill to tell you the costs I payed, but the price (compared to more western located EU countries) should be attractive, if only not killed by the shopping costs of a heavy stuff like an engine. Will get back with the number.
Cheers!
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