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KTM 50SX - Martin & Slater ??

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Hello

Its time for new piston for the KTM50SX-PRO-SR. First, is it common to use a oversize piston in those engines or do most run the standard size piston?

Next, anyone tried Martin & Slater pistons or any other brand?

Another thing to those of you that have experience with this bike - can you name few of the most critical preventive maintenance actions to keep the KTM healthy.

Once again - BIG THANKS to all of ya in this community for your inputs and help. :thumbsup:

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Avoid anything Martin and Slater. The quality is lower. If you know that going in and decide to still buy it, then that is fine also. As for pistons, the OE is a Vertex and they have a select fit system. You will need to remove the cylinder to determine what "letter" piston you have now. It will be at the base of the liner, on the carb side. Also marked on top of the piston, but carbon makes it hard to see. Also, measure the base gasket thickness, but "that exact size and one larger and smaller. The piston can vary in heigth, even by a smidge and you need to set the "X" dimesnion, this is done with base gaskets.

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Thanks toyota_mdt_tech

I take your word on it - and stay away from M&S. I was hoping I could find out what piston size to order in advance so when I have time from work and start to prep that little KTM I could have the parts ready. The outside of the cylinder says "353H" but maybe that not what we are looking for??

Another thing I see people discuss is the Spark plug resister cap. Mine says NGK Lbo5emh. Is that the proper one or is there one better for the 2005 KTM50SX Pro Senior?

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Thanks toyota_mdt_tech

I take your word on it - and stay away from M&S. I was hoping I could find out what piston size to order in advance so when I have time from work and start to prep that little KTM I could have the parts ready. The outside of the cylinder says "353H" but maybe that not what we are looking for??

No, its not going to be that easy. :thumbsup: :thumbsup: That is just cast. The letter will be "stamped" on the cylinder base, not the gasket surface, but the bottom of the sleeve itself. I suppose you could take the head off and see if you can find the letter on top, but I have never had good luck with that. Usually, the carbon conceals it and by the time you get it all cleared away, you cant make out what it was.
Another thing I see people discuss is the Spark plug resister cap. Mine says NGK Lbo5emh. Is that the proper one or is there one better for the 2005 KTM50SX Pro Senior?
Get the NGK TB05EMA. The number you have will work fine (the 05 is correct) but the TB05EMA is the best one. Here is a link to the caps via the TT store :thumbsup: The OE KTM one is made by NGK and is troublesome not to mention, way over prices ie $20+ :thumbsup: Is you kid racing this bike? Are you familar with the clutch service that is required. I mean, heavy clutch servicing. Setting up the cupped washers and the different variations depending on your kids riding skills. You can really tune these auto clutches. I went through 3 years on the KTM SX50 PS LC and we ran 2 bikes, one just for backup! They are a lot of work, but lot of fun too! PM me if you want my "secret clutch stack combo". You can get literally every part you need for these little bikes from http://www.k2parts.com when it comes to the clutch service, even that plug cap. Great source. If you buy the OE clutch washers, it will break you!

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I think I just have to remove the head/cylinder and get the right number myself asap. I just got a little confused about what piston to use because I wanted to buy one on Ebay since it said "This kit is a STD BORE( 39.50MM ). WILL Fit years KTM 50SX , years 01-06." According to this it should be a no-brainer buying a piston - but I decided to check here anyway. So when in doubt, lets double check.... Still thanks for your input.

I wont label myself as a master mechanic, I mostly have worked on the lawnmover but Im trying to do my best (and become better) at supporting my kid riding. He does occational race too. Yes Im beginning to see that these bikes require super strict maintenance schedule, mostly the clutch. I always feel the bike is gona explode and cant wait for him to grow into a proper 65cc motorcycle.

What I´ve learned so far from maintaining the little KTM is that I should never remarry a younger wife. Much like the KTM the feeling of having a young trophy wife must be anxiety, too much work, too much maintenance. So in a way Im thankful for the strange lessons the KTM has taught me.

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The KTM is fun, but yes, like a trophy wife, consumes time and money. I used to have 2 clutches on hand, one freshly overhauled and a freshly overhauled one on the bike. So if I had an issue, I could swap it out in minutes. In addition to a spare bike!!! :thumbsup:

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Strangely enough, here you can buy a piston for the KTM that seems to be universal for many models :thumbsup:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=35618&viewitem=&item=150272491816&_trksid=p3907.m29

Aftermarket pistons are usually made loose enough to work in all engines of the same model. But KTM uses a "select fit" system, which menas varting sizes barely. The idea is you can keep clearances more precise. Think of it as fine tuning. Vertex pistons are the best and also OE for KTM. Many have used Wiseco with no trouble, others havent had that good of luck.

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Funnily Enough if you have a look under a "factory" KTM piston it has VERTEX stamped/Cast into it....... all we have ever done is purchase VERTEX pistons from EBAY for a fraction of the cost of OEM KTM50

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