KTM 2-Stroke Piston Rings

This video shows where the piston ring gaps are located in a 2-stroke KTM 250EXC. Due to pins in the ring grooves of the piston the ring gaps can only be installed in one position.

[@CADProjects1]

Thank you Tokyo Offroad, you make maintenance on a dirtbike easy.

[@jarimo97]

It’s so easy to notice that there’s an engineering background in your explanations. This is one of the most enjoyable channels for me!

[@mixalis6168]

Same here, very, very good channel..

[@maverick2242]

Quality instructional video mate, you should def do more, few can match your clear and well explained tutorial 🤙

[@TokyoOffroad]

Thanks for the positive feedback. Yes, I aim to make more instructional videos and have an ever growing list of ideas. But feel free to suggest what you'd like to see...

[@jraymondh6985]

I’ve heard that “180 degree” a number of times and thought “huh??? .... Why???”. Thank you for proving that wrong.

[@jackmilan74]

I love watching your videos, they help me a lot to get closer to my bike and use my head and hands to improve it! Keep feeding us with your talent

[@tonyrichengod9280]

Thank you sir! These videos are very helpful!

[@Alaayedi]

Great video

[@matp1102]

the whole 180 degree thing is far more important in a diesel engine... a lot more compression going on and generally a lot more blowby, so the 180 degree rings help to slow down the blowby... still doesn't stop a heap of oil reaching the intercooler lines in my car though, lol. Always informative, no nonsense video... love your work!!

[@Scottstunts]

Thank you for sharing your wealth of information.

[@0cernnunos0]

Very informative and thank you for taking the time for making these videos.

[@sptnk87]

Awesome video as always, keep em coming sir.

[@richpickard1680]

Another great video.thanks!

[@xhulkdieselx]

Who ever said the end gaps should be 180 apart hasn’t rebuilt one of these motors and should probably just pipe down

[@desmonchild]

What he said

[@michail1963]

180 apart is very courageous move indeed

[@mixalis6168]

Probably the same person who disliked this vid !!

[@prawny12009]

Usually you will stagger piston gaps on a four stroke piston to help reduce oil consumption and ring blow by. On a two stroke the ring gaps will be fixed in position by pegs to prevent the ring end catching in the ports. Whoever said 180 apart is talking rubbish, the only way you could do that is if the ring lands are designed to miss all ports at 180 apart but I've never seen a two stroke designed that way.

[@milosbgd]

Very nice described, thanks!

[@endurobk7156]

Is it normal that I have one piston ring with a N and the second one doeasnt has any markings on it? I have done a top end rebuild and I'm not sure if there was a N on the upper piston ring.

[@louisstagg8847]

One of my rings says 1t and the other says 2t which groove does what ring go in

[@endurotrash4549]

Very cool

[@jeffreysisti6653]

My 2018 ktm 250 xc-w rings did not have a mark showing what side is up or down. It's a Wiseco piston kit. Any idea why?

[@TokyoOffroad]

jeffrey sisti - I just checked the Wiseco website FAQ and found this: My new Wiseco piston kit has flat rings, how do I know which direction the rings are installed? A. Look closely at the ring near the ring end gap, and you will see a mark on the ring. This mark indicates the top side of the ring, so make sure that the ring is installed with this mark facing up. As a rule, if there is no marking, then the ring can be installed with any side facing up.

[@jeffreysisti6653]

@@TokyoOffroad thank you for your quick response. I checked yet again and I'm sure there was no markings. Thanks for your help, love your videos!

[@reidvarland5958]

so helpful!

[@alxmole2004]

I have a 2015 ktm 250exc and I was wondering, do you need to adjust the ring gap that comes with an aftermarket piston kit?

[@TokyoOffroad]

For an OEM kit you shouldn't need to adjust the ring gap. For an aftermarket the instructions should include a min/max ring gap spec and you must ensure the ring gap is greater than, or equal to the minimum gap spec.

[@MrTuckerbox]

Hey Mark great video as always! My ring end gap on an 17 250sx 80hr piston (still looks good) is .7mm. Oem rings are super expensive. Am I best just to order the top end kit or get aftermarket rings (if they fit). Any help appreciated.

[@TokyoOffroad]

My recommendation is to use an OEM kit.

[@EddiNice]

Great video. I need you help, I am rebuilding a 125 and it is a project bike. The piston is used but it looks clean and I want you opinion whether it is really clean and it will last or I will need to replace it. I can send you some pictures, thank you.

[@TokyoOffroad]

Eddi Nice - My advice is to first visually inspect the cylinder for scratches and wear marks, then measure the cylinder using a bore gauge and confirm whether it’s within spec. KTM service manuals detail what measurements to take and the limits. If it’s out of spec and worn too much it would be best to get it replated

[@francoisros]

Thanks for the informative video. I am wondering what would happen if the ring was installed upside down. In other words if the mark faced downwards?

[@TokyoOffroad]

Typically rings which are marked are tapered (or shaped in some way) to ensure a good ring bore seal when installed in the correct orientation. However, some rings have no marking (square cross section) and can be installed either way up. Just be careful to check the rings for markings when installing and always put the markings up.

[@quikcolin]

Hey Mark, I recently replaced my OEM head on my 17' 250 XC-W (20 hours on the bike) with an RK Tek head. Something I noticed is that I had some "up and down" markings on my cylinder walls. Similar to what you can see in the cylinder in this video. Almost identical (beautiful cross hatching, but some vertical up and down). My cylinder walls are silky smooth - you can't feel anything with your finger nail. Just curious if you had any insight on why that is? Is it normal on a 2 stroke? What's the reasoning for it? The guys at KTMtalk said not to worry about it. I must admit, the thought of it has been stuck in the back of my mind.

[@TokyoOffroad]

Light up down marks in the cylinder seem to be normal. The cylinder in this video (only 5H) has them too. If you can’t feel them I wouldn’t worry about it.

[@quikcolin]

Tokyo Offroad good to know! Thanks so much :)

[@cityofplant]

I have a 2014 150sx how often should i replace the piston and piston rings? I only do track 2-3 times a week. Thanks

[@TheHuckHD]

Jimbo there’s a Manuel for a reason.....

[@TokyoOffroad]

I'd recommend starting with the service intervals listed in your manual and derate those based on the riding you do. For the 2014 150SX the manual specifies that the piston should be changed every 20H. If you're keeping the bike pinned wide open for extended periods of time then you'll want to follow what the manual says. If however your riding is more trail riding, with only brief wide open bursts, then you can derate the intervals specified in the manual (40H, or possibly longer). I personally don't have experience with the 150, so I'd recommend asking other 150 owners for advice if you're seeking to stretch out the service intervals further. A good way to monitor ring wear without tearing down the engine is to perform regular compression testing. It only takes a few minutes to do a compression test, so you could do it every oil change, or every other oil change. Keep a log of the results and this can be a useful guide to help you decide when to do an overhaul. The good news is that a 2-stroke piston kit is relatively cheap.

[@sethjeffreys3055]

Wish you guys would have a section on the 2017 aer 48 and the updates ktm did in 2018 on the aer 48 thanks love you guys besafe

[@TokyoOffroad]

The XC model isn't sold in Japan so I don't have any experience with the AER fork.

[@lucastaylor5575]

Found a mass on dank gherkin stuck in my piston ring help what do I do

[@TokyoOffroad]

My recommendation is to not eat hamburgers while working on your top end...

[@lucastaylor5575]

Tokyo Offroad to late mate

[@desmonchild]

what oil do you use?

[@TokyoOffroad]

For 2-stroke premix oil I use Motorex Cross Power 2T mixed at 60:1 as recommended in the KTM operator's manual. It's readily available in Japan, seems to provide a good level of lubrication based on my last top end overhaul, burns cleanly and mixes easily with gasoline even in cold weather.