KTM 2-Stroke Top End Inspection after 150H/295H 

I use Motorex Crosspower 2T mixed at 60:1

@@TokyoOffroad 60:1.. nice

@@TokyoOffroad 60:1 for all conditions?

@@NirHason Yes, 60:1 is all I've ever used in this bike and is the mixture recommended by KTM in the manual.

If you use the Maxim Castor 927 Say 36/1 to 40/1 You will not have the black carbon on your pistion at all. Go video I like.

Measuring the compression is a good way to monitor ring wear. But unfortunately doesn't tell you what piston wear is occurring. The majority of piston wear will normally happen on the exhaust and inlet skirts. As piston skirt wear increases the amount of piston rock, or slap will increase, resulting in increased stress on the skirt. Eventually the piston skirt will crack and fail resulting in damage to the head, cylinder, conrod and possibly bottom end too. As such I think it's best to change the piston long before it is likely to fail. Piston wear can be minimized by good engine warmup procedure (let it warmup slowly to operating temp before giving it hard throttle), use a good quality premix oil and keep your airfilter fresh and oiled correctly. There is no easy way to check inlet side piston wear without removing the piston. To check the exhaust skirt wear you can remove the exhaust and look in through the power valve port an visually examine the skirt while moving the piston up and down (put the bike in gear and bump the piston up/down using the back wheel). I made this video showing this method: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-AlrcK5FMZok.html

ehm TPI 2stroke models??? HAHAHA

You are so wrong lol

Thanks! Pleased you’re enjoying the content...

Archie Leeming probably at the 300hr mark id say to be safe

Danny Compton - Yes, 150H on the same piston and rings. The rings wear very little on these bikes.

Wisecos last way longer. Forged is a lot stronger than cast

It was coal lol.....

It’s a two stroke engine. Oil is mixed with gasoline to lubricate the crank and piston. The oil buns and leaves carbon deposits on the piston crown, head, power valve and exhaust.

It's probably Castor based oil. Castor Based oils always leave the inside of the engine black with soot, it doesn't burn very clean, it is one downside of Castor and the other is Castor oil has a tendency to separate in fuel when stored so you need to shake it up well. The upside of Castor oil is it can withstand higher heat so if you are running on the lean side now and then the Castor will tolerate it more but to be honest any properly jetted soigne should not be getting that hot. I personally don't like using Castor due to the soot problem and the fact is can separate form the fuel if stored, I prefer a synth oil myself.

AuMechanic - No, I use Motorex Crosspower 2T which is 100% synthetic oil. Mixture is 60:1.

​@@TokyoOffroad​ That's not too good for a Synthetic oil to produce that much soot like like Castor does. Soot doesn't do any good in the engine and given time it will foul parts and build up on exhaust port and expansion chamber surfaces.. If it was mine Id be looking at some other oil that doesn't leave soot like that. Alternative is it might just be running too rich.

I plan to do the top end on my 2019 KTM 250 TPI at 80H (currently just under 40H). I'll be sure to make a video and compare it to my carb model. From what I've seen from other owners, piston wear is higher on the TPIs. It will be interesting to check and see firsthand...

Allen Evans - Motorex Crosspower 2T at 60:1.

Yes I did. I perform compression tests fairly regularly to monitor for any changes. I didn’t see a a change in compression from the last top end overhaul do was sure there wouldn’t be any gross damage.

My recommendation would be to overhaul the top end on these bikes every 100-200 hours, depending on hop you ride and how fresh you like the bike to feel. At 200H I suspected the ring end gap would be at, or greater than 0.5mm (the Max Vertex ring end gap spec). The top end is relatively cheap and easy to overhaul, so I can’t see much point pushing the intervals longer than this.

Kristjan Hočevar - Thanks for subscribing. I’ll plan to make and upload the bore measurement video by early next week. Please wait a little longer...

Jeff Minnion - I’d recommend checking your valve clearance every 80H (and adjust if necessary) and doing a top end overhaul every 200-300H depending on how hard you ride it. I’m sure you could run the top end much longer, but the 200-300H should ensures it’s performs well and minimizes cylinder wear.

Go hard son!

Or leaner jetting

Yes, 25H is way too soon unless you have a problem. The KTM recommended interval is 80H, or 40H if used for motor sport. For trail riding and if you take good care of your air filter 150H should be no problem. There was no significant change in compression after the top end overhaul, although the bike did feel fresher after.

Way way way to soon. That’s the interval I do my yz125 and it’s a single ring engine that I have to live on the pipe with doing anything technical uphill

There is no ring service schedule specified in the manual. The manual does specify a piston change interval period of every 80H, or every 40H if used motorsports. OEM pistons are supplied with new piston rings. I made this video regarding piston ring wear in this engine which you might be interested in: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-aC-K9r_-lIc.html

A KTM OEM 2-stroke top end overhaul kit (piston, rings, wrist pin & clips and gaskets) cost is about $200. Once a year that’s not really much money IMO.

mullaway - Performance was still fine and compression and hadn’t changed from the last change, so I don’t think it was an issue....

I'm up to 400H now on this bike. Will probably do the bottom end at about 500H...

@@TokyoOffroad cool. Do a video about it when you do the bottom end 😁. Nice videos

@@daph7017 - Yes, will do for sure...

Mototrex CrossPower 2T at 60:1

Artis Grietens - It’s up to you. Motorex Cross Power 2T mixed at 1:60 is recommended in the manual

Tokyo Offroad yeah!! i use motul 800 oil !!! Ok when i do rebuild top end then i know😂 how black my piston be!!😂

Do what the manual tells you to do and only that ....1:60 . that's what it is jetted for

The ring gaps are staggered. On the piston there are two ring end location pins on the intake side. The end gaps sit here, slightly staggered. This video clearly shows the location of the pins and also shows the ring end gaps passing over the intake port in the cylinder. May be of interest: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-K6gzvgV8uIs.html

Motorex Crosspower 2T at 60:1

Motorex Crosspower 2T at 60:1

@@TokyoOffroad Thanks. How many hours on the bottom end?

I see your other video shows 295 hours on the bottom end. Thanks for the video. The oil is giving you very good top end life. I think that is what I am going with now. Did those rings also have 150hrs on them? Did you measure the ring end gap on the old rings?

@@grant31781 - Yes, both the piston and rings were 150H. Yes, the ring end gap measurement shown in the video was the old ring (top one).

@@TokyoOffroad Wow. The rings in my 2013 250XC at 94 hours had a gap 4 to 5 times larger than yours! I bought the bike used. He ran Amsoil Interceptor at 50 to 1. I am guessing dirt got in. The cylinder and piston did not have scratching. This will be the 2nd top end. My new rings have a .43mm gap. I did measure the bore multi times with a telescopic bore gauge and a micrometer and all measurements were in spec.

old sport - LOL

No, it's a 2017 KTM 250 EXC with a Keihin 38mm Air Striker Short and STIC metering block. I also have a 2019 KTM 250 EXC TPI. I read that the TPI oil injection varies between 70 and 150:1 (depending rpm, throttle position, load): transmoto.com.au/ktm-two-strokes-engine-development/?fbclid=IwAR3wEjFWlynOPPFK5yLUnq6B9Z3dY1n94dzYJH9Cw5tfoVaoQGPcBOzhQVg