Compression Testing 2-stroke Dirt Bikes
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- Опубліковано 14 чер 2017
- This is how I compression test my KTM 250 EXC using an OTC 5606 Compression Tester Kit. If you measure the compression of your bike when it's new you can use the result as a reference point to compare test results there after and determine what condition the piston and rings are in.
www.tokyooffroad.com/ - Авто та транспорт
I have very similar compression tester. I noticed that sealant with orings is bad. There is no force to keep oring in place to seal correctly. I used soapy water and saw bubbles. I replaced oring with bushing from pług and it is slightly better.
Great videos. Looks like you have a nice set of tools also.
nicely jetted bike thou ur plug looks perfect!
My 2019 TE 300i has 280 hours and runs like new. The compression reading is 195 lbs at sea level. I use the electric starter to test for consistency. There is no logical reason to replace the piston assembly until there is a noticeable drop in compression, drop in power, smoke, or rattle. I fully expect to get 400 hours out of the stock top end. The new TPI bikes run the oil mix ratio between 60-1 and 100-1, depending on load and temperature. I ran the first spark plug 120 hours and it never fouled. These numbers are hard for some guys to believe, and old habits die hard, like running 40-1 mix ratio and replacing the piston every year. These new bikes use top quality materials, and a conscientious owner can ride a very long time just replacing consumables such as brakes, tires, wheel bearings, fuel, and oil. It is critical to avoid overheating and intake air contamination to see this kind of service life. Of course, your mileage may vary, depending on the above factors. In addition I would note that the 300’s make greater torque at low rpm, and this is another key to their longevity. Less rpm’s equals less wear. Semi truck motors regularly deliver 1-1,5000,000 million miles of service pulling heavy loads principally because of the low rpm ceiling, durable construction, and extensive oil capacity and rigorous filtering systems.
Unfortunately these pistons do not last forever. Piston skirt failure will occur at some point if you never change the piston, which will probably also damage the cylinder, conrod and crank. I like to keep my engine fresh and I think a top end overhaul period of 150H is good for how I ride my bike (confirmed by measuring the piston and rings). The overhaul cost is relatively low and is quick and easy to do so I'm happy with this interval. If you wait 400H you will have a much higher risk of piston skirt failure (high cost to repair if it happens) and also increase the cylinder wear due to more piston rock. As such I would not recommend waiting this long. Most people see to do a top end overhaul every 100 to 200H and that would be my recommendation.
my ktm 125 (2019) after new piston change reads only 8 bars; despite that engine starts from first kick and runs as clock
hi have maybe someone had a same problem. Compression is 14, new plug tuned carb for weather, but i can't start motor. Before looks like i had very reach, because plugs lasted to 25-30 hours and engine stalled quite often
This is all basic stuff but you explain it PERFECTLY.
Are you an engineer by profession?
Yes, I'm an electronics engineer.
the meter is new and I have already tried it with other bikes and discarded that reason, do you think that the injection system requires this compression so as not to overheat and not scratch the cylinder?
in cold I got 120psi and hot 115psi. with 20 hours of use do you think it is necessary to change the piston kit?
A Great video for those that don't know how to do it. Your compression PSI is impressive for the hours you have on it. This is a direct result of the quality of premix 2-stroke oil your using, ratio mixed, propper warm up, as well as not beating it to death (over reving all the time). Would you mind sharing what oil your using and what ratio you mix it at? I've had OK success with a few different oils, and less with others. That being said, I'd like to find one brand and type, and stick with it. Thank You for help, the videos, and your time. As always, When in doubt, Gas It....!!!! Ride safe my friend.
Moto Bob - I use Motorex Cross Power 2T at 60:1
Definitely very impressive longevity of that top end.
How longer the hose of the compression tester, the more times you have to kick ! Mine is 1 feet, 3 kicks and 225 psi ! (151 hours) . Great video !
Massimo Broccoli damn, you sir either know how to ride a 2 stroke very well or baby the hell out of your bike
Would you expect to see around 210psi for all rebuilt top end 2 stroke bikes? Does the cc jave any bearing on the figures?
you just won another subscriber :)
great video lots of info thanks!
Just one question, do you say 80 hours ? Great video. Thanks.
My dad has ridden his 1999 cr 250 and has never change the top end, I think it’s about time we for a over haul
How low from your usual testing results be considered "bad"?
Question (to which I sure others would like to know the answer) - now that the TPIs no longer come with a kick starter, is there any change in the testing procedure?
No, you can use the e-start to turn the engine over instead. Just make sure the battery is fully charged so it turns over nice and quickly.
What is it original?
210psi can use avgas100ll???my bike compression tester reading around 190psi...I didnt try to push my psi more,I worries my bike will jemmed...
So if I have an adapter that doesn't occupy the same volume as the spark plug, it won't give an accurate result? People have told me that it will just take more kicks but that doesn't sound right to me.
M4TT4TT4CK6161 - The compression will be a little lower. If your goal is monitor the health of the engine over time by taking measurements and comparing them to a reference reading taken with the same setup when the engine was fresh, that probably doesn’t matter. But if on the other hand you want to get a good idea of the absolute compression you’ll be able to take more accurate measurements using the correct adapter.
how many hours do you have?..for a new bike this is OK in an older bike (2007 - 2010 xcw or exc) I don't think that it would be that high.
I have a 2007 exc 250 and the test showed me 165 - 170 in sea level after a top end build. ( I have 436H)
When I did this measurement the bike had done 90 hours. I fitted an SX head (high compression) at 10 hours.
What is normal compression on 2 strokes? Does it vary depending on engine displacement? I have a 2011 Husqvarna wr150 that runs very good but I feel like I got no power when climbing or even on straight aways! It’s my first 2 stroke?
I have a 97CR500 and new top end compression standard for this bike is around 160 psi. A CR250 similar year would run easily over 200+ psi. It changes from bike to bike, there is no standard psi for all dirbike engines.
Outstanding. I have a question. How does one check if bottom end is required for rebuild? Is there a similar tool? Or you simply just go by hours?
There are several ways to check the health of the bottom end. The first is listen to the engine. If you've known the bike from new it should be relatively easy to identify any new strange noises. Crank bearings going bad will start to get noisy. The second is feel for up-down play when you pull on the conrod while overhauling the top end (conrod big end bearing, crank bearings). You should not be able to feel any play. The third is measure play during top end overhaul (I plan to make a video in the future). And lastly go off how many hours the bike has done. Typically a KTM/Husky used for trail riding should go longer than 500H before requiring a bottom end overhaul. You could decide on an hour interval, split the cases and overhaul the bottom end. If going to the trouble of splitting the cases I'd would recommend replacing all the bearing while you're in there.
@@TokyoOffroad thats just perfect thank you and please make a video when you get the time. Subd. Oh and not sure if this makes any difference but i have a race kart 125cc 2 stroke. Im pretty new to all this. Again a big thanks!!!
Aren't you supposed to hold the throttle wide open when doing a compression test?
KE8AMR - Many people make a big point about that. I’ve tried both (throttle wide open and closed) and got exactly the same compression result. So IMO it doesn’t make any difference. Don’t forget that even when the throttle is closed the slide still allows some air in. If it didn’t the engine wouldn’t run at idle.
It makes a 40 psi difference in my car... Much different scenarios though
Yes, hold the throttle open (almost 20psi difference on mine)......Why bother kicking???? We have electric starters. Hold throttle open push start, my gauge results were 4psi higher w/electric start at 172psi vs. the kicker 168psi (stock head) and wearing your ass out sucks with the newer JUNK shorter kicker. I just did the top end on my '17' 250xcw, have the same tester used in video. I also went with a .45 base gasket, piston edge at tdc is just a smidgen/gnats hair below edge of cylinder wall...damn near at 0.
You should always have throttle all the way open when testing.
Mark, Is it nessecury to open throttle in full when we kick starter to put compression in cylinder for test?
Thanks,
I've tried throttle wide open and throttle closed and get the same compression test result. So in my experience it doesn't matter.
@@TokyoOffroad Thanks a lot
Tokyo,
Did a compression test on my 18 TC250 (stock engine) with 29 total hours and 2 on new piston/rings. Compression read 185. Just curious if this is an acceptable measurement considering your reading was considerably higher. I know someone who read 200 psi on a 18 KTM250sx with 50 hours. I know all bikes are different but would like to be sure. This is my first time doing a test and only did it to do a standard check since I bought it used.
What elevation did you perform the test at? I'm close to sea level (about 50m above). The higher the elevation the lower the measured compression will be.
Tokyo Offroad pretty much right at sea level in Jacksonville, FL.
@@chrisb4772 - 185psi for your bike does seem a little bit low. But if the bike is running well it could be down to the compression tester. If you know someone else with the same bike, or an SX you could try testing their bike with the same tester and see if there's a difference. To monitor the engine the relative difference of compression tests is important.
If a bike has low comp but still runs ,but has to be jump started and mention it's A4 yz250f , what should I do first change rings,opiston ,and or head?
My recommendation for a 4-stroke engine would be to do a leak down test. The result of the leak down test will not only tell you whether the engine is good, or bad, but also, by listening where the the air is leaking from, whether the issue is with the rings, intake valves, or exhaust valves.
Hi there,
I'm considering buying a 125sx which apparently has 'low compression.' What can be the cause of this and can a top end rebuild solve the problem? Owner said the bike started and ran but had low compression and the cylinder looks like its ok! Thanks in advance, your videos are great and very informative!
The most likely cause of low compression is worn rings. Yes, a top end overhaul (replace the piston, rings, wrist pin, and clips, conrod small end bearing) should fix the problem.
@@TokyoOffroad Brilliant, thanks so much and keep these great videos coming!
@@MrCrazyivan01 - And you'll need a gasket set too...
@@TokyoOffroad Yes I plan to order all the parts once I purchase the bike and have a good look at what I'll need! Thanks once again!
What's the relation between theoretical compression ratio and measured compression? On my Yamaha with an am6 the documentation says it has 1:12 compression ratio, does that mean it should actually test at 12 bars? I measure 8-10 which many say is normal for a 2 stroke. I can't find a clear answer and have even found different lengthy explanations that conflict eachother.
Dan vogel-essex - Yes, ideally a 12:1 compression ratio would measure 12bar at sea level. if your at higher elevation the the measured compression will be lower. And of course the engine is not ideal (ring seal not perfect) so readings will be lower. For this reason it is a good idea to take a reference measurement when the engine is in good condition so you can compare future measurements to your reference.
@@TokyoOffroad thanks for this! Sounds like I should go ahead and do some top end work.
Good video
I just checked my tx300 its at 100 psi after only 60 hours but i have no baseline as i didnt check it when i first brought it , seems very low still
- Rexy - 100psi is way too low. There must be something wrong with your engine, or the compression tester. If you know someone with a 300 try measuring theirs with the same tester. Is your bike running OK? What elevation did you perform the test at?
@@TokyoOffroad thanks for the reply, oh really?
im at sea level, bike runs fine plug is black/brown everything seems all good, i thought it was lacking a little bit of power from when it was new but thats all as far as im aware of.
@@enduro-parts-aus Just checked the compression on my 2017 TX300 last night....160hrs on the top end. 170psi @sea level
@@daverossignolful yea i was expecting maybe like 150psi , i think the tester might be no good, because the bike runs fine
Good channel and vids. I see you are professional. A lot of mechanics could learn from you. Why not to do this test with e-start and charged battery? I did this test with e-start and kickstarter. I ahieved 165 and 180 PSI so it definitely depends on piston speed.
I’ve tried kick start and e-start and got very similar results. I also tried throttle open and closed and got the same results. Obviously if your battery is low you may get lower results though.
So if you have a bike without a kickstart, you can just use the starter motor to build compression in the same way?
Yes, that is no problem, so longer as the battery is fully charged and the starter motor works correctly
When people say "the motor" might need replacing in a 2-stroke, does "the motor" mean just the cylinder head and it's contents (piston, rings)?
2-stroke overhauls are typically termed top end (piston and rings replacement and inspection of cylinder) and bottom end (conrod replacement, crank overhaul (or replacement), replacement of all bearing, inspection of gearbox). It would not be typical to purchase a whole engine as most manufacturers don't sell assembled engines.
Great video. Does KTM provide the required psi measurements for the bike. I have a 2019 250 tpi and i could not find it in my owners manual?
Thanks. No, I've never seen any published compression numbers from KTM. This is why it's a good idea to test your bike when it's new, or just been overhauled, so you have a good reference number to compare to.
@@TokyoOffroad THx i live in China at the moment and i cant buy this tool - They have short 14 m head but long one not so sure - how long is this long 14 if you can measure that would be great.
@@jacobworld333 - Ideally the same length as the spark plug threaded portion. The long adapter I have is about 16mm (not including the o-ring). An actual spark plug measures about 16.6mm (not including the crush washer).
@@TokyoOffroad Thx a lot - I tried to find it here but no luck. What would be the procedure if i use the short one? just compare results every 10 engine hours and set up a base? c if it changes? Advice thx in advance.
With the short adapter you will measure lower compression. But if you always use the same setup you’ll still have a reference you can compare to. It only takes a couple of minutes to do the test so it’s a good idea to measure frequently, especially if the engine starts feeling different.
210 psi is really good pressure.
does that bike has a chrome cilinder or not ?
Franklin Hidalgo - The cylinder is stock KTM 250EXC. It’s nikasil plated. The head is a higher than stock KTM SX Head.
Yz 125 Only runs from a bump but once running it's fine. Just done this and it's at 45psi but it all looks okay inside am I doing something wrong?
daniel jordan nicol - 45psi is very low. Either there is something wrong with your compression tester, or you need new rings.
Yes you in all 4 stort
150 hrs ??😂 not on a sx 125 mx race bike they don’t. 20 -30 hrs tops. Ps love the channel
I assume you’re pushing the kill button. Do you hold the throttle wide open and do you have fuel in the bowl still?
You should make sure the plug cap is away from anything it could arc on to, or press the kill switch. The throttle position doesn’t matter. I’ve tried wide open and closed and get the same results. If there is fuel in the bowl you will get some build up in the crankcases and cylinder and it may prove to start a little more difficult than normal after the test.
how many hours should i get out of my 2017 sx250 top end. gear oil is changed every 3 rides and air filter changed every ride. and mixed 60-1 and i currently have 50 hours on it but everything seems to be strong
It sounds like you take good care of your bike. How long the top end lasts will also depend on how you warm up your bike from a cold start and how you ride it. For the riding I do I change the piston and rings every 150H. If you race and have the bike pinned flat-out a lot then 80H, or possibly less would probably be a good interval. In this video I examine one of my 250 pistons after 150H: ua-cam.com/video/8hFqWWUh1xI/v-deo.html
ok awesome thank you i normally warm it up good. now i let it idle and give it some revs in neutral. ive hear some guys ride it under powerband to warm there two strokes
Hey man, I have a 1990 KTM EXC 250, I bought the bike off of craigslist awgile ago and ran a compression test and it won't climb over 30 psi, I don't know if I need to plug any certain part of the engine, everything is on the bike and hooked up except for the seat. I'm pretty lost when it comes to working on bikes so I was curious if you knew what could be causing the bike to build almost no pressure...btw the exhaust pipe is not totally secured but is on pretty good and there is a small oil leak, other than that I'm completely lost....any help would be appreciated! thanks
Aaron Mack - Assuming that your compression Tester works OK and that it is sealing well in the spark plug thread, it sounds like your piston rings are worn and need replacing. As this bike is new to you it's probably a good idea to buy and install a new piston kit (piston, rings and small end bearing).
Tokyo Offroad Thanks so much man 👍, I'll try that out
Aaron Mack -Be sure to use new base and head gaskets on re-assembly
Tokyo Offroad I'm sorry, a new base? head gasket base?
Aaron Mack - yes, replace both the base gasket and head gasket when you put the new piston and rings in.
Hi just yesterday i bought a
2016 Ktm exc 125
And it has 58 hours on the piston should i already change it ?
For a 125, if it’s been ridden hard then yes, it’ll probably be time to change it.
Dont get it, why does it go up during kicks...shouldnt the pressure release from the exhaust port? I mean why is it building up with each kick...
Takes multiple compression cycles to "fill" the hose and gauge.
I was wondering that too haha
Same here. I though he was gonna plug the exhaust and intake first. I need some serious help lol.
what stops the bike pumping fuel and oil into the cylinder while you're doing a test like this?
The fuel tank is removed during the test
Good morning Sir. Can you please tell me, at what altitude, did you perform this test? Thank you in advance.
And if you have any knowledge, about how one should adjust the values, based on the altitude you are at. I have a 2016 KTM 250 XCW . I just had the piston and rings replaced. I have a Slavens S3 head : I am using the low elevation ( 0 to 6K feet ) insert. I got 180 psi compression. Same procedure as you do, with the same equippment ( as per your recommendations) . I am right now at 5250 feet altitude and a temperature of 66 degrees Fahrenheit. I thibnk 180 psi is a bit low. Do you agree?
aiturbide - My house is approximately 30m above sea level. The power valve adjustment shouldn't have an effect on the compression test. Have you tried repeating the test? Make sure you kick the bike strongly and until the pressure stops rising. If you get the same result it's probably correct. I'm not familiar with the head you purchased so don't know what compression to expect with it and the insert you're using. Maybe try asking on KTMTalk.
Tokyo Offroad : Good evening. Thank you very much , for your reply and for your time. We checked my son's 200 XCW, that just has it's top end done. He got 150 psi. As you said on the video, I will test and see, how it changes in time. Good evening and have a great week. Thank you very much!!
@@aiturbide Have you redone the test? I am curious as after new piston+rings the compression on a friend's bike is a little bit lower than before the piston change (170 vs 190)
@@sorin.n good morning Sorin. I have not redone the test. I have changed bikes , but have not redone that test. After the first piston change ( piston A) one changes to piston B which has a bigger diameter. Perhaps your friend replaced it with a piston type A ??? I buy on ebay the Vertex kit but choose type B ( others state it as type II). Check that out. Hope that helps you.
Thank you! Will let him know. 👍
May be you should take off exhaust and look at piston condition. Also a vacuum and pressure test. Several times I had good compression with tester but Piston was scored. Just my 2 cents
Richard Tessier - Was your experience with KTM 2-stroke engines, or something else? After how many hours of operation did you notice the piston scoring? What do you think caused the scoring? Dirt ingestion, or something else? In general people seem to be getting long hours (~200H) on their recent model KTM 2-strokes.. As such my plan is to change the piston and rings every 150H, unless I notice a change in performance, or compression . For a recreational rider like myself I don't think this is unreasonable. If I were a professional racer, or always rode in very dusty/sandy conditions I might well come up with a different maintenance strategy.
I have been working on 2 strokes since the 60's. When Pentons were sort of Ktm's I'm not here to bash your work. I like this site. There are many reasons a compression test isn't 100% fool proof. Yes it could be dirt,water,air leaks.crank seal leakes etc.etc. Yes have found Ktm 2 strokes Not making that amount of time. Funny How Ktm is coming out with oil injection. Yamaha had it in the 60's early 70's. We took it off because it was unreliable. Doesn't hurt to take exhaust off and look in with a flash light to check piston and ring condition. Good Luck Safe Riding
Richard Tessier - Thanks for the clarification regarding your experience. 'll have a look next time and see what I can see through the exhaust port. Regarding the new KTM TPI for 2018, it isn't only oil injection, it's a 2-stroke fuel injection system, into the transfer ports, which is new. We'll see soon how well it works...
I understand that they are fuel injected. When i worked for a factory team in 70:s. We tried it on dirt bike. Found it didn't produce as much power as our.walbro carb modified engines.
Richard Tessier - Yes, I'm doubtful the performance will be as good. But with reduced emissions it does at least ensure a future for 2-strokes in the near term...
Do you need to take out the oil when you going to do the air test? Please reply someone
No, you don't drain the transmission oil when doing a compression test.
Tokyo Offroad so i leave the oil there
Yes, leave the oil in. Make sure the spark plug cap can't spark to the frame, or something else metal while you kick the bike over. You can hold the kill switch in if you're concerned about this.
Tokyo Offroad oh it cuz my pw80 2003 accelerate by it self when i turn it on
Tokyo Offroad i even have videos about my pw80 that has problem. It on my channel
My gas gas 125 2013 ec has 90 psi, is that too low?
Yes, that sounds too low. Either your top end needs overhauling, or your compression gauge is not working correctly.
Do you know what your compression was when the bike was relatively new with the stock head?
I changed the head to an SX head when the bike was new and didn't measure the compression with the standard head. Sorry...
Tokyo Offroad well i have 2017 TE250 with 76 hours and i got 140psi just wondering if that was good still
140psi seems a bit low. A stock head should be 170psi, or more I think. Did you compression test it when it was new? One thing to note is that altitude will affect the compression test result. The higher you are the lower the compression result.
Jakob Fagen
I just bought a brand new Ktm 250 sx 2018 left over I’m around 2000 ft up from sea lvl and compression seems very week with stock head can any1 give a little guidance here .... maybe lectron carb would fix ?
Tokyo Offroad
What head did you use?
When I service a top end do I just change the rings ?
You may get away with just doing the ring/rings... but it all depends on the condition of you piston and cylinder, you need to take some measurements such as piston/cylinder wall clearance, after examining your piston and cylinder for obvious issues such as wear marks/scuffing.
There is no point just doing the rings if you have an A sized piston and your cylinder has enough wear that it needs a B sized piston.
after I have done a top end rebuild I use it for about 40 or 50 hours then I replace the rings only and then use it for about another 40hrs, then I rebuild the top end again, sometimes go from an A piston to a B, or from a B to a C if I have had the bike for a while, it all depends on the bike, no bike is the same.
hey at what pressure to replace the piston??
The compression measurement, when monitored over time, gives a reasonable indication of the ring condition. If the reading starts dropping off then you know it's time to change. Regarding the piston, it would need to be grossly damaged before it would significantly change the compression result. As such the compression test result should not be used to determine whether the piston needs changing. For regular trail riding on a 250, or 300 my experience has been that 150H piston and ring change interval is good.
What kind brand pipe guard you using?
Kyle Peterson - Originally I used the carbon guard which comes stock with the Sixdays model. Then I used a Pro Carbon guard when I first switched to an FMF Gnarly pipe. Currently I’m still using an FMF Gnarly pipe, but with no guard
Is the guard worth using? I mean do they protect well or am I better off using guard money towards and new pipe when it’s beat
What issues would there be with using the electric starter to do the compression test? Curious as the 2020's aren't coming with kick starters
noControl - In my experience, if the battery is fully charged and the starter system is in good working order you’ll get the same results as using the kick starter.
greetings Tokyo Offroad
I am from Ecuador and my motorcycle is an TPI 250EXC, I imagine that the compression must be the same as a carburetor but in this it does not reach more than 120psi, it has 20 hours of use, you think it is normal or something bad is happening with the segments and piston?
120psi is very low. Either there is something wrong with the engine , or there is an issue with the compression tester you have, or the way you're using the tester. Have you used the compression tester on any other bikes before and got a good result, or is this the first time?
you failed to mention that during the test..hold the throttle wide open..
It's because I've found that holding the throttle wide open results in the same compression test result as when the throttle is left closed. Even if the the throttle is closed air can still enter the engine, or it wouldn't idle.
my friend rode 400 hrs on a 300 RR 2014 without a failure...true story...
I believe you. However, considering the cost of a top end overhaul to the cost of a piston failure, I don't intend to try to find out how long the piston can last before catastrophic failure ;-)
@@TokyoOffroad What happens in "catastrophic failure" when piston failure occurs?
@@alantaylor6691 A catastrophic piston failure (typically the piston skirt would fail if used for an extended period of time) would wreck the cylinder, head and possibly the conrod and crank too. Yes, it get's expensive if the piston fails. Which is why I would always recommend conservative top end replacement periods, especially considering the relatively low cost of a piston kit and ease of change.
@@TokyoOffroad Just saw some images. I can see how a piston skirt breaking apart would cause that kind of damage in there, as well as the crank. Not good! Thanks.
will this work for a 2019 beta 300rr?
6 Gear Pinned - Yes, it’s the same method on your Beta.
@@TokyoOffroad thank you for fast reply!
@@TokyoOffroad will the same kit work aswell?
6 Gear Pinned - Yes, your bike (AFAIK) uses the same style of spark plug as my KTM so the same OTC compression tester will work great
@@TokyoOffroad i have a kx250 is it the same method to do?
That means u use 115 to 120 octane
No, I use premium pump gasoline which is 100 RON octane in Japan.
forgot to mention to hold the kill switch while doing it.
Ray Eh - Yes, it certainly doesn't hurt to hold the kill switch while testing and I know that Slavens and some others recommend it to avoid sparking and potentially damaging your ignition. However, the distance from the plug cap conductive clip to the opening of the rubber boot is about 1". This would require a voltage of about 60,000V to arc through air, which is higher than a typical spark plug voltage. With this in mind, if you place the plug cap out of the way while testing, with nothing poking down inside the cap, there should be no chance of sparking, or damaging your ignition.
Not 150 200 you need to do it it 40 hours
WHAAAATTTT. you can't be SERIOUS...... 150 to 200 hrs on a top end rebuild. That must be a joke right? I know it all depends on what type of riding you do, but if your seriously advising people to change the piston at 150-200 hrs you really shouldn't be doing Fix it videos lol.
On the carb model KTM 250 and 300 2-strokes most people overhaul the top end every 100 to 200H. On my 2017 250 EXC I did my first top end overhaul at 145H and second at 295H. I made a video showing the engine parts at 295H if you're interested. Compression hadn't changed, ring gap still good, piston wear minimal, cylinder still looks good. For the riding I do I think 150H is a reasonable interval for top ends. If I was racing I'd probably reduce the interval to every 100H. When I rode Hondas (I had a series of 3 CR250s in the late 90s/early 2000s) I'd do the top end every 40H and it needed it. Late model KTM engines are very well built with excellent quality parts. Keep your air filter clean and use good quality 2-stroke oil and they last a long time.
This is the video which shows the inspection of the piston and rings (150H) and cylinder:
ua-cam.com/video/8hFqWWUh1xI/v-deo.html
Believe me, if the top end needed overhauling at shorter intervals I'd do it...