Holly shit I was surprised this dude had less than 100k subs! So much knowledge and clear explanations

Best top end two stroke video on the interwebs

I'm not expert engine builder, but i rebuild a handful every year for myself, family & friends. My #1 piece of advice for anyone doing a topend is checking ring end gap. I haven't seen one come out oh the box in spec in a long time, not sure if it manufacturing short comings, or if the suppliers simply want to build the spec to the tight dimension, but I've had to file rings on the last dozen top ends ive had my hands on, both 2 & 4 strokes.

@HPRaceDevelopment

3 ай бұрын

Good on you. Most people slap them in and hope for success. You should also check piston to bore - you’d be surprised what we find occasionally.

@MrIh8hondas

3 ай бұрын

Just did a top end on a 2002 CR250 for a friend. Used a Wössner piston and the rings were actually gapped correctly out of the box. I was surprised.

@jannep6772

3 ай бұрын

@@MrIh8hondas Same thing with my 1992 KX 125 also with Wössner piston.

@dancollins8453

3 ай бұрын

Same on my 300 Wossner seam to be top notch

@mick6491

Ай бұрын

True did my first top end ever on my 300 last summer and the ring end gap was way too tight.(vertex)

Perfect, Speak on point, no bullshit. Clear speaking, accurate information. Thank you👌🙏

Excellent video!

Thank you for your time and very detailed explanations!! You are a great contributor to our sport! Answered several of my questions in this video and also in your replies. You commented on proper break in, could you give us your method? Sad to see the trolls, keep up the good content!

Thanks, HP Racing! Awesome

informative video, thanks👌

By the way, I'm really looking forward to your 300sx development.

I have 60 hours of motocross on my 300sx. I noticed it looks like I have a polished area half way down the cylinder about the size of a nickel. I think i may need a diamond hone if there is no cross hatch left. What piston to bore clearance for running an A vs B size piston? How much bigger is a B?

Thanks for this. Picking up my bike friiday. Was doubting with all the negative talk about the piston shattering. Great info. Got a question tho. Should I stick with the recommended motorex 2t @ 60/1 or is there something better. I'm an ex.motocross racer mostly riding track in northern ontario canada.

@HPRaceDevelopment

2 ай бұрын

We feel 60:1 is not so smart! At minimum 40:1

4:08 I installed a brand new top end and very similar but much less pronounced mark like that appeared. I saw it while checking the top of the piston with an endoscope some time ago. Pulled out the exhaust and reached with my finger and I couldn't feel it so I left it as is. Weird thing is I checked yesterday if it got worse but to my surprise it just completely disappeared. I didn't know it was a common thing though.

@Jake-rp9cv

3 ай бұрын

I've experienced the same thing. Did a top end, then took it back apart because the powervalve wasn't working, and those marks were there. Put it back together and did a top end 30 hours later and no more marks.

@HPRaceDevelopment

3 ай бұрын

yep. Its superficial. Over time the ring and oils and carbon can do exactly as you describe

Nice video. What's your thought on piston sizing for all the guys doing it at home without a reliable way to measure the cylinder? I know everyone says "after X hours, slap in a size B". X might be 50 or 100 but doesn't really matter. I don't agree with this philosophy. I've run original size A pistons on cylinders with 300+ hours on them. I did put a size B piston on my 23 300xc because it was the only piston I could find last fall. I've just been careful to let it get up to temp gradually. but I wish I could have kept size A in it. I'll probably go back to an A next time...

@HPRaceDevelopment

3 ай бұрын

I mostly run "A" in two stroke stuff even when bore worn some. If it's a slow speed trail guy then now - but hard mx or hard use the extra clearance is nice.

@tkrey23

3 ай бұрын

thanks for reply!@@HPRaceDevelopment

What size squish band clearance do you recommend for the 23 300 engine, stock or either side of the parameters? Cheers for all your helpful videos!

@HPRaceDevelopment

2 ай бұрын

We think people chasing this miss the boat. It does a tiny bit but not much - and without ecu tuning it's hard to move it far enough to make a difference you can really like. I've yet to see a situation where tightening it up adds power - people keep telling me this is what it does but I keep testing it otherwise.

@BhysReal

2 ай бұрын

Appreciate it cheers

two of these on rimar v-twin will be nice

@HPRaceDevelopment

3 ай бұрын

He is essentially running same thing - just using carbs

@strandschep5749

3 ай бұрын

Rimar already uses 300cc ktm cilinders

What piston do you like on 2022 150sx being ridden for single track/woods style stuff.

@HPRaceDevelopment

3 ай бұрын

Stock

Can I use scotch brite on my cylinder if I have gray spot from the piston?

@HPRaceDevelopment

3 ай бұрын

depends on the gray spot - scotch brite doesnt do anything to the plating if used by hand - so you can try it. But if you have worn through the plating to the casting - it wont help you

@elkku2934

3 ай бұрын

@@HPRaceDevelopment Ok. I saw that gray spot when I was changing the piston and decided to just do nothing about it. Now I have ridden like 25 hours on it and its working good so I was just wondering if I should do something about it when I change my piston next time. I was able to see some cross hatching there but that gray spot took most of it away on that one spot.

If the ball hone doesn’t do anything then 1: why does it look like it does? 2: why do they make them and why does everybody use them? And 3: if the cylinder looks like the one in the video are you just leaving it?

What about the 2024 KTM65 my nephew got one of the first ones in and it only ran for two hours then the engine failed. It has been repaired but it took two tries to correct the problem with certified mechanics doing the work? So could you tell us anything you know about the problems with the 65 motor? Those light transfer marks in the cylinder are gone with some scotch brite and then a ball hone. You have to really wash the cylinder of any motor after doing that and there will be no residue left to ruin your motor and the rings will seal just fine. This works on all two stroke motors whether it be motorcycles or chainsaws and the motors run great!

@HPRaceDevelopment

3 ай бұрын

My feelings and years of trying various methods and dyno testing remain - ball hone is so you feel good about yourself when you do work. its functionality is basically worthless. As to the 65 im told they have some cyl casting issues or powervalve fitment issues or both.

@forrestebert5276

3 ай бұрын

@@HPRaceDevelopment Yeh that’s exactly what was wrong with the bike both of those areas. The bike was supposed to go to the #1 plate rider but he’s not confident and going to use his ‘23 Husqvarna instead! They wee supposed to have taken care of those from the ‘23 model but I guess not? 🤔

Top end maintenance intervals for TBI same as past?

@HPRaceDevelopment

3 ай бұрын

hasnt been a 300sx in years - hard to know!

I actually read on wiscos website that there rings are supposed be used at tighter spec than oem, (unless i read wrong). The rings for my bike were tighter than oem and still put the piston on and has been running for about 15 hours now?

@mozer30

3 ай бұрын

Imo you should always go by the part manufacturers spec as they have done the testing. The oem specs are specific for oem parts only.

@Jake-rp9cv

3 ай бұрын

Wiseco recommends .004" of ring end gap per 1" of bore. Derek said his rule is .5%, or .005" per 1" of bore.

@HPRaceDevelopment

3 ай бұрын

I havent seen any dyno charts from wiseco, have you?

@adriangalvez5104

3 ай бұрын

@@HPRaceDevelopment i havent but why would dyno charts matter?

@HPRaceDevelopment

3 ай бұрын

@@adriangalvez5104 Jake said we should listen to what the manufacturer says my reply was to his comment - but for everyone. Doing so would assume wiseco actually tests their product…which they dont. We do…and come up with specs that actually work for what we see.

I put Apex head on yz250x at 21 hours, piston top had 0 darkness, 0 carbon. Looked like new piston and felt oily. Same with inside of head, no darkness, no carbon.

@HPRaceDevelopment

3 ай бұрын

your too rich

how long do most motors last? I want to know when to do engine rebuilds and its really hard to tell on the internet. for two strokes with mx riding, wot, high revs, not insane but quite hard running usually, how long will a top end go before the piston is either too worn or the material has fatigued to the point of danger? also for the bottom i guess a good general rule of thumb is that the bottom end (including conrod) should last twice as long as the top so you generally do your bottom end every second engine service right? is it good practice to replace the rod too in case it is suffering from fatigue and lost a lot of its structure integrity? since you are a performance shop i was hoping that you guys could give me a straight answer unlike the rest of the internet which probably doesn't even know what a piston looks like. if possible do you guys also know the hours for 4 strokes and good engine rebuild practice for them too, like how often to replace the piston and rod and stuff like that? and how do these service intervals change for moderate riding such as trail and calm riding were you don't push the motor hard much? sorry for the spam of questions.

@jannep6772

3 ай бұрын

With 2-strokes it depends of the engine size, how much oil in the premix and what oil is used, how hard you ride it etc. With 4-strokes it also depends of the engine size, how hard you ride it and what oil you use and how often it will be changed. Also if you are using a forged piston or cast piston top end service hours can change. I´m sorry but there isn´t easy answers for these questions. @HPRaceDevelopment can continue if needed....

@HPRaceDevelopment

3 ай бұрын

Most - but not all - owners/service manuals are pretty close. Ktm suggests 15 hour top ends on 125s.

@garbageman3992

3 ай бұрын

@@HPRaceDevelopment strange. I thought the service manuals were extremely low hours compared t reality for liability reasons. I have plenty of friends of people I know at the shop who have up to 140 hours on a stock ktm 2 stroke for hard racing. I think that is overboard and i would do 80 ish hours for hard racing but its hard to tell what the best service interval should be.

@HPRaceDevelopment

3 ай бұрын

@@garbageman3992 when we work with top level amatuers or pros, the service manual is usually not often enough. if you do the engineering math on high cycle fatigue you will find it lines up with the oem manuals.

@garbageman3992

3 ай бұрын

@@HPRaceDevelopment yeah the pistons especially need to be replaced frequently as they are aluminum and thus they fatigue even under low loads, they fatigue quickly too. but what are your thoughts on conrods? since rods are steel and have a fatigue limit where they will theoretically last a lifetime if they are never pushed beyond it. do rods get pushed beyond the limit even at low rpm's or can a motor that is never pushed hard theoretically live on one conrod for like 1k hours? if pushed hard like mx racing does the rod fatigue at a similar rate to the piston, should it be replaced as often as the piston?

casting/surface defect or crack on right side @ 3:11?

@nicoloco5923

3 ай бұрын

I thought i saw the same thing too and went in comments to see if anyone else caught that

@HPRaceDevelopment

3 ай бұрын

Looks like it - but it's just a discoloration - the bottoms have some sort of coating from the OEM - not sure what it is, looks like an anti corrossion coating

Did this bike have a Stock Ecu Tune or Upgraded?

@HPRaceDevelopment

3 ай бұрын

Both! Last 5 hours on our custom tuned GET ecu

@mrmoparrr

3 ай бұрын

I have a Brand new 23 TE 300 He ‘ haven’t ran it yet ‘ it’s only been started once. I want to change the Oem Piston out for Wiseco or Wossner . Wonder which you’d Recommend?

@HPRaceDevelopment

3 ай бұрын

Whichever you like more...just make sure you measure it and bore before you install and do a proper break in@@mrmoparrr

Every since I've started using AMS oil in my 2 stroke, I've never had the coating rub off like that. Just something that I've noticed. It could be due to something else.

@mikeschlup5279

3 ай бұрын

Amsoil?

@HPRaceDevelopment

3 ай бұрын

Weve had poor results on that oil - notably the plating around the exhaust port will rub away 40-50 hours

@ncopp4358

3 ай бұрын

@@HPRaceDevelopment Interesting. What oil do you recomend?

@HPRaceDevelopment

3 ай бұрын

@@ncopp4358 there are a lot of good ones - motul800 is always top of that list and maxima k2 or some of their tundra and scooter line ups are good

I'd never buy an injected bike unless I also found a way to make the jetting richer. They come from the factory jetted lean to pass emissions tests. Look at how the top of this piston has no clean wash. That means it got too hot due to not enough fuel droplets contacting it to cool it down, leaving areas near the transfers and boost port clean of burned oil. Also look at how much oil burned onto the sides of it. Not good. It needs a more heat resistant oil that is made to work with injectors. But at least it's not too too lean which is known by burnt oil under the piston crown.

@HPRaceDevelopment

Ай бұрын

sadly you are far off base - but hey ignorance is bliss!

This must be a race bike, ive pulled pistons out of 250's and 300's with double the hours and it didn't look anywhere near as bad as that, but they were medium speed single track riders.

@HPRaceDevelopment

3 ай бұрын

What wear? The coating coming off in 90 percent of this piston is just the coating coming off as I described. It appears to have gone through one or 2 too short of warm ups followed by hard track action where we see minor polishing on both sides. Trail bikes dont see as many cycles per hour as mx bikes. Hours a shitty measurement of usage

@TepcoCycleRepair

3 ай бұрын

@@HPRaceDevelopment I didn't say anything about wear. The burned oil at the ports and on the crown is more than I see on these mellow ridden trail bikes.

@HPRaceDevelopment

3 ай бұрын

@@TepcoCycleRepair If the rider doesnt make/use much power they dont produce any heat load. power is heat.

Dont like using my finger nor a pick tool. I was shown to use a ball point pen to check for scratches. If a pen catches diamond hone fast.

@HPRaceDevelopment

3 ай бұрын

Doesnt matter what u use - plating is incredibly hard. But good tip for “size” of imperfection that might be troublesome.

@denniswilder3014

3 ай бұрын

@@HPRaceDevelopment try a ball point pen lol. Be surprised what a pick and finger misses

@HPRaceDevelopment

3 ай бұрын

the tip final diameter is all that matters for this test....hence why profileometers are extremely pointy @@denniswilder3014

Is this evidence to how hot and lean these 2 strokes run?

@HPRaceDevelopment

3 ай бұрын

huh?

@HPRaceDevelopment

3 ай бұрын

This particular example would be on the slightly richer/cooler side of tune up.

@Profabdesigns

3 ай бұрын

KTM as well as other new generation 2 strokes have to be running lean compared to old school types to get past CARB and euro standards. I raced off road/desert in open class for 20+ yrs. We never thought 2 strokes would make a come back. Are you using a forged piston?

@HPRaceDevelopment

3 ай бұрын

These bikes don't pass any emissions standards in sx or xc form - and I can garuntee you they don't pass any standard on the TBI. Premixed fuel, and two strokes will NEVER pass. Additionally the concept that "lean" is what makes an engine pass emissions is flat wrong. If you dig into what they are testing for and the actual standards - you will see that going leaner isn't the answer to passing emissions, as leaner burning mixtures produe NOx. two strokes by their nature have a large amount of unburnt fuel that migrates through the engine into the exhaust and out - which dramatically increases their "hydrocarbon" ouput in testing. There is no way around it with the scavenging system a two stroke has - and unless you direct inject it after the exhaust port closes - it's a significant amount. To put it flatly - a two stroke will never pass without some exceptions to the rules. The good news is - they currently dont' have to pass - and the usa/carb standards are incredibly lax - but only applied to non race models which ktm is smartly re naming line ups to get around. @@Profabdesigns

The wiseco doesn't have a pin height difference? Really? They gave that up? Rule of thumb measure everything. We were making 65-72hp on gas 20 years ago from 250cc trx and cr..what is that 300 making?

@bigrich7026

3 ай бұрын

Get rid of that bottom ring too.

@HPRaceDevelopment

3 ай бұрын

@@bigrich7026 In race applications single ring is good. This is a vet rider who wants 50 hour changes - dual ring is fine. On my dyno id pay good money to see a 65 hp 250cc on gas. This 300 as it sits on our dyno is 50-52

Feel like I just got a diploma

The elephant in the room here is there was zero measurable wear on that piston. Don't change it if it an't broke. Maybe put rings in it but I bet there would be zero compression increase once the new piston and rings are broken in. 300's can do 200-300 hours on the factory piston. Most of the wear in happening in the barrel. If you want that fresh factory feel - replace the piston and barrel. Otherwise leave well alone - spend time getting jetting perfectly right for the day and you will get more out of the bike.

@HPRaceDevelopment

Ай бұрын

You might want to do a little research into high cycle fatigue and how it relates to aluminum. Visible wear is NOT the primary concern on parts changing. Its the wear you cant see that results in shattered pistons, snapped connecting rods, etc. Do yourself a favor and google high cycle fatigue - then dig deeper into cast aluminums, then into cycle counts of a piston on a 2t at 6000 and 8000 rpm averages per hour - you might find you never want to push a piston too many hours ever again