Post by: racer142 on July 27, 2013, 06:05:46 AM
Crank is locked up but the cylinder and had are fine. I found no damage other than the piston and crank. My question is how long should a crank last? I would guess this one hat 100 hours on it pretty easily. Curious if that sounds about average or not. About to buy a new crank and need to know if I should stick with hot rods or go wiesco or oem. Any thoughts?
Post by: Stusmoke on July 27, 2013, 07:59:33 AM
Post by: evo550 on July 27, 2013, 11:09:11 AM
How many hrs on the piston ? A broken skirt is usually caused by to much clearance between piston and cylinder.
Looks like a 125 piston, so 100hrs on a 125 crank is getting long in the tooth.
Post by: cnrcpla on July 27, 2013, 01:30:34 PM
Quote
Are you sure the crank is not just jammed with a piece of the piston?x2, check this out. If there is shrapnel in the bottom end, the crank has very little clearance between the cases and itself, so even a very small piece can be jamming it up. Also could be pieces in the main bearings.
Post by: racer142 on July 27, 2013, 02:18:16 PM
Post by: SachsGS on July 27, 2013, 02:30:54 PM
Post by: motoman356 on July 27, 2013, 07:51:32 PM
Post by: Stusmoke on July 27, 2013, 09:31:04 PM
Post by: racer142 on July 27, 2013, 10:43:47 PM
Post by: Stusmoke on July 27, 2013, 10:52:30 PM
Post by: cnrcpla on July 27, 2013, 11:04:00 PM
Post by: racer142 on July 27, 2013, 11:10:29 PM
Post by: Stusmoke on July 28, 2013, 03:28:23 AM
Post by: TMKIWI on July 28, 2013, 04:20:02 AM
Post by: Stusmoke on July 28, 2013, 04:40:14 AM
Post by: scotty dog on July 28, 2013, 04:51:20 AM
Post by: TMKIWI on July 28, 2013, 04:56:11 AM
And there are better ways to measure thats for sure.
Is my information wrong?
Yep.
.007? You mean .07? A feeler gauge that is made to 7/1000ths of a mm is rather small... I've always gone by no more than .04 mm clearance.
Post by: Stusmoke on July 28, 2013, 05:02:59 AM
0.002" or 0.5mm is correct.
And there are better ways to measure thats for sure.Is my information wrong?
Yep..007? You mean .07? A feeler gauge that is made to 7/1000ths of a mm is rather small... I've always gone by no more than .04 mm clearance.
Maybe maths is different in new zealand... But from where I come from, .002 inches = .05 mm. Which would mean that my information was in fact, correct. .002 inches, does not equal .5mm which is a distance easily noticed on a conventional tape measure.
Post by: TMKIWI on July 28, 2013, 05:38:43 AM
Fixed.
Post by: racer142 on July 29, 2013, 02:17:34 AM
Post by: evo550 on July 29, 2013, 03:30:43 AM
Post by: racer142 on July 29, 2013, 05:01:49 AM
http://twostrokemotocross.com/forum/general-two-stroke-talk/the-rebuild/msg47335/#msg47335
But it has since had a year and a half of hard riding on it and I kinda got curious how long it was going to last.
I'm no newb but I've never built a mood bike before. I had am uncle that went pro in flat track and mx in the 70s and he always made the comment "shift up". He always believed if you couldn't rode it locked throttle everywhere then there was no reason to mod the bike and for the most part I agree. But since it's blown I'm going to look into upgrading. But for what is worth I'm 23 racing the b class with a 9 year old basically stock 250 and have put a couple 16 year old kids with daddy's money and $20, 000 dollar bikes to shame. But I'm kinda wanting to build the bike a little different this time.
Post by: TotalNZ on July 29, 2013, 05:45:28 AM
There are little things you can do while the cases are apart though, Matching the barrel to the crankcase is pretty easy and should make it run a little harder. Also if you haven't already done so you should measure and set your squish. Also do your best to remove all the carbon from inside the expansion chamber, 100+ hours worth of carbon will kill the performance of that pipe.
If you do get an aftermarket complete crank, take it to your local engine builder and get him to check it's true. They might be able to improve on how it comes out of the box.
Post by: Stusmoke on July 29, 2013, 07:35:46 AM
I'd start with the suspension, that'll make the most difference in the real world.
There are little things you can do while the cases are apart though, Matching the barrel to the crankcase is pretty easy and should make it run a little harder. Also if you haven't already done so you should measure and set your squish. Also do your best to remove all the carbon from inside the expansion chamber, 100+ hours worth of carbon will kill the performance of that pipe.
If you do get an aftermarket complete crank, take it to your local engine builder and get him to check it's true. They might be able to improve on how it comes out of the box.
x2 on every point, particularly the first. horsepower won't do much good if your suspension tires you out. Getting suspension revalved and resprung for your weight and abilities is where I would send my money.
Post by: racer142 on July 29, 2013, 07:37:23 AM
Post by: Stusmoke on July 29, 2013, 07:44:31 AM
Suspension is sprung for my weight and gold valved. Also regeared the bike with a14 tooth front sprocket to smooth the bike out. Not to be rude but I've been doing this pretty successfully for a couple years. I know the basic steps but I'm looking into a few mods. I've always ridden stock bikes and raced 4 strokes so I'm asking where and what to do that's two stroke specific that's all. Thanks
Fair enough. Assuming you're in the states which I'd guess you are, Pro circuit is a good place to start for motor work. I'm in Aus so I have no direct experience but I've heard nothing but praise from their customers. There was even one dude at my local track who sent his KX250F motor away to PC for a serious ovehaul. He was considering proposing to his bike, even though the postage for his motor back and forth just about cost as much as the valve train work he had done
Post by: racer142 on July 29, 2013, 07:57:24 AM
I'm not the fastest guy around for sure but I do know how to handle a dirtbike a little lol.
Post by: racer142 on July 29, 2013, 08:03:50 AM
x2 on what everyone else said. And I made the 125 assumption by teh size of the piston relative to your hands. So i'm now thinking you have mammoth hands. Rule of thumb for replacing pistons is every second ring(s) change. Piston and rings, rings, piston and rings, rings, piston and rings, rings etc.And for the record I am slightly larger than the average mxer but not much. 6 foot tall and #200lbs or 1.8 meters and 91 kg for those on the metric system. He's is a pic of me next to my bike on a lift we had just bought
Post by: TMKIWI on July 29, 2013, 08:58:17 AM
Eric Goor is well known but there are lots of good engine builders around.
A bare minimum would be to match the cases and set the squish.
Post by: Stusmoke on July 29, 2013, 11:31:44 AM
Like I said not trying to be rude just making a point. It bothers me when I ask a question and get an answer unrelated to what I asked lol. My gf does that lol. Anyways here is a few pictures for reference to me on the kx
I'm not the fastest guy around for sure but I do know how to handle a dirtbike a little lol.
Yes the bum whips make any rider envious. Let me put it this way: I would love to be able to send my motor to pro circuit. But as TMKIWI said, big companies aren't the only ones who know their way around a motor. I'd be inclined to send mine to PC because I've never heard of someone who was unhappy with the invisible rocket boosters that PC strapped on their swingarms. In addition to that, it was good enough for factory Kawasaki riders back in the day.
Post by: lauterbacher on July 29, 2013, 03:21:03 PM
Post by: cnrcpla on July 29, 2013, 06:06:36 PM
Post by: evo550 on July 29, 2013, 11:17:22 PM
Like I said not trying to be rude just making a point. It bothers me when I ask a question and get an answer unrelated to what I asked lol. My gf does that lol. Anyways here is a few pictures for reference to me on the kx
I'm not the fastest guy around for sure but I do know how to handle a dirtbike a little lol.
Not trying to be rude....but being a good rider, doesn't make you a good mechanic and vice versa...but to answer your original question 100hrs on a crank is too long for a fast guy, but you already knew that right
Post by: racer142 on July 30, 2013, 01:46:46 AM
Post by: cnrcpla on July 30, 2013, 04:27:05 AM
Post by: racer142 on July 30, 2013, 05:17:43 AM
Post by: evo550 on July 30, 2013, 06:58:44 AM
Check out ktm 250 dyno report. (red is scalvini)
http://www.scalvinipipes.com/ScalviniDyno-KTM2502t.html
Post by: Stusmoke on July 30, 2013, 07:21:57 AM
Scalvini pipes have a reputation of good top end gains without any loss to bottom and mid. Not sure if they do one for a kx though.
Check out ktm 250 dyno report. (red is scalvini)
http://www.scalvinipipes.com/ScalviniDyno-KTM2502t.html
Thats impressive gains. On paper anyway. I've been hunting for something that would pull further into the top end without loosing the torquey, hooked up bottom end that I love. Now that I've found it, the price frightens me
Post by: evo550 on July 30, 2013, 08:17:22 AM
Scalvini pipes have a reputation of good top end gains without any loss to bottom and mid. Not sure if they do one for a kx though.
Check out ktm 250 dyno report. (red is scalvini)
http://www.scalvinipipes.com/ScalviniDyno-KTM2502t.html
Thats impressive gains. On paper anyway. I've been hunting for something that would pull further into the top end without loosing the torquey, hooked up bottom end that I love. Now that I've found it, the price frightens me
Oh Yeah!! $$$$, but you would seriously have the toughest looking pipe on the start line.
Post by: Stusmoke on July 30, 2013, 10:08:54 PM
Scalvini pipes have a reputation of good top end gains without any loss to bottom and mid. Not sure if they do one for a kx though.
Check out ktm 250 dyno report. (red is scalvini)
http://www.scalvinipipes.com/ScalviniDyno-KTM2502t.html
Thats impressive gains. On paper anyway. I've been hunting for something that would pull further into the top end without loosing the torquey, hooked up bottom end that I love. Now that I've found it, the price frightens me
Oh Yeah!! $$$$, but you would seriously have the toughest looking pipe on the start line.
Sure would
I gotta say it feels pretty awesome to leave hopped up 250Fs for dead on a bone stock bike The funny thing is, at the start, they shoot off the pad (yeah concrete 
) While all the 250 riders get more wheelspin than bite. As soon as we hit the soft, loamy dirt though, its like we got flung out of a slingshot. WHAAAAAAAAAAAAPPPP straight back with them. If it wasn't such a short start (it would be lucky to be 80 metres), they'd get eaten up in that lovely dirt.
Post by: Camstyn on July 31, 2013, 10:25:09 AM