Need Advice for 02 yz426f


13 replies to this topic
  • joshr2007

Posted May 14, 2011 - 01:04 PM

#1

Hello all!
I just bought this bike from a buddy. It is a 2002 yz426f that he told me was b bored to a 450. This thing is hard as heck to kickstart as I have found most bigger bores are. Well I just wanna know if someone can explain to me how to Find TDC on this thing. I pull decom lever and push down and it is still really hard then while still holding it I let it come back up and push it back down again. This time it was much easier. So on the third motion down is when I try to kick start it and nothing. If I kicked it a few more times about 1 or 2 on the next one it is as hard as ever to kick and I restart the process. Someone help! Is there 2 times in the 4 stroke that the piston hits TDC? When I try to kick start it should I clutch and decomp lever? I have already looked into getting hot cams but will that effect it since it was bored out? I will also ask the shop to determine the correct displacement just to make sure. Thanks very much! I have always googled my problems for my bikes on here and thumpertalk always had the best answers so I decided to register so keep up the good info!

  • grayracer513

Posted May 14, 2011 - 01:25 PM

#2

You don't find TDC, just the start of the compression stroke:

http://www.yamaha-mo...troke_vid_a.mpg

http://www.yamaha-mo...troke_vid_b.mpg

  • houndog426

Posted May 14, 2011 - 01:44 PM

#3

save yourself the trouble GET THE HOT CAM KIT, the bore shouldnt have anything to do with it, but you might have to re-jet the thing when your done. the only way to measure the bore size is to remove the head and cylinder kinda pricey and worthless unless there are strange noises comming from the engine or you just want a new top end

As for the starting prosedure you cant explain it in text you realy should have someone show you or spend a weekend kicking the crap out of your bike until you get it down, good luck... i know how you feel ive been ther.

  • Yamaryder29

Posted May 14, 2011 - 02:47 PM

#4

I gently push the starter down until I feel the resistance increase, Then I bring the starter back to the top and give it one good kick and it usually fires on the first try. I'm also running a hotcam exhaust cam

  • joshr2007

Posted May 15, 2011 - 02:18 PM

#5

Thank a million! I spent about 40 minutes yesterday trying to kick this thing and I was told the wrong way! Imagine that. This is my first big bore bike 4 stroke so I am still getting used to it. After I watched that video you attached I went out did exactly as it said and it fired right up! Which leads me into my next problem.. I let it warm up put the choke back in and it started smoking from the engine area. Not sure where exactly so I turned it off and inspected what I could checked oil and such but found nothing. I did have a pretty bad storm yesterday and it did get knocked over for a while but I let it set for about 5 hrs before touching it. Do you have any advice for this problem? Things I could check or look at? Like I said I am gonna do a fluids change and flush coolant and put in new. Also I heard about the frame screen or something? No idea where that is at and can't find it in manual so if you could kind sir help me out again I would appreciate it!! Thanks

  • Yamaryder29

Posted May 15, 2011 - 02:44 PM

#6

The screen is where the oil line attaches to the frame. It looks like a 19mm bolt with a nipple attached. It is at the bottom of the frame directly below the frame drain bolt.
If the bike fell over, you could of had radiator fluid or something spill on the surface of the engine. This would cause smoke when the motor warms up. Was the smoke coming off the surface of the motor? I would wash it off, check fluid levels, then start it up, check for oil pressure, it explains how to in the manual. If the smoke is coming from the surface, sounds like fluid spilled when it fell. Just let it burn off, it won't take long, maybe 30 sec to a min.

  • joshr2007

Posted May 15, 2011 - 05:06 PM

#7

I just bought this thing from a guy a know and I rode it around just fine I got it home and I had trouble starting it ( due to lack of knowledge with a big bore 4) IT has been worked to a 450 he told me. So After kicking it for like 40 minutes yesterday I got nothing but I watched a video that someone showed me on here and boom 2nd kicked fired right up! I let it warm up and I put the coke in and I was about ready to hop on it and I noticed it was smoking a little bit. I checked fluids and it has oil and coolant. What are some quick checks I can do myself? I am knowledgeable but not a mechanic so anything might help. The other day we had a bad storm and it did get knocked over. Could it be because of that and maybe its just burning oil somewhere else? It is white smoke. Like I said I will take tank off and radiator if I have to to look at some stuff. Just tell me what to look for please. I just don't wanna drive it and have my piston seize and then I have to worry about that. Thanks so very much and this forum rocks!!!

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  • joshr2007

Posted May 15, 2011 - 05:07 PM

#8

Ok so I just fired it up and it started to smoke again at idle.. When I ran it around the yard a bit it didn't smoke at all or that I could notice. Even when I stopped it took a while for it to start smoking again. It does have stock exhaust on it and it has supposedly been bored from a 426 to a 450 not a lot I know but could this be the culprit? I mean I could see why. Should I try getting an after market exhaust that. The way I understand it is maybe it has too much heat and when I run it it keeps it cool enough to not smoke but when it just idles it will. Also if I did run it that means the engine would seize and I would need new cylinder and piston and all that right? It would damage the walls I would understand and the piston but if that were to happen could I just buy a new topend and put in the 426 displacement again? I mean it wouldn't ruin the piston rod I wouldn't think. Also how much would a new top end cost? I got a super great deal on this bike from a buddy and If i have to drop 1000 for a complete new top end I will still have came out on top. Thanks!
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  • Yamaryder29

Posted May 15, 2011 - 05:16 PM

#9

Is the smoke coming out of the exhaust?

  • houndog426

Posted May 15, 2011 - 05:25 PM

#10

one should realy not let these bigger four strokes sit idle for an extended amount of time anyway. but you realy need to find where the smoke is comming from, they do have external oil lines with banjo fitting and copper washers that can fail, and if you can check for smoke in the shade its a little easier pin point where its comming from. also dependeing on how bad the top end is damaged it can be from $250-$700 if you do it yourself.

hope this helps some!

  • joshr2007

Posted May 16, 2011 - 02:29 PM

#11

I started it up again today and let it warm up a few minutes and rode it around and no smoke. To me it felt like the engine got really hot really fast but I imagine I am just being paranoid. I am curious as to where the oil strainer is that I keep reading about? If it smokes again I will inspect it and see if I can find the spot. All I seen was it coming up from around the engine and I thought it to be too much to be coming from the exhaust alone so I killed it and started looking for any outside damage. Thanks again for all the advice this site truly is a money saver and really helps further my knowledge! RIDE!

  • Yamaryder29

Posted May 16, 2011 - 03:28 PM

#12

The oil strainer screen is where the oil line attaches to the frame. It looks like a 19mm bolt with a nipple attached with the oil line atteched. It is at the bottom of the frame directly below the frame drain bolt.
If the bike fell over, you could of had radiator fluid or something spill on the surface of the engine. This would cause smoke when the motor warms up. Was the smoke coming off the surface of the motor? I would wash it off, check fluid levels, then start it up, check for oil pressure, it explains how to in the manual. If the smoke is coming from the surface, sounds like fluid spilled when it fell. Just let it burn off, it won't take long, maybe 30 sec to a min.


Have you checked for oil pressure? and btw, the oil strainer won't make the bike smoke.

  • nor-calYZ426

Posted May 16, 2011 - 09:35 PM

#13

Dont let it idle more than a minute. You got to keep air moving through your radiators to keep it from getting hot, putting around the yard's not gonna keep it from getting hot either. Great bike though once you get em figured out

  • gscx

Posted May 16, 2011 - 09:38 PM

#14

You need a manual. Badly





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