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Yz 250 Goes Kaaabooom!!

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I was out ridding yesterday, after a few weeks of not ridding due to a ankle injury. I was hitting and few jumps and putting around. I go to hit the tabletop we made and while i was in the air blipped the throttle a few times and soon as i hit the ground the noise i heard was horrible. The sound of metal on metal and knowing that your piston just grenaded and jammed up the bottom end. (Havent taken it apart yet but that would be my educated guess:excuseme: ) Well did some searching this morning and saw this complete bottom and top end kit. http://www.motosport.com/offroad/product/COMPLETE-TOP-BOTTOM-END-KIT/?prodId=781986&catalogId=108726&refine=1&sMMY=YAMAHA%3BYZ250%3B2003&srchHistoryURL=v7cu5kst%7C%7CparentCategoryID%7E1%5EsuperParentCategoryID%7Ecategory_root%5EparentCategoryName%7EDirt%5EcategoryID%7E4%5EcategoryName%7EDirt+Bike+Parts%5EsubCategoryName%7EEngine+Parts+and+Accessories%5EsubCategoryID%7E75

I know the top end part of the kit is good. About these Hot Rod Cranks are they any good? Also how hard is it to sprlit the cases, i am mechanically inclined and are there special tools needed. Any info would be aprreciated.👍

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I just rebuilt both the top and bottom end of my 250. Check E-bay. I got an OEM piston kit for a little over $100 and a Wiseco Crank kit for $200. Splitting the cases isn't that hard. You'll need a few tools, clutch basket holder, case splitter, crank puller and a flywheel puller. All can be bought from Rocky Mountain. Watch the how to videos on the rocky mountain site. They show you how to do the bottom end and it happens to be a YZ 250 motor! Also, while you have the cases apart, check your tranny bearings. Mine were rough so I replaced them as well. I almost forgot, if youdon't already have one, get a manual.

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Maybe its tranny and not motor? Either way it could get spendy!! 👍 Sorry to hear

tranny is a good chance to, im praying for it to be just the crank and top end. If its the tranny im gonna have to spend money on both, ill be in there already so ill probabley end up rebuilding everything.

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tranny is a good chance to, im praying for it to be just the crank and top end. If its the tranny im gonna have to spend money on both, ill be in there already so ill probabley end up rebuilding everything.

Since you're in there, you might consider the WR tranny mod.. Its well worth the money in parts, and if you're in there anyway, ya know? 👍 I think the parts run just over 200.00 for the 3rd - 5th gear sets.. (98 WR400F) If you have broken gears and want to stay with stock gearing, I have two sets of YZ stock gear sets 3rd-5th.. Good luck man

Tate

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Since you're in there, you might consider the WR tranny mod.. Its well worth the money in parts, and if you're in there anyway, ya know? 👍 I think the parts run just over 200.00 for the 3rd - 5th gear sets.. (98 WR400F) If you have broken gears and want to stay with stock gearing, I have two sets of YZ stock gear sets 3rd-5th.. Good luck man

Tate

what are the advantages/disadvantages to the wr tranny mod?

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what are the advantages/disadvantages to the wr tranny mod?

If you only do the 3rd-5th, you will obviously gain top speed because 4th and 5th are geared taller while keeping a moto tranny 1st-3rd.. You can gain between 10-15 mph over stock.. Down fall is a pretty big gap from 3rd to 4th as 3rd gear is actually slightly shorter than stock..

If you did 1st - 5th you get a shorter 1st, same 2nd then the 3rd-5th described above.. Downfalls here are that to run the 1st gear you have to mod the cases a smidgen to make it all work.. BUT, you get the complete WR trans and allows for some sweet gearing options...

👍

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Ugh, ewww, mmphhh . . . excuse me, I just threw up in my mouth :lame: . Sorry to see that Pete, looks like you'll need to get in to the bottom end as well to make sure you remove all the debris. Do you know how many hours were on that piston? Are you sure you didn't hear any rattling coming from the top end the last few times you rode it?

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I usually can feel the difference when the top end is on its way out, but this time i couldn`t because i had a shitty tire and all it was doing was spinning any way so i didn`t feel much of a difference. The amount of hrs are unknow i have been putting off doing the top end for a few weeks and now look :bonk:. When i think about it now i was ridding alomst 25 hrs a week this whole summer so i should have done it a long time ago. Oh well all the parts are ordered and hopefully ill be on the dirt this coming weekend.:lame:

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My '02 YZ250 was about in that shape when I bought it....I collected all the parts and took the motor in pieces to a local motor guru. He spilt the cases and fixed everything perfectly for $200 in labor including reconditioning the cylinder, PV, and reeds. I put the rest back together myself and have essentially a brand new motor for around $525 total. I ended-up with a kick ass fun practice bike for around $1K. I figure I could put another few hundred in it and not be negative value wise.

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well i know for sure i need crank bearings its completely locked up (just my luck) so i orderd the top and bottom end as well as a new cylinder. I think i can save my head. Yea its cost a pretty penny and i also ordered a trailtech vector to keep track of hours so this doesnt happen again lol

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just got done redoing the top end in my bike... although the power increase i got was probably not worth $120... peace of mind is i suppose! i was just about to regret it until i saw this thread lol

but good luck man

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I got a Hotrods crank in my bike - I think I remember reading that they bought weisco cranks or the other way around or whatever but that they are the same thing now. Steve at Moto814 said he liked them and there were good quality.

That is one bad thing about the OEM piston - at end of life they crack and grenade - weisco not suposed to do that, but I think I like stock pistons fine. My bike has a weisco piston in it, but I had the cylinder replated by motousa or something like that (will have to check) and they matched it to the piston that went in it, so I guess I'll go with one again. Only think is you gotta get the break-in right with a weisco and warm it up properly before taking off.

HARD lesson learned by me - ALWAYS split the cases anytime something has came apart in the topend - I ruined a brand new OEM cylinder and topend kit by not doing that and thinking I had got it all out. Warmed the bike up and rode about 1/2 mile and it sucked some junk back up into the cylinder and PFFFT. Had to push that dang thing back out of the woods to the truck. :lame:

If my tranny ever comes apart, I'd for sure put the WR gears in it I think. I dont know they'd be of much use in the eastern US where I ride, but I'd like to try them once and see.

....

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My '02 YZ250 was about in that shape when I bought it....I collected all the parts and took the motor in pieces to a local motor guru. He spilt the cases and fixed everything perfectly for $200 in labor including reconditioning the cylinder, PV, and reeds. I put the rest back together myself and have essentially a brand new motor for around $525 total. I ended-up with a kick ass fun practice bike for around $1K. I figure I could put another few hundred in it and not be negative value wise.

Thats pretty good... where did you go for the work? I am in Az too!

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If my tranny ever comes apart, I'd for sure put the WR gears in it I think. I dont know they'd be of much use in the eastern US where I ride, but I'd like to try them once and see.

....

It's said that the WR 3rd gear is about a mid second to mid third in the YZ close ratio. This could work beautifully if you have the right terrain where you could put it in third and leave it there.:lame::bonk:

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