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VFRCaptBob

Bob's 2002 YZ250F build

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Restoring my 01 YZ426F and 02 YZ250F. Been riding the 426 while my oldest rode the 250 and as he is 22 yrs old, a college rugby athlete and riding way more aggressively than I am capable. It's time to switch bikes.

So while the 426 gets a full refresher of suspension, bearings, chains, sprockets, tires and major tune up, the 250 is getting a much more extensive Bob's  build to suit me better especially in the tight stuff.

Did my big bore research and am leaning toward either the Weiseco 83mm 290cc for $398 on ebay .https://m.ebay.com/itm/YAMAHA-YZ250F-WISECO-290CC-83mm-BIG-BORE-CYLINDER-KIT-YZ-250F-01-08/292387065181?hash=item4413a08d5d:g:qVAAAOSwc1FXbUM4

or the cylinder works kit on Rocky Mountain Which is basically a 270cc kit. The power from the 250 never was bad but i recall all the times that more power saved me on some overly ambitious climbs. So it gets at least a 270cc bump and the crank balanced to the top end with new bearings since it has some hours on it too.

While I am at it new wr stator and fly wheel, maybe rekluse clutch and either halogen or led light kit. Suspension revalved and and sprung from Too Tech. Rick did my 426 in 08 and it is still a Whoop tamer and happy landings ride all day beast.

Any oppinions that may serve to make this bike even better and avoid costly pitfalls are appreciated. I'll continue my research and update this thread at the snails pace I progress. I have to cap cost on this as i have a new purchase of a used dual sport to make once all this work is completed. At that point the 250 becomes my woods bike.

Also hope to start riding with some of you S.California members in the future. Pumping the brakes on my sportbike riding career and get back to my roots riding more dirt.

Edited by VFRCaptBob

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Great suggestions. Auto decomp cam and fuel screw are done.

 New style cam chain tensioner sounds great. I'll look into it. Got a link for it? I forgot to do hot start toggle lever. :facepalm:

 My son has been unmerciful to the suspension so i will expect the full rebuild plus parts.

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I ordered that 290 kit. The seller was good. I did have a issue with the cylinder lining up on my dowl pins on the case. I took pics and sent it back. The exchange cylinder is currently on its way back to me now. Sitting next to the athena 290 cylinder that got destroyed, the wiseco is not as well made. I'm going to run it because at this point I'm kinda stuck with it, but I would probably go for the athena or a cylinder works kit if I had to do it over again. I didn't want to dump a whole lot into the bike since I bought it as a basket case. 

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On 2/4/2018 at 9:18 AM, YAMAHA NICK said:

I ordered that 290 kit. The seller was good. I did have a issue with the cylinder lining up on my dowl pins on the case. I took pics and sent it back. The exchange cylinder is currently on its way back to me now. Sitting next to the athena 290 cylinder that got destroyed, the wiseco is not as well made. I'm going to run it because at this point I'm kinda stuck with it, but I would probably go for the athena or a cylinder works kit if I had to do it over again. I didn't want to dump a whole lot into the bike since I bought it as a basket case. 

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Im thinking of doing a big bore top end on my 04 flat track bike this summer.  So the wiseco is a no go?  When you say its not as good in quality as ATHENA or Cylinder works, can you give specifics? Thanks

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Im thinking of doing a big bore top end on my 04 flat track bike this summer.  So the wiseco is a no go?  When you say its not as good in quality as ATHENA or Cylinder works, can you give specifics? Thanks


The casting on this particular cylinder does not appear or feel as solid as the Athena cylinder my bike destroyed when the cir clip came loose. The cylinder is not branded wiseco as the ad depicts. The only thing wiseco in the kit is the piston. I’m still waiting on the exchanged cylinder to arrive. The cylinder I received initially was not machined properly and the receiving holes in the cylinder that mate to the dowl pins in the case were off by about a couple thousandths. There was also a large shaving stuck in the water jacket. It was easy enough to remove but has left me skeptical about the QC of this cylinder. The Athena I have is perfect as far as quality of material and machining. Like I said... if I could do it over, I’d spend the extra 100ish and get a different kit. The seller however has been really great to work with. They gave me no resistance with the return. The shipping was fast since they are in Ohio and I’m Ga. I got the complete bike albeit in pieces for $350. I’ve got roughly $800 in it right now. If it runs good and I don’t come across anything that concerns me I’ll put a little more in it. 1k is my max budget. If it looks like it’s going south then I’ll part it out and easily recoup my cash. The other reason I went with this cylinder kit is because honestly the bike will probably see less than 15-20 hrs a year. Hell, I only put 13hrs on my 07 250 last year. My 125 will get the most hrs and it will probably be less than 40. My schedule being a fireman 24on 48 off with daddy daycare eating up the 48 doesn’t lend itself to a lot of seat time.

The ad has a make offer option so I did haggle a little. I’m sure the seller would appreciate me not disclosing the final price on a forum so I’ll keep that to myself. Pm me if you must know. IMG_1517872299.689146.jpgIMG_1517872333.232241.jpg

As far as the 290 goes... it is great. The power is awesome. I got the bike from a good friend, so I did get to twist the throttle a few times before it crapped itself. The BB does not like to be wound out on top. You could pretty much put the bike in 3rd or 4th and go anywhere. We ride flowing single track mostly with a few hills here and there. I don’t know how well it’d do getting strung out on a oval track but I’m ignorant to FT racing.

When the cylinder gets here I’ll be updating my thread about the bike. I’ll update on the build and specs.

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Appreciate the imput on Big Bore kits. Still tangling with my YZ426F swing arm shock and linkage bearings. Once I get it done and back together it's time for the 250. Also a trip to Harbor Freight to pick up a proper bench vice or maybe even a press tool. I can't even get the seals out of the linkage. First timeritis on swing arm and linkage bearings. Going to aquire a seal removal tool and heat up the parts then use the vice and socket method after much youtube study.

These are likely original parts in this bike since 2001so likely they are seized in there very well. All the bearing so far look intact. I repacked the swing arm bearing and was considering  only doing the shock and linkage. 

 

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Posted (edited)

Bit of a thread revival. I had to take care of some very pressing issues on my rental property which led to some unforeseen problems with my health which led to my YZ426f sitting completely torn down on the lift for months. Luckily I kept the hardware organized and completed the work on the Big Kicker. Problem now is my kicking leg is healing which means I'll be riding the YZ250f sort of like I had planned anyways. 

So now the 250 sits completely torn down with a cylinder works big bore kit and varios other parts on order while Rick at Too Tech will rebuild it's suspenders. I've had to scale back plans as my injury is resulting in less hours working and income is not as fat as it was. Plus our Ocotillo Wells trip is coming up in December and I have to be done with bike projects well before that.

But I'm getting healthier overall so it's worth it. Plus I manage to hang on to most of my dirtbike money stash for a plated button start dirt bike.

Got to love yamahas. Haven't opened up the 250 in years and only one intake valve slight tight. 

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Edited by VFRCaptBob
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Glad you skipped the eBay kit. I went through two of them before having the seller send me a full refund. Those kits were crap.

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Posted (edited)

Early xmass of shiny new kit for the old iron. Pardon my enthusiasm. Never done a piston or cyl kit before. After this bike is finished I just picked up a 2001wr250f from a friend who stopped riding. Bike won't start but has been sitting a long time. May end up plating that one since used WR250f stators are rare and expensive. 

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Edited by VFRCaptBob
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First top end since my Hodaka 100. Getting the cylinder over the piston was rough. Once there things started falling in place. I'll put the cams in tomorrow and button everything up. Suspension is back from Too Tech should have it ready to ride before next weekend.

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Spent better part of saturday researching cam timing on using autodecomp cam in my 02 YZ250F. Old info is hard to find. 13 pins between 12oclock marks. Intake set normal. Is this correct?

Going to wait for confirmation. I have plenty of assembly to do around this for today

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Thanks. Here is the link I went off of for my cams. 

I have to run to Cycle Gear to get a front tube so I can mount the new front tire. Then I can finish the whole chassis today. 

My next big step will be Jetting for the 270cc. I have found a setting listed on TT. Any input is appreciated. Ride mostly below low, high desert. Gorman below 2,000'. May do a little riding up in BigBear Alt. 5000' but can monkey with the FS and jetting for those rare rides.

Main #175

Pilot #42

Fuel screw 2 turns out

JD red needle 3rd clip

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On 2/2/2018 at 1:36 PM, VFRCaptBob said:

Great suggestions. Auto decomp cam and fuel screw are done.

 New style cam chain tensioner sounds great. I'll look into it. Got a link for it? I forgot to do hot start toggle lever. :facepalm:

 My son has been unmerciful to the suspension so i will expect the full rebuild plus parts.

Yamaha changed the came chain tensioner in 2003. The Yamaha part # for the 2003+ tensioner is 5TA-12210-10-00. It's $60 on RMATV.

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Look into picking up a newer front end (forks / triple clamps) on eBay. In 2004, Yamaha went to 48mm fork tubes, but these were still the still the old style open chamber forks. Stay away from the 2005 YZ forks. They are the first version of the dual chamber forks and they have issues. The best forks are 2006 and newer. Triple clamps vary slightly between YZ and WR, and there are two different length steering stems. The 125 and 250F's used a stem that's 10mm shorter than the 250 2T and 450F's.

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So just an update. I put the motor back together and went through the carburetor. Everything seems to work normally except the motor won't start. My guess after double checking the cam timing at TDC , double checking the carb and spark is that I put the cams in at TDC but 180 degrees out. So my next attempt is to disassemble the cams and turn the flywheel one more turn to TDC and re assemble. Is this right? I am not a very practiced mechanic. How can I avoid this mistake when doing my next rebuild? May as well change the timing chain this time around as well. 

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