thump chump

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Jun 20, 2001
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Time has come to rebuild my 250f.
My question is: I have always used OEM parts in the past with my two strokes. However, I ended up using Pro-X, since my sources tell me that there parts are OEM. But, I have not seen any Pro-X top end replacement parts for the 250f, only Wiesco and Arias. I have no experience with either.
I get a much better, and I mean MUCH, deal on the the Arias or Wiseco parts as opposed to the OEM parts.
What has been your experience?

Thanks-
 

motoman393

Member
Nov 12, 2000
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I personally have had bad luck with Wiseco, and I know others who have also had bad experiences with their products. The Wiseco pistons are great for 2 strokes IMO but for four strokes it is a new ball game. They must have closer clearances and be closer to "perfect" if you will! And the company I believe that has the best 4 strokes pistons is JE pistons, you can get them from White Brothers. I have used these in YZ400's, XR400, XR250's, XR200's and a few others (I will use them in my 426 whenever the time comes) and the fit and finish was far superior to Wiseco! I havent had a Arias piston before so I havent got the foggiest on that one. But you cant go wrong with JE in my opinion. Im sure others will disagree but hey that is what a B-board is for right? Hope this helps!

Garrett
 

Rich Rohrich

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I've put quite a few four-stroke engines with Wiseco pistons and they work quite well. But like any forged slipper skirt racing piston, if the person assembling the engine doesn't take care to set clearances and torque values correctly you'll have issues.

The majority of problems I've seen in these situations have more to do with the mechanic than the manufacturer of the pistion. Bad mechanics can turn any good product into JUNK.
 

yz250-effer

Member
Nov 4, 2000
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Time to rebuild already??

Just curious if you mic'd anything to determine if it was time to rebuild, or if you just determined by loss of power/acceleration. I have been meaning to do a compression test on mine, but keep procrastinating. I got mine in nov. and it still seems as strong as day one. How long will these top ends last?
 

thump chump

Member
Jun 20, 2001
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top ends- 250f

My understanding is that you should put a piston and rings in about every 5 hrs. Of course, depending on your riding style this could change. I was told that Brandes rode 4 nationals with the same top end. My bike has around 20hrs or so, easy. I would rather do the work rather than take a chance of breaking a skirt and roaching the engine. That can get rather expensive!

I am also hoping that Pro-X, or similarly reputable company, makes a rod kit as well. I do the bottom ends on my two strokes, but have never done a four-stroke. Other than the cam timing, I don't think that it will be that different. I am procrastinating as well.
 

thump chump

Member
Jun 20, 2001
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top end time-

Actually, I've heard from a couple of different sources:
1. The owners manual
2. Big Gun Exhaust
3. Pro Circuit R&D
4. Sources within YMUS racing

What I was told was that the piston skirts have a tendancy to break after extended hours. All of this of course depends on how hard you ride. But I can not afford to loose a bottom end at this point. That would run me about $2.0k plus, even after calling in favors!

I would rather due preventative maint. than risk a major break. And I race pro, 2 classes every weekend. SO I know that I have approx. 20 or so hours on my current piston.
 

bashn

Member
Dec 6, 2000
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I just replaced my piston and cylinder at 20 hrs (big bore kit). I carefully measured piston clearance and ring gaps. Everything was well within spec. I would put them back in and run them for another 20hrs without hesitation. Keep in mind that I race this bike hard and change oil every three races.

Mark
'01 YZ267F
 

thump chump

Member
Jun 20, 2001
76
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top ends- 250f

What is the pressure test amount? Maybe I could just pressure test the top end for now.

I also change the oil every ride.
 

bashn

Member
Dec 6, 2000
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I don't know why your so obsessed with your top end. Tear it down down once a season for complete inspection. Replacing the piston once a season wether it needs it or not is good insurance against catastrophic failure due to cracking or hidden flaws. If your name is Tim Ferry, then by all means replace your top end every 5 hours! An easy way to check your top end is to bring the piston up to the compression stroke and rest the wieght of your leg on the kick starter. It shouldn't move for a couple seconds. If it moves quickly or hisses, then you should definately look at your valves and piston/rings/cylinder. This isn't very scientific, but you can do it every time you ride, and you will have a clue as to the general condition of your engine. Personally, I think 5 hours is ludicrous.

Mark Boyd
'01 YZ267
 

thump chump

Member
Jun 20, 2001
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obsession..

....my obsession is due to my 2-stroke having a catastrophic failure 1 week before the first national. It was only three months old. All of a sudden, my bike started vibrating badly, so I pulled off the track. Upon inspection, I found my bottom motor mounts had broken. So I yanked the engine out, and decided that I'de rebuild it. I discovered that the one of the crank bearings had let go, and in the process of those few vibrating seconds, had toasted my bottom end, left case half, and my cylinder. Total cost was about $2.0k. And my entire racing budget for the three nationals on the west coast. So I am very paranoid about it. Had I rebuilt the bike a month earlier, I'de be at Washougal this weekend.....

Upon closer inspection, I could not find any evidence of dirt in the crankcase.
 

Rich Rohrich

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Given the fact that you are racing this bike hard it's a very good idea to follow Yamaha's service schedule (in the manuall) for the piston and rings while keeping a close eye on the crank.

Using Mark's suggested feel-o-meter method is probably OK for guys just play riding or putting minimal race time on the engine, but it's a recipe for broken parts for serious racers. These are NOT XR250s and you can't treat them like it.
 

thump chump

Member
Jun 20, 2001
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preventative maint

El Mucho Grachios

Thanks for your reply.

Now I pose another question. You seem quite knowledgeable in the world of four strokes. So, when I do have to feather my clutch, I feel modulation through the lever. I asked Doug Dubach about this, and his reply was that he would have a fix for this very soon. Fine and dandy, but what causes this? I thought it was due to the basket having ridges on the fingers from use, and that a simple replacement basket would solve this. But after Doug's comment, I am wondering if there is something more than what I thought it was.....:think
 

Rich Rohrich

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Re: preventative maint

Originally posted by thump chump
So, when I do have to feather my clutch, I feel modulation through the lever

I'm not really sure what you are getting at here.
 

thump chump

Member
Jun 20, 2001
76
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modulation

I can feel the clutch "pulsing." It like the point of engagement changes. Typically, the feeling of the clutch through the lever is very smooth, but in this case, it feels vague, sorta grinding, almost as if the clutch surges back and forth with the engagement, which translates to the feeling of the pulse in the lever. I hope that works- I'm not the best at visual descriptions. :)
 

yz250-effer

Member
Nov 4, 2000
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I would have to agree a little bit.

Originally posted by bashn
I don't know why your so obsessed with your top end. Tear it down down once a season for complete inspection. Replacing the piston once a season wether it needs it or not is good insurance against catastrophic failure due to cracking or hidden flaws. Personally, I think 5 hours is ludicrous.

Mark Boyd
'01 YZ267

I got a 4 stroke so I would not have to do top ends all the time. Personally, I have not seen any evidence that the 250F is more fragile than the 426 - and the success of the 426 is why I got the 250F in the first place. I guess the real question ( and time will tell ), is how long does a 250F piston last with x amount of hours? Assuming the oil and filter are well maintained, of course.
Heck, I put 50-60 hours on my 98 kx250 with no loss of compression. I would think a 4 stroke piston would last at least twice as long as a 2 stroke piston. Even at higher rpm and compression. Mine has 70 -75 non-racing hours on it so far, I think. I plan on a tear down around it's 1 year anniversary to check specs. The yamaha manual does not give an piston/ring replacement hour guideline that I could find. Just " as required". What does that mean? I know we are not talking about an xr here, but the 250F still gets great 4 stroke lubrication that a 2 stroke does not. Kind of a tootsie roll pop quesion. How many bites to the center? How many "normal" hours will the 250F piston last?
 

thump chump

Member
Jun 20, 2001
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hours

It all depends on how hard you ride your bike. In my 250 2-strokes, I have to replace the rings at least once a month, or every 4 races. If I don't, I can tell a big difference in my power. Keep this in mind, I ride 4- 20 min motos each weekend, at the pro level. I also go through clutch fibers in 6 weeks. I go through a lot of parts. I also have to replace my suspension fluid once a month. Or I can tell a huge difference.

With this in mind- I have seen several 250f's grenade. It is not a pretty site. I do not think that the reliability of the 250f racing at the pro level is even close to that of the 426. I rode the 400 in 98' and 99'. The only problem I had was with breaking clutches and baskets. However, I have seen the piston skirt of the 250f fail. The Yamaha owner's manual does state to replace the rings every 5 hrs of use, and inspect the piston. But for about $100, it just makes comon sense to me to go ahead and replace the piston. Preventative maint. Had I done a top end on my 2-stroke 250 earlier this year, I would be in WA right now. But I waited 2 months before checking everything. BIG mistake.
What I was initally looking for, were the pros and cons of using the different pistons available for the 250f. What I have learned in the past two days is that it will be awhile before Pro-X will be allowed to release OEM pistons.:(
 

GlennP

Member
Jun 6, 2000
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What some people may not understand is that there is more to the top end replacement issue than the wear factor. Wear doesn't break skirts, fatigue does. Clearances may be within spec, but the piston may be ready to let go. I used to ride/race Bultacos in the 70's, so I learned this from experience. Do a Bul top end now, or a whole Bul motor later! Same with the 250F now.

(Actually, sometimes it didn't matter what you did. Bultacos had mechanical suicide tendencies.)
 

thump chump

Member
Jun 20, 2001
76
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Bultaco-

You know, with the luck (or lack of) I've had this year, I would swear that my bikes were made in Spain! but I really think they were made on a Monday at 8:00 am or Friday at 4:30 pm........:think
 

DualSportr

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Aug 22, 2000
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The majority of problems I've seen in these situations have more to do with the mechanic than the manufacturer of the pistion.

Wiseco uses a cheaper forging than Arias JE or Ross. Also, the Wiseco piston is MUCH heavier than a forged piston from Arias, JE or Ross (yes, I know Wiseco and JE are owned by the same company, but the forgings they use from Alcoa are different).

If you want to talk properties and failure rates Rich, I'm not the person with the specs - call my boss or call JE and talk to John Noonan, or Ross and talk to Honda Jim they'll give you an earful.

For anything larger than 70mm, Wiseco pistons have excessive flex. If they are bored in large enough to account for that flex, then you have an engine running with excessive tolerances.

JE, Arias and Ross pistons can be bored in at very tight tolerances - .0015" for pistons up to 76mm, and .002" up to 100mm. This means longer life and better ring/cylinder grip.

Wiseco is a great option for a cheap rebuild, or for a race two stroke which needs to be rebuilt often.

There's very few techs who would recommend them for a four stroke application, or for ANY larger bore engine.

Regarding replacement rates on a race YZF 250 - in dyno testing, we've found 5 - 10 hours does start to show some signs of piston fatigue and wear.

This would indicate that a replacement in this time frame would be smart.

If you're someone who rpm's the YZF lots, also keep a close eye on the timing chain. If it's stretched at all, replace it. Timing chain failure has caused more damage on the YZF's than anything else we've seen.

BTW, Yamaha doesn't have any rods (or complete cranks) in stock for the 250 yet. Probably not for another 2 months!

The good news? we haven't seen any rod failures from regular use yet.
 

thump chump

Member
Jun 20, 2001
76
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PJ Posting-

Thanks for the info.

Timing chain huh? So it sounds like I should go ahead and replace the rings, piston, AND timing chain now! Oi! I need to go round up some more sponsorship! I was told that Pro-X won't have pistons for several more months due to the fact that they have an agreement allowing 1 yr for the OEM to sell first. So it appears that I will running stock, which I feel is best, just more expensive.
 

Rich Rohrich

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Originally posted by DualSportr
JE, Arias and Ross pistons can be bored in at very tight tolerances - .0015" for pistons up to 76mm, and .002" up to 100mm. This means longer life and better ring/cylinder grip.

While I'm a big fan of Arias and JE (never dealt with Ross) I've tracked the progress of a number of Wiseco bigbore YZFs and XRs set at similar clearances without seeing any evidence of a need to run them loose. The reliability rate that Eric Gorr has seen from Wiseco big bore pistons has been exceptional. Of course you have to keep in mind that these are being run in properly plated barrels that are correctly finish honed so that likely improves the reliability rate over some of the less desirable methods being used in some shops.

How EXACTLY are you guys measuring the "excessive flex" that you described? I'd be really interested in learning more about the methods used.

PJ - BTW, your package is on it's way :) It got buried on my desk . DOOOHHH
 

SFO

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Feb 16, 2001
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So Noonan is working at JE now?
I remember making gs1100/gsxr conversion cylinder studs for him when he was at Arias.
I have not had problems with weisco pistons since '76.
I was also 13 and had problems requiting the difference between tighten and loosen.
I can't believe people still muddy the weisco name, kinda an old school prejudice.
I have had excellent results with weisco in all of the motors I have built in the last few years.
There are other piston brands that I cannot report this level of succes with but I don't want to toss any more stones.
 
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