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Wiseco Pistons Vs. Oem

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I recently did the top ends on my sons 2005 yz125 and my yz250. I replaced both with Wiseco pistons. Several older veteran riders we ride with say I should have used oem pistons. We mostly trail ride and my son does race some hair scrambles. Which piston is better from everybodys past experiences? Thanks

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Wiseco! Wisco pistons are forged, and lighter, Stock are a weaker cast piston.Anybody who tells you stock cast pistons are better than a nice strong forged piston, really doesnt know too much about pistons.

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Forged slugs cold slap there asses off, then when they get warmed up there ok. OEM have tighter tolerances than a off the shelve weisco. I always use OEM pistons, haven't had a problem yet. Weisco would be a good choice if your going to punch out your cylinder to match it with a new piston. If your just going to do a standard top end job, just order 1 size over piston. O and i know a lot about pistons, Forged are exactly the best buddy.

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Forged slugs cold slap there asses off, then when they get warmed up there ok. OEM have tighter tolerances than a off the shelve weisco. I always use OEM pistons, haven't had a problem yet. Weisco would be a good choice if your going to punch out your cylinder to match it with a new piston. If your just going to do a standard top end job, just order 1 size over piston. O and i know a lot about pistons, Forged are exactly the best buddy.

Pretty much everything he said

Weisco is a great piston but.

Does seem to fit a little looser than a stock.

Can have some slap when cold.

Seems to put more wear on the cylinder than a stocker will.

Is great if your having your cylinder punched and having it matched to the piston.

Stock is the way to go on a stock bore.

Stock will put less stress on the cylinder.

Fits tightly.

Just feels right.

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You guys are killing me... I have YZ 250 cylinder size C. Just ordered a Weisco kit... now ya'll got me scared! I understood that the size differences (A,B,C,D) were like 40 ten thousanths and just not a problem. My understanding was that you have to warm the bike up better with a forged piston so you don't have a cold sieze. Other than that I was under the impression that the Weisco would last a lot longer, never break a skirt and was overall just a better piston. Never used one though and I don't want any slap or rapid wear on the cylinder!! Do I need to cancell my order? :censored:

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If you can cancel, go ahead...

If not, no big deal. A weisco wont hurt. I mean its a great piston. Its just that its not as good for the stock cylinder as much as the stock piston is.

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I love Wiseco pistons. I started using them after I picked the LAST OEM piston out of the bottom end of our cr 80. The cast pistons tend to break apart when they are ran too long. The forged stays in one piece and I like that.

Team Yamaha used a forged piston in their YZ 250. Team Suzuki used the Wiseco 808MO6640 in RC's championship winning RM 250....it takes the same piston as our YZ 250's.

I have the RC piston in my bike a tthe moment. Its quiet. No extra noise. It is also lighter than the stock cast piston. Before you swear off forged pistons, try one of these. TT store is a great place to order the pistons (any) from. Quick delivery and a discount. Most everywhere else wants full retail for this piston. I had my special order Wiseco in two days. Who said there were no benefits in living close to Vegas????

I think they are all decent. I am suspicious of that Namura Tech thing sold on ebay, but have no reason to be so.

Try them all and make the decision for yourself. No harm as long as you replace any of them on a regular basis.

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You guys are killing me... I have YZ 250 cylinder size C. Just ordered a Weisco kit... now ya'll got me scared! I understood that the size differences (A,B,C,D) were like 40 ten thousanths and just not a problem. My understanding was that you have to warm the bike up better with a forged piston so you don't have a cold sieze. Other than that I was under the impression that the Weisco would last a lot longer, never break a skirt and was overall just a better piston. Never used one though and I don't want any slap or rapid wear on the cylinder!! Do I need to cancell my order? :censored:

No, dont cancel. Try it for yourself. Really, I would have recommended one to you. The other guys do have valid points....I would never say a word to discredit them. I value their opinions.

This bike is easy to work on. The entire job takes a few hours if you go slow. Try it out and report back to us.

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No, dont cancel. Try it for yourself. Really, I would have recommended one to you. The other guys do have valid points....I would never say a word to discredit them. I value their opinions.

This bike is easy to work on. The entire job takes a few hours if you go slow. Try it out and report back to us.

Alright..Im curious enough to get it and I'll let ya know what I think- just had a little panic attack! Ha... One question though, can you enlighten me on the heat cycles needed to break in? I know how to break in the OEM but this will be the first time with the forged piston.

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Alright..Im curious enough to get it and I'll let ya know what I think- just had a little panic attack! Ha... One question though, can you enlighten me on the heat cycles needed to break in? I know how to break in the OEM but this will be the first time with the forged piston.

I would just do the same.

By the way... I have broken some skirts off of weiscos too. Guess any piston will break if pushed past it limit or if something ant right.

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if the cylinder is a C then order a size D piston, then after that bore out the cylinder match a weisco or sleeve it to match a A piston and so on and so on. Its apples and oranges when it comes to pistons. Yamaha and other OEM companies know what there doing when it comes with internals so i trust them. Everyone thinks that aftermarket is the best in the world, when the OEM is just as good. People get a new bike, dont even ride it and throw on pipes and other garbage, when in fact the bike is fast as hell out of the crate.

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I think any of them can break as well.

Lots of people heat cycle the new pistons. Ed, from Wiseco, said thats not really necessary anymore, but do it if you feel better in doing so.

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Now I have replaced a few pistons in 4strokes and 2strokes. like at least a 100, its my job :censored: so I'd like to throw in my 2 or even 3 cents. Weisco seem to be an ok piston but they need extra clearance than factory spec or they have a tendency to seize, actually even a little more clearance than weisco writes on the box. Oem pistons tend to last a little longer and are made to a much higher tolerance than weisco. meaning if you took to identical pistons and measured them, how close the sizes are.

Any piston will crack and break if you use it to long, it will slap in the bore and fatigue the skirt until it falls off. also note 90% of all oem japanese pistons are made by ART so they kind of know what they are doing. so for me its OEM or Pro-X they use ART pistons. unless I want a big bore/high compression piston. and for 4-strokes I would go with a JE forged piston theyre badass. 4 stroke cylinder heads are too expensive to go cheap on the piston.

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KLX, that sounded good until the last line. Did you check into who owns JE pistons?

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So, is it common to get piston slap with a Wiseco piston? I have only ever used OEM but have been wanting to try a Wiseco piston. I have a D cylinder.

Is it common to get piston slap due to lower tolerances and if so is it only when cold before the forged piston expands?

Will I have to replate/bore my cylidner much sooner because the Weisco is harder on it?

Thanks guys, jus curious as I have never tried them..

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I've been using Wiseco pistons for 20 something years and have never had a problem. I've never heard of one cold slapping either, but i'm not going to say it doesnt happen. Anyways, Wiseco makes a quality product and I have never been disappointed with them.

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Why the heck do I do this to myself??:censored: But here goes anyway.

Disclaimer......I am in no way connected to any OEM company nor do I sell OEM parts any longer. I do not hate aftermarket companies as some might think nor do I take pleasure in discrediting the good company, Weisco. I might add that at this point in our race program we do use Wiesco products.

Now, there is absolutely nothing wrong with using either stock or Wiesco pistons in your bike. The thing is, I never liked the one size fits all deal that Wiseco offers for one thing and the other is the fact that you need to spend some extra time in the warm up period before you go blasting off down the trail. Proper warm up is necessary with either OEM or Wiesco but more so with the latter. I'm not talking about just the break in period, it's every time to start the cold engine with a Wiseco in it you need to let it come up to temp before screaming off down the trail or a cold seized piston is a possibility. That can be as much a problem as picking the pieces of an OEM piston out of your bottom end that should have been replaced the season before.

Now a cold seized piston is not Waseca’s fault nor is it the fault of the OEM's that you ran the bike beyond the point that it was designed to go. OEM's use these type pistons in stock bikes for a reason. Whereas you would think that if the Wiesco or other aftermarket pistons were so much better the OEM's would use them instead. OEM's don't just use cheap stuff in their bikes to make more money, they use certain parts because they are best suited for the what the engine was designed for and so they can do this at a price people can afford to buy. If they were to put out a bike that had the high dollar RG3 triple clamps, the extra thousand dollars we spend on suspension, Fasst bars, $900 wheels, ported and polished cylinders the bikes would be too expensive for people to buy.

Yeah, if you let your stock top end go for 3000 hours, yeah you are asking for trouble. But the same can be said for the aftermarket pistons also. That's the problem with the stock pistons in that they will hold compression longer and run so they are easier to neglect and end up with a piston skirt coming apart from neglect. With aftermarket pistons, Wiseco in particular, they will start to lose compression and power once they have reached the end of their lifespan. The thing in the stock bike where people just use their bikes for fun it's not really about the strength of the piston the OEM's are after. It's giving the people that buy these things something they can ride and enjoy for years to come at a price they can afford to pay.

You still have to maintain the bike no matter what is in the cylinder. The cylinder and parts are wear items just like tires and spark plugs are. They wear out and need to be changed over time; you wouldn’t run your bike with a tire that had cords sticking out the side or with no knobs on it, would you?

You can see the tire needs changing but you can’t see inside the cylinder so you keep running it til it blows the skirt and destroys the cylinder and then they want to blame the OEM piston for letting them down. The Wiseco pistons just lose compression after awhile and then it becomes obvious that service is needed. Which I guess could be a good thing, especially if you are one that neglects the proper service intervals in which you service your bike.

With all this said, no, if you put a Wiseco in your cylinder it’s not going to blow up your bike. Just warm it up good before you go off to the trail. They are good pistons and give you good service.

A good rule of thumb to go by is if you don’t race the bike and your riding is just trails and knocking around you would be better off keeping it stock. You will ride longer between piston changes, how long depends on a lot of factors like fuel type, oil you use, rpm you run, general maintance, etc. The cylinders are lettered and when you replace the piston, replace it with the same piston that is stamped on the cylinder and in most cases you are all set. You still need to measure the bore dimensions to be sure and also check the ring end gap before you close it up and then ride. Don’t get cheap and try to get by with just changing out the rings. That is just not good shop practice and it will cost you in the long run.

Wiseco is a good choice if you run the bike to its limits. On the track in a competition situation you are already doing piston changes every 10 to 20 hours anyway and in that respect it would be cheaper to go with the aftermarket pistons. Again, this comment is not intended to trash Wiseco but here goes; that is the main reason we use Wiseco pistons in the race bike. They are cheaper than OEM, and, we are forced to do top ends every 10 or 12 hours and that ensure we keep the catastrophic failures down to a minimum. Once the pistons get that many hours on them they just start to go away and get weaker by the lap so we have to change them out often.

Aftermarket or stock they all have their place and both have their ups and downs. You have to decide what’s best for your application. I have tried to give both sides of the equation with what I have written without it turning into a pizzing match. Either way you should be ok.

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