This is why you don't run a CAST piston

[quincyman]

I have been riding the same KX500 for 10 years. I am not trying to avoid legitimate maintenance. I have only fried one piston and that was my fault not maintenance issue but rather carelessness after doing carb work. I failed to tighten the airbox side clamp and it sucked air. Boy did it run nice until it seized.

I generally ride by the seat of my pants. I can tell if the bike is starting to lose power and not run up top par. That's when I change pistons. Usually that is a lot more than 50 hours. I have never run a cast piston before, which is why I was asking questions.

I believe there is such a thing as needless maintenance for a recreational rider. We don't put near the abuse on a bike that someone who races regularly or spends a great deal of time in the sand. I don't race and only do sand when it is a part of the ride (not a big dune rider).

I know KX500 riders who are running the same piston after 5 to 8 years of ownership. I doubt they ride near as much as me. I ride every week all year long unless deep snows prevent me. But that riding is now shared between 5 bikes. There was a time when the KX500 was my only ride.

When I saw those pictures and the caption that cast pistons do this I became concerned because I have just installed my first cast piston. If it is the very nature of cast pistons to break apart then I don't plan on running one for too long. But I put the money out and didn't want to panic for no reason. Hence the question.

I put out more money keeping my 5 bikes running right in a year than most do in 5 or more years. So I just don't want to be installing a new piston for the sake of it rather than need. Kinda like the guys who change oil after every ride. 9 times out of 10 that is needless over kill but certainly will never hurt their bikes by doing so. And if you can afford go for it.

I will pull my piston after 50 hours just to check for the hairline cracks. I suspect that is the only way I will find out what I want to know. It sounds like that will be the wisest course of action.

[maddoggy]

i find it's better to maintain your bike rather than repair it after a failure. maintanence is almost always cheaper than repair. you guys have alot more years experience on a bike than i do so if you are unanimously against cast pistons there must be experience talkin'. i'll heed the advice and steer clear of the cast. thanks for the info.  MADDOGGY

[Friar-Tuck]

 Doggy, BDI, and all
 I think sometimes reading and typing online doesn't always come across as intended.
Sometimes its a blatent shot at some one and sometimes what I type and what someone else reads may be quite different.  I would have to think as someone earlier stated where and how a person rides, terrain, money avail to spend, amount of hrs. on the bike  and how their equipment is maintained surely must be a factor in the longetivity of the components.
  I think 99% of us are here 'cause we just plain love to ride.

  I'm sure we all might not agree on much more than that, but heck thats not all that bad, is it??    Please keep coming by and chiming in, lots of guys like me learn more on a few bike forums like this one than spending gobs of money on magazines or the places where it seems flaming and starting fights online is more important than sharing information or hooking up a place to ride.
 I don't have an old school machine/bikeshop nearby to hang out at and riding time seems to get harder and harder to come by.
  Cast v Forged   Ford v Chevy  Kawasaki v Honda  Synthetic v Standard
     Competition; its everywhere, and probably what keeps us all on our toes to try to get a little better.   
      Take Care,
 Tuck \o/
       

[quincyman]

I'm sorry for being rude I'm begining to wonder why I answer questions on hear. I try my best to pull from 25 years of expeirence and I'm not allways right. I have blown up bikes in every way possible and I have made very expensive mistakes learning a lot of things the hard way. I agree lots of people change their oil to much. It Is hard to over maintain a bike. I ride the hell out of my bikes and they have to be maintained at a race level, can your filter be to clean or perhaps your chain could be adjusted and lubed to good. maybe 50 hours is not the right amount of time. Ride your bike every weekend for a year then check it and then at that point you should start checking it every time you ride because catching them with cracks is luck. Usually your engine will look like the ones in the pictures you see on this post soon after they develop cracks. you could have cracks you can't even see without magnafluxing it. If you want to run your bike until the piston and rings are worn out to the point the bike does not run good any more thats your deal but if you don't want the whole engine to grenade and cost thousands of dollars to fix use a forged piston. P.S. thats 50 hours of engine run time you can go riding all day and only log three hours on your hour meter three hours at 35 mph is 105 miles

I do pay attention to what people write on these lists. I also try to evaluate where the rider is at in experience. Sometimes people spout what the hear and not what they know (which can also help if what they heard is the truth).

I took seriously this issue about the cast piston and am glad that folks are willing to add information to the thread. Through the years I have made my riding experience much more pleasurable buy reading these lists. Often catching things before they happen cause some one brought it up in a thread and 20 other serious riders jumped in to share what they know.

I am not a bad mechanic myself but am well aware of the fact that my knowledge has come from the school of hard knocks. When your education comes through hard knocks there are usually important gaps in what you know that a professional takes for granted when he works on a bike. Being aware of my own ignorance keeps me from getting to set in my ways about things.

I guess what I am trying to say is thank you for taking the time to discuss this issue.

[Polar-Bus]

Well, i've owned 9 new KX's since '83, and run countless stock cast pistons in every one of em', and never had a cast piston "granade fail". I've lost 1 crank (completely my own fault, sucked some sand), and lost 2 top ends, one from a blown base gasket, and the other from ? (never really figured it out). Both top ends were easy repairs. I hear a lot of pro's and con's to Wiseco's, but in my opinion, when something works so reliable for over 20 years (cast), i'll stick with them.....

[don46]

When I saw those pictures and the caption that cast pistons do this I became concerned because I have just installed my first cast piston. If it is the very nature of cast pistons to break apart then I don't plan on running one for too long. But I put the money out and didn't want to panic for no reason. Hence the question.

 

Just so we're clear, you say you have just installed your first cast piston. Stock pistons are cast, Wiseco are forged. With 5 bikes, I think this was a misunderstanding becuse surely you've changed pistons before now and if you've used stock, then you've used cast. For my money it's only wiseco, both 2t and 4t.

[quincyman]

When I saw those pictures and the caption that cast pistons do this I became concerned because I have just installed my first cast piston. If it is the very nature of cast pistons to break apart then I don't plan on running one for too long. But I put the money out and didn't want to panic for no reason. Hence the question.

 

Just so we're clear, you say you have just installed your first cast piston. Stock pistons are cast, Wiseco are forged. With 5 bikes, I think this was a misunderstanding becuse surely you've changed pistons before now and if you've used stock, then you've used cast. For my money it's only wiseco, both 2t and 4t.

When I purchased my 1994 KX500 it was 3 years old. It had a Wiseco piston in it. I replaced it with a Wiseco everytime I did the work. Which was 2 pistons in about 8 years. But this time around I installed a newly replated cylinder in the bike. The folks who did the replating recommended stock pistons (Cast) because of closer tolerance. They claimed greater longevity if the bike is taken care of properly. So I went ahead and let them order a stock piston for the cylinder.

Then I happened to be browsing this list and I saw this thread and the pictures. I now became concerned if I had done the right thing. Not knowing if this was a trait of Cast pistons or if the fellow who blew the piston was to blame I started asking questions. My hope was that this was unusual. I still don't know the answer to that question but enough doubt has been placed in my mind that I will be monitoring this new piston closer than I ever did with any of my Wiseco pistons.

Since I have been asking questions I have found that there are those who adamantly will argue on both sides of this issue.

My bike is running great and I rarely ride in such a way that much stress is placed on the piston. Trail riding is very slow compared to desert. I do ride the KX in desert from time to time but mostly on trails. I will most likely put 1000 miles on the KX this year. It shares riding time between 4 other bikes. I will tear it down and put the magnifying glass to it after 1000 miles.

The only other 2 stroke I own is a 05 KDX220. I replaced the stock piston in it with a Wiseco immediately after talking with Fredette racing. Fredette racing claims that only the 220 needs it's cast piston changed out because the skirts will break. He says the KDX200 stock pistons do not have this problem. So according to him it is not all cast pistons. Here are two bikes that are identical except for the bore and porting.

When my four strokes start wearing out but are still running good I sell them not rebuild them. Or I trade them in on a newer model. I have never had a stock piston go out of a four stroke.

[Brett]

With the process of forging the material has to have reasonable flowing qualities and therefore means are eutectic in composition (roughly 12% silicon) This material spec has a higher coefficient of expansion compared to hyper eutectic (16-18% silicon) so therefore has to be set looser when cold to allow more room for temp growth when getting to operating temp.  Cast pistons are more often than not hyper eutectic, so run tighter tolerances and have less slap when cold.  Hyper eutectic pistons are less ductile then eutectic, so when worn and having excessive clearance are more likely to break than eutectic.  But hyper eutectic pistons are much harder wearing due to higher silicon content so will last longer and provide ring seal for longer.
Ok so thats the material comparo, now for structure/design.
Now we are talking two strokes only ignore anything you have heard/know to do with fourstrokes as fourstroke pistons are of completely different design and this design lends itself extremely well to being forged.
So think of the forging process as having a bowl and a lump of playdough in the middle now push your fist into it and the dough flows aroung your fist, now remove your fist and you are left with the dough formed into shape.  The major limitation of the forging process is that the die (fist) only gets pushed in and removed from one direction severly limiting the designers ability to have webbing and the like to give it structural integrity.  Now a casting die set is generally made up of 3 or 5 core inners, they are clamped together and the melt is cast around it.  Then in the case of a 3 piece core set the innermost section of the core is removed, the one of outer-inners if that makes sense is slid across to where the middle one was then removed and same goes for the remaining outer-inner core.  Then the 2 piece die set is opened and out comes your piston casting (with riser and ingates still attached.  The casting process allows the ability of undercutting pin bosses and creating intricate webbing design.
Now due to my bike having a LA sleeve i am stuck to using wiseco (as wossner dont make em) and from my experiance they collapse (no not break they are ductile but the out of roundness which should be greater in the thrust direction changes to being greater in the pin axis direction) I believe this is due to the piston being quite big with no webbing to speak of at all and being af a more ductile material.
So in summary i recommend using a cast piston ie stock or pro-x, vertex whatever.
If someone could take a photo of the inner of both a cast piston and forged for comparo it might be better understood than my ramblings.
Oh and while your there chuck a micromoter on your old pistons and post the out of round.

[BDI]

Basically what you are saying Is when a cast piston reaches the end of It's life cycle It breaks and when a forged piston reaches the end of It's life cycle It becomes deformed? How do you feel about cast pisons In boosted or high compression aplications my bike Is 15:1 and I run Vp cmp oxygenated fuel should I use cast or forged? I looked all over and could not find a cast piston to take a picture of  but I did have a forged wiseco piston so If any one has a cast piston for comparison here is my picture. 
                          P.S. out of round Is 0.05