Piston questions

NM_KDX200 · Post by **NM_KDX200** » 02:02 pm Dec 20 2005

Alright, KDX people...look at these pictures of KX125 pistons, please:

From left to right: Wiseco, OEM, Pro-X

What is the function of the large ports? Note that the Wiseco has small round ports while the OEM and Pro-X have large blocky ports.

From the bottom, note that the Wiseco has a single hole for the piston pin lube, while the other two have two holes. I would think that two would be better than one, but maybe the single hole in the middle is stronger and puts oil on the pin better? Or maybe it doesn't make any difference?

Any other comments on the pistons? The Pro-X is obviously new, the OEM was used for a single AX season, and the owner of the Wiseco used Bel Ray MC-1 at 50:1. When I put a new ring on the current piston, it was very clean- looked like the Wiseco with the OEM top.

The reason I'm asking all this is because I've been using OEM and Pro-X in my KDX and going thru the perennial personal debate about "Which piston to use?" I'll probably stick with Pro-X. But I'm curious about the difference in the ports.

m0rie · Post by **m0rie** » 03:34 pm Dec 20 2005

Thats strange, i've never seen a piston with those ports before. Must be to improve cylinder scavenging? I bet the ports on the Wiseco are small because they hang over the cylinder (transfer?) ports and if you had a cold seizure could really hang up on the edge of the ports.

NM_KDX200 · Post by **NM_KDX200** » 06:19 pm Dec 20 2005

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m0rie wrote:Thats strange, i've never seen a piston with those ports before.

Here's a Pro-X KDX piston:

And BTW- anyone got a use for this?? As you can see, it's .050 oversize. Cylinder must be bored. I bought it on ebay a couple years ago and didn't check the part number. Mistake.

canyncarvr · Post by **canyncarvr** » 07:26 pm Dec 20 2005

Those aren't ports...they don't 'port' anything. I think..........

You're referring to the indentions, cutaways...whatever, right?

Still, good question. Ha! I don't know!! Something to do with heat (gives the piston someplace to 'grow' to?) I'd guess, although I'm looking at an RD (2-stroke Yamaha engine) piston that has no such indention on the exhaust side.

And the bottom Pro-X has 'em on the intake side.

Something to do with machining?

I've spent some time looking up piston design and such on the web. Haven't found anything that describes what the things are for.

m0rie · Post by **m0rie** » 07:38 pm Dec 20 2005

They struck me as odd because I don't remember them on my Wiseco KDX piston. I'd like to know what they are for as well.

NM_KDX200 · Post by **NM_KDX200** » 08:56 pm Dec 20 2005

canyncarvr wrote: You're referring to the indentions, cutaways...whatever, right?

Right. The whatchyamacallit things on the side of the piston that are often mistakenly called "ports" by pure spodes.

Them thangs....

Suction?

RBD · Post by **RBD** » 11:24 pm Dec 20 2005

Cast pistons like the OEM and Pro-X are a many piece mold (3 on the in side), allowing them to be made strong without a lot of weight (keeping strength and lightness).

wiseco pistons on the other hand are stamped (forged using only a single piece die) from a lump or piece of aluminum. A forging can only be stamped without a lot of divination in under cutting and shapes. So they will bore holes in the sides over the piston pin holes to lighten them (most of the time the weight is more than there OEM counter part)

Extra oils holes on the OEM pistons is normal and just helps with lubrication, the wiseco's are only drill in one place to cut production costs (note much older wiseco pistons use to be drilled in two places as the OEM pistons.

m0rie · Post by **m0rie** » 11:44 pm Dec 20 2005

Ron - Would the lighter weight of the cast piston make a difference in the performance of a KDX? Inda asked a question similar to this a while ago but I don't think there was ever a satisfactory answer given.

GS · Post by GS » 02:36 am Dec 21 2005

Hi Morie,
It sorta makes sense to me that any rapidly accelerating part, ie piston..pin..rod...would take less power to do just that if it weighed less? Or, put another way, wouldn't the engine be able to built revs quicker?
At my level of riding I think a small difference in recipricating weight would be hard for me to notice........just my 2 cents

Post by **Indawoods** » 08:37 am Dec 21 2005

I was under the impression that the Wiseco KDX pistons were considerably lighter and stronger than OEM.

My spare bike has a Wiseco in it and it raps faster and higher compared to my Pro-X pistoned KDX.

KDX220PHIL · Post by **KDX220PHIL** » 08:56 am Dec 21 2005

I would think compression would play a bigger factor and weight very little.

Forging (pressing the metal to shape) should result in a stronger piston becasue the metal does not have to be heated to the extent it would when it is cast in a mold. When the metal cools down from being cast it forms grains ( that surface you see on cast objects) that reuslt in poor ductility.
When a metal is forged it tends to bend easier than it does break, casting is just the opposite. Forging will result in a stronger surface as well unlike machining.

So I would think the Wiseco would be the strongest of the bunch.

IdahoCharley · Post by **IdahoCharley** » 11:38 am Dec 21 2005

I believe KDX220phil is "on the mark" on both the wrist pin and piston construction.

When Wiseco prolite pistons first came out I know a few people on the KTM forums and sled forums were comparing the wiseco piston weights to OEM piston weights and determined that indeed - wiseco's claim of a lighter piston was true.

I do not know of anyone who has compared the weight of a KDX OEM piston verses a Wiseco piston but I'm betting some will soon and hopefully post their results in this forum.

Quality forged pistons IMHO are better pistons (than quality cast pistons) provided that you are deligent during break-in and warm-up your motor prior to running it hard. This is due to more of the piston material molecules being in a specific alpha/beta phase.

I don't know about the relative factors concerning compression verses weight. But certainly less recipating weight on the rod will allow the engine to rev up faster all other things being equal. Also should not the lighter piston result in less stress on the connecting rod and crankshaft?

NM_KDX200 · Post by **NM_KDX200** » 11:53 am Dec 21 2005

1) the KX125 pistons are weighed and they're marked on the pistons in the photo. The Wiseco was 10 grams lighter- 150 gm vs. 160. that's less than 10%.

2) a lighter piston would rev faster, but it will also de-rev faster, will it not? Thus, less "torque", less of a flywheel effect. I'm not sure I'd want that on my KDX.

Still haven't decided if I'll stick with Pro-X or try Wiseco on this piston change. It probably doesn't make any difference, all things considered. Call me anal, but I like the fact that Pro-X offers A, B, C pistons.

KDX220PHIL · Post by **KDX220PHIL** » 12:23 pm Dec 21 2005

"a lighter piston would rev faster, but it will also de-rev faster, will it not? Thus, less "torque", "

I would think so, but I doubt 10 grams will make much difference. Theoretically, more momentum with the heavier piston. So with more mass, more inertia it would take more force to slow it down, resulting in more torque.

Being the owner of a 220, I would prefer the Wiseco, as the Pro-X appears to be a rip-off the oem piston. I like the idea of a stronger piston that is less susceptible to wear and the peace of mind of a quality forged piston.

Post by **fuzzy** » 12:55 pm Dec 21 2005

Call me anal, but I like the fact that Pro-X offers A, B, C pistons

That's really why the wiseco needs to warm up more as it's more like an 'F' piston. That being said it will have the tightest clearance on just about any cyl. This 'extra tight' clearance is still in spec, but you certainely want a good warm-up. This is also why it makes more power. To make the most power you want to run the least amount of piston clearnace you can get away with witout sticking it....

GS · Post by GS » 01:04 pm Dec 21 2005

Now hold on there.....that piston comes to a stop at BDC as well as TDC. So how can this add to the flywheel effect? Takes more energy (if it's heavier)from the who shootin' match to get it back up to speed each time it stops. Reciprocating vs. rotating mass, which would be trying real hard to maintain its rotational speed(energy) in the absence of forces that were decelerating it.
...am I wrong here?
Greg

KDX220PHIL · Post by **KDX220PHIL** » 01:22 pm Dec 21 2005

Aha, now that I think about it, you're right!

No flywheel effect for sure. And actually, I bet that a heavier piston results in less torque. takes more force to bring it up to speed, takes more force to change directions.

RBD · Post by **RBD** » 02:43 pm Dec 21 2005

Oh Boy......

Well it looks like I hit the old Hornets nest with a stick by giving my opinion on this subject. I have been an engine builder and machinist for over 35 years and was giving my opinion on wiseco and OEM pistons.

In the past wiseco pistons did not have the hole drilled above the piston pin hole and the machining on the inside of the skirt (which made them extremely heavy). Then they started to drill the extra holes and called them Pro-Lites and made you pay more for them (the way they should have been made from the beginning). Now wiseco only makes pro-Lite pistons (at least the ones I use on the engines I build).

Someone said that cast pistons have a grain to them...... well maybe if you want to call it a granular structure, but it has no grain to it like a piece of wood, it is more like the structure of concrete. Also note the OEM pistons use a three piece mold on the inside of the piston to under cut and rib the piston pin boss to the under side of the dome. You could never do this with a forging

Now for the wiseco's, it defiantly has a grain to them (like wood). The piston is made from a solid disk blank and then it is put into a die and under tremendous pressure and formed into a piston. This process creates tremendous heat (almost to a molten state).

This is something to think about, that forged piston has a definite grain and has a memory of the original shape. I believe this is why the engine had to be warmed up slowly as these piston distort and expand unevenly, it also has to do with the extremely thick top of the piston.

I am not recommending one piston over an other, but as an engine builder and machinist I do prefer the OEM cast pistons. Wiseco are ok and you can cut all kinds of port windows in them and make the main intake window much larger.

AGAIN....., this is my opinion and 30 plus years in the business

GS · Post by GS » 02:58 pm Dec 21 2005

Thanks Ron...I am certain that everyone here really appreciates your opinion and experience.
Much thanks!!
Greg

KDX220PHIL · Post by **KDX220PHIL** » 03:07 pm Dec 21 2005

Sorry I was refering to a grainy surface, I meant rough. A sharp, rocky surface, that could potentiallly cause a break.

Ron, the tremendous heat you speak of when forging, i was under the impression it was not hear as hot as the temp. the metal must be heated to when being cast (molten).

Wouldn't cooling down from a higher heat result in poor ductility?
What about the density of the piston, would it not be denser and therefore stronger?

I do agree with the grain on forging and that the piston could expand and distort unevenly, but I thought the OEM cast pistons are not as strong, less ductile, with week spots all along the surface and maybe this is why many people have had them blow up in their 220's?

Thanks for your input

*EDIT* I'm not trying to start anything, i really do appreciate your input and I am KNOW you have far more experience and knowledge than I do on the topic. 30 Years, wow, thats longer then I am old!!!

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Piston questions

Piston questions