interesting topic on offset pins http://www.motorcycleproject.com/motorcycl...ows-offset.html

the flat head fords in 1951 had offset pistons

here is a link to a 1954 chevrolet truck manual talking about pin off set.: http://www.1954advance-design.com/Document...rig_Page46.html


I still can find no referance to balancing pistons but by all means if you can remove extra material from a piston weather intake or exhaust side i would remove it for a faster revving motor.

 

QUOTE(C-Leigh Racing @ Nov 22 2010, 07:42 PM) index.php?act=findpost&pid=52581In a round about way trying to understand all things, what we might be forgeting is the fact, does Wiseco, Wossnor, Pro-x, Art Sudco, any of the piston MFGs want to make a piston that would last any lenght of time by,,,, balancing them, stress releaving them, heat setting them, like they should be doing in the first place to justify the outragous prices they are charging for them. I dought it very seriously.
Neil

Neil you bring up a good point…!

Not trying to defend any of the piston manufactures, however; I will play devil’s advocate and say the problem of cost (in my opinion) comes from numerous issues. The first and most obvious one is lack of quantity being produced & sold. If piston manufactures would sell thousands of 250R piston kits a year instead of a few hundred, costs would go significantly down, the competitive market economics would drive prices down and quality up.

The nature of high performance pistons dictates the need for special high Silicon content materials, these materials are in limited use to specialized industries such as high performance engines. Only 2-3 sources exist for High Silicon Piston material world wide, MAHLE being the primary source for most pistons being manufactured (Wossner) outside of the Wiseco product line. Again; as long as sales are limited to a specialized end use like ours, material costs will remain very high.

The processing of these materials is governed more and more with unreasonable regulations that impose higher and higher costs on manufacturing; the result is the end user, in this case us, pay the “outrages prices” as you clearly stated.

The answer to lower prices is beyond our capability & control; like most things in life, we are victims of our own surroundings and have very little influence to enact any meaningful change.

Carlos.

 

In a round about way trying to understand all things, what we might be forgeting is the fact, does Wiseco, Wossnor, Pro-x, Art Sudco, any of the piston MFGs want to make a piston that would last any lenght of time by,,,, balancing them, stress releaving them, heat setting them, like they should be doing in the first place to justify the outragous prices they are charging for them. I dought it very seriously.
Neil

 

QUOTE(All250R @ Nov 22 2010, 11:47 AM) index.php?act=findpost&pid=52546Carlos, do you have any data/findings regarding the weight effects of material removed for a boost port, or are you just suggesting a common sense approach? Obviously, the effects are going to depend on other characteristics, so I wonder what situations it's more or less important in that you'd want to weigh out, if you have that data.

Otherwise, yea, it seems like maintaining balance couldn't hurt unless you introduce another issue by removing the material, of course.

Real data or documentation, NO.

I don't believe even Wossner, Wiseco or any of the major piston manufactures can provide reliable data to support a balanced piston either. Nor do I believe any data or documentation exist to support the 1MM wristpin offset, yet; all modern day piston manufactures have some amount of wristpin offset built in; usually .8MM-1.1MM. Wossner and I believe Wiseco as well go to great lengths to follow a "balanced" piston approach when possible, just look at the latest Wossner's and how they have machined the inside of the piston relative to the location of the piston port window…

If we understand that not all innovations are a result of precise Research & Development, we can begin to realize supporting data is not necessarily easily available and sometimes not desired due to the added expense incurred to document. Sometimes, "if it works, leave it alone" is good enough…and in worse cases; major manufactures do not want ANY data to be found in engineering CE or Technical History files that may allude to an issue or problem in a design or product.

In reality, none of us can present reliable data and neither can most small to medium size manufactures, and those few that can, choose not to do so because of the associated expenses. Those that do, usually present flawed data or data doctored to support the product they are selling. Real, reliable, true data can only be achieved when all variables are accounted for, all equipment calibrated to a known standard and in a lab setting. Shop data is basically useless…

As an example; most will believe the offset .8MM-1.1MM wristpin we find in modern day pistons is a result of brilliant dedicated engineers, developing a great new innovation, yet that was not the case. The offset wristpin is the byproduct of a manufacturing error. As the story goes; hundreds of pistons were produced with a wristpin hole drilled & bored exactly 1MM off center by mistake. These pistons shipped and saw usage out in the field; reports came back saying how much better this particular lot of pistons performed than any previous lot. After much testing, it was determined the wristpin had been drilled in the wrong location by 1MM…It was after the fact that engineers determined WHY the pistons with a 1MM offset wristpin performed better than a centered wristpin. It was then determined that an offset wristpin allows the piston to "roll" from full velocity to zero velocity at TDC & BDC ("softens piston shift"), thereby; reducing reciprocating stress, side wall forces and allowing for lighter pistons to be designed. Hence; modern day piston designs incorporate "offset" wristpins…

So unless we are willing to spend tons of time, money and resources, common sense is our best alternative. Keep the pistons designed balance platform, if you remove material from one side; try to remove material from the opposite side without weakening the piston to the point of failure…

Carlos.

 

Carlos, do you have any data/findings regarding the weight effects of material removed for a boost port, or are you just suggesting a common sense approach? Obviously, the effects are going to depend on other characteristics, so I wonder what situations it's more or less important in that you'd want to weigh out, if you have that data.

Otherwise, yea, it seems like maintaining balance couldn't hurt unless you introduce another issue by removing the material, of course.

 

Rss396:

You are correct trying to “balance” a piston if you’re not a manufacture or an extremely good builder is very difficult. That is why I suggested weighing the piston prior to cutting any port window, recording the amount of material removed and removing an equal amount on the opposite side, in this case the exhaust side. We are trying to keep the piston within the designed “balance” the piston manufacture intended.

Note modern day pistons are manufactured with an offset wristpin, anywhere from .8MM -1.1MM depending on the manufacture and application. This out of center condition reduces shock, reciprocal stress and softens piston shift at TDC and BDC relative to the rod. The offset wristpin location places the piston at a slightly different location than the top of the rod, it also shifts weigh slightly to a different “balance” point than if the wristpin was dead center of the piston.

It is this “balance” we want to keep when adding window ports or removing weight from pistons. Piston manufactures go through great lengths to design and improve piston performance. It only makes sense to try to keep that “balance” as it was designed and manufactured.

Carlos.

 

??? that a 265 & you got to go from the 68.25mm to the 68.50 or hes got to go from 68mm.
If the old model TRX piston is used, the Wiseco will have the window. If it is the YZ250 or late model flat top CR250 piston in it now, it probably wont have the window.
Neil

 

cons
shorter piston life. the port will start cracking and the piston will break, eventually. somewhere around 45 hours you need to pull the reed cage and check it. every 20 hours or so after that. its alot more prone to fail as the bore clearance starts getting higher

pros
supposed to allow more volume to be induced into the crankcase quicker. better low-mid, off idle response.

I've ran ported and non-ported pistons, I cant really tell any difference.


it just depends on what you are after, some guys run race fuel, change pistons every 60 hours, real mainentance/jetting intense - always after that last 5-10% of added performance. if thats you, then get the port.
I run pump gas and like to go a couple years on pistons, so no port for me.

 

I can't say I have heard of anyone balancing a piston from front to back.

I think it would be pretty hard to do the 86 style piston with its large cut away.

Plus I don't think it matters because the piston's side thrust will over come any small amount of weight imbalance.

But I have been wrong before so please correct me if I am wrong

 

QUOTE(ceaserthethird @ Nov 21 2010, 03:03 PM) index.php?act=findpost&pid=52460Took my LRD PV Cylinder over to LED for Hone & piston kit.

Turns out It will need a Bore ~ 69.50mm & Wiseco piston

LED Recommended to - BOOST Port the Piston.

What's the Pro's and Con's ?

Adding a piston boost port will help keep your piston running a little cooler as well as provide additional lubrication to the wristpin and upper rod needle bearing area. It will also improve intake flow to an extent if flow was an issue to start with. It will also reduce reciprocating weight and therefore; theoretically allow the engine to rev quicker and possibly higher. As part of an overall porting & flow package, piston port window sizing & location will help direct flow were it needs to be, however; I don't see how just cutting a window port will help; it won't unless you get extremely lucky and "hit the sweet spot"…

The trick is not to just cut any window at any location on the piston; normally you will want to position the piston port close to the bottom ring grove, however; not so close as to weaken the bottom ring grove itself.

If a window port is added to the piston, the piston should also be re-balanced. Weigh the piston prior to cutting the port, and then remove an equal amount on the opposite side (exhaust side). This will need to be accomplished by thinning the piston wall from the inside on the exhaust side. Re-balancing your piston, will dictate the size of your piston port, you cannot go to thin on the exhaust side. Start with a small piston port, and then see how much you can effectively remove from the exhaust side and adjust port window size based on the equal amount of weight you can remove from the opposite side.

If done correctly, it takes a bit of work since piston wall thickness varies from brand to brand, era of manufacture and bore size. The question then becomes is all the time and effort really worth it…?

In my opinion, unless the addition of a piston window port is combined with re-balancing the piston and part of an overall porting and bench flow package, it is not worth the effort and you will not see a noticeable performance gain. Your time and $$$'s may be best spent in other performance gain areas.

PS: Note that on properly designed and manufactured pre windowed pistons such as found on Honda, Wossner or Wiseco (to name a few), the piston window port weight reduction has been compensated on the intake side (side the port is on) with added material, so as to keep the piston balanced and reduce the amount of material that is needed to be removed from the exhaust side.

Carlos.