standard piston question

kdxquebec · Post by **kdxquebec** » 02:30 pm Nov 30 2005

If I go to the kawasaki dealer and I buy a standard oem piston for my original plated cylinder,what will be the letter written on the top of the piston? (89 kdx 200)

A or B ?

thanks

Post by **fuzzy** » 03:06 pm Nov 30 2005

The corresponding letter should be stamped on your cyl. Doesn't really matter. I'd buy a wiseco personally.

kdxquebec · Post by **kdxquebec** » 03:36 pm Nov 30 2005

Oh. Where should be the stamp on the cylinder? I really do not know where it is.

canyncarvr · Post by **canyncarvr** » 06:02 pm Nov 30 2005

If you buy one from the dealer...it's like a box of chocolates:

You never know WHAT you're gonna get.

Maybe an 'A'. Maybe a 'B'. Maybe something else.

What does it matter what's stamped on the cylinder? If you know that you get the right piston from Ma Kaw?

Anyway...the cylinder is marked toward the front toward the top...on 'H' models anyway. The piston is marked on the crown toward the front (where the arrow is that points 'forward').

If you are taking out a wiseco, it won't have such a marking (a,b,c,d etc) on it.

Keep in mind the difference between the alpha designations amounts to less than 1/2 of one thousandth of an inch. There are not ring sizes to match the different piston sizes. They (rings) are the same for the different alphas.

kdxquebec · Post by **kdxquebec** » 07:27 pm Nov 30 2005

Chocolate box! Did you saw the Forest Gump movie?! lol

I asked this piston question because ...3 years ago ,I bought from Ebay a new Oem piston-rings combo for my bike . Never installed it. The piston has a ¨A¨ ink stamp on it.

But when I look in my manual all the pictures with a piston on it, shows a B punched mark on the piston. hummm. why? thank C.C .

I am confused.

My piston and cylinder (both are original 1989) was measured at the shop. All the kit is still in the kawasaki specifications.
The piston is not cracked and scored even on the intake side.He suggest me to put new rings,pin bearing ,circlips then and close that baby with new gaskets.

He said : those pistons are indestructible and much thicker and nicasil is a way much better than the newer ones belive me.... so to avoid problems keep the winning solution.¨Re-open in 2 years to inspect and clean the top end powervalves.

what do you think?

canyncarvr · Post by **canyncarvr** » 07:56 pm Nov 30 2005

The pictures in the manual may have a 'B' on them. Guess they have to have some letter, 'eh? While you cannot specify what piston you get when you order a piston from your dealer..you likely WILL get a 'B'. So I've been told, and so I've gotten from the dealer. BUT...it does not always happen that way.

re: 'nicasil is a way much better than the newer ones..'

I don't get this part. The older plating is better than the newer plating? I don't know, but wouldn't doubt it.

IF your piston shows no wear after two years of use, you are either lucky, your oil is wonderful, or God loves you. Ha! Maybe more than one of those...

Anyway, if I had a used piston that measured 'right', had no scratches on it (I don't know how that could be), I'd probably put new rings on it, scotch brite or ball hone the cylinder, put in a new bearing and go. Or...

...what you said.

kdxquebec · Post by **kdxquebec** » 08:39 pm Nov 30 2005

you said ... gess they have to have some letters ... ok I understand.
I said ...Nicasil is better than the newer ones............he must be wrong

Btw I use motul 510 but who cares?

C.C my piston is 16 years old not 2 years old... (I mean,I run the factory 1989 original one). The piston I bought 3 years ago was never installed.

The original piston has no deep scratches.Only normal non-abrasive lines.

kdxquebec · Post by **kdxquebec** » 09:45 pm Dec 01 2005

hi.

this is the original piston

http://www.bikepics.com/pictures/476364/

This is the bad left powervalve

http://www.bikepics.com/pictures/476366/

RBD · Post by **RBD** » 09:52 pm Dec 01 2005

Your power valve is junk and MUST be replaced!

Not a bad looking piston for the age.....

Post by **fuzzy** » 09:46 am Dec 02 2005

You could use that 'A' piston you already have. As CC mentioned they are BARELY different. The ABCDEF is to make up for slight clearance changes due to wear in the plating when doing piston swaps...we're talking microns here. No normal shop equipment can even measure piston clearance to this level. A wiseco is like an 'F,' and this is why they tend to need warmed up to avoid cold seisure but make slightly more power. An 'A' in a 'F' cyl is still within spec for piston clearance.

kdxquebec · Post by **kdxquebec** » 11:16 am Dec 02 2005

Thanks for the info!

KDX220PHIL · Post by **KDX220PHIL** » 11:27 am Dec 02 2005

A Dial bore! Is this not normal? I use 'em all the time!

http://www.longislandindicator.com/Reso ... ndard.jpeg

m0rie · Post by **m0rie** » 11:33 am Dec 02 2005

Phil would that be accurate enough?

canyncarvr · Post by **canyncarvr** » 11:36 am Dec 02 2005

**edit**

The number listed for the Wiseco is the bore size listed in their pdf file, NOT the size of their piston. And of course, it is in mm, not inches.

So:

A later post wrote: Fuzzy is indeed correct about 'all this crap'.

..and I've been guilty of it before.

The sizes listed in the Wiseco pdf are indeed bore sizes...not piston sizes.

Please accept my apologies for all the crap.

The gist of the post remains true. The point was and still is 'not trying to split hairs' but to make a point about piston/cylinder measurement.

**end this edit**

There is one way to figure out what piston you need.

FIGURE IT OUT!

You first check the cylinder geometry. Considering the plating, port edges and such to be fine, the cylinder should be square. Ha!...square of course not meaning that it ain't ROUND...but that it is the SAME 'roundness' from the top to the bottom. A cylinder is going to usually show the most wear (larger diameter) at the top because that is where the rings are slammed against the cylinder surface when the sparky goes p-o-p! The combustion pressures force the ring(s) against the cylinder surface. That pressure decreases as the piston travels downward.

Anyway..a 'square' cylinder will measure the same diameter at the top as at the bottom.

When you know what that measurement is, you choose a piston to fit. That 'fit' will vary depending on what the application is.

No, the following is NOT written for 2-strokes. The point of putting it here is to show the '..what the application is.' part.

Wiseco FAQ wrote:
What kind of piston-to-wall clearance can I run?

A. The factors that affect this are cylinder wall thickness, whether the block is filled, the overall compression height of the piston, piston material and thickness, and whether a marine engine is to see fresh-water cooling. Most small blocks get .004 piston to wall clearance and most big blocks get .005 due to the use of our 2618 high-strength alloy. For heavy blower and nitrous applications, Wiseco recommends adding .001 to the standard clearance. Special note: Clearance numbers are taken 1.300 down from the oil ring land-Not 90 degrees from pin centerline.

In a 2-stroke dirt motorcycle, you're looking for the piston-to-cylinder clearance to be .003-.005". THAT is a very general statement.

Consider this: (from his website)

Eric Gorr wrote:
Letter Designations on Cylinders and Pistons

The Japanese manufacturers use a letter designation system for plated cylinders. They intend for you to order replacement pistons based on the letter designation printed or stamped on the cylinder. This is the reason why they need this type of system. In mass production you can't guaranty that all parts will be exactly the same size. The size variance is based on an acceptable level of quality. Tool bits become dull, temperatures of machine tools change through production runs, and machine operators have inconsistent performance. The Japanese manufacturers have between two to four different sized pistons and cylinders. Normally labeled A, B, C, and D. If they only had one size, the piston to cylinder wall clearance would vary between .001 to .006 inches. In the standard Japanese alpha labeling system, A denotes the smallest bore or piston size and every letter after that is slightly larger, usually in increments of .0015 inches. The danger is that if you try to put a D piston in an A cylinder the piston to cylinder wall clearance will be so tight that a seizure might occur.

The emphasis in the above is mine. Note that statement does not apply to the Pro-X alpha designations. They vary by .01mm, or .00039", or a bit less than 1/2 of one thousandth of one inch. Yeah...I said a 'bit less'. Obviously, if you look at it from a % point of view, it's nowheres near close to 1/2 of one thousandth of an inch.

blah blah and more blah...

Size matters!

Get THE RIGHT size piston for your bike.

Amen.

KDX220PHIL · Post by **KDX220PHIL** » 11:59 am Dec 02 2005

Yep, each division (the small ones, on the pic) represent .0001", there are dial bores that come with divisions that are .00005". The large numbers represent .001". Also the larger length of the needle, the easier it is to estimate numbers between each division, like an angle the farther away from the origin, the greater the distance between each division. I have used some with 3" screens.

With a 3" screen (1.5" needle for example), and the same graduations as above (+or - .005), 100 graduations, that would make it 3.6 deg. or...ummmm.. lets see... .0942" between divisions, easy enough to estimate .00003". That would make it .1884" between divisions on a dial tool with 50 divisions with + or - .0025"

These tools are only as good as the operator, they take a very steady hand + technique, and they require constant calibrating. That is what that ring is for, a standard to calibrate the tool.

KDX220PHIL · Post by **KDX220PHIL** » 12:02 pm Dec 02 2005

I agree with CC, HAHAHA.
.010" is about 2.5 times the thickness of an average persons piece of hair or 2.5 times that of a sheet of paper (loose leaf).
That is a lot in my books.

m0rie · Post by **m0rie** » 12:13 pm Dec 02 2005

Thanks for the info Phil. I've always been interested in how the machining process works and the tools that are used. Always looked like it would be fun!

dave04kdx · Post by **dave04kdx** » 12:19 pm Dec 02 2005

"These tools are only as good as the operator, they take a very steady hand + technique, and they require constant calibrating. That is what that ring is for, a standard to calibrate the tool."

The above statement is so very true! I worked in a high volume CNC production machine shop for years. We made parts that had a tolerance of plus or minus .0003. 6 different people measuring these parts would pretty much always get 6 different measurements. The only way to accurately measure the piston and cylinder clearances in our bikes is electronically with an elaborate holding fixture.

We pretty much have to trust that the inspectors at the factory are doing a good job. If I remember right Inda got his cylinder bore measured at a place with a mega buck machine.

canyncarvr · Post by **canyncarvr** » 12:22 pm Dec 02 2005

Oh...a bit more fun....

You piston is likely not 'square', and neither does it GROW as it heats in an even fashion.

Pistons are measured on particular axes. Check YOUR piston provider for THEIR spec. Try it! Meaure your piston front-to-back (exhaust-to-intake) just below the second ring land. Measure it 90º to that, from one pin hole to the other at the bottom of the skirt (if you have one!

). Hhhmm...not the same, 'eh?

There are many many ways to fit a piston to a bore.

..not NEARLY as many correct ways to do it.

Cheers!

re: These tools are only as good as the operator, they take a very steady hand + technique, and they require constant calibrating.

Brother!! Aint' THAT the truth!!

That's why, if I really want to know the measurement of an engine piece...I take it to someone that can figure it out!

KDX220PHIL · Post by **KDX220PHIL** » 12:29 pm Dec 02 2005

"The only way to accurately measure the piston and cylinder clearances in our bikes is electronically with an elaborate holding fixture. "

Yep a CMM, coordinate measuring machine. It is computer controlled by a program that checks various geometrical characteristics of the part. It feeds this inoformation back to the operator, if the dimensions are good or bad. This is obviously a very basic description, they are complicated.

http://www.f1engineering.com/images/cra ... %20cmm.jpg

however, mopst of these dimensions are that are near impossible to measure with hand tools, like position, concentricity, angularity, parallelism, perpendicularity... etc. GDT.

A bore can be measure with hand tools to a very close measurement, but the roundness, position of the axis would be very difficult.

GDT- http://www.engineersedge.com/gdt.htm

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standard piston question

standard piston question