TOPEND REBUILD QUESTIONS

[blaze]

HELLO NEW TO FORUM. I HAVE A FEW QUESTIONS ABOUT A TOPEND REBUILD IM DOING. I HAVE A 04 KDX 200 THAT I HAVE OWNED FOR ABOUT 2 YEARS NOW AND IT RUNS GREAT. ONLY REBUILDING IT BECAUSE I REALLY HAVE NO IDEA OF THE MAINTENCE HISTORY ON THE BIKE AND AS A LEARNING EXPERIENCE. FIRST QUESTION IS ABOUT CYLINDER DIAMETER. I MEASURED THE CYLINDER AND IT IS MEASURING 2.5981 THIS WITH A DIAL BORE GUAGE AND TELESCOPING GUAGES AND ACCORDING TO MY SERVICE MANUAL SPEC IS 2.5994--2.6000 WHICH MAKES MY CYLINDER SMALLER THAN SPEC, HOW IS THIS POSSIBLE ON A ALMOST 20 YEAR OLD BIKE? I ALSO MEASURED THE PISTON TO 2.5924 SPEC (2.5961--2.5967) WHICH I ASSUME IS JUST SMALLER FROM NORMAL WEAR BUT CORRECT IF IM WRONG THAT MAKES MY PISTON/CYLINDER CLEARNEC .0059 (SPEC IS .0031--.0035) ALMOST DOUBLE AND THE SERVICE MANUAL SAYS IT CAN BE A LITTLE LARGER BUT DOESNT REALLY SAY BY HOW MUCH. EVEN IF I GET A NEW SMALLEST PISTON ACCORDING TO SPEC (2.5961) MY CLEARNCE WOULD STILL BE .0020 AND THE MANUAL IS VERY DIRECT IN STATING DONT GO UNDER SPEC OR PISTON COULD SIEZE IN THE BORE. SO DO I NEED TO GET A SMALLER PISTON THAN STOCK? ALSO IS THE PISTON I HAVE STOCK OR AFTERMARKET? THANKYOU FOR HELP.

[KDXGarage]

Welcome to kdxrider.net.

Did you run a hone inside the cylinder? I hope not and that is just afternarket plating with porosity showing.

Did you clean the piston top?

Don't take this the wrong way, but I assume you measured the cylinder in the wrong location.

What are the vertical scratches??

[bufftester]

That's a standard (66.00mm) Wiseco piston (p/n 711M0600) As KDXG said, remeasure in the correct locations

For piston, 16 mm up from the bottom of the piston skirt 90° from the piston pin hole and you should be >65.8. Yours is at 2.5924 which is 65.84 (or basically at the wear limit)

For cylinder service limit 20 mm from the top, front to rear and side to side and you should be < 66.1. yours measured 2.5981 which is 65.99 (again, very near the wear limit)

For piston to cylinder you remeasure the bore near the bottom of the pistons stroke. Subtract the diameter of the piston from this measurement of the cylinder diameter to get the piston-to-cylinder clearance and you should be 0.079 – 0.089 mm ( or .0031-.0035 inches) Your math is off using the numbers you wrote down above (2.5981-2.5924=.0057 not .0059)

Regardless, if those are pores showing in the coating the cylinder needs to be replated. If you didn't hone it then likely the PO did which is a big no no for these engines.

IIWM I'd replate the cylinder and replace the piston (and send it to the replates so they can match it).

[Goofaroo]

What is the end gap on the rings?

It’s a bit of a puzzle you’ve presented. Like KDXGarage said it is most likely a replated cylinder.

If the ring gap is reasonably good and the bike was running well you could just clean everything and run it until it starts slapping. It might run for quite a while. Did you happen to check the compression before you took it apart?

The other option would be to send it off for a bore and replate. You’ll get it back to factory spec and end up with a new forged piston. It all depends on how much you want to spend as to what you do.

This does seem odd though. A reputable plating service would have most likely not have undersized the bore.
Are you confident in you micrometer being calibrated properly and your ability to measure it? It might be worth a shot to take it to a machine shop and see what they come up with before you go any further.

[Goofaroo]

Oops. I didn’t see bufftesters reply before I posted. He’s right. It should probably be replated but I have certainly run some cylinders that looked worse. lol

[KDXGarage]

I am assuming it was replated. Porosity can show up during this time. It is not an issue.

Get an OEM or Cyclepedia service manual.

I am curious as to how the angled scratches got there.
If it is not severely gouged, there is no need for boring it to a larger size. It's not a Camaro.

[blaze]

I DID NOT HONE THE CYLINDER I DID CLEAN IT WITH TYPE F AND SCOTCHBRITE . I KNOW I MEASURED IN THE RIGHT LOCATIONS BUT MAYBE I DIDNT MEASURE IT CORRECTLY OR MY MICROMETERS AND DIAL BORE GUAGE ARE NOT THE BEST OF QUALLITY. SO TODAY I TOOK MY CYLINDER TO A BUDDY WHO WORKS IN A MACHINE SHOP WITH OUT TELLING HIM THE MEASURMENTS I GOT AND THEN COMPARED AND HE GOT THE EXACT SAME MEASURMENTS DOWN TO 10000 TH . MEASURMENTS ARE ACURATE. SOME OF YOU THINK IT GOT REPLATED TO THE WRONG SIZE AND THATS THE ONLY THING I THINK CAN BE ALSO.
IF I DO JUST GET ANOTHER WIESCO AND RUN IT. WILL THE CLEARENCE BE OK OR WILL I HAVE TO RUN A SMALLER PISTON? WHAT IS THE EXACT DIMENSIONS OF A NEW WIESCO PISTON? ALSO THE VERTICAL MARKS ARE FROM TELESCOPING GUAGE AND MY BUDDY ASSURES ME THAT IS JUST MARKS NOT SCRATCHES . ONE LAST QUESTION WITH THE CLEARENCE THAT BIKE HAD WOULD IT OF AFFECTED THE COMPRESSION BEING SO BIG? ALSO TO THE FIRST COMMENT I AGREE WITH STATEMENT ABOUT PISTON BUT MY CYLINDER MEASURMENT IS NOT TO THE WEAR LIMIT IS SMALLER THAN STOCK.I POSTED MORE PICS OF PORES JUST TO SEE IF YOU GUYS REALLY REALLY THINK ITS TO BAD TO RUN.THANKS AGAIN.

[Goofaroo]

Did you check the ring gap?

I would just deburr the piston and run it again. How was it running when you took it apart? Any piston slap? It’s hard to tell by the picture but it doesn’t look too bad to me. I would guess that this bike ran just fine. Clean up the piston and combustion chamber. If the gap is okay in the rings you could reuse them but it would be best if you installed them in the original orientation.

Or you could order a new piston. bufftester seems confident that it is a standard Wiseco. That would certainly make sense.

[kick]

I assume your friend is a machinist that used a different set of measuring instruments. I just think there may be some error in your measurement. You can give wiseco a call and ask what the outside diameter is with tolerance for a stock piston.

[KDXGarage]

CAPS LOCK :-)

If it was running fine with a Wiseco, then buy another Wiseco piston kit, a new small end bearing, a gasket kit and fresh coolant.

Reassemble and ride.

[G22inSC]

I concur with what KDXGarage said above. Grab another Wiseco and necessary parts, measure your ring end gap and rock on.

I would be willing to bet your measurements are off. Even with the correct tools, these type measurements are somewhat of an art. They are as much by feel as they are just measuring. If it's not something you do every day I would rely on a shop to do it for you. That is what I do.

[blaze]

So im back to the bike. I called wiesco today and they say my measurement of 2.5983 is correct. They said they show a bore measurement of 2.5984 for a 04 kdx 200 and they piston they sell is 2.5964 . They said it will have piston/cylinder clearence of .002. So i guess the kdx manual i have is wrong regarding cylinder measurments. But still have a question when u guys measure your cylinders what numbers do you get.And is .002 enough of clearence cause the book says i need .0031 to .0035 clearence and to not go lower. And i heard that forged pistons even need more clearence as they expand more and faster. Also talked to plating guys and they said the porosity i have is not bad and in some cases is a good thing.

[bufftester]

The porosity is a non issue. If it was running fine before, I'd do the same as the rest already said...new piston, rings, small end bearing and ride.

[blaze]

can somone who has rebuilt there topend and actually measured everything reply. What clearences do you guys have when you put a new piston in.

[ericr]

can somone who has rebuilt there topend and actually measured everything reply. What clearences do you guys have when you put a new piston in.

I had Millenium replate my cylinder. I shipped my new Wiseco piston to them along with the cylinder. They bored it to 2.6000. That gave 0.0036 clearance. The Wiseco rings were a little overgapped from the factory. Spec is top - 0.010, bottom - 0.013. Both were 0.012 out of the box. KDX220 rings are even looser out of the box.

Here's the page from my rebuild thread where I discussed this... viewtopic.php?f=77&t=22266&start=60