Cracking open the top end, but what am I doing?

[oic0]

Ok, the clack / knock has scared me enough and I need to fix the loose center power valve. What am I looking for to tell if the piston is loose though? Do I measure the piston at the crown and compare it to the width of the bore? After that, what is acceptable? it is supposed to be an oversize wiseco.


*edit* sorry about the brevity of that. All the supervisors were gone and my co-workers decided to leave early. Told me to get up and go or I'd have to set the alarm I dont even know the code for.

Anywho, how does this work with cylinder plating? If the plating is good you get a new piston and if the plating is wearing off you get it replated? otherwise it is all piston? I read the top end rebuild guide and did a search but came up a bit empty handed on how you measure to see if the bore is servicable.

[KX5Zuki]

The piston should be .004-.005 smaller than the bore. Look for flaking on the cylinder walls, deep scratches on the piston.

[dean350b]

The service manual says you should measure the bore I believe 30mm down from the top edge where the head bolts on.

I just used a dial caliper from the top and from the bottom of the bore, I got the results I needed.

Write down that measurement.

You need a service manual to find out the max service limit for your year bore size. If it is not at the max service limit, and the bore is not all beat up, scratched and Nikasil flaking, then just hone it or scotchbrite it lightly, and be done with it.

Measure your piston, grab it from the top directly across the center with a dial caliper. Look for the largest number you can achieve with the calipers.

Write down that measurement.

Measure in many different places around the piston. Again, look for the service limits, and....then take the measurement of the piston and subtract that number from the masurement of the bore.

You need around .004-.005" difference, the piston smaller than the bore. Anything greater (example: .007") and the piston will slap in the bore.

I used a new Pro-X brand piston and rings that was .001" oversize in my 22 year-old KX500 bore. Worked great, I ended up with .005" piston to bore clearance. The Pro-X piston from Dennis Kirk was like $100.00

One of the most important things to do is to de-gunk your KIPS valves with oven cleaner before you start prying on them to get them out, clean the bores that they seat in, clean the valves, reset the valve timing per the manual.

Look for cylinder cracks in a bright light.

New gasket kit, etc.

If you need to re-plate your cylinder, send your new piston to the shop with the cylinder, they will mate them together for you perfectly.

[oic0]

Did compression test today. 165-170 psi slightly warm after just a few kicks. Probably could have kept going up a few more psi but was tired. (could still keep your hand on the engine). Changed the jetting from 168 needle at 4th to 165 needle at 3rd. Runs much better now in the mid range. Can rap the throttle from any rpm range and it lunges forward while lifting the front wheel. Jetting feels pretty much spot on, maybe half turn in on the air screw for perfection.

Started too late today but tomorrow it comes open to find the source of the knock and see whats wrong with the power valve.

[oic0]

Ok got it apart. Cylinder looks great. Piston looks great. No play in the rod.  Looks like there aren't many hours on them. I suck at measuring and couldn't get any consistent measurements but I didn't see any signs of slapping damage.

Powervalve center slide pins were worn out and there was a shiny beaten spot on the corner of the center slide body where it looks like its been beating against something. Turned pins around, most powervalve play is gone now. Timed it right (tried some "easy" guide I found online for an hour unsuccessfully. Used the marks and the guide on halibergs.... got it figured out in 5 minutes....)

Got it all put back together. Still makes a knock sound. I'm just going to run it till it blows up then I will deal with that.