suddenly too rich

[tschisi]

~100psi, again.

Leakdown test:
The engine holds the under pressure rather good, but when i wiggle the flywheel it decreases faster.
Splitting...

btw, a ktm 144sx piston works nice for sealing the k5?s exhaust port 

[Goat]

With a new plating on the cylinder I wouldn't run that old piston. It has already been formed for the old plating and wont have the right clearance all the way around. probably egg shaped and causing some of your compression issues. It's best to use a new piston & rings with new cylinder plating.

[tschisi]

Sure a new piston would be better, the old one is just for testing.
But i don?t think the old piston could cause my compression problem when coating and rings are new?!
I?m also afraid the seal isn?t the solution, because when i did the compression test i put a large amount of grease on the seal so it couldn?t suck (much) air.
It didn?t make any difference... 

[Motorrad]

Sure a new piston would be better, the old one is just for testing.
But i don?t think the old piston could cause my compression problem when coating and rings are new?!
I?m also afraid the seal isn?t the solution, because when i did the compression test i put a large amount of grease on the seal so it couldn?t suck (much) air.
It didn?t make any difference... 

Curious... whats your ring end gap?

are you sure the ring lands were clean? free of burs? proper spec?   this could cause a re-occuring issue when using the old piston...

[tschisi]

I haven?t measured the gap, can do this when i have dismantled the engine again.
I?m not planning to run the engine long with the old piston, but it has to run first...
Is it maybe possible that the 100psi are standard for not broken in coating and rings?
Guess i still won?t be able to start the engine with that value...

[Friar-Tuck]

Measuring the Ring Gap
  '83-'86     0.20-0.40 mm  or  0.008" - 0.016"  (new)    Service limit  0.07 mm  or 0.028" 

 '87 -'04    0.15-0.35 mm   or 0.006" to 0.014  (new)    Service limit is also 0.7mm   or 0.028"

 Put the ring in the cylinder and use the piston to push it down about 1/2 inch from the top evenly spaced. 
( Start the ring in the cyl by hand & then use the top of the piston to push the ring where you want it in the bore.  This should have gotten you pretty close to having the ring squared up in the cyl.)
  Now use a feeler gauge to measure the width of the ring gap.       
  This info is from the Clymer pg. 174 table 6

 If you have to open up the gap, a small ignition file and patience are in order, work slowly. You don't want to chip any edges of the area your filing.  (most of the rings have coating and will Chip if you push too hard with the file or stone)
Squeeze the gap closed  and make sure the ring faces meet squarely.

I take emery cloth and lightly run around the rings edges and piston groove to remove any possible burrs from the cutting/machining process.  You're not trying to sand the  down the corners, so easy does it.
 
Here is a link to a great write up with help from Mr. Do or Die, ( DoorDie one of our members) from 2005,  http://www.hallbergs.net/kx500/

Tuck\o/

 

[Motorrad]

Measuring the Ring Gap
  '83-'86     0.20-.040 mm  or  0.008" - 0.016"  (new)    Service limit  0.07 mm  or 0.028" 

 '87 -'04    0.15-0.35 mm   or 0.006" to 0.014  (new)    Service limit is also 0.7mm   or 0.028"

 Put the ring in the cylinder and use the piston to push it down about 1/2 inch from the top evenly spaced.  Start the ring in the cyl by hand & then use the top of the piston to push the ring where you want it in the bore.  This should have gotten you pretty close to having the ring squared up in the cyl.
  Now use a feeler gauge to measure the width of the ring gap.       
  This info is from the Clymer pg. 174 table 6

 If you have to open up the gap, a small ignition file and patience are in order, work slowly. You don't want to chip any edges of the area your filing.  close the gap and make sure the ring faces meet squarely.

I take emery cloth and lightly run around the rings edges and piston groove to remove any possible burrs from the cutting/machining process.  You're not trying to sand the  down the corners, so easy does it.
 
Here is a link to a great write up with help from Mr. Do or Die, ( DoorDie one of our members) from 2005,  http://www.hallbergs.net/kx500/

Tuck\o/

Another old timer trick... a OLD ring broke in half... works as a great ring land cleaning tool/scraper...

[Friar-Tuck]

  Yep, Another good tip Mo-Rad, 
 
 There is also a ring land / piston measurement to take.  Click on the thumbnail, bottom left of page.

[tschisi]

Ring gap is 0,22mm.
I will do the bottom end rebuild (which will take a year or so) first, everything else would be non-essential right now...