Maintenance & Technical > KX500 Original

Help smashed or melted spark plugs

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BMH:
I would like to know how to do a leak down test :-)

KXcam22:
BMH,
  That is an interresting problem.  I have seen similar to that before but long time ago and can't recall the specifics.  I doubt that it is piston mechanical damage.  I run the BPR8ES, the "P" projected nose plug.  It is longer and there is still lots of room.  If you recall the shape of the head, the chamber makes it is impossible for the piston to hit the plug without huge damage.  I remember now:  I broke a piece of piston skirt off and it made it through the transfer port and was bouncing around on top of the piston, hence every so often it would bean the plug and close the gap.  I suggest that you take off the exhaust pipe and have a quick peak at the cylinder/piston to inspect for possible damage.  One thing that is nice about a 500 is that you can do a pretty good internal inspection by shining a light down the plug hole and looking up the exhaust port.   On another topic, it is possible to overheat so fast that the coolant won't boil over.  I once had a CR500 CDI go south.  Was breaking it in at the time, all conditions perfect, but it would seize every few minutes.  Took 7 seizes to get back to the truck.  I was stumped until I noticed later that night that I had no spark.  Hope this helps. Cam.

Hillclimb#42:
 That's probably it Cam, maybe a broken ring during break in. Its a pain to stick the piston in the jug and hold the rings where they are supposed to be, especially if you do it alone. Something is in there. You might as well pull off the top, because no matter what it is, it has to come out. The head has a domed combustion chamber, like cam already pointed out, so the plug would never hit the piston.
  Whats the leak down test going to show on new motor? If it leaks off compression, wouldn't it still need a visual inspection and repair?  If it doesn't lose any, wouldn't you guys still have to pull off the top end to fix it, no matter what is causing it? Seems like that test would only confirm there's a problem, when that's obvious. What would that test tell BMH about the cause?

hughes:
BDI is concerned due to the guy saying the plug looked melted. Pressure testing the engine is great way to check main crank seals, crank case halves, intake boot etc. to ensure the engine is not sucking air from another source.

KXcam22:
Just for some similar info.  I once assembled a snowmobile engine but got the timing way off. Ran fine but burnt a hole through the piston in about 15 minutes. It can happen fast. Its hard to tell from the photo it the plug is melted or mechanically bent. Cam.

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