RM250 compression problem

 

 Very low hour 06 RM250.  Was running great, son said it started wanting to
die when he let off of throttle. No power loss, nothing seemed wrong other
than not idling. shut it off and when he tried to restart... very little
compression. I checked the plug to make sure it was tight. Before I tear
down and replace rings/piston what else could cause low compression on a 2
stroke?

--
Rob

 

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It's only got one ring, so they don't last that long.

Other than that, I'd check for problems with the reeds, and maybe an
air leak, if you don't find anything else wrong (including blockage in
the carburetor passages or pilot (slow) jet.


         Wudsracer/Jim Cook
          Smackover Racing
         '06 Gas Gas DE300
        '82 Husqvarna XC250
           Team LAGNAF
        

 

Tore it down...small chip out of the front of piston, no damage to cylinder.
I hope it blew it out the exhaust. You recommend OEM or aftermarket
piston/ring set?

 


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  Stock piston are always good quality, but most mx bikes use only one
piston ring. I much prefer a two ring piston and it's longer service
interval.

  My favorite aftermarket piston kit, available in the US, is sold
here as the Athena brand kit.  They are quality pistons manufactured
by Wossner in Germany, and have a non-stick coating on the sides of
the piston. All the 200cc and larger Athena piston kits that I've seen
have two rings; which I prefer for longevity of service.
 (The Wossner pistons that were supplied as OEM GasGas pistons had no
coatings on the sides.)
 I like Vertex pistons, but the replacement rings cost almost twice
what the Wossner and Wiseco rings cost.
  Wiseco pistons have given me excellent service.

  Use new gaskets in your reassembly.

 The piston might not have been your problem. I've seen two stroke
engines run fine with a piece of the skirt broken off. It will depend
on what part of the porting the broken piece covered.  So...  while
you have the top end down, check and clean the powervalve assembly and
check the reeds.  Clean the carb's passages, while you have it off to
check the reeds.


  Good riding and wrenching to you!

Jim



         Wudsracer/Jim Cook
          Smackover Racing
         '06 Gas Gas DE300
        '82 Husqvarna XC250
           Team LAGNAF
        

 

Hell, the motor has less than 10 hours...it looks new on the inside. My
concern is the exhaust  valve. It looks like the ring may have caught on it
as it looks like one side of it sticks into the cylinder maybe 1/2 mm. When
I tear it all down, I'll see if there is an adjustment.

Rob