05 rm125 won't start after top end rebuild

12/7/2016 11:29pm
Hey guys, just did the top end on my 05 RM 125 and when I went to start nothing, have tried everything pulled all apart re assembled twice. I notice the first time I disassembled the ring had come out of the groove on the piston could that have ruined the ring?
Everytime I try to start it the plug gets soaked in oil any help would be great!
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12/7/2016 11:57pm Edited Date/Time 12/8/2016 12:05am
Update
This is my plug after trying to start it (this was a brand new plug), have tried hill starting it also just rolls and a real low brap barp sound.
did a compression test come up with 60psi
Has spark
Have fresh fuel mixed at 40:1
Has brand new vforce reeds
Brand new pro circuit expansion chamber and shorty
12/8/2016 3:02am
*UPDATE*
Put the old piston and ring back in, got 150psi on the compression gauge and started first kick.
What would I have done wrong for the new piston to not work?
Paw Paw 271
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12/8/2016 6:42am
May be it is just not a good fit to the cylinder. I would suspect the ring end gap was way out of spec. What was it?
Are you 100% sure you had the new piston facing the correct direction?

Paw Paw

The Shop

BobPA
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12/8/2016 7:45am
sounds like you may have hurt the ring
12/8/2016 10:27am
May be it is just not a good fit to the cylinder. I would suspect the ring end gap was way out of spec. What was...
May be it is just not a good fit to the cylinder. I would suspect the ring end gap was way out of spec. What was it?
Are you 100% sure you had the new piston facing the correct direction?

Paw Paw
Ring gap was 0.25mm I was told by the guy that checked my bore and supplied me the piston it should be between 0.20 and 0.30. Going to get a new ring and try again after the weekend, just glad I got it going for the weekend lol
Paw Paw 271
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12/8/2016 11:45am
Be sure to compress the ring while installing the piston into the cylinder.

Paw Paw
12/8/2016 5:28pm
Be sure to compress the ring while installing the piston into the cylinder.

Paw Paw
Thanks for your help paw paw!
Bruce372
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12/8/2016 11:10pm
Don't forget, the numbers on the ring are visible from the top just in case it's a directional piston ring
Bruce372
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12/8/2016 11:11pm
And if it's a rm125, it's a really good idea to run the expensive oem plug
12/11/2016 8:36am
Sounds like you got the wrong parts, measure both piston diameters and get back to us.
12/13/2016 12:54am
Sounds like you got the wrong parts, measure both piston diameters and get back to us.
This is the piston kit I got, I think I have damaged the ring when installing as it now looks like an oval when it's sitting flat. Going to get a new ring and have another go. I checked the gap with feeler gauges, if the ring gap was to small would that affect compression?

12/13/2016 12:55am
Bruce372 wrote:
And if it's a rm125, it's a really good idea to run the expensive oem plug
Yeah I got the OEM spark plug, not cheap! But better then having to do a full rebuild if the plug snaps.
seth505
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12/13/2016 11:18am
It does sound like your ring is messed up. I set my 125 in the teens, like .015"
12/13/2016 11:22am
seth505 wrote:
It does sound like your ring is messed up. I set my 125 in the teens, like .015"
Yeah the guy at the shop said to set it to .02-.03, will have to get a new ring and try again! The first time I put it in I didn't realise there were holes the ring end had to sit in -.-

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