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I'm thinking I'll check them again @ 4500 miles when I do the next oil & filter change. It wasn't too difficult to get in there to check the valve clearance. It helps a lot to prop up the front of the fuel tank, so you can see what you're doing.
 

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I swiped this from the Adventurerider NX250 forum, to point out mileage and valve clearance. Better to check too often that too rarely.

"Well I mentioned the fact that I was after a 250 to a friend of mine and he told me about an NX250 that his wife had, and didn't want anymore. I got pretty excited as I remember the NX250 (and the NX650) very well. I went to get it the next day, and bought it from the wife for $300. I'm not sure if I paid a fair price... the bike is very beat up, missing fairings and side covers, needs a new seat and battery, has a funky title, and does not run. On the other hand, it supposedly ran quite well when it was parked a year ago, allegedly has less than 10,000 miles (according to the odometer.... but it's hard to believe considering the poor condition of the bike) has tons of tread left on the trailwings (which are not cracked), and hell, it's an NX250! I'm not too worried about getting it started... the spark at the plug looks good, I cleaned the carbs, and I am now waiting for some valve shims in the mail (valves were all too tight, especially the intakes). I am hoping the valve adjustment will do the trick and the engine will fire up."
 

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Discussion Starter #84
I will have to recheck them again in a few thousand miles.
It's been a few thousand miles (13,000!). I popped the plastic off and raised the front of the tank this time as I knew some adjustment would be needed. I also bought a new set of feeler gauges since I forgot to bring my other ones home from work. $13.00 buys a nice set with 24 blades from .004 inches up. All inclusive in .001 inch steps. I had to put a bend part way up from the tip but they then worked perfectly even if they won't tuck away into the case anymore. Both intakes and one exhaust didn't budge. The left exhaust had tightened up further and needed .11 mm less. This makes my intakes .20mm, left exhaust.31 and rt exhaust .29 mm. I used the same gasket over again for the third time. Bet it still won't leak. The spark plug still looks like new with a perfect light grey burn.
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Thanks to newexplorer for posting this link to photos of the procedure.
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2012 Honda CBR250R Valve Adjustment Procedure - Page 2
 

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Previously I've had a dealer do my valve clearance inspection and adjustment since it was new in 2012, but now that the bike is older I decided to try the job myself. The hardest part is all the body disassembly needed to gain access to the top of the engine.

Once I got the valve cover off, I was so pleased to find out that the valve shims can be replaced without removing the cams! The rocker arm shafts slide out of covered holes on the side of the cylinder head, allowing the rocker arms to be pushed back out of the way, which gives access to the shims without removing the cams. At 26,000 miles, the intake valve clearances are well in spec, but exhaust valves need to be opened up a couple thousandths. Engine looks completely new inside...go Honda!

Here's a photo with the rocker arm in place:


And here's a pic with the rocker arm moved out of the way (I've already pulled out the shims with a magnet):
 
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