Monday, October 3, 2011

Adjusting Valves - A necessity for small displacement engines

I believe I mentioned that the motor in my NX was rebuilt. If I didn't, I apologize. It seems that owner #1 (I'm owner #3, owner #2 had the motor fixed) managed to run the engine low on oil and wipe out the camshaft and intake valve (the donor motor came with the bike). For those of you familiar with this series of Honda motors, you already know that keeping the oil level up is a major concern (especially if you have leaks or consumption issues). I've heard a few knowledgeable people say that it's OK to overfill, slightly. The extra oil will be pulled up to the head by the cam chain where it's best used (for this motor). An oil change refill is .95 US quarts (0.9 liters) according to the shop manual. That extra .05 quarts (0.1 liters) is what I mean by "slightly".

I've put about 2800 miles on the NX since I purchased it in January 2011. I checked the valve clearances when I bought the bike but figured the motor needed some break-in time. This past week I could hear a slight ticking while the motor idled. 2800 miles is plenty of time for the valve train to become broken-in. So, I adjusted the valve clearances over the weekend. Here's the page from the shop manual:

I know that's a little small to read so let me enumerate the steps;

  • Note: the engine must be cold to adjust the valves (below 35º C / 95º F).
  • Remove the fuel tank (to do that, remove the side panels, remove the seat, remove the tank fairings, disconnect the fuel line and then remove the tank).
  • The manual does not say this but I also remove the spark plug. First, it allows you to check the condition of the plug tip and, second, it means you don't have to fight against the engine's compression when trying to find Top Dead Center on the compression stroke.
  • Remove the valve hole adjusting caps (15/16" or 24mm)
  • Remove the crankshaft hole cap and timing hole cap. In the image, these caps have a slot (for a large screwdriver). My NX uses caps with Allen (hexagonal) sockets.
  • Rotate the crankshaft counter-clockwise and align the "T" mark on the flywheel with the index mark on the left crankcase cover. The "index mark" is a slot cut through the threads in the timing hole. Rotate the crank slowly because it's easy to miss the ("T") timing mark.
  • Make sure the piston is at TDC (Top Dead Center) on the compression stroke. I've found the easiest way to do this is to find the ("T") timing mark and then make sure the valve rockers are "rocking". That is, they will be loose (a relative term), you can move them slightly up and down and hear the 'tick' as the rocker hits the valve stem. Also, my motor turns past TDC very easily. So, don't be surprised if you find yourself repeating this step a few times. I use a 1/2" breaker bar and 14mm deep socket. If you use a ratchet, the motor may spin past TDC.
  • Check the valve clearance by inserting a feeler gauge between the adjuster screw and the valve stem.
  • Valve Clearance (Intake and Exhaust): 0.10 mm +/- 0.02 mm (0.004 inch +/- 0.001 inch)
  • In the pictures, the feeler gauge is shown attached to the pack. I find it much easier to remove the one gauge you're using from the pack. Now, bend the gauge into an "L" shape and insert it into the hole on either side of the rocker. This will allow you to find the gap between the rocker and the valve stem much more easily. It's also provides better feel when you're actually adjusting the clearance.
  • Adjust the clearance by loosening the lock nut and turning the adjusting screw until there is a slight drag on the feeler gauge. Hold the adjusting screw and tighten the lock nut.
  • Tools: 10mm x 12mm combination box end wrench (see image below) and adjusting wrench (Honda Part #: 07908-KE90000). I have an adjuster tool from Suzuki. They're the same. I understand that a wood deck screw with the square hole (available from home improvement stores) works as well.
  • Torque: 16 N-m (1.6 Kg-m, 12 ft-lb) Lock nuts may come loose if the proper torque is not applied. Don't over tighten, replacing a rocker is not fun.
  • Replace the valve hole caps
  • Reassemble in reverse order.

The engine is much more quiet and starts more easily now. The inspect/adjustment interval is every 2500 miles. I'm trying to figure out if there's a way I can scan my shop manual to PDF and post it here. I may have to create some sort of "archive" or "resources" page or something. I'll keep you posted.


  1. Nice work.

    I bought a nx125 1 week ago.

    Mine has done 23.000 km's. This winter i'm going to service the bike. Already bought a chain/sprocket set, new sparkplug etc.
    Parts which are rusting i'm going to repaint etc.

    Keep up the good work!!

  2. Thanks for the kind words. Congratulations on your purchase. Based on my math, that's about 15,000 miles which means your NX's motor might be due for a valve adjustment as well. Let me know if there is anything specific that you would like to to blog about. If you posted pictures on AdvRider, I saw them. Obviously, I won't be able to address anything regarding the front (disc) brake and/or the master cylinder. But, everything else looks about the same. Enjoy!

  3. Dave, from the noise I hear I think I'm facing major motor work on the NX125 I have. Think an XR200 motor would swap in, Lifun makes a whole motor for $350, seen them on ebay:


  4. Sorry to hear that you think your NX's motor might be shot. I gave some thought to seeing if an XR200 motor would swap in. Either that or a motor out of a Reflex (not the scooter, the TLR200 that Honda sold in 1986-87). I could not find a donor bike or a motor, in my area, to compare/contrast. There's a person, local to me, that works for Honda motorcycles. I asked him and he seemed to think that the best choice for the swap would be the XR200 motor. However, his thoughts were that the crank is different and therefore the case would be wider (than the 125 case). I would not suggest buying something until you're sure it will work. Perhaps your local Craigslist would have an old XR200 bike/motor for cheap. That way you wouldn't be out $350 if the Lifan didn't swap in. If you do look into it and it does work, please let us know! BTW, the 250cc motors (XR/XL 250) definitely will not swap in.

  5. 15 k is alot of miles that makes me feel better about only having 8. I saw an nx engine on ebay for 450 you would be alot more satisfied with that than a lifan trust me I have never heard anything good about them. They just don't compare to Honda's. please be generous with the junk motor I would pay good money for some of the parts off of it. I hope my comments arn't too short or too facebook like I try and be helpful in any way i can.

  6. With proper care an maintenance your NX's motor should last a long, long time. Honda has been making a version of that engine since the 1970s. They are tried and true. 15K miles should be nothing for that motor. Interestingly, I've heard nothing but good things about the Lifan motor (there are others that I've heard nothing but bad things about). I know quite a few Hondas with Lifan motors and the owners seem very happy. $450 for a running NX125 motor probably isn't a bad deal. They are quite simple to rebuild and parts are still available (although, they may not come from Honda).

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