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Thumper · 04-06-2023, 05:02 PM

Pete... adjust those valves. It is pretty easy on these 172FMM engines and it WILL make it run better.

Remove the spark plug, remove the side cap an put a 14mm (15mm?) socket onto the end of the crankshaft (stator side). Open the sight capjust above the stator, and you are halfway there.

Pop the exhaust valve cover (crescent will do). Rotate the crank counterclockwise to the | T mark. The valve is open, or closed. Rotate it another 360 degrees, it is open or closed. When you figure out which is valve closed (gap open), set it to 0.001-0.002" I find that this is 1/8th turn from gentle full close to no gap. Cap it up and repeat on the intake... done. This gap just barely feels perceptible by hand on the rocker. Perfect.

This is OHC, and there are no long rods to exacerbate heat changes, so these are tight clearances.

Go for it! Tell us if it makes any difference. It may idle more stably, rev quicker, more smoothly. And it will protect those valve seats!

04-06-2023, 05:02 PM	#1274
Thumper Join Date: Feb 2021 Location: Kansas City Posts: 2,615	Pete... adjust those valves. It is pretty easy on these 172FMM engines and it WILL make it run better. Remove the spark plug, remove the side cap an put a 14mm (15mm?) socket onto the end of the crankshaft (stator side). Open the sight capjust above the stator, and you are halfway there. Pop the exhaust valve cover (crescent will do). Rotate the crank counterclockwise to the \| T mark. The valve is open, or closed. Rotate it another 360 degrees, it is open or closed. When you figure out which is valve closed (gap open), set it to 0.001-0.002" I find that this is 1/8th turn from gentle full close to no gap. Cap it up and repeat on the intake... done. This gap just barely feels perceptible by hand on the rocker. Perfect. This is OHC, and there are no long rods to exacerbate heat changes, so these are tight clearances. Go for it! Tell us if it makes any difference. It may idle more stably, rev quicker, more smoothly. And it will protect those valve seats! __________________ -NOS 2020 KTM 250SX (2-stroke motocross) Last edited by Thumper; 04-07-2023 at 02:57 AM.
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