How To Check And Adjust Screw-Type Valve Clearances | MC Garage

You guys asked for a vid on checking valve clearances, so here it is! Yep, I totally cheated and used the easiest bike to work on—Kawasaki’s Z125. This bike uses old-school-type screw-type adjusters, not the more complicated and challenging shim setup that’s found on most modern bikes. But don’t worry, we’ll cover that in another video. For now, we’re starting small (literally and figuratively) with the Z. After all, plenty of bikes on the market still use screw-type adjusters!

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Metal parts expand as they get hot, and the clearance between your engine’s cams and valves is there to account for that expansion. If that clearance increases, you’ll end up with a lot of valve-train noise. If the clearance decreases—as it often does on the exhaust valves as the miles stack up—the valves may not seat fully. If that happens, it won’t be long before hot exhaust gasses burn the valve. And then you’re really in trouble.

The service interval for checking the valves and the procedure itself is different for just about every bike, so as always, review your shop manual for your bike’s specifics, but this demonstration from MC Garage will give you a rundown of the steps involved in checking and adjusting screw-type motorcycle valves.

Allow Bike To Cool And Remove Parts
First up, your engine needs to be cool, so let it sit overnight before you start working on it. With most bikes, you’ll need to remove the bodywork, gas tank, air box, and other parts just to get to the cylinder head cover and valves. That’s one of the reasons most people don’t want to deal with checking their valves. The other reason is that on most modern bikes, adjusting the clearance means removing the camshafts, and that freaks people out.

Set The Engine To Top Dead Center
Then, you need the engine to be at the top dead center (TDC) on the compression stroke, meaning the piston is all the way up and both valves are closed. To get there, remove the spark plug so the engine is easier to turn over, then remove the inspection covers from the side of the engine and put a socket on the rotor bolt and turn the motor counterclockwise until the “T” on the rotor lines up with the reference mark on the cover. That “T” stands for Top, as in Top Dead center. If you go past it, just keep going for two more revolutions. Don’t try to turn the engine backward or you’ll be grinding it against the starter clutch. You’ll notice there’s an “F” on the rotor as well, that’s an ignition timing mark that you can ignore, but it does serve as a head’s up that the “T” mark is about to appear.

The goal here is to put the engine in a position where the cams are not pushing on the valves. If you’re lined up with the “T” but there seems to be some pressure on the valves, you’re probably at top-dead-center on the exhaust stroke. Turn the motor over 360 degrees and you’ll be at TDC on the compression stroke.

Measure The Clearance Of The Valve With A Feeler Gauge
The intake and exhaust valve clearances will be listed on a sticker on the frame and in your shop manual. Select a feeler gauge that’s in the middle of the range and try to slip it between the adjuster and the top of the valve. Sometimes you have to bend the end of the feeler to get it to slide it parallel. Not sure how to use feeler gauges? We have another MC Garage that breaks it down for you.

Adjust The Valve Clearance By Turning The Screw
Okay, so you found a valve that’s out of spec. Don’t give up on the bike just yet! On engines with shim-type adjustment, you’ll need to pull cams, but with screw-type adjusters you just need to loosen the locknut and then turn the screw in or out, depending on if you need to close or open the clearance. Not much, maybe a 1/16th of a turn will open it up quite a bit. Use trial and error until you think you have it.

Read the full guide on how to adjust crew-type motorcycle valves on Motorcyclist: https://www.motorcyclistonline.com/mc...

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01:30 Start With A Cold Motorcycle Engine
01:35 Turn The Engine To The Top Dead Center On The Compression Stroke
02:45 Take Note Of The Valve Clearance Specs
02:50 Select A Feeler Gauge And Slide Under Adjuster
03:10 Tighten Or Loosen The Screw Adjuster
03:40 Recheck The Clearance After Turning The Engine Over By Hand