SOHC.co.uk Forums > CB500/550
how to clean valves properly
taysidedragon:
--- Quote from: deltarider on January 10, 2022, 10:29:49 AM ---Hope someone can teach me on this. Is it true that some valves are special and are not supposed to be lapped and if you do, you will do more harm than good? Second question: what is it precisely, that causes valves to wear?
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These old bikes mostly use steel valves which need lapping in to get a good seal. Race bikes and some modern high performance bikes use exotic, lightweight materials which might need special treatment. That's beyond my 'need to know' knowledge.
Valves wear because they are opening and shutting thousands of times a minute. The valve seat is getting hammered by the closing valve every time. Any wear in the valve guide means the head of the valve can move sideways a little and then the valve doesn't seat exactly on the seat and that causes more wear. HTH
McCabe-Thiele (Ted):
--- Quote from: Seamus on January 10, 2022, 08:59:40 AM ---There is a tool for lapping valves. Fits in a battery drill and it oscillates the valve. Saves loads of time and sore palms.
Had mine for about 35 years and still going strong. They have something similar on Amazon for about 20 quid
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I had one of those tools for many years but eventually the plastic casing cracked so I had to bin it - it worked okay but I still found the achiles heel was the same as using a manual stick - the cup comes off the valve.
https://www.ebay.co.uk/itm/402108621845?epid=27017016881&_trkparms=ispr%3D1&hash=item5d9f8aa415:g:IPwAAOSw5BVeW9bP&amdata=enc%3AAQAGAAACoPYe5NmHp%252B2JMhMi7yxGiTJkPrKr5t53CooMSQt2orsS%252BMKizvpuEDUfX4dvRWfUzURblK36%252BPNf4lX6vgxusHh0GHwCj0dJ%252BH1Ebar3rSvQXHHlOooirdet7SZ5H7h0OGGiMHgxuLEBJ8KzWOj8GsVY%252FlgrqLPYc3v9SwUudsvKNrDj8vGl%252FEX1wrFPODxM2zJIZCcETQ7%252BmT9bKdqNVfh%252B0xuIINfIAJRsRlQOwMZAIZM8ZFSw3E30HZNGueMJOBBaKvX50Xo%252BT%252BS7D%252FNh%252FM2Di1NecTc8Ge0hyJh7yjLplGvkc%252Fzy%252FbD0cdEQsKShM1%252BuWg0w%252F99ycu3fZ6lg4Xo5JJ%252BdriAYUeNCUoJVCI3vaOPpIgclSVGLuUv%252BVfYoVX98U7HugW%252FNe8zcB0xMHe3tOZ5Y97Xg%252Bzq06ezth3BK1mBCgWfpPf%252B%252BdZDGFzy4tPu%252B1gWPZGRxDChw5HDiTia4lSUUA%252BQlTBU2%252BHS61FB82rk3yNlMwFe2cpYAUQS2lr9A7LnK1blM9ZSXNph3zcZNrhhF8anuU0zc2y8KCd%252BVWYK4NE2Wzi%252FEgqgjYkb6ZQVx1o%252BQ5RkLyuvxyMsFMHMY7zg%252Bmb2zCBAZz0epUSD5emDdHvHjus97O%252F1yeI2GjhzH0hs5OXz63I7nM9rPsWAcS5kyucZcR8JNT8FZ81Wp9CwoKmKUjF%252F9pZnU982QaXZZ3jlT982pGi2a%252FYNDYT6jIZj3BWzdnAXmVl%252BJHg%252Fzw2ozkOgPnXyy7UtAL7qod8IkhN2PSA%252BLAaMuf0uG6NEbf4eGCEsVYopWPkWx2TU1Td%252FVa3kHVjUtnOllTv5ILwsuaw4JfuyGcLe%252FpwdoeKB8spvkhcwwR6FklmJREj3%252FBLnP7WxuMOvgEncrQeMsTw%253D%253D%7Cclp%3A2334524%7Ctkp%3ABFBMopbFushf
heli_madken:
My tip to stop the cup coming off the valve - find the stickest chewing gum you can!!
Oddjob:
The easiest and to me, the best way to lap a valve is to use a tap wrench, the chuck type. Fit the valve with paste attached and grab the exposed stem with the chuck. You can then pull against the valve whilst oscillating the valve at the same time, far better than spinning the valve. You can vary the amount of pressure depending on how bad the surface is. You can check the condition of the face by lowering the valve as far as the chuck allows and inspecting the face. One of the better things about this method is that when you think you have a seal leave the chuck attached, fill the port with petrol whilst pulling on the valve, if it leaks past the valve head you can easily spot it, if it doesn't you have a decent seal without having to fit the springs etc. Of course you check the seal when the springs are attached using the same petrol method. Even a very small leakage can be seen by the petrol just misting through.
I had to do 24 valves on a CBX head one time and this method was the one I used. The sucker method is exactly that, for suckers. Believe me, this method really works.
Example of a chuck type tap wrench, make sure the jaws are big enough to take the stem diameter but at the same time make sure the chuck with fit down the valve spring hole.
https://www.ebay.co.uk/itm/393855967252?hash=item5bb3a52014:g:RYoAAOSwQeNh2Y1d
The very best tap wrench is the Snap On as it has a spanner fitment, saves you trying to grip the wrench with your fingers to get it tight enough.
https://buy.wesco.com/Tools-and-Installation/Drilling-Tapping-and-Milling-Tools/Tapping-Tools/Tap-Wrenches/SNAP-ON-TOOLS/Tap-Wrench-1-4-1-2-in-Tap-High-Carbon-Steel/TD50/p/78582828061-1
You could buy a normal one like the first link and grind some flats onto the chuck I suppose.
kevski:
--- Quote from: RBoss on January 10, 2022, 10:45:29 AM ---
--- Quote from: deltarider on January 10, 2022, 10:29:49 AM ---Hope someone can teach me on this. Is it true that some valves are special and are not supposed to be lapped and if you do, you will do more harm than good? Second question: what is it precisely, that causes valves to wear?
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Additional question to this, what would make the valves special (do I have them? ::) )
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Generally nothing as long as the seating area is in spec, seats can be two or three angle.
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