Valve Adjustment


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cross
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Re: Valve Adjustment

Post by cross »

Nice write up!
I did leave my valves at the highest gap by the manual.
I've been riding my bike a lot, I think that I put about 4500 miles since bought it in February and I love it more and more.
I will be taking a road trip with few friends from San Diego to Morro Bay which is going to my first long trip on a bike and j can't wait.
Sasha

'82 Honda CBX
'99 Triumph TBS
'01 Honda Valkyrie

:auto-sportbike:

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herdygerdy
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Re: Valve Adjustment

Post by herdygerdy »

Just one more thought on setting valve clearances.

I am kinda' old school and was very much used to dealing in the Imperial measurement of "thou' " instead of this modern metric malarkey. Over many years, I figured I had developed a pretty good idea of what 1, 2 or 5 thou' looked and felt like, but definitely not so in the metric world (I'm a bit slow that way!)

Then one day, I had a MAJOR "light bulb" moment and I will only ever use metric measurements on CBXs from now on. And here's why.

Example 1 - Tight valve.

Lets take a "280" size shim that is currently installed in a bucket. That shim when measured metrically via a micrometer will measure (you guessed it) very, very close to 2.80 mm thick.

Now let us assume you measure your valve clearance with the "280" shim in place and you find it is a 'tight' one at .04 mm. And you are aiming to set the clearance at the wider end of the allowable range (a very good idea for reasons previously stated in this thread) at 0.13 mm.

So you need to put in a SMALLER shim to achieve your target 0.13 mm clearance. But how much smaller? That's SO easy to find out using metric measurements and simple addition and subtraction.

From your actual clearance (0.04 mm), SUBTRACT your target clearance (0.13mm). So we have 0.04 mm MINUS 0.13 mm = -0.09 mm. (Note that is a 'negative' 0.09 mm and not a 'positive' 0.09 mm)

Now ADD that figure to the current installed shim thickness (2.80 mm). You get 2.80 mm PLUS (NEGATIVE 0.09 mm) = 2.71 mm. And that 2.71 mm (or "271"), is the precise size of the replacement shim you need to get to your target clearance of 0.13 mm.


Example 2 - Loose valve.

This time, let's take a valve with a "275" installed shim (ie; it is 2.75 mm thick). And let us say the valve clearance this time is loose at 0.18 mm and our target clearance is still 0.13.

So clearly we need to put in a THICKER shim to take up the extra clearance. But how much thicker? Again, its just simple maths using metric measurments.

Using EXACTLY the same calculations above....From your ACTUAL clearance (0.18 mm) you SUBTRACT your target clearance (0.13 mm), so we have 0.18 mm MINUS 0.13 mm = 0.05 mm.

Now ADD that 0.05 mm calculated figure to the thickness of your currently installed 2.75 mm thick shim and you get 2.75 PLUS 0.05 mm = 2.80 mm.

Once I realised how simple it became using metric all the way, I simply calculate the required shim size and can install that being confident it will almost always be perfect first time.

I will never go back to using the old Imperial for this ever again.

Hope this helps.

EMS
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Re: Valve Adjustment

Post by EMS »

:D :D :D Tony, Besides the fact that the CBX is a metric bike and designed with and around the metric system, I think it is all rooted in what we are used to and grow up with.
As you have no problem visualizing thousands of an inch, I have a hard time getting my arms around the sizes.
I know by looking at the numbers that a 19mm wrench is larger than a 17mm wrench, but I have trouble telling what's larger, a 3/8 or 23/64... ;-)

hondaman160mph
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Re: Valve Adjustment

Post by hondaman160mph »

I have another question about valve clearances. I checked my valves clearance at 12,603 miles and all were between .003" and .005".
I have put on 1,376 miles since then,how many miles can I expect to put on before adjustment is required? I know the book says check every 4000 miles .
I also read a post were Dave mentions using a 2 piece valve adjustment tool that doesn't require rotating the engine to replace shims. How does that work and were can I get one?

daves79x
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Re: Valve Adjustment

Post by daves79x »

Jeff:

If you had .003-.005 inch clearance at 12,000 miles, you are good for another 12,000. 12K is the magic number for CBX valve adjustment. Get them right at 12K and you'll likely never change another shim for as long as you ride it. The valves are bedded in by 12K and rarely need adjusting after that. My '79 has 45,000 miles on it and I think I've changed one or two shims after the 12K mark. Now if you run way up into the 70-80,000 mile range, you'd better check them as things will start to wear. I've serviced 2 80,000 mile CBXs pretty regularly and neither have needed shim changes in years.

Dave

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asacuta
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Re: Valve Adjustment

Post by asacuta »

My intakes are stable, but some exhausts need to be loosened when I check the valves every 6000 km or so. As the bike ages (60,000 km), the exhaust valves lose clearance at a faster rate. The big changes on the exhaust side started about 30,000 km; up until then, they were stable. I changed none at 6000 km, none at 11,000 km, none at 29,000 km, 4 at 32,000 km, 11 at 43,000, 1 at 48,000 km, 4 at 57,000. Over this time, none of the intakes needed changing.
Al

hondaman160mph
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Re: Valve Adjustment

Post by hondaman160mph »

That's good news Dave,going to put my carbs back on that you repaired for me and I will be good to go.
Does anyone have a white plastic crankcase oil catch tank they would be willing to sell me? Mine had a crack in it when I bought the bike and I sealed the crack with silicone but now the bracket has broken off and it's just laying in there loose.

Jeff

hondaman160mph
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Re: Valve Adjustment

Post by hondaman160mph »

I just found a tank on Ebay. Looks perfect in the picture so I bought it,$19.00. Looks like I can change it by removing the inner fender.

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cross
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Re: Valve Adjustment

Post by cross »

My bike had 24km when i did valve adjustment and i think i changed about 10/12 shims to make them all perfect at .13mm
I bought seome and swapped some around. It runs great now
Sasha

'82 Honda CBX
'99 Triumph TBS
'01 Honda Valkyrie

:auto-sportbike:

daves79x
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Re: Valve Adjustment

Post by daves79x »

Biggie question is: when were they last checked before 24,000? My guess is a long time. Glad none were zero clearance. But if you were just fine-tuning them to .13, then maybe not.

Dave

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cross
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Re: Valve Adjustment

Post by cross »

Since you reminded me, one exhaust valve was to tight to check. I had to put in a thinner shim to measure.
Sasha

'82 Honda CBX
'99 Triumph TBS
'01 Honda Valkyrie

:auto-sportbike:

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