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1979 CX500 Custom, 12k miles, Vetter fairing
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Discussion Starter · #1 ·
The Owner's Manual says valve clearances should be .08mm/.10mm intake/exhaust.

The FSM says valve clearances should be .10mm/.12mm intake/exhaust.

...Which one is right? Which one destroys engines?

I'm new. I've never done this. I was just getting started. And of course I'm dead in the water looking at 2 sets of conflicting data. I'm searching this group for insight.

Owner's Manual:

Font Circle Number Monochrome Pattern



FSM:

Font Rectangle Circle Writing Handwriting
 

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Look at the difference between the two settings, about .001". That is not much difference.
A lightly loose valve is better than one which is too tight.
 

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1982 cx500tc turbo
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Hi
I would use the Owners spec
Also the FSM spec would work as well
a bit on the tight side and that might make them nice and queried
I have not set my valve lash on my running CX500C yet
but I can assure you mine will be set to the tight side and rechecked HOT to see where they are at
being all aluminum block and cylinder head they will grow with heat and that will open up the valve clearance

YES some one will tell you a storry

TLD 🇨🇦 🇩🇰
 

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1979 CX500 Custom, 12k miles, Vetter fairing
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Discussion Starter · #5 ·
Whoa... so everyone here so far says these measurements, given to the thousandth, don't matter? Yikes! Why are the two main sources of data for this apparently important adjustment DIFFERENT FROM EACH OTHER? If it doesn't matter: when would it start to matter? Should I just ballpark it? I'm just baffled. Why wd the FSM have us set a gap ON THE TIGHT SIDE rather than CORRECTLY? Why would one part of Honda argue with another? I have to say that even though I don't understand anything I'm not ready to go eenymeenyminymo on this one.
 

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Whoa... so everyone here so far says these measurements, given to the thousandth, don't matter? Yikes! Why are the two main sources of data for this apparently important adjustment DIFFERENT FROM EACH OTHER? If it doesn't matter: when would it start to matter? Should I just ballpark it? I'm just baffled. Why wd the FSM have us set a gap ON THE TIGHT SIDE rather than CORRECTLY? Why would one part of Honda argue with another? I have to say that even though I don't understand anything I'm not ready to go eenymeenyminymo on this one.
Then take it to a shop and pay $$$$ A couple thousands of and inch is not going to be noticeable in most cases. you are not running a bike on a racetrack at 10K RPMs I'm assuming
 

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I don't know the official reason for the difference between the owner's manual and the factory service manual. Have a look at the dates each was published. Sometimes mainrenance standards are revised. Perhaps that has happened in this case. I'd go with the most recent informationn.
 

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1979 CX500 Custom, 12k miles, Vetter fairing
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Discussion Starter · #8 ·
I'll just wing it I guess! And go by the sound when I'm done. ... I also notice that my bro's feelers that I borrowed are only .002, .004, .005 -- no .003 at all! So I'll just do my best. I'm happy to do that. I just figure when a big company gives a spec to the thousandth that it's for a reason...
 

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The difference is negligible and for the most part beyond the skill level of most Saturday mechanics.
One thing is certain, too loose is better than too tight.
That said, doing both valves with the same feeler at the same time is by far the most accurate because of rocker shaft clearances. This I think, is most important to alleviate wear on the shaft and rockers.
When finished, the feeler gauge should have a bit, just a bit, of drag. Too much is a crapshoot as it might be tight, and too loose is the same, just safer.
Too tight and the valve runs too hot because it's cooled by the seat, too loose and the clicking is a bit more noticeable. Way too loose and the wear on the components accelerates.

HOpe this helps, Capt. Frank
 

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1979 CX500 Custom, 12k miles, Vetter fairing
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Discussion Starter · #11 ·
I'll do my best and listen for the difference! We'll see what the gaps are to start. My bike has 12k miles. Nice! I'll record the sound before and after. ...A further funny thing is that my brother's feelers are wrong for the FSM but right for the Owner's Manual! FSM wants the .003" which I don't have. ...So I'll just go w the .004 and .005 that the Owner's calls for and call it good!
 

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You may know this already. When the crank is at the TL mark check the valve clearance If your feeler gauge won't fit chances are that you are on the wrong stroke. In that case turn the crank one full turn until at the TL mark again. Now you should be able to insert the feeler gauge.

A check on your adjustment is to try to insert the next larger feeler. If it goes then the clearance is too large.
 
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Just a guess here, but the OWNERS MANUAL is directions for Joe Schmo, the FSM is written for professional mechanics, where they can be expected not to err on the tight side, which is more likely to cause burned valves. 🤷🏻‍♂️
 
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Curious though, I don’t recall this observation coming up before.
 

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I have Clymer, Haynes, FSM but it is just for the GL500/GL650. The Haynes shows CX500-A, CX500-B, CX500C-B and all 650models .004/.005 with all other 500 models .003/.004. I also have a book that has an article from Motorcycling Monthly, Feb. 1979, that gives the .004/.005 numbers for the CX500-A. The Clymer and GL500/GL650 FSM both give the .003/.004 numbers for all 500 engines. But I have set all my 500 engines at the .003/.004 with no blown engines. Until you brought this up I wouldn't have known there was a differance. You have a CX500C-B, I think you are on the right path. Good luck with valve setting.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Another indicator of TDC on compression: when all the valves are closed, the pushrods can be rotated easily with a light touch.
 
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I don't know the official reason for the difference between the owner's manual and the factory service manual. Have a look at the dates each was published. Sometimes mainrenance standards are revised. Perhaps that has happened in this case. I'd go with the most recent informationn.
yes...I recall slight differences for the clearances in the FSM addendums....

a quick look at the 1980 Addendum is .004/.005
 

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1979 CX500 Custom, 12k miles, Vetter fairing
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Discussion Starter · #19 ·
I love a 15 minute adjustment that involves two different possible readings of the same marking.
 
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Mines a 1881...the Addendum and owners book match.....so no procrastination....

the differences are minor you have posts suggesting either....
 
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