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Posted by paul c on June 21, 2008, 10:13 am
Ted Mittelstaedt wrote:
> Hi All,
>
> OK it's valve adjustment time for my 1980 CB750. So before pulling the
> cover I
> went by my local Honda dealer parts dept and asked about shims since I'm
> sure I'll probably
> need 1 or 2. To my disappointment they had none. (plenty of the small size
> shims
> for newer bikes, nothing for mine though) They can order them - if I want
> to wait
> a week, and the shims are $8 -each-.
>
> So now what? Do I go to the trouble of taking everything apart just to
> get some
> shim measurements then putting it all back together, waiting a week, then
> taking it
> all apart again? Do I get an expensive shim kit that I'll never use 99% of
> the
> shims in the kit? Do I call around to other bike repair shops with the bike
> apart
> and ask if they have a shim in the measurement I need that they will sell or
> swap?
> Do I scavenge bike wrecking yards for hashed-up bike engines that I can get
> for a song?
>
> Any ideas of where I could quickly get a few shims that I need for a few
> bucks would be most appreciated. What do other people do? (besides
> take it to some mechanic and let it be his problem?)
>
> Ted
>
>
Apparently (just saying this based on a couple of links I found), Toyota
twin cam engines use 25 mm diameter shims, so do some Triumphs and quite
a few Yamahas - perhaps Toyota shims will be easier to find locally.
By the way, I've never adjusted any kind of shimmed valves, but suspect
I may have to soon on a friend's 1982 CB750C - am a little puzzled that
clearance is supposed to be something like .05 mm whereas the shims
people seem to be selling online for cb750's all seem to vary in
thickness by exactly .05 mm. I'm assuming that if the valve springs and
tappets/cam surfaces aren't too worn then usually valve wear would cause
clearance to become tighter over time (I'm guessing because of valve
shoulder wear), so one would likely find after measuring that clearance
needs to be increased. Say for argument's sake that one finds it is
necessary to remove .03 mm of shim thickness, wouldn't that mean
removing, say, a 2.35 mm shim and replacing it with a 2.32 mm shim? Or
do these bikes come stock with several shims whose thickness isn't a
multiple of .05 mm or is my understanding all balled up?
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