Things you probably should know, but don't.

"When seating the tappet shim, be sure to face figure printed surface
to the tappet" is what it says in the manual. Which has made me realise
that despite 37 years of spannering, I don't know what a tappet
actually is, & have never needed to know - until know.

My instinct says it's whatever the camshaft presses against, so in this
case it's the buckets, & the numbers on the shims should therefore be
facing upwards (it's shim-under-bucket).

I gave up relying on the way things were installed previously as a
guide years ago, & this is a good example of why - most were facing
down & a couple up. Although I'm struggling to see why it would make a
difference in this configuration.

What say the FOAK?

 

The only thing that occurs to me is that it's to prevent the numbering
rubbing off, but then there's nothing really 'rubbing' against it I
guess?. I suppose it /could/ be a difference in the surface treatment
one side to t'other, but I doubt it.

 

Something that small will be through hardened (not surface treated).

 

That sort of matches what I thought. I thought that with a OHV setup
the cam moves the pushrod which moves the rocker arm, which is
connected to a tappet[1] which moves the valve.

On a OHC, there's the cam lobe acting directly on the bucket as you say.

According to Wiki(pedia!):
"Properly speaking, a tappet is only that part of a rocker arm which
makes contact with an intake or exhaust valve stem above the cylinder
head of an internal combustion engine"


[1] As in the things that "taps".

 

CT escribió:

http://tinyurl.com/68etaf

 

It because the rocker arm (when they use them) taps the top of the poppet
valve, so the arm is the "tappet" Or "tap-it". Probably, but no fucking
guarantee that what I just typed makes any sense or is in any way true. I'm
sticking with it though.

 

That was going to be my reply, including the "tap-it" bit as that's where it
taps it, thus setting the "bit where it taps it" clearances. At least that
is how it was explained to me all those years ago.
I'll stick with it too.

 

I was sorta asking both really. Is does seem obvious that they go a
specific way to protect the stamps, but not why that's necessary with
shim-under-bucket where the shims are sandwiched between two lumps that
only move up & down.

The only reason I can think of is that the stamped face goes against
whichever object it's most likely to stick to, so the other side gets
the hammering when things are loose. All the shims were stuck to the
buckets in this case, so when I eventually find a dealer who isn't a
complete waste of fucking space[1] & get the shims I need, I'll stick
'em in stamped side up.

The only time I've thought of a tappet as an object is the hydraulic
tappets in most car engines. Other than that, it's just a generic term
for whatever you adjust or change to set the valve clearances in my
mind.

[1] Cagiva dealer has no shims. Other local dealer said they had on the
phone, but when I went in they'd sorted me some big shims as used in
Triumphs rather than the little ones I asked for. George Whites were as
usual a complete waste of time.

 

It does make sense, & is probably where the term originally came from,
but it's obviously not true when talking about engines without rocker
arms.

 

<snip>

Yeah, unfortunately they're all the makes covered by George Whites,
which means a trip to the other side of town with no guarantee they'll
have any.

 

Yersh. I called them this morning & they spent five minutes checking
the computer for the first size & said "we've got eight of those", then
another five minutes on the second size resulted in "they're special
order only". Trying to get them to just check what they've got in the
workshop seemed to confuse them.

 

One word - work.

 

Only another 20 years to go before I can jack it in & concentrate on
being poor for a few years before dying.

 

Although the valves are still tapped. Adjustment is totally different, but
the top of he valve still gets a tap every time i opens.

 

I can't think of any other explanation as the term describes the action
perfectly.

I should bloody well hope so.

 

As is -Citizen- -Sm- Mr Auvache.

 

Only when I'm having a shit week. Normally I'm a right little ray of
sunshine.

 

Thankfully work came to an end, so I took your advice & tracked some
down. All back together now & running sweet as a nut. I'll double check
the TPS & synch tomorrow, then it's dyno time. My guess is 112bhp.

 

But they don't, the bucket rotates, otherwise you get the cams digging
into one part of the bucket. Certainly on Alfas, that have a split
cam, one lobe was fractionally higher than the other to make sure the
bucket rotated. It didn't work though, and the boxer cam buckets wore
like bastards. But they were pioneers in this respect. [1]

AOL. Tappets comes from the OHV days, where the rocker arm was
adjusted against the valve, The tapping was what you could hear when
you rocked the rocker arm. Sadly, all that's long gone with OHC and
hydraulic 'tappets'

Paul.

[1] Visionary design, or Alfa unreliability, take your pick ..

 

Your're right. I took the bike home today at lunchtime. Lovely it was,
sun shining, bike running on song and tyres sticking on corners ....

Then I went back to work

Paul.