Valve adjustment on Ford V6?
Eur van Andel
Following the book, I adjusted the valves on the Ford V6 engine
of a friend of mine. I shouldn't have, because it has hydraulic
valve lifters, which you shouldn't adjust. :-(
The engine is a 2 liter V6 and the car is a 1980 Ford Taunus:
I don't know it's name in the states, or if that engine
was ever used there.
The manual speaks about a valve clearance of .35 inlet and .45 mm exhaust.
When I adjusted this, all the clearances were to small.
After adjusting, the engine made a loud clicking noise and seemed to have
lost some power.
The valve adjusters are simple bolts screwed in the rocker arms, but they
turn very heavy. (seems to me the way they are locked)
My manual says that you don't need special tools to adjust, just turn firmly.
OK, now the questions.
How do hydraulic valve lifters work, anyway?
How should I adjust them?
Is it true that you never have to adjust these things?
How come then it doesn't work now?
Help!
eur
Phil Nelson
>Dear Netters
>
>Following the book, I adjusted the valves on the Ford V6 engine
>OK, now the questions.
>
>How do hydraulic valve lifters work, anyway?
>How should I adjust them?
>Is it true that you never have to adjust these things?
>How come then it doesn't work now?
Years ago, I adjusted the lifters on my '63 Ford 390 V8 by loosening each
one with the engine running, until it started ticking, then tightening it
back up until the ticking stopped. I can't remember who told me to do it
that way, but it seemed to work OK for normal driving. I did snap a few
pushrods doing 70 in 2nd gear, but I don't think that was due to the
valve adj. BTW, a '63 Country Squire station wagon is kind of sluggish
with only 4 of 8 cylinders working :-).
--
Phil Nelson . [ames|pyramid]!oliveb!tymix!pnelson . Voice:408-922-7508
To make an apt answer is a joy to a man,
and a word in season, how good it is! Proverbs 15:23
Codesmiths
Why do valves need a clearance ?
The ideal valvetrain should be be perfectly rigid, and transmit its
forces from one end to the other without any lost motion. This
implies zero clearance. Lubrication is also needed, and this requires
a certain amount of clearance, to provide a lubricant film between
moving parts. A traditional system with solid lifters used small &
tightly controlled gaps between the parts, allowing sufficient
thickness for the oil film, but small enough to not introduce much
backlash. As the gap size was known & carefully set, it could be
compensated for in the camshaft profiles. A common problem here is
thermal expansion, especially with long pushrods on OHV engines - the
reason why there are different clearance values quoted for hot & cold
engines.
How do hydraulic valve lifters work ?
Hydraulic lifters come in various forms, but most have a common
feature; they contain a piston & cylinder mechanism filled with oil
supplied under a fairly constant pressure from the engine's oil pump.
The lifter is inserted somewhere in the linkage between the cam
follower and the valve stem, usually as part of the cam follower
(tappet) itself. It can vary in length, controlled by the oil
pressure inside it. Because the mechanism effectively produces a
constant force on the valvetrain, over a moderate range of length
variation, it can absorb differences in the length of the valve train
whilst still exerting the same ideal force on the oil film on the
camshaft & valve stem. At slow speeds, a coil spring would work
equally well (and has been used before), but at the high speeds of
modern engines the spring tends to bounce and lose valve travel. In a
hydraulic tappet, the oil pressure in the cylinder acts as a spring,
but because of the narrow passageways inside the tappet, and the
incompressibility of liquids, it doesn't suffer the bounce problems
of a spring.
Why do I need to adjust them ?
There are always manufacturing differences in the finer adjustments
of an engine, especially things like the length of the valvetrain. On
an OHC engine, these inherent differences fall within the range of
the hydraulic tappet itself and no adjustment is needed (or even
possible). In an OHC engine, with long pushrods & rockers, then the
potential range of error is much greater and may well be beyond the
tappet's inherent ability to compensate. In this case, the adjustment
must be set initially, but this does not need to be as accurate as on
a solid lifter engine, nor does it need to be re-adjusted
periodically.
To set the tappets, consult the manual. As I'm not familiar with your
engine, I'm afraid I can't really help much. The lubrication of the
tappets is important though; some need to be initially primed with
oil & some need a setup sequence of adjust once, run engine, then
adjust again.
Andy Dingley din...@cix.compulink.co.uk