Ron,
Standard rocker ratio = 1.6. (22,5 : 36)
Lift of the standard cam is 6.5 mm. (27.5 : 34)
Lift of the inletvalve is indeed 9.9 mm.
Sure 6.5 x 1.6 = 10.4.
The difference is taken up through normal flexing
of the pushrods under load and normal tolerances
of the rockers/rockerarm.
Bent pushrods may be a result of not having the
preload set as it should be.
Preload is measured with heads and rockers installed.
The pushrodseat of the lifter should be 1 - 1,5 mm
beneath the spring of the lifter.
Ideally all should of course be the same.
Adjustment can be made by either adjustable pushrods
or by shims under the rockerpedestals.
If the preload is not correct (too big) this can result
in bent pushrod(s).
Difference in preloads between rockers can be the
result of different depth in the seats by the valves.
When valveseats are recut the valves sit deaper in the
head and so stick out higher towards the rocker.
Lex.
Holland.
11:10
Aan: Buick-Rover-V8 Mail List; RRO List; AU LRO List
Onderwerp: V8 Cam lift
Does anyone know the correct figure for the cam lift on a Rover V8 engine?
I just pulled the inlet manifold etc to replace leaking valley seals on my
Range Rover. As the motor has about 180,000 km (112,000 miles) on it, I
thought I may need to replace the camshaft and the hydraulic tappets. In
fact, I ordered the tappets before I pulled the motor down as I had at least
one, maybe two noisy ones.
But the tappets and cam seem almost perfect. I checked the lift of each of
the lobes (by a crude method of measuring the height of the top of the
tappet (lifter) from the tappet guide at full lift with vernier calipers.
Subtracting the height at minimum lift gave an approximate lift. There were
slight differences across the inlets (6 - 6.4 mm) and also across the
exhausts (about 5.65 - 5.9 mm). Does anyone know the normal range of cam
lobe lift? The RR 1970-195 workshop manual states the valve (as opposed to
cam) lift is 9.9mm. But this is a product of the cam lobe lift and the
ratio of the input to output rocker arm lengths viz., 25mm : 33 mm = 1.32.
So if I divide 9.9mm valve lift by 1.32, I get 7.5mm as the correct valve
lift. But my cam doesn't appear to be suffering significant wear. However,
my cam is not original. The motor was bored and stroked to 4.6 litres,
that's why it has about 180,000 km (the Rangie has 335,000 km on it).
If I need to, I'll refit the rocker gear and measure using a dial gauge on
the end of the rocker. But, I think that pulling the motor down further to
replace the cam wouldn't be cost effective. By all reports, an engine with
this mileage should have a badly worn camshaft.
But what is interesting is that there are two bent pushrods, one of them
quite badly. Both are on the inlet valves of the second cylinder back from
the front in each bank. By the wear pattern on the side of the pushrods
where they have been rubbing against the cylinder head, they were bent quite
some time back. I don't know much about hydraulic lifters. Is it possible
that we've had a lifter pump up and become solid?
The only other things I can think of are a sticking valve (bent?) or
over-revving of the engine. Any suggestions?
If you ever do this job, don't forget to buy the heater hoses (I forgot).
To replace those two at the back of the manifold would be almost impossible
with the plenum chamber and air ram block in place. Also replace the two
from the water pump to the tubes at the front of the manifold. I forgot
those too.
Ron Beckett
'86 Range Rover 4.6L
Editor, Webmaster & Database Manager Hillman Owners Club of Australia
http://www.hillman.org.au
Editor, Land Rover Owners Club of Australia (Sydney Branch)
http://www.localnet.com.au/~lroc
Personal web site http://www.users.bigpond.com/hillman
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