causing a rattling sound with an RV8 engine?
Andreas Gloor in Switzerland raised the question: "Are
there members who experienced valve problems? More precisely
who has experienced valve rattling as soon as the engine is
heating up a bit? It sounded a bit like a 4 cylinder engine
is running next to the V8." He provided a copy of a short
report on this matter which was published in Sign Post, the
Swiss Centre's magazine reproduced alongside.
Nic Houslip and Tony
Lake provided some comments on the likely cause of the rattling
See the full RV8NOTE463
with valves on MG RV8
A few years ago I had a somewhat strange experience with the
engine of my MG RV8. One day I was waiting at a traffic light
and I heard the sound of a 4-cylinder engine next to my V8.
Strange. There was no other car standing nearby. I drove on
and at the next traffic light I could hear the strange sound
again. When I took the MG for a ride out of the garage again,
everything was fine, but as soon as the engine was warm again,
there was this strange rattling sound.
I took the RV8 to a workshop as I suspected that something
was wrong with the valve train. It sounded to the mechanic
that the valve clearance was too big. However, the V8 engine
has a single camshaft and hydraulic tappets to compensate
the valve play. So the hydraulic tappets were replaced and
for a short time the problem seemed to be solved. Until, yes
until the rattling started again. It increased to a really
In a further workshop visit the two cylinder heads were then
removed and no defect was found. But there were hard glassy
deposits on the valve seats and the valves were leaking. The
valves and seats were reworked and also the cylinders and
pistons were checked, but without findings. The problem seemed
to be solved and for a while nothing rattled anymore.
But the joy lasted only two months and then the hammering
noise was back again. Rocker arms and shafts were checked
and a test run was made without valve covers, because there
was the suspicion that something was wrong with the lubrication.
Nothing. Only a tar-like mass was found in the intake manifold
and on the valve discs and valve shafts. The question from
where did it come? The workshop owners discussed the matter
during a natter; but nobody knew what to do. The petrol tank
was searched with an endoscope and the petrol filter was sawed
open, but no residues were found.
I asked my mechanic if there were any rubber fuel lines that
were dissolving. Answer: no. So it could only come from the
tank. As a chemist, I know that there are deposits which are
not necessarily visible, because they are gel-like or glassy.
So I asked the mechanic to flush the tank but no brown or
black residues or mucus were found. BUT: from then on the
problem with the valves was gone.
the chemist's point of view
The MG RV8 had been in service in Japan for a long time and
was operated with the gasoline available there. Now the MG
was on the road in Germany and Switzerland for a longer time
and the gasoline quality changed here: new additives and alcohol
(keyword ethanol, E5 and E10). Possibly there were residues
in the tank for a long time but they were quiet. The new additives
and especially the ethanol slowly dissolved the dormant deposits
and transported them through the injection system into the
combustion chamber where they coked (tarry and glassy mass)
and thus hindered the free movement of the valves.
The symptoms reported suggest a loss of oil supply to one
bank of hydraulic tappets, if the tappets are empty they clatter
The blockage will be caused by quite a large object at the
beginning in one of the galleries drilled the length of the
block that supply oil to all the rotating and reciprocating
parts. It seems to be able to move since the noise does disappear.
Did the oil pressure gauge show a change in pressure? It maybe
that since it is pumping against a dead end on one bank for
a period that there is a sudden increase in pressure before
the relief valve opens wider.
There is no history, so it might be that there has been a
component failure in the past that left some debris. The debris
must be located somewhere in the passages after the lub pump
outlet, it might even be from a broken tappet, but it is hard
to imagine what else could get in there.
In my experience this kind of complaint is not uncommon after
a component failure. Unless oil galleries, sump, pipework
and oil filter housing are cleaned properly another failure
will occur. It often requires a complete teardown to account
for all the failed bits.
Comments from Nic Houslip
Tony Lake's explanation seems to be most likely, but as an
alternative solution the experience of a member at the last
Aldon Dyno day may throw some light on the problem, as the
member arrived with an RV8 that made an awful clattering noise,
almost everyone suspected hydraulic tappet problems. On a
dyno run it was down, if I recall correctly, to about 140BHP.
The exhaust gas analysis readings indicated fuelling problems
and then he mentioned he had fitted aftermarket injectors.
Replacing these at a later date with correct OEM parts cleared
the clattering tappet noise and returned the power to the
The condition of the combustion chambers and the valves in
the attached pictures would indicate a slightly rich (*
see note below), but different mixture in cylinders between
banks, whereas we would expect them to be similar. As a precautionary
measure, either replace with a new set of the correct injectors
or if possible, take the old ones to a Bosch service centre
and have them run a test on all 8. Then check the injector
rail for a loose part inside that could temporarily block
the fuel rail - an old injector grommet or similar.
The injectors are a Piezo electric crystal driven actuator,
this opens the orifice very quickly and with great force (relatively).
My suspicion is that if there were an intermittent shortage
of fuel pressure in the Injector rail due to a blockage, the
injectors may be noisy. I would also suspect the fuel pressure
regulator that maintains the fuel rail at a fixed pressure
above manifold pressure (so the injection amount is accurately
related to air flow) as this has a diaphragm and could be
suspect and might give over rich running.
replacing hydraulic tappets
When replacing Hydraulic tappets there is a requirement to
check that the correct preload is on each tappet, although
normally it is correct, but again might be worth investigating
Searching on internet "Hydraulic tappet preload"
will return several videos on how to do it. This is VITAL
if the heads or Block have ben machined.
* Note -
the mixture richness, carbon may be the results of not driving
the car hard enough, the Swiss are very observant of speed
limits and there are few motorways where you can drive hard,
but it is essential to do so. RV8s tend to fail emissions
at an MOT unless you drive to the MOT station via a motorway
and have some decent acceleration periods to clear the cobwebs
out - and bring catalysts to max working temperature.