Improving reliability and
reducing servicing costsCHAIN-DRIVEN CAMSHAFTS
Realising that should a camshaft belt break
in an interference engine (all four valves per
cylinder engines) an expensive rebuild
would be needed, Suzuki has concentrated
on chain-driven camshafts from 30hp
upwards. Located at the bottom of the
vertical crankshaft engine, the chain runs in
an oil bath and should last the life of the
engine. Honda also uses chain-driven
camshafts in its BF135 and BF150.
From 2011 onwards Mercury engineered its
75hp to 150hp four-strokes with chain-
driven camshafts, following on from Verado
models that all have chain drives designed
not to ever need replacing, unlike belt drives
that can fail without warning.
ELIMINATING VALVE CLEARANCE
ADJUSTMENT
Pioneered by Mercury in its Verado range
and now down to 75hp in naturally aspirated
models, roller cam followers where the
camshaft rocker lobes are kept in constant
mesh with the valves eliminate the need for
valve clearance adjustment. Kind of like
hydraulic valve lifters used in traditional
Holden and Ford sixes and V8s and some
Suzuki and Mitsubishi car engines.
run their outboards at WOT for extended
periods, so this is really of little concern.
LEAN BURN
Pioneered by Honda in its ECOmo
system, engines run with air:fuel ratios
as lean as 18:1 mid-range, only reverting
back to the normal 14.7:1 at or near
WOT. Honda’s “Blast” system also
increases the air:fuel ratio to 12:1 for
faster hole shot then once planing leans
out to 18:1. The overall result is improved
hole shot combined with excellent
mid-range fuel efficiency and of course
reduced exhaust emissions.
Suzuki and Yamaha also use lean burn
in their larger four-strokes.
VARIABLE VALVE TIMING
Again pioneered by Honda this system
holds intake valves open longer for
better engine “breathing” and increased
power and torque in upper rpm ranges.
It’s mainly used in larger outboards and
has been adopted by Suzuki and Yamaha
where the intake valves are kept open
across the bulk of the rpm range.
LPG-POWERED
OUTBOARDS
The option of LPG has been around for a
while now, with Mercury offering LPG or
propane kits for its smaller four-strokes.
But Tohatsu has developed the world’s
first dedicated LPG outboard that runs
on a separate gas cylinder. Known as
the MFS 5C LPG, it's de-rated from its
MFS 6C counterpart but still develops
the same bottom-end torque. Switching
from petrol to LPG reduces NOX (acid
rain) emissions by 30 per cent, carbon
monoxide (kills living creatures) by
a whopping 56 per cent and carbon
dioxide (global warming) by 15 per cent.
Switching to LPG also transforms
running qualities and the loan 5C LPG
was the smoothest running single-
cylinder five I’ve ever tested, simply
because the LPG burns hotter and
drier for a more thorough combustion.
For anglers who do a lot of trolling it’s
unbeatable in its power range yet it has
the grunt to easily push a seven-metre
yacht when the wind fails.
To reduce engine running
temperatures on hot sunny days the 5C
LPG is pure white.
In my opinion, providing the gas
cylinder installation is well engineered
with overboard drains (LPG is heavier
than air and can quickly fill a bilge)
and sniffer sensors, LPG is the future
of boating with internal combustion
outboards.THE WRAP
Obviously I haven’t touched on diesel
or electric outboards, which are other
topics by themselves. Diesel has
advantages such as even better fuel
efficiency and lower running costs than
petrol or LPG but exhaust particulate
emissions are still a concern.
Lithium ion batteries have
revolutionised battery technology with
much greater range for weight and
aren’t affected by being left partially
discharged. Of course these batteries
can’t be recycled like lead acid batteries,
so how expended units will be disposed
of creates another concern.
The most important aspect of
manufacturers complying with ever-
tightening exhaust emission regulations
is that the modern outboards are nicer
to live with on a daily basis. They start
easier, run way better and use a lot less
fuel. Sure they’re more complex but
providing dealer technicians are trained
in the use of diagnostic tools, keeping
modern outboards in peak tune is a
helluva lot easier.
For an old fart like me it’s hard to
believe that all these tech changes have
occurred in just 20 years. Wonder what
the next 20 years will be like!tradeboats.com.au 35Future Engine Tech