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The ‘Husky’ 125-175
Big Bore Enduro Special
Ever wanted a real enduro bike? Ever
wondered what it takes to make one when the factories don’t quite get it
right? We are going to take a look at a VERY special small bore enduro
bike that was created by the author in the late 1980’s, - long before
the KTM200 was ever dreamed about.
Big
Bore Kit - Off the Shelf Sir! - You'd be so lucky!!!
WANTED: Enduro Bike - Must be light,
fast, torquey, supple supension for tree roots and rocks, sharp turning
yet stable and well behaved at very high speeds. In short a torquey ‘pull
you out of any situation’ yet scream to the moon engine, in an
ultra-lightweight super nimble chassis.
Dated
looking now - but the hottest ticket around in 87'. Some of the
standard features that were really good on this bike, were frowned upon at
the time by the American magazines, - Like a flat seat/tank junction that
allowed you to easily transfer your weight up front. The Yank testers
didn't like the 'feel' of a bike you sat 'on' instead of 'in'. Of course
all good dirt bikes have seats like this now!
A question that has to be asked is - why
build a bike when there was so many to choose from? That can be
answered by taking a look at its contemporary competition and events that
it was designed for: Starting with the bigger capacity bikes, 250cc
2-strokes were out of the question - not because there weren’t any good
ones around, because in fact there were some stunning ones around, which
had engines to die for, both Husky’s and KTM new how to build fantastic
enduro engines, but due to their weight they were ruled out.
Remember the first rule of any enduro is
‘you have to finish!’ Now having houred out in the first morning of
the first day of a particularly wet and boggy British National 2 Day
Enduro Championship event one year, when my 250 Husqvarna became wedged in
a deep gully. Weight became of primary concern, - I wanted a bike I could
lift out of almost any situation - no matter how gnarly!
Pistons:
Aftermarket DT175MX piston on left, dwarfs the Husky 'Mahle' piston.
The Yamaha piston was modified by shaving away excess metal. This
lightened it, improved gas flow, kept it cool and also aided lubrication -
hence reliabilty.
Note: Shamfer on skirt bottom helps keep oil where it belongs - on the
barrel wall.
There were two 200cc bikes around at the
time – the Honda XR200, a great fun bike but about eight years out of
date - no go and no suspension. Kawasaki were replacing their ageing air
cooled KDX 200 with a new water cooled version. And the superb Yamaha
IT200 never really made it to these shores – but was also now an ageing
design. Kawasaki’s water cooled KDX turned out to have many faults, - it
was as heavy as a 250. Had poor suspension and the wide exhaust expansion
chamber would wedge the bike hard in muddy ruts – if the enormous front
fork under-hang hadn’t already done it!
 Now
the 125cc enduro bikes were very light and nimble. Powerful little engines
and their suspension was top dollar too. In fact the KTM and Husqvarna/Cagiva
offerings of the late eighties were very accomplished machines – capable
of winning world championships in the right hands. BUT and this is the
crucial bit – NOT if your over 14 stone and that was without all the
race kit on!
Small Ends:
Cagiva little end 'Top', an expensive but high quality item, far outlasted
the Yamaha little end pictured below it.
Note: the difference in needle roller widths for starters!
125cc enduro bikes are great fun, but the
narrow power-band demands a lot of input from the pilot. You have to be
‘on the case’ at all times, - if you get caught in the wrong gear at
all your in trouble. And the heavier the rider, the worse this situation
becomes!
Now as it happens, back in 1987, seven
special evaluation 125cc enduro bikes were imported to the UK. They were
modified World MX Championship winning Cagiva’s, decked in white livery
and badged as Husqvarna’s. Of the many trick bits that were fitted to
these as standard, a few really stood out at the time - six speed wide
ratio gearboxes (unheard of then – and now on a 125), Ohlins rear shock,
Marzzochi forks, hard hitting high horsepower power-valved watercooled
engine. Great ergonomics – comfy seat and very narrow twin radiators.
This engine put out over 40bhp – but at
over 11,000 rpm. As many will testify not always ideal for trickier enduro
going! But this engine unit was going to prove to be the perfect base for
the authors big bore 175cc special.
Boring
or what!: Compare the hole size in the middle of the modified barrel
'175cc' on left - to that on the 'fairly' standard 125cc barrel on the
right!
Note1: You couldn't just bore the original barrel this big - there
was not enough metal to do it. So the complete guts from a DT175MX barrel
was 'inserted' - just like that!
Note2: The flat sides on the right hand 125cc barrel, were due to
previous 'heavy duty' mods, when this little baby was one of four 125cc
cylinders grafted side-by-side in an ultra special 500cc GP road race
engine!
Modifying the motor – 175 into 125
will go!
Stage 1: Drill the 125cc barrel out
seriously oversize – like there was no barrel walls left at all!
Stage 2: Next grind all the fins off
a Yamaha DT175MX barrel, so that only the iron liner is left with a few
millimetres of ally around it.
Stage 3: Machine these parts to fit
each other ‘very well’.
175 into
125 will Neatly Go: Tiny Cagiva engine packed gobs of power.
Note1: This bike was sold as a Husky, but when all the stickers
fell off - it stated Cagiva everywhere! (see the barrel 'Cagiva' marking.)
Note2: Inner tube strapped around front of radiator hose to prevent
brush damage from brambles etc.
Note3: The hand welded exhaust front pipe can clearly be seen.
Note4: Fuel pipe
from petrol tap travels across to an inline fuel filter, which can just be
seen under the tank.
Stage 4: Heat one, freeze the other
– then press them together tightly with a thermal bonding adhesive.
Stage 5: Spend hours matching
transfer ports up and gas flowing.
Stage 6: Make a new oversize
powervalve assembly.
Stage 7: Fit a new Wiseco 67mm
diameter 175mx piston.
And voila, we have a 175cc killer motor. If
only life was that easy, – well we still had a few more little items to
sort, but that was basically it.
What
Goes in Makes all the Difference!: The inlet ports on the left hand
big-bore engine, had to be redesigned and opened right up to let the new
engine breathe properly.
Ancillary Problems!
A new larger expansion chamber had to be
designed to work together with the new engine. The carburettor had some
new passageways drilled to accommodate extra adjustable jetting. The
powervalve governor spring was ground thinner to lower the rpm at which it
opened. New ignition timing curves had to be developed along with a
special lightweight flywheel. But the final motor was well worth it,
unbelievably well worth it.
Managing
the Gas Flow: The exhaust and transfer ports in the new cylinder liner had
to be ground to match the original 125 barrel carefully by hand.
Note: How thin the cast iron liner is at the base, compared to the all
alluminium 125cc barrel on the right.
Even at low rpm the slightest touch of
throttle made the front wheel paw the air. It would easily outdrag any
KDX200 or 125MX bike, yet had an engine that was as smooth as silk, - true
electric motor style power delivery. It would pull down low – yet rev to
the moon. All who tried it over the years without exception stated "I
wish I had an engine like that".
Now all I
had to do was learn to ride properly!
Big
Headed or What!: To keep the compression ratio within optimum power
limits, the cylinder head and combustion chamber needed serious work.
Note1: The top picture clearly shows weld around the spark plug
hole and the cylinder head face. Both these areas had been built up by
approximately 2mm each. A) To keep the spark plug protruding the correct
distance into the combustion chamber, and B) To provide enough metal to
machine the new 'hemi-squished' combustion chamber design.
Note2: The lower picture (the authors Mk1 '175' head design) shows
how the cooling has been improved by increasing the water passage way
openings and also by adding extra 'holes' near the exhaust side of the
head to aid circulation and cooling (more power = more heat, therefore
increased cooling was necessary!). The combustion bowl seemed huge
compared to the original 125. The poor burn pattern shown by the carbon
deposits, were due to incorrect ignition timing during testing.
Final Touches -
In the interests of finishing 2 day enduro
events by minimising mechanical risks, speeding up maintenance and making
things easier for the rider, many other useful modifications were also
made to the rest of the bike.
Quietly
Powerful: A specially fabricated silencer was designed to work with
the hand built one-off expansion chamber. This gave a really broad power
spread from 7,500-11,750rpm.
Note: The under-slung 'boost' chamber below the main silencer unit.
The seat was turned into a quick release
item. A neat auto chain tensioner was fitted to the bottom roller
assembly. An underbelly exhaust guard was welded to the chassis. Front
mudguard spray extender fitted. 4mm thick dural plate bonded to the
radiator sides to prevent impact damage. - And many many more. Etc.
Please
Release me - let me go!: The 'inner tube' rubber bands provided simple
yet effective quick release and storage. The mudguard 'crossed rubbers'
held an ingenious secret quick fit tube! (in the days before mousses.).
The seat side mounting brackets were filed into 'slots', so the seat could
just drop into position over the normal mounting bolts and was held on the
bike only by the rubber strap across the seat mounted ally bracket fitted
at the rear.
The ‘Husky 175’ ended up a quiet,
reliable, road legal super fast racing package, that was a truly
exceptional bike in its day – the only thing that ever let it down was
the rider!
The author kept and raced the bike for
eight years when eventually a catastrophic engine failure at the
Natterjack British Championship round ripped the internals of the barrel
in half. The damage was irreparable and the bike was eventually converted
back to a 125cc engine, with which it still runs today – but with a new
owner.
Three
Mods to Make Life Easier: Hassle reduction and easy maintenance are
important factors in 2-Day British Championship Enduro rounds.
Note1: Wheel weights on the spokes kept the bike shake free at 70mph
on the roads.
Note2: Grab handle welded to wheel spindle meant quick one-spanner
wheel removal.
Note3: Tough Dural plate attached to strengthen chain guide block.
Brushing
up the Act: Alluminium brushguards didn't exist in this country in the
eighties until the author invented 'Knuckle Dusters'. This bike was also
fitted with a tiny digital speedo. Both these products were successfully
sold to an eager market, by his own off-road accessory company
Electraspeed.
Note: Mudguard extension prevented mud-spray on riders goggles!
Weird
but Wonderful: The 'V' shaped expansion chamber didn't catch rocks or
get jammed in ruts!
Note1: Exhaust guard bolted to the lower frame sticking forward,
prevented any harm to the the pipe when straddling large trees or rocks.
Note2: Fibreglass cladd pipe was whisper quiet - and strong!
Note3: Tie wire from brake pedal to frame prevented sticks and
undergrowth from jamming the rear brake on.
Was all the work worth it? In a word
yes, during its heyday no other bike was comparable. Eventually – and
many years later, KTM cottoned onto the idea of a powerful lightweight
bike and their 200EXC was born.
Author and Bike owner – Adrian Harris
(Biker)
Would you have the
patience to build one?
If you have
built an interesting special
- no not just bolt on bits like the ones most of the magazines feature to
boost their advertisers money pockets!!! -
A real one-off special - something a bit different - something we can't
all go out and buy! Then
contact Biker
here and we will be pleased to do a feature on your bike!
PS. IF
you enjoyed this feature and would like to see more like this on Biker's
Website - PLEASE email the author
to tell him!
(And if you didn't
please also tell him - Otherwise you never know what rubbish you could end
up reading here next time!!!)
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