The reliable Honda 400EX is still very much a
contender in racing circuits, but NOT with a stock motor under the
plastic. The stock Honda 400EX just does not have the power output
that the newer Z400 / KFX 400, Yamaha Raptor, or Cannondale do.
That said, we believe the 400EX is currently one of the best buys
on the used ATV market. A new sport quad is going to run you more
than $6K out the door in stock form. Now consider a nice 400EX on
the used market for $3,500 to $4,000. Chances are that for the same
amount of total investment, your used 400EX may OUT-PERFORM that
brand new showroom quad.
To make sure our Project 400EX can keep up with the
new showroom equipment, we visited Tudor's Performance in Corona,
CA. You may remember Tudor's from several years ago when they
helped us with Project Quadzilla. While the Tudor's Performance shop
was literally a sea of yellow Suzukis, Jeff admits to having built
more Hondas over the years than he has Suzukis. Along with others,
in the shop was a sweet Z400 with a Tudor's 470 stroker kit and a
Yamaha Raptor getting a 730cc kit and custom intake for a single
While we had decided to have Tudor's assemble our new
440, to minimize downtime, we pulled the cylinder and top-end off
our 400EX and shipped it to them ahead of time, so the cylinder
could be bored, the head ported and the valve job performed. Yes,
this disassembly can be done at home by most novice mechanics. With
the help of a Clymer service manual and a couple mechanical buddies
to oversee our work, we had the motor apart and ready to be shipped
in under two hours.
Here is the intake on our 440EX head. The Tudor's porting
involves a number of things. The casting flashes are knocked down,
the transition between the port and valve seat blended and
radiused, and the intake is matched to the intake manifold. The
exhaust is ported to have a 26.5mm exit diameter which matches the
exhaust pipe and is polished more than the intake side. The intake
is left with a slightly rougher texture to help atomize the
With the porting done, the head is ready to be assembled. This
Motion Pro tool makes it simple. Tudor's perfomed a 3-angle valve
job and reground and lapped the valves. Since we would be using a
Stage 1 drop-in cam from Hot Cams, the stock springs were
cylinder has had the stock sleeve removed, been bored, and sleeved.
The sleeve was then finish-honed and the cylinder decked. The
sleeve was prepared for a 88.5 mm piston and can be bored at a
later date for a 89 mm piston on the next rebuild. Officially our
Honda will be about 435cc but we will call it 440. Prior to
installation the cylinder was cleaned using ATF fluid. The ATF
fluid is high detergent and does an amazing job of cleaning the
cylinder while adding a little oil at the same time.
piston is a custom JE piston built to Tudor's Performance specs. It
is an 88.5 mm piston designed for 11:1 compression. Yes, we could
have gone higher, but we were looking for a good reliable mid-range
motor that would run on 92 octane pump gas. Prior to assembly the
ring gap needs to be checked. We did find two of our rings needed
to be filed to achieve proper gap. The edges of the rings were also
de-burred to make sure they move freely. The piston is used to
square the rings in the cylinder when checking ring
start the installation with the cylinder. We preloaded the piston
using a ring compressor. The next step is a two person job - one to
set the cylinder down on the bottom end while the other installs
the piston pin attaching it to the rod. Make sure you have a wire
on the timing chain so it does not fall down into the motor. Now
torque the cylinder down and install the head studs. You will need
to double nut the studs for installation.
When the cylinder is done you can install the head.
You will need to thread the wire with timing chain up through the
head again. Install the head bolts and torque them down, then you
are ready for the new camshaft. No core needed.
Hotcam 400EX camshaft does not use the OEM automatic de-compression
system. You will need a press to remove the sprocket holder from
the stock cam and then to install it on the Hotcam. Do NOT press it
on using the ears but rather the inner diameter. Align the dot on
the end of the camshaft with the open spline on the holder. Line up
the timing mark on the left side of the case. Your cam lobes should
be facing down and both marks horizontal to the head and one mark
straight up and down.
Next Tudors installed the head cover. At this point you can
adjust the valves to the specs recommended by Hotcam. Set cold the
intake should be at .13mm and the exhaust at .15mm. With the motor
buttoned up we are getting close now. Don't forget that the
camshaft will need to be broken-in at initial startup. The engine
should run above 3000RPM for 20 minutes with very light
we can install our Edelbrock carb. You may remember the original install on Project 400EX. We have had
such good luck with the Edelbrock carb that we wanted to stick with
it on the 440. Prior to the install we sent our carb down to
Edelbrock so they could install the 440 retro-fit kit. The carb was
rebuilt and the 440 kit installed. We bolted the carb on and
connected the throttle cables.
Next up was the Tudors Performance high rev ignition box.
Unlike some of the XR boxes that many sell, you will not have
starting problems with this 10,000 RPM ignition box. Simply unplug
the stock CDI and plug this one instead.
440EX fired right up after we primed it. We ran it for 20 minutes
in the Tudors Performance shop with a large fan blowing on it to
keep it cool. We can't wait to ride it.
Next month in Part 2 we will tell you how well the package
works and bring you a full dyno report. We should have a couple
Hare Scrambles complete so we will know just how well the kit works
on the track. We expect to have a competitive, reliable machine, as
happy in the wooded trails of WORCS events as it is playing in the
dunes on the off-weekends, without breaking the budget.
Last but not least was installation of the new stainless 400EX
system from Bills Pipes. The system bolted up perfectly with no fit
problems and looks AWESOME.
Tudor's Performance designed the TRX440
Midrange Power Big Bore Kit to be reliable and is priced at only
Kit includes the Big Bore Sleeve (installed), JE Forged Tudor's
Performance 11.0:1 Piston kit, Midrange Head Porting and Valve Job,
Drop-In Midrange Camshaft, Hi-Rev + 1000 RPM Ignition Box and our
No-Blow Cylinder & Head Gasket.
1727 Commerce St Unit B
Corona, CA 92880