Unicam > SOHC

I've read a few remarks in forums and comments sections of moto sites about Honda's choice to use a "cheap inferior" SOHC valve layout on the VFR1200FA. I want to explain the differences here and clear the air.

Technically,  the Unicam design is a Single Overhead Camshaft layout. There is one camshaft (per cylinder bank) placed overhead of the valves. But this design, which is unique to Honda, has some key differences and advantages.

A conventional SOHC cylinder head has a camshaft mounted down the middle of the head with a rocker shaft on either side. The valves are opened with rocker arms. It's simple and effective, but there are some disadvantages compared to a DOHC design... The main disadvantage is the added reciprocating weight from the rocker arms. The added weight limits the engine's rev ceiling. Another drawback might be the compromise of the combustion chamber shape. The spark plugs and ignition coils cannot be placed in their most efficient location: top center of the combustion chamber. The camshaft sits in the way.

On a DOHC cylinder head, the camshafts are placed directly over the intake and exhaust valves on opposite sides of the head. There are no rocker arms or shafts and the ignition coil and spark plug sit directly over the center of the combustion chamber. It can rev higher than a SOHC but it requires a bit more maintenance and it's bulkier.

Honda's Unicam is a hybrid of both designs. There is only one camshaft, but instead of sitting down the middle of the head, it is located directly above the intake valves, like a DOHC. The intake valves are opened from directly overhead through a solid lifter. (with shim adjustment) The exhaust valves are opened with tiny little roller rockers, one for each valve. The exhaust valves are smaller and lighter than the intake valves, and they don't open as far... so the added reciprocating weight from the rocker arms is less of a factor, and high RPMS are still possible. There is also less stress on the cam drive compared to a DOHC. Just one (shorter) chain is required to turn the camshaft, and a larger sprocket is used for more torque multiplication and less stress on the chain. The chain also doesn't have to bend through a complex path, so a simpler cam chain tensioner (with less potential for failure) can be employed. Valve adjustments are slightly simpler than a DOHC, because the exhaust valves have threaded adjusters at the ends of the rockers, which eliminates half of the tedious shimming work.

Honda introduced this design for 4-stroke motocrossers and off-road bikes. The reduction in bulk and mass is especially important to compete with flyweight 2-strokes. It made sense to employ this design on the big V4 for the VFR1200F. V4s are bulky engines and are tricky to package compared to the typical inline 4 on most sportbikes and the Unicam design helps make it a bit more compact. (smaller overall than the DOHC VFR800 motor) Very little performance is sacrificed compared to a DOHC and maintenance is a bit simpler.

Honda CBR250R

Honda have announced that their redesigned CBR250R will be offered in Canada and the USA next year. When Honda brought the CBR125R to Canada a few years ago I liked it so much that I bought one. It was by no means a high-performance motorcycle but it was great fun to ride

This new CBR250 would make a great "little brother" to my VFR1200F. Don't tell my wife.

Honda VFR800X Adventure

Honda have been releasing teaser sketches over the last few weeks that hint at an upcoming V4 "adventure" style bike which will be unveiled at the Milan show next month.

From what I can see, the bike they've come up with isn't an "enduro" style adventure bike like the BMW GS or KTM 990 Adventure, but more of a "standard" sporty roadbike meant for sport touring... much like the Suzuki V-Strom, Kawasaki Versys or Triumph Tiger 1050.

This was the original sketch. Some of the enthusiast boards started buzzing about a VFR1200-based adventure bike. The sketch clearly shows the continued use of the "layer concept" fairing as debuted on the VFR1200F... which will surely be incorporated into all future Honda sportbikes. The sketch also clearly shows an upright riding position with high handlbars.

This is the second sketch that was released a week later. The styling reminds me of the Versys. The layer concept fairing is shown again and Honda hinted at a "floating instrument panel"

This final sketch was released today. Clearly this isn't meant to be a true enduro adventure machine, but more of a "real world" sporty standard bike with an upright riding position that should be comfy for long distances. The bit of engine and frame visible is clearly carried over from the VFR800 VTEC, and not a derivative of the new 76' unicam V4 in the VFR1200. Maybe I'll be proven wrong but this to me looks like the replacement for the VFR800. There looks to be a lot of carry-over parts, including the wheels and conventional fork. If they've made it a bit lighter and more rideable than the 800 it could be a big hit. If what I think is true, and it's a re-styled VFR800 then the price should be quite reasonable too.

edit: The bike in the 3rd sketch doesn't have a brake pedal but the second sketch clearly shows 2 levers. These sketches usually contain important clues so I don't think that's just an oversight. You can clearly see a pulser ring on the front rotor for ABS... I wonder if Honda have fitted a simpler combined ABS that is operated only by a hand lever? I could imagine it having a delay valve which progressively increases rear braking. Can't wait to find out.

Stebel Nautilus Air Horn (second horn upgrade)

I shared my horn upgrade post on VFRdiscussion.com and a few different people recommended installing a Stebel instead.  I was curious, so I did some browsing around and learned that the "Stebel" is an Italian-made 12V airhorn that is obscenely loud. I consider myself obscene so I went ahead and ordered one up from the good people at Twisted Throttle.

The biggest obstacle with the Stebel is its bulk. It incorporates a compressor and is rather large. There's no possible way that it would fit in the stock location (the previous FIAMM barely did) but I found a perfect location.

I noticed that the ABS controller bulges out quite far from the frame on the right side of the bike. The space on the opposite side of the frame is vacant and the fairings are symmetrical so it stood to reason that there would be room in that location. Hell there was even a threaded hole on the frame to use as a mounting point and a chassis ground nearby to make wiring easier.  After this photo was taken I reinstalled the top fairing / headlight so I could make sure I had clearance where I needed it.

As you can see, the Nautilus is substantially larger than the previous Fiamm and immensely larger than the stock "meep meep" horn.

A device like the Nautilus draws substantially more current than the stock horn, and therefore has the potential to fry the light duty horn switch. The solution is to wire it through a relay. Basically a relay is a heavy-duty switch which is contolled by a light-duty switch. This also allows the new horn a direct connection to the battery so it can blast away to its maximum effect. I'm not very skilled electrically... this would be my first encounter with a relay and I learned all this as I went. I used the aid of a handy online tutorial. I wanted a clean installation so I bought some quality automotive connectors and a fuse holder.

I used the soft metal bracket from the Fiamm, test-fitting it and bending it into a "Z" shape that would keep the Nautilus tidy against the frame.

Here is the Bosch relay that came with the Nautilus. All hooked up. The heavy white wire is my power wire. I used some heavy-duty speaker wire from an old kit I had. Comically, this wire was labeled "subwoofer".

I drilled a little hole in the inner cowl where I would mount the relay next to the upper harness connector.

I secured it with that old favourite fastener of mine... a windshield screw. (I have a package of them) It is the perfect size and provides a "shock mount".

Here is the red relay secured in place.

And here is the Nautilus bolted in tight against the frame in the desirable downward-facing position. This is exactly where the bulky ABS controller mounts on the opposite side of the bike. I test-fitted the left fairing panel to make sure it fit.

Here is the fuse holder and the power wire running up to the relay:

I briefly tested the horn inside the garage... big mistake. I gave myself a splitting headache. It's FUCKING LOUD!!!

I wheeled it outside to test it properly and piss off my neighbours. Turn your speakers all the way up and press your ear firmly up against one of them to fully appreciate the experience:

http://www.youtube.com/watch?v=DFFZaosVoho

Quartet Harness

 Honda offers a "quartet" harness that makes it really simple to hook up factory accessories. (such as the heated grips or 12v outlet offered on the Honda web site) Since it's cheap and I already had the bike peeled, I figured I'd pop one on there. I ordered from David Silver Spares once again in the UK. It was cheaper than buying from a US dealer on ebay.

The instructions are simple. Locate the waterproof accessory plug. It is electrical taped to another harness. Remove the tape and the dummy plug.

If you pull back the cover you can see the 4 plugs for hooking up the factory accessories.

Use the supplied zip tie and clamp to secure the harness firmly in place.

Now I just have to get some accessories.....

MotorcycleUSA Comparison

http://www.motorcycle-usa.com/12/8188/Motorcycle-Article/2010-Sport-Touring-Shootout-V.aspx

Pretty much mirrors how I feel about the VFR.

I like this comment in particular:

“Sometimes I wonder what market Honda was trying to attract. I think the VFR was designed for a young man who just doesn’t want to give up his sportbike, but wants to do a little more travelling… so just take a sportbike and add some bags.”




Yep sounds about right.

Thinking out loud RE power limitation

I have another theory on the torque limitation in first and second... It might be to keep the side gear case with its coil spring / cam damper from blowing up. A sudden high-torque hit will bang that cam into the coil spring really hard.




I wonder.....

Switchable Power Modes

Electronics aren't my strength but I figured out that I could wire a DPDT (Double Pole Double Throw) switch to change modes between the normal restricted mode and the hacked de-restricted mode. Why bother with a switch? Dutchgixxer has de-restricted his VFR1200 and reports that he considered changing it back to stock because the torque was so responsive in 1st and 2nd gear. His bike wanted to wheelie and spin if he wasn't cautious with the throttle. Also, the inaccurate gear position sensor could get annoying in the de-restricted mode. I figured a switch would be nice if I changed my mind, that way I wouldn't have to go back in and keep changing it back and forth.

I decided to place the switch under the seat. This way it can't be switched on the fly... I will have to stop the bike, take the key out of the ignition and unlock the seat to access the switch. I don't want it to be changed on the fly because if it were changed in 1st or 2nd gear on the fly, the interruption in the signal could cause a fault, thereby triggering an engine light which in itself doesn't have any negative effects but it's annoying to clear the trouble code.

The first thing I would need to do is repair the wiring that I hacked up near the harness. I kept it tidy with shrink-sleeve insulation and wire ties.

 The gear position sensor sits on the end of the shift drum, right next to the shifter spindle. I removed the
shifter linkage and the plastic side cover to gain easier access.

On the inside of the frame spar there is a connector for the GPS. The connector needs to be released from its clip. The group of wires with the woven insulation goes directly into the GPS>.

I spliced 2 lengths of wire into the 3rd gear wire on the ECU side. I would run them up the inside of the frame and under the tank to the battery area.

This is the DPDT ON-ON switch that I picked up from Radio Shack. There are 6 poles. I ran the 1st and 2nd gear wires on the GPS side to the middle poles. The 2 3rd-gear wires ran to the outer poles on one side, and the 1st and 2nd gear wires on the ECU side ran to the other 2 outside poles. Now when the switch goes toward the 3rd gear side, the 1st and 2nd gear wires will be shorted to the 3rd gear wire therefore the ECU will receive a 3rd gear signal when the bike is in 1st or 2nd. When the switch is in the other position, the bike runs normally.

This is the plug coming from the GPS. The first and second gear wires are cut and the opposite ends run to opposite poles on the switch.

This is my crude schematic. You can see that when the switch is on the left side, the ECU (on the right) can only receive a 3rd gear signal.

I drilled a little hole in one of the baffles under my seat to mount the switch. I sealed the 6 terminals up with a blob of silicone and taped it up tightly. The 6 wires were tidied up with some wire ties. When this switch is in the "up" position the first 2 gears are de-restricted.

Here is my switch:

I threw on a helmet and rode the naked VFR up and down my street a few times, stopping in between to switch "modes". The result is exactly what I expected... In the de-restriced mode the hesitation before 5500RPM is gone. Instead, the torque rushes full-on from idle. It's drastically more responsive. It makes the natural restriced mode feel sluggish.

Gear Position Sensor Mod... or... "how to de-restrict power in first and second gear"

One of the most common complaints of VFR1200 owners is the power restriction in first and second gear. My dyno runs from an earlier entry clearly show the "torque hole" that occurs in first and second. I've speculated that the reason for the restriction is to reduce wheelspin in the lower gears. (when Honda should have just equipped the bike with proper traction control) I've also speculated that the restriction was the result of a "traction map" that reduced the throttle opening at those specific RPMs in 1st and 2nd.

A fellow enthusiast on a discussion board argues that the restriction is a result of a timing retard in those circumstances... which I have no reason not to believe. (this would be a much simpler solution to execute)

That same enthusiast (dutchgixxer on vfrdiscussion.com) hypothesized that the restriction could be eliminated by "fooling" the ECU into thinking that the bike was in 3rd gear while in first and second. This would mean that it would revert to its full power map. He studied the wiring and provided a simple schematic on how to fool the ECU.

The VFR1200 has a very sophisticated gear position sensor (GPS) that uses an extremely accurate potentiometer on the shift drum. I suspect that this is "trickle-down" technology from the DCT version where the GPS plays a crucial role. Each gear position has its own wire going into the grey serial plug on the ECU. This makes it relatively simple to fool the computer.

I can't take credit for the concept of this modification, but I am pleased to provide a set of instructions.


The tank must be lifted to gain access to the ECU.

The grey connector is unplugged.

I cut a slit in the shrink sleeve to gain easier access to the wires. I separated the black and yellow wire. This is the 3rd gear wire which is grounded when the GPS detects that the transmission is in 3rd gear.

I carefully stripped away a bit of insulation and spliced in 2 short pieces of wire. I twisted them together, used a little blob of solder and taped it up.

The black and brown wire is the first gear wire and the light green and red wire is the 2nd gear wire. The third gear wire is spliced into the 1st and 2nd gear wires on the sensor side. I taped the ends of the wires on the ECU side to prevent shorting.

All taped up and back together. Now when the transmission is in 1st or 2nd gear, the ECU will get a 3rd gear signal. Full power will then be available in those gears. The only drawback is that the gear indicator display will give a false reading in 1st and second. It will read that the transmission is in third gear.

It could be a while before I ride again but I'll report back on how the mod changes the power delivery.

EVAP Removal Mod

The VFR1200F is equipped with an evaporative emissions control system. The purpose of this system is to comply with California Air Resources Board vehicle requirements. It draws fuel vapors from the fuel tank, stores them in a canister, and then purges them into the throttle body to be burned in engine combustion rather than evaporate into the atmosphere.

It's bulky and unneccessary so I took it out. My "green" European readers may find this offensive but this is a motorcycle blog, not a political blog so I'll avoid discussing the perceived environmental consequences here.

Here is the diagram for the system in the repair manual:

Here's what it looks like, located under the tank behind the rear cylinder head.

I joined the fuel tank breather hose to the evap drain hose, essentially bypassing the canister.

This is with the EVAP tray removed. Underneath the tray is a heat shield for the rear exhaust headers. The rear shock is also visible here.

I plugged the "purge solenoid valve to throttle valve" hose with a big bolt. This line goes to a manifold under the throttle body which splits it into 8 individual lines, 2 going into each intake port. To thoroughly remove the system, you could remove all the lines and insert vacuum plugs in the holes. It would be a lot more work and likewise a lot tougher to reverse if you had to.

The tray is reinstalled but with the solenoid and canister removed. I duct taped the solenoid plug and throttle hose to the tray so they won't rattle around.

This is what was removed. I threw it in a box of stuff I've removed from this bike... the box is starting to get heavy.

As was the case with the PAIR solenoid, the EVAP solenoid does not provide feedback to the ECU and therefore shouldn't cause a trouble code or malfunction light by being removed.

Throttle by Wire

Here you can see the throttle grip being twisted but no movement from the throttles. The only thing the throttle grip moves is a throttle position sensor. The position of the TPS is interpreted and cross-referenced with other data, run through feedback loops and algorithms before the computer tells the motors how far to open the throttles.

PAIR Removal

Most new Hondas (and other new motorcycles) are equipped with a PAIR or secondary air system. PAIR stands for Pulsed Air injection. It is sometimes also referred to as a smog pump. The purpose of this device is to burn off unburned hydrocarbons in the exhaust in order to meet emissions requirements. They typically only operate during high-vaccuum conditions and work by drawing filtered air from the airbox and pulsing it into the exhaust port. On closed-throttle decelleration the PAIR system can usually be heard popping... it sounds like a backfire. Here's a basic diagram from the repair manual:



I like to remove this equipment for a few reasons:

1. I don't think it's neccessary. I'd be willing to debate its pollution-fighting merits if anyone cares but I'll spare you the rant for now

2. Removing the system eliminates a lot of clutter in the engine bay, making maintenance easier.

3. Dyno tuning becomes simpler, as the system confuses the tuner's "sniffer" that measures the air/fuel ratio.

4. It's fun to take apart motorcycles and put them back together. :) Especially Hondas.

Here's how it went. First I lift the tank and support it with a strap:

Next I take off the airbox cover.

This is all the crap (bugs mainly) that came out of the air filter when I banged it on the floor:

Top view of the inside of the airbox. The layout of the throttles repeats the offest layout of the cylinders with their growly firing order.

There is a little hole in the side of the airbox where the PAIR draws air in.

From the outside: this is the suction line that feeds the PAIR

Bottom of the airbox and ECU removed:

The 2 silver pods with hoses attached are the PAIR valves for the rear cylinders

To get to the front cylinders I had to remove this engine shield that sits over top of the cam cover. The manual says to remove the throttle bodies to get this out but I didn't want to go that far. A bit of wrangling and some skinned knuckles and I popped it out:

Here are the front PAIR ports, housed in one double-sized pod: (look next to the hose and hose clamp)

Rear cylinder head with PAIR valves removed and the holes left behind:

The holes need to be covered up, as they drop right down into the combustion chamber. A "block off kit" is needed. There won't be much of a demand for kits for the VFR (typically this mod is only performed on race bikes or heavily tuned bikes) but I studied some parts diagrams and found that all recent Honda sportbikes use 1 of 2 different valve assemblies. Multi cylinder heads (CBRs) use a pair of twin-port units while single cylinder heads (RC51) use a single valve unit. I contacted Kyle Racing and ordered a CBR kit and a RC51 unit.  Here are the plates, machined out of aluminum and anodized in black:

I spread on a very thin layer of gasket maker and slapped them in place. I was careful not to over-torque (and thereby ruin a cam cover)

Here are the rear block-offs bolted in place. On the right of the image you can see the motor that controls the throttles.

The double-sized front block-off bolted in place:

This is what was removed: 4 pair valves and their associated hoses as well as the control unit.  Unlike the purely pneumatic system on my CRF250x, this one is run off a solenoid. I was initially concerned that its absence could throw a fault code, but after studying the trouble code guide and wiring diagram, I don't think it gives feedback to the fuel injection system so it shouldn't be an issue. If it does trigger a fault code, I can remedy it by shorting the wire with a 25 ohm resistor which will "simulate" the presence of the solenoid.

The intake port had to be plugged, otherwise it leaves a hole into the airbox where debris can be sucked in. Typically a hose cap is used. I used a windshield screw. (the type with the expanding rubber  nut and washer)

Then I just had to put it all back together. I was careful to lay the wiring harness correctly as Honda intended. It only fits one way, and it fits perfectly.  I also made sure to clean all of the internal airbox and throttle parts so dust won't be sucked in.

This mod doesn't increase performance, but it gets rid of a lot of bulky unneccessary junk and it gave me a good excuse to dig into the guts of the bike and learn how it all goes together.