Difference Between Cison FG-VT9 Panhead vs RETROL R29 Knucklehead | Stirlingkit

The Panhead is an overhead-valve motorcycle engine from the late '40s to mid-'60s originally, so nicknamed because the rocker covers resembled cooking pans. The valve covers on these bikes was a stamped metal pan, hence the name. A Knucklehead has a rocker box assembly that looks like a couple of knuckles and was produced from the mid-'30s to the late '40s. so what's the difference between the Cison FG-VT9 and RETROL R29? I'll write about the R29 in just a bit, and compare and contrast each of the engine’s differences.

Cison FG-VT9 Panhead vs RETROL R29 Knucklehead

Let's compare two of the latest & best engineered miniature V-twin gasoline fueled 4-stroke OHV engines. Both are awesome engines - but which would be best for you?

The specifications of the Cison V2 and Retrol V2 are as follows:

Over a year ago now, Stirlingkit and Cison released their FG-VT9 miniature-scale 9cc Panhead engine. The engine was immediately loved and well received by both beginner and advanced scale-engine lovers all over the world.

-The look and detail of the Cison V2 engine alone caught everyone’s eye. At first to some, it seemed “too good to be true” that such a well engineered and built running scale engine could even exist….but Cison proved their V2 was definitely a reality.

Source: ML

Looking at the Cison V2 engine, it is available in an all silver & chrome version, as well as a silver & chrome version with black cylinders aka ‘jugs’.

The silver & black finishes are anodized to prevent corrosion, and the rocker covers & cam box cover are chrome. Internally, both versions are the same.

The Cison V2 is approximately a 1/5 scale engine. Although 9cc’s of displacement may sound small… the FG-VT9’s exhaust sound, isn’t!

Any engine or Harley lover would love its signature sound. Cison has captured Harley’s voice; that “gallop, potatoe-potatoe & thump” perfectly.

The setup for the Cison V2 is quick & easy. It comes fully assembled and ready to run; all the owner needs to do is supply a fuel tank, battery for the CDI, a cordless drill for starting, and premixed fuel.

Install the CDI spark plug wires on the spark plugs, plug in the Hall effect sensor wire, and finally the battery to power the CDI.

The FG-VT9 starts easily, and it's 2 needle carburetor is easy to adjust. Idle is as well easy to adjust, to raise or lower the idle speed.

As the engine “breaks in” lower idle speeds are easily achieved.

The FG-VT9’s durability is outstanding.

I have both the silver version & black version V2, and have easily put over 80 hours of run time on each one. I use a desk fan to keep the V2 cool when extended running. The V2’s heat dissipation is very efficient.

I can say this engine simply loves to run.

The V2 can be also purchased from Stirlingkit with a base & fuel tank, but — it's also right at home running in the palm of your hand!

it's signature vibration makes for a great hand massager & warmer.

Cison offers V2 upgrade parts such as different fuel tanks, an adjustable Hall sensor, a scale air cleaner, and even a scale kick starter set… for those who want the full effect of kicking their V2 to life.

RETROL R29 4.2cc Knucklehead

Don’t let the tiny size of the RETROL 4.2cc R29 Knucklehead fool you… It’s just as real of an OHV 4 stroke engine as the 9cc Cison V2.
-it’s just 1/2 the size.

Like the Cison V2, the R29 is also a complete, ready to run miniature scale engine. It includes everything needed to run. The engine can be started with the included pull cord or starting shaft. Other than three AA size batteries to power the CDI ignition, a cordless drill (to use the included starting shaft) and pre-mixed fuel.
Like the Cison V2, the R29 also requires 2 stroke oil to be added to the fuel, for lubrication.


The R29 is one extremely detailed miniature engine. Even the tiniest details have been accurately replicated, such as the simulated rocker box ‘top oiler’ line, oil pump, etc. One of my favorite details of the R29 is it’s spark plugs. The spark plugs are very unique. They are 1/4 32 thread like other miniature spark plugs, but the R29’s plug have a black base and thinner ceramic body that replicate a vintage Harley plug perfectly.

The R29 comes packaged in a very attractive black sturdy box, with a stamped chrome picture of the engine on the lid of the box. The engine is safely packed in a foam insert that ensures a safe delivery.

After three AA batteries are installed, add your fuel, open the needle valve 1/4 to 1/2 turn open from seated, and the engine is ready to start.
R29 immediately came to life using a cordless drill. The engine has a solid idle and an awesome sound!! I couldn’t believe how great this little engine sounds. Throttle response was also impressive, right out of the box.
The R29’s carburetor has a main mixture needle, a low speed adjustment and idle speed screw, to fully dial in the engine.
Right out of the box, I was impressed at how the R29 can achieve a very low idle RPM.

The little RETROL R29’s “voice” is different than the Cison V2, because of the displacement difference & exhaust design.
Like the Cison V2, the R29 has a signature vibration, that definitely adds to the engine’s scale realism!

The R29’s CDI ignition system and batteries are fully hidden within the wooden base. An ignition OFF / ON switch stops the engine.

After I ran 2 tanks of fuel through my R29, I found that it can be started by a flip of the flywheel, even from cold.

When comparing the Cison V2 and RETROL R29, both could be used for an RC application. In my opinion, the Cison V2 would be the better choice for RC use because of its size, crankcase mounting tabs, and the ribbed pulley on the flywheel.

In conclusion, the Cison V2 and RETROL R29 are BOTH outstanding engines that will impress -any- gearhead who loves internal combustion & motorcycles.

Jon in Kentucky

2022/11/30