During the winter of 2006, following a series of costly engine failures in Classic B Team Race models, a group of enthusiasts started looking at replacement engines for the commonly used OS 25 FP and LA ABN engines.  Most of these engines had variable piston and liner fits from new. Replacement piston and liner sets proved to be the same, with most out of round. There was also a tendency for the nickel plating to easily wear off at the top of the liner.  A new Classic B Team Race engine had to be found!
 
The new candidate would ideally be a readily available engine in current production with a hard chrome plated liner, either an AAC set-up or a genuine ABC engine. It should not be too expensive to purchase, be easy to modify and have good spare parts stock.
 
Following advice from two well respected engine builders, the newly released Brodak 25 engine was chosen as a prime candidate for investigation and development.  Although this engine is developed for general sports and stunt use, it does have a connection with racing through F2C engine designer and builder, Sergy Ivanov, from Moldova.  
 
Initial examination of the Brodak .25 showed that it did indeed have a racing heritage, with high quality workmanship evident thought-out the design. It had a hard chromed liner and a perfectly round piston with exceptional fit. The materials were the same as used in Sergy’s racing engines. It also had a large inlet port, adequate transfer and boost passages and a very efficient low volume crankcase design.
 
Photo Inset above (John Hallowells Brodak 25 powered Rocket)
 
Our engine builder set about blueprinting the motor and setting up the engine for Nelson style plugs and heads.  The engine proved very simple to modify without extensive reworking on the basic design.
 
 
Modifications include:
 
1. Redesigned and larger venturi to match inlet ports and gas flow.
 
2. Blue printing and matching of high silicon hard chrome plated liner to allow longer and more reliable racing life.
 
3. Incorporating Nelson heads and HD plugs, with special head shape and squish band design to improve power.
 
4. Balanced crankshaft, gas flowed transfer ports with matched inlet, transfer/boost and exhaust timing.
 
5. Exploit very low crank volume for better starting, running and good fuel economy.
 
6. Dimensions are such that in most cases this engine can be simply retrofitted into an existing model built for an OS 25 FP, LA or a Thunder Tiger 25.
 
 
Performance
 
Initial testing showed that the engine was easy to run in, started well and had plenty of speed and an abundance of laps on a 30cc tank, using mild range fuel.  One significant advantage with this engine is that it does not have a heavy brass liner. The hard chrome is attached to a high silicon alloy liner insert.  This saves weight and allows for a better piston and liner fit.  Also heat dissipation is much better than an ABN engine and a lean motor run will not have a tendency to quickly overheat.  Starting was excellent hot or cold and the engine was still easy to start when running lean and hot when in search of extra laps.
 
Testing was with a range of commercially available propellers and suggested the power curve was best suited to standard APC Sports 7x7 and 7x8 propellers. WARNING ! We have withdrawn our recommendation to use RAM 8x6 propellers due to a series of three catastrophic blade failures using these props.  
 
Our recommended prop is now a Bolly 8.5 x 6 cut down to 7,5 x 6 with tip reshaping.
 
For Information on Breaking in the B25R go to: Breaking in the B25R Engine
 
Availability
 
Brodak B25R Mk IV engines are currently being prepared (8/2007) and will be available to those interested in using these engines for Classic B racing.
 
If you wish to order an engine please contact either:
 
 
or John Hallowell ( classic.b@pacific.net.au)
 
 
 
 
 
 
 
 
Brodak B25R Development
Standard Unmodified Brodak 25 Stunt Engine
Brodak B25R Classic B Racing Engine
Aussie Nats Classic B- Finalists 2006-7
K.Baddock/J.Hallowell, M.McDermott/R.Justic, L.Smith/ M.Wilson
Internals of the B25R engine
B25R Mk III internal parts  including modifications
Mark IV version internals