O'Donnell SS .21 pics

The new and highly awaited 3.5 cc off-road engine from O'Donnell has finally hit the European shores this week! Here's some pics of its internal parts and in an hour or so I will publish some newly taken shots of it assembled also. :)




The cooling head is 60 mm in diameter...!

The SS .21 engine comes with a combustion head-button for turbo plugs. There is also a O'Donnell #97T plug included. Also included are a button for normal threaded plugs. As standard are two 0.15 mm brass shims installed for a total of 0.55 mm squish height with the turbo head-button and 0.7 mm with the same shims and the std head-button.

On booth head-buttons the outermost squish is flat (about 50% of the width) and the inner most is slightly angled. The total volume is about 0.18-0.185 cc measured with a O'Donnell plug installed.

The brass sleeve is hard-chromed and has a simple and effective designed port layout with three intake ports and nicely (not huge = nice) exhaust port. There is no signs of any chrome burrs - very good. :)

The transfer ports are quite wide...

The booster port.

Piston and liner. It looks like the piston is not cast but billet type.

The con-rod is bushed at booth ends of course. Two oil-grooves on the piston. BTW, the piston has a completely flat top.

The crankshaft is 14 mm in diameter at the thick end and it looks cleanly designed. No silicone-ramp in sight that can come loose - nicers. :)

The crankshafts outlet so called "turbo-scoop" has a slightly different flow design then what most engines use.

Crankcase from above. Booster and one of the transfer channels are seen. The head is fastened with std M3.5x16 mm socket head (hex) screws.

The exhaust gasket in silicone seems to be of the std size. Thats good as all normal headers like fron Sirio, Nova & Hong Nor etc will fit. The crankshaft bearing fit was really nice on this motor - nice and just the right amount of looseness. Std socket head M2.5x8 mm screws are used at the backplate.

The booster channel in the middle flanked by booth transfer channels.

Double o-rings in the front box for sealing the carb.

The carb lock (6.9 mm in diameter) is sealed at booth ends with o-rings and is of a "double-squeeze" type.

Tip, if you want to remove it from the case - dont pull/push it out in one piece - you will break the o-rings. Unthread the screw and pull booth parts out at booth ends so to speak - you will save the o-rings.

The aluminium carb has a 15 mm throat diameter and an "thermo insolating" sleeve pressed on. As standard there is a 7 mm plastic venturi installed and a separate 8 mm venturi is also included.


The rear cover with its two funny loocking channel/grooves thaty match the transfer channels in the crankcase.

O'Donnell Racing Products

Distributed in Scandinavia by Minicars.

You wanna see how the engine looks assembled? Klick HERE.