I was surprised one morning (woken up, working nights) with a phone call from Paul Landels from “Just Engines”. “Malc – eh! Could you do an engine test for me?” “Um, well OK – what, when, wotsit?” “It’s an O.S.40 with a Davis Diesel Conversion and I know you love diesels”. (Well, he sold me most of ‘em – from 1.5cc to 10cc MVVS and Irvine), plus I have just bought a new laser 80 diesel. Lovely beast. And my usual glut of Ollies. “Every home should have a couple”.
OK, here we go. The motor arrived. The usual blue with a variety of APC props and the head conversion which is very well made and inscribed ‘Davis Diesel’. The instructions are very comprehensive and easy to understand – even for me!
The conversion is very easy to carry out. Remove silencer if fitted to motor; undo and remove the four head screws; insert a piece of balsa or softwood into exhaust port, piston being at bottom of stroke (no metal please Gents). Carefully lift glow head until it comes free from liner. Carefully remove alloy gasket from glow head and replace on diesel conversion (make sure ports are aligned in engine). Replace head and screws and tighten down evenly. That's it all over – easy eh
Down to the nitty gritty – or how to start the Beast
Having had glow motors converted to diesel before, I was a bit wary about the carb being on the large size – diesels only needing a very small choke size. But, there is no mention of this in the instructions so here goes…. Engine mounted on test stand, neoprene fuel pipe replacing silicone between remote needle and carb. Motor connected to tank and tank full of my homemade Ollie brew. But Model Technics 1000 or 2000 is just as good if you don't make your own. Throttle open, place fingers over Venturi, three turns open on fuel needle. Rotate prop to draw fuel through line into motor. Allen key inserted into compression screw. Right – engine now damp start flicking with throttle just about 1/3 open, raising compression with other hand about 1/2 turn. Engine started after two flicks of prop motor running well, tune in more comp, less turns on needle, approx. 2 1/4 turns open. Good throttle response, just what I wanted. Engine primed, 12x6 prop, two flicks and away.
Throughout the test, hot or cold, this motor was only started by hand. It started within three flicks and the response to throttle was excellent. From idle to sudden full throttle, even jerking the wire, it responded. The only time adjustments were made was when prop sizes were changed.
In its glow form it is not that powerful but as a diesel, it has shown to like a large prop as the torque is greatly increased. For sport and vintage radio assist, it is excellent choice. I would like to have tried props up to 14” with higher pitches but time prevailed.
The motor has had about 1 1/2 hours running from new. On strip down there was no apparent wear noticeable. During running there was no hardening of running throughout and the motor held its running settings without alteration. The OS 40LA proved to be a very good and easy to set up engine.
A conversion for the LA 46 is also available.