|Name||Taipan Mk 7 Series 64 Plain Bearing||Designer||Gordon Burford|
|Bore||14.66 mm||Stroke||14.43 mm|
|Type||Compression Ignition||Capacity||2.436 cc|
|Production run||unknown||Country of Origin||Australia|
|Photo by||Ron C, Maris Dislers||Year of manufacture||1963-64|
First, let it be known that the engine here is not an actual Taipan Mk 7 Plain Bearing Sport engine from 1963-4. It is a modern reproduction built by David Burke (DB). DB was one of the driving forces in a group of builders known as SPEED Inc and this engine was just one of their projects. If it looks rather authentic, that would be because DB has a deep affection for Taipans, and many of the original dies!
I tend to classify limited production run replicas as either fun, or serious, with the discriminator being heat treatment—and no prizes for guessing it's the one with hardened and ground shafts and liners that are the "serious" ones. This is not to imply anything negative about engines with soft steel shafts and liners. Built well, they will start easily, run just fine, and give a good working life. What they won't give is crash resistance and tolerance of hard use in a hostile (dusty) environment. For that, you need to get "serious", hence my rather arbitrary distinction. DB's engines are serious engines.
The SPEED Inc project for this engine had members machine crankcases, backplates, etc and press in an unfinished bearing. They also machined crankshafts leaving an allowance for grinding to finish size after heat treatment. This would be carried out in batches as the cost for one-off jobs is just too great to even consider. Following hardening and grinding by DB, completed components were to go back to the builders for final assembly and machining of the remaining "soft" bits. Well, what with one thing and another, years passed, and SPEED wound up. But DB, undeterred, kept things moving for those who had done their bit and in December 2009, he contacted builders from the T15S64PB project offering their now finished bits back, or a complete, running engine. Being lazy, yours truly took the latter option, so the engine I have is probably not my original machining—especially as I have, at long last over the years, learned the value of reading and sticking to the drawings—more on which later.
The Real Mk 7 "Sport" 2.5 diesel
The real Mk 7 Taipan 2.5cc plain bearing (PB) engine appeared on the market in 1963. It was the only model to which the factory officially nominated as a "Sport" engine. This was to avoid confusion with the Mk 6 dual ball-race model which continued to be available (although Ron Warring's May '62 review of the Mk 6 BR in Aeromodeller classes it too as a "sport" engine). The head of the first version of the Mk 7 was anodized red and it had four blackened 4-40 hold-down screws and a black 2BA compression lever. The main crankshaft journal was rather massive to provide 1/8" thick walls for the bushing and the equally massive 1/2" crankshaft it carried. This allowed a large 9/32" gas passage. As usual, the front of the shaft was knurled for the force-fit "splined" prop driver. The shaft thread was 1/4-28 which is the same as we'd expect on a 35! Gordon made 'em strong to take plenty of abuse in the harsh Australian school ground environment, meaning lightness was not a factor.
The transfer system was similar to "Oliver" porting with four angled transfer passages being drilled and steeply angled to intersect the exhaust pillars, thus providing overlap of transfer and exhaust. However unlike the Olivers, the passages were simple holes, not squared at the top corners. Below the exhaust band, the liner tapers to provide transfer. It is a loose fit in the crankcase bore, depending on the rather uncertain centering provided by the head bolts. The cast iron piston is flat topped with a large, solid floating wrist pin. The conrod is machined from aluminium.
The crankcase web between venturi and the front of the cylinder protrusion was thickened to provide anchorage for a starter spring retaining screw, though engines with a starter are seldom seen. Several variations in production are noted in Maris Disler's Burford Book . So examples exist with no anodizing and matt, sand-blasted crankcases. The sample tested by Maris gave a peak of 0.29 BHP at 12,500 rpm.
The SPEED S64PB 2.5
The reproduction is a faithful copy, although differences exist if you know where to look. The crankcase is a very faithful gravity die casting with the Taipan signature "T" embossing on the left and the "2.5" embossed designation on the right (pilot's perspective, engine upright). These were provided by engraved pins the slid into holes in the die. Quite a cunning idea as not only did this provide an attractive circle around the embossing, it allowed the pins to be shared by different dies resulting in a considerable cost saving as die engraving is hideously expensive! The cases seen here are "in the raw", as it were, being for ball race versions of the 2.5 and 1.5 Taipans.
Internally, the engine is quite faithful to the original too. The screw-in backplate extends well into the case to minimize case volume and prevent excess travel of the conrod. On this example, the thread on the backplate extends rather too far forward, requiring DB to give it a touch with the grinder at one point to prevent the piston striking it at BDC (a backplate made faithfully to DB's drawing would not suffer this problem).
Time for a run. Where's my test stand? My props? My diesel fuel? Hmmm... Can't find the 9 x 4 and even worse, the fuel bottle is just about empty and the ether has probably all but evaporated, still must give it a go. After some frustration on an APC 9.5 x 4.5 (unusual, but I have a stack of them for some strange reason) I gave up and fitted a 12 x 6 wood to find the settings. This worked, even on my worn-out fuel and after a brief run, the wood was replaced with the APC. The engine was tight as evidenced by needing the compression backed off after it heated up. So to be kind to the engine, only a very brief period peaked out was attempted, during which the tach indicated 9,300. Maris' table shows 9,600 on a 10 x 4 APC. More diameter, but less pitch, so my figures suggest the repro is in the ball-park with an original. With all fuel exhausted, no more testing was possible. The engine itself had run relatively cleanly, but it was h-o-t hot! And the comp back-off had been evident again, so much more running is indicated to get this one up to useful condition.
The SPEED replica is faithful to the original in appearance and performance. The most obvious difference is the silver dome topped comp screw (the originals would be black with a flat top). The needle is wrong too, but that is easily fixed (see Maris' book for what should be fitted). The head screws are 1/8 inch Whitworth, cheese head, with slots, but unlike the originals they are bright plated, not black, and threaded for their entire length. The engine weighs approximately 6 oz—the same as an original—which is one of the heavier Tiapans, none of which were considered to be light-weight. But for all intents and purposes, it is a Taipan and like the originals would give years of faithful service, provided you can get the fuel!
|||Dislers, Maris: Gordon Burford's Model Engines, self-publsihed, 2009, p107.|