Let’s start the strip in the usual place, by removing the pressure die cast alloy backplate. This has bright machine-finished internal and external mounting flange surfaces and, cast into its centre, is its new country of origin – ‘China’. With an internal flat at the top for liner / piston clearance, the backplate sits deeply in the crankcase and is fastened by four M4 Allen bolts. Sealing is by a rubber ‘O’ ring that’s fitted in a machined-in groove just inside the retaining flange.
The next part for removal is again pressure die cast from alloy – the very large, heavily finned semi-rectangular cylinder head. This is retained to the crankcase by four M5 Allen bolts and sealed by a copper head gasket. The top 8.5mm of the cylinder liner is deeply recessed into the cylinder head to aid heat dissipation – an area that Super Tigre pay a lot of attention to, in getting rid of power-sapping, engine-distorting heat. Copious finning both above and below the combustion chamber extends to the rear of the head and to the top three fins on the cylinder, cooling the parts of the head and crankcase that are out of that vital blast of cooling air. This is an area that’s often overlooked by other manufacturers; if there’s insufficient cooling here then things get out of shape pretty quickly and the performance of the engine suffers – in fact it could be seriously damaged. The combustion chamber is of the hemi type, surrounded by a wide squish band with the long reach 1.2V plug mounted centrally in a brass insert.
LINER, PISTON & CONROD
Now it’s down to the hard-working internals. The G-2300’s steel liner is very firmly fitted in the crankcase to dissipate heat when the engine’s running, so a small amount of heat had to be applied to the cylinder fins to effect the liner’s removal. Since Super Tigre have been producing ringed engines for over 50 years, their knowledge of steel liners is second to none. Precise boring, honing and hardening, very accurately cut porting and the all-important material selection for the alloy piston, steel liner and piston ring leads to first class sealing and a very long, trouble-free life.
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Super Tigre were one of the first manufacturers to use their own derivative of the Schneurle-ported liner, which they called Transfer Super Tigre (TST). It used up to six transfer ports (nominally three each side of the exhaust) plus two large, angled kidney-shaped boost ports at the rear, opposite the exhaust; these boost ports were a feature of Super Tigre’s early very high performance crossflow engines. The G-2300 displays this heritage with large twin exhaust ports and four precisely cut, angled transfer ports (two each side of the exhaust) and two large, kidney-shaped boost ports at the rear opposite the exhaust. The liner’s hardening process is very much in evidence, shown by the black finish just below the large retaining lip at the top, extending to the inside edges of the porting and to the chamfer at the bottom of the liner.
Before removing the piston and conrod assembly I put a small mark on the piston crown at the front and also on the rear face of the conrod to aid reassembly. It’s important to get the piston orientation right or the ring could get trapped in the porting and break. What’s more, the piston skirt has been cut at the front and rear to align with the transfer ports. The rod was also marked as it has a slight offset to the big end and angled oiling hole that helps pick up the all-important lubrication for the hard-working big end bearing.
Both piston and conrod are removed by the usual method of rotating the shaft to TDC (Top Dead Centre), gently easing the rod from the big end bearing and then simply withdrawing the assembly from the top of the crankcase.Article continues below…
The die cast high silicon content alloy piston is finished externally by honing, with the lower skirt machined for lightness, porting and flywheel clearance. Two large internal webs support the hardened steel gudgeon pin – a bored, fully floating unit of 8mm diameter that’s retained at both ends with wire circlips. A single mehanite piston ring is pegged by a pressed-in, hollow, split roll pin.
As for the conrod? CNC machined and made from high tensile alloy, with bronze bushings for both big and small ends. It’s bored at both ends for lubrication, with the bottom oiling hole being bored at an angle.
CRANKSHAFT & FITTINGS
Before removing the crankshaft, let’s have a quick look at its fittings. Starting from the front, first in the firing line is the steel prop’ nut, which has a 5/16UNF thread and is machined at the rear to recess into the chamfer-faced, alloy bar stock prop’ washer. Behind this lies the alloy prop’ driver that’s turned from bar stock, helically cut on its driving face and chamfered internally for its split brass lock cone. A puller had to be used to remove the prop driver as once a prop’ has been fitted the driver locks firmly on the shaft. With the fittings now removed it just takes a very firm push to remove the crankshaft from the ‘case. Before inspecting the ‘shaft there’s still one more fitting to come off, and that’s the small brass spacer that’s been chamfered internally at the rear and sits on the output part of the shaft just behind the front bearing.
Super Tigre crankshafts are probably the strongest and straightest fitted to any model engine. This is due to the quality of the nickel chrome steel plus the crank web (flywheel) and crank pin (big end) forging that ensures correct grain flow. Along with the correct heat treatment (hardening) it’s a combination that makes ST shafts the toughest you can get. Finishing of the G-2300’s crankshaft is by way of very fine grinding to its big end pin, mainshaft and output shaft working surfaces, giving an almost chrome plated appearance.
Starting from the rear, the substantial (9mm diameter) big end pin is supported by a fully counterbalanced flywheel. Immediately in front of the flywheel the 20mm diameter mainshaft is very accurately cut, with a large, timed intake port, which leads to the 14mm diameter, gas- flowed transfer passage. Moving along we come to the 8mm diameter output part of the shaft, which is supported by the front bearing; the last 25mm of the crankshaft is cut with a 5/16UNF thread.
To describe the very high quality, pressure die cast, heat treated alloy crankcase as ‘robust’ would be something of an understatement. Take the twin triangulated reinforcing webs at the front of the casing and the large square carb’ mounting boss (bored and fitted with a pinch bolt), for example. Add the four axially running webs that continue from the backplate mounting bolts to the front of the maincase, the large engine mounting lugs and large silencer mounting flange that’s been bored for the two silencer adaptor mounting bolts, and you can see that the case is built like a brick outhouse. What’s more, there’s further strength coming from the three very prominent cast-in gas passages. Oh, and as previously noted when discussing the cylinder head, we mustn’t forget the extended cooling fins to the upper rear section that aid cooling to the back of the cylinder.
Looking inside from the rear reveals the large, high quality rear bearing. The front bearing is of equal quality and sealed on the outside to keep dust and dirt at bay. The inside of the case is machined for conrod big end clearance, and the crankshaft passage has been double machined to reduce shaft friction. There’s also a small, machined groove running axially between the intake boss and front bearing to suck back any excess fuel.
Completing the tour of the case internals is a brief look at the three cast-in transfer passages, which are angled and nicely gas flowed to align with the liner porting. The overall casting quality of the crankcase is excellent, very crisp with no pockmarks or blowholes; finishing is by fine blasting. All machining is to a similarly high standard.
The twin needle Mag carb’ has been constantly developed and updated over many years. A fully sealed unit with a machine-finished, die cast alloy body, its steel throttle barrel has a choke bore of 11mm and a very finely ground finish to its working surfaces to give smooth operation. The adjustable throttle arm is from nylon, whilst internally the throttle barrel is fitted with a sealed brass idle jet, the main jet / spray bar and sealed fuel nipple also being turned from brass and fitted with a very good steel ratchet. The carb’ is secured to the crankcase by a steel pinch bolt, lock washer and retaining nut; sealing is by rubber ‘O’ ring.
The G-2300 is the largest engine to come with a silencer as standard; it’s a three-piece unit with an adjustable tail pipe. The heavily finned front part is die cast from alloy and contains the mounting flange and sealed brass pressure nipple. The simple centre-section is turned from alloy tube and sealed to the die cast rear part, which has an offset outlet pipe. Finally, the whole assembly is held together by a 3mm diameter through bolt that screws into the tail portion of the silencer and is retained by a lock nut and washer.
The G-2300 comes with two fuel recommendations, Model Technics Big Brute straight or Flair Black / Gold. However, as Flair is my local brew, that was my choice for the test. Fitted with an 18 x 8” Smart wood prop’ for running in, the ‘Tigre was given a good hour to permit the engine to bed in. As with all the ‘Tigres I’ve tested it performed faultlessly, requiring half a dozen flicks for the initial start and only 1 or 2 flicks after that, from either hot or cold.
Testing was performed using the standard Super Tigre silencer and glow plug as supplied. No alterations were made to the slow running needle after the running-in period and only a couple of clicks were required to the main needle to suit the various prop’ sizes. After an extensive test the engine was stripped, a close inspection revealing no visible signs of wear. Good stuff.
In my opinion the Super Tigre G-2300 offers excellent value for money. And as for power delivery, well it certainly pulls my 73” span Extra 300 around with great authority. A big pussycat to start and operate, this Chinese-manufactured feline’s a cracker!