Takegawa 124 Engine Build

Takegawa 124 Superhead + R Engine Build

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Detailed here is the build up of a 124cc, Takegawa Superhead + R equipped, five speed, electric start Honda engine. Excellent reports of power and torque have been reported by users of the 124cc Takegawa Superhead + R kit, so it was decided that this would be the route to follow. Takegawa themselves quote 17 PS @ 11000 RPM for the 124cc kit with the S20 cam and a PE28 carburettor. This build would use a PWK28 so we are hoping to achieve close to those figures. Due to the reputation of five speed gearboxes and the kick start mechanism being fragile, it was decided to build this engine with electric start. Although this would eliminate kick start and first gear starting damage, the downside was the fact that the heavier electric start flywheel added more rotational mass to the crankshaft assembly.

It was decided to build the motor using Cub 90, GB6 crankcases. We had built several motors before using these cases, including a 106cc with DRP piston and barrel, modified 70 head and Honda fast road cam and a 114cc with DRP piston, barrel and Ultra head with Takegawa R15 cam. A Cub 90 electric start donor engine, complete with generator and starter motor, was procured and stripped down. Upon inspection it would appear that the motor hadn't done many miles and certainly looked liked it had never been pulled to bits before. The underside of the cylinder barrel showed the usual signs of corrosion but the rest of the motor was in very good condition. The crankshaft, clutch and gearbox, although not being used this time will probably turn up in another rebuild.

In order to fit a 54mm bore cylinder and a five speed gearbox some machining work must be carried out on the cases. The barrel opening must be bored out to 57mm and the cases need to be relieved for the mainshaft fifth gear to clear. The centre spigot of the countershaft needle roller bearing must also be removed and the oil pump discharge orifice needs enlarging to suit the pump being used. With this build a Takegawa Super oil pump was being used, therefore a 2mm hole was required. Before machining the crankcases were degreased and chemically cleaned.

Crankcase opening bored to 57mm. Crankcase relieved for mainshaft 5th Gear.

Once all the machining operations were completed the crankcases were cleaned once again prior to assembly.

A Honda SS50 five speed gearbox had been acquired for this build and although the first gear ratio is a little low when compared to after market five speed boxes, the remaining four gears offer good ratios for a high revving motor. The gearbox was in excellent condition with little if any signs of wear. The original SS50 kick start accompanied the gearbox but would not be used.

Selected gearbox bearings were fitted to the cases and the cam chain tensioner assembly and oil pump drive gear and shaft fitted. New oil seals were fitted to the gearbox countershaft and gear change shaft.

The five speed SS50 gearbox was disassembled, cleaned and checked over before being put back together and fitted to the left hand crankcase. As stated before the SS50 kick start was not going to be re-used as it was not the pre-engaged gear type. The original Cub 90 kick start was in good condition and was cleaned and fitted into the casing. The teeth engagement is as good as the original SS50 item but being pre-engaged it should not damage the first gears the odd time it may be used. The Takegawa Super oil pump was fitted to the right hand crankcase and the cylinder head studs fitted prior to the cases being joined together .

Gear cluster and kick start fitted. Takegawa Super oil pump installed.

The 54mm stroke Takegawa crankshaft was fitted to the left hand crankcase along with the locating dowels and the gasket and the right hand crankcase installed. The crankcase bolts were fitted and the crankshaft end float measured at 0.3mm. The optimal end float should be between 0.05 and 0.1mm so the cases were separated again and a 0.2mm shim fitted into the left crankcase bearing housing. The cases were rejoined together, the bolts torqued up and the crankcase end float measured again.

Completed left hand crankcase. Joined crankcases.

With the cases together the neutral switch, cam chain, tensioner roller and stator blanking plate were fitted.

It was decided to lighten the flywheel as it was already a bit heavier than a standard Cub 90 item. It turned very true and only required minimum adjustment to balance. The flywheel, starter clutch and chain were then fitted and the starter motor bolted in to its mounting as the sprocket was slipped on to its splines.

Lightened flywheel and starter motor drive.

The generator cover and sprocket covers were treated to a nice coat of paint stripper to remove the scratched and faded original silver finish. The covers were then polished rather than repainted.

At first it was thought to use a Takegawa three plate crankshaft mounted clutch, however after some thought and recommendations it was decided to fit a five plate, mainshaft mounted clutch. Takegawa had recently introduced a version of their special clutch which fitted gearboxes with the standard gearbox by utilising a mainshaft extension. A complete kit was obtained from the USA at an extremely good price. The clutch was installed without any problems and the cover fitted. The cover was a new die cast design unlike the previous sand cast offerings from Takegawa. The oil filter was primed and fitted into its housing.

Completed five plate super clutch.

The cylinder head was supplied with the valves and springs fitted and was definitely a piece of engineering art. Only one rocker shaft was supplied and no tappet screws and nuts, which was a little surprising in such an extensive kit, so to do the job properly new parts were purchased to complete. The camshaft and rockers were fitted and the tappets adjusted on the bench, the roller rockers requiring 0.08mm for the inlet and 0.1mm for the exhaust clearance when cold. The tappet covers and oil cooler take off plate were then installed to complete the cylinder head prior to fitment.

The piston and cylinder were fitted as per normal. The cylinder supplied with the kit was the new "V" type which is said to offer improved cooling over the original version. The cylinder head was fitted with its 0.25mm thick alloy head gasket and the camshaft timed up. Normally the camshaft sprocket is fitted to the chain prior to fitting a cylinder head, but with the Superhead it is done after assembly. A new NGK spark plug completed the build.

The completed engine.

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