73 Honda CB750 Custom Build Part 20 – Starter & Alternator

The starter on an engine is a DC motor that rotates the crankshaft of the engine to get it started. Once the engine is started, the starter must have some sort of mechanism that uncouples it from the engine or else it would spin too fast and be destroyed. Automotive starters have a built in mechanism called a bendix drive that engages and disengages the drive gear with the engine’s flywheel. Starters on motorcycles utilize a one way clutch known as a Sprag Clutch. It will allow torque in one direction only and slip in the other direction.

The alternator is a device that produces an AC electrical current when rotated. The center portion known as the rotor is an electromagnet. It rotates within an outer winding of metal and wire called a stator. Each component functions as an electromagnet with multiple north and south poles. When in rotation, these opposite poles pass by each other and produce and electrical current in their windings via magnetic induction. The AC current output then passes through a bridge rectifier which converts it into a DC current that can charge a battery.

In this week’s video I’ll take a look inside both of these components, test them, and then install them in the engine.

Keep on hackin…

73 Honda CB750 Custom Build Part 17 – Shifter

That crazy shifter mechanism is together! Over 20 parts make up this assembly and if you haven’t taken it apart yourself it can be a real challenge to figure out. After some research on the interwebs and finding a few videos on YouTube I managed to put all the pieces together in the right order.

I have found the OEM parts breakdown drawings to be of help with things like this. Most of the online parts suppliers use these drawings to help you identify parts when ordering. Here’s an example showing the “gearshift stopper” assembly.

Gearshift stopper

Here’s a picture of the completed assembly on the engine.

cb750 shifter assembly

I usually print these out along with the parts description pages to help me determine bolt and screw lengths as well.

cb750 parts diagram shifter assembly

In this week’s video you can follow along step by step and see just how this whole thing goes together.

Keep on hackin…

73 Honda CB750 Custom Build Part 16

In this episode the cylinder head gets installed. One thing to note is the absence of four dowel pins and rubber seals that would go between the cylinder and the head on the four inner head studs on the exhaust side of the engine. I did not have these parts in my collection of goodies from the previous owner. Early CB750 engines did not have these dowel pins and seals. They were added later to help the oil flow back down into the bottom of the crankcase. There are four holes in the head that collect the oil after it has been pumped up to the camshaft and allow it to run down through the same hole the cylinder head passes through. These parts are no longer available so I just left them out as in the earlier engine. I’m guessing they were added to help prevent oil leaks between the head and the cylinder as the engine accumulated high mileage.