Topic: Starter gear dilemma. Pulling rotor - last minute snafu

[greenjeans]

Building up a 1970 CB750 for myself (finally) and have run into a last minute emergency.  Long story short, I just noticed my crank has no starter gear.  It's a vintage, lightened, balanced and polished. 

I should be able to get it off by simply loosening the rotor bolt and using a gear puller right? 

How is it (starter gear) fixed to the crank?   I don't see how on mine - perhaps it has been machined smooth???

Does anyone in Texas (DFW area) have one I could buy and pick up today or tomorrow?  I need to get this baby buttoned up for a show in Denton by Thursday evening.  http://dentonmotorcycleshow.com

It is part 4 in the photo below.  HELP PLEASE!

[madmtnmotors]

NO!

You could damage the rotor with a gear puller. There is a proper tool for this that threads in where the rotor bolt was removed and it pushes the rotor off of the end of the crank. Get the proper tool.

[greenjeans]

Not sure I'll be able to get that tool in time.   Found a video where the guy used a std puller and a small whack with a hammer.     Would a puller really damage that thing ?   It looks pretty dang solid.

Won't be an issue unless I can find the actual gear in time.

Anybody familiar with how that gear  locks into place.   It may be that my crank is machined down, and I couldn't use one anyway.   I'll have to put the cover off tonight and give things a closer look.

[Bodi]

The rotor is made of rather soft alloy with iron/steel magnetic poles molded into it. The clearance between the rotor and stator/field coil is fairly tight. It can, indeed, be damaged with a gear puller (been there, got the T-shirt).
The OEM Honda special tool is a T-handled threaded shaft, probably hardened. Several aftermarket places sell a hardened threaded stub with a hex head - like http://www.cb750supply.com/products/9/tools. Either will work.
If you can get a simple 20mm x 1.5mm bolt, that would work too. A hard (like grade eight) one would be best but they are not easy to find. Some rear axles will also thread into the rotor, but I would be worried about stripping the axle threads as the tapered axle end doesn't leave a lot of threads engaged - and the axle is relatively soft steel.

[greenjeans]

sourcing a bolt now.  Luckily I have a pretty good source for bolts here in town.

Anybody know how the gear is fixed ?    Is it pressed on as well ?     It may be a moot point if the crank has been modified not to use it.

[enwri]

Doesn"t the gear ride on the polished journal on the crank or rotor, with the one way clutch in it's centre? not actually attached but floating on the rollers.
Can't remember how it's retained laterally.

[madmtnmotors]

How long will it take to get a replacement rotor if you damage yours?

[scottly]

The gear isn't locked to the crank; it floats on a bronze bushing on the smooth crank surface. The starter clutch is mounted on the back side of the rotor, and locks the gear to the rotor when the gear is spun by the starter. If the rotor has been lightened, the provision for mounting the clutch may have been removed. There is an oil hole in the crank that supplies oil to the bronze bushing in the gear. This may have been blocked with a sleeve when the starter was deleted.

[paulschell]

Apologies in advance, this isn't about your question in your post!

I was just wondering where your rear cowl came from? Homemade? Looks gorgeous, such a clean build!

Paul

[scottly]

Here are some pics:

[Bodi]

Note that the rotor is just a taper fit, there's no key. But that taper will not want to fall apart. If it's balky, tighten the puller as much as you can and leave it overnight under tension. If it's not free in the morning retorque it and bash the tool end with a dead blow or lead hammer. If no joy, start heating the rotor with a propane torch. You can get it really hot with no problems - there are no permanent magnets inside to demagnetize by overheating.

[greenjeans]

About to pull the cover and take a look.  I don't remember a hole on the crank, like in the third photo above.  I may done before I start. start.