Topic: CB750 removing starter - what else should come out?

[Kickstart]

I'm working a dedicated CB750 race engine and decided to remove the starter to save a couple of pounds.

However, I'm not sure if I should keep the "reduction gear" hardware  between the starter motor and large "starter clutch" gear behind the flywheel.  I know the shaft is needed as it acts as a locator down for the cover - I'm keeping that, I'm just not sure about the reduction gear and large thin washer ("setting plate")

Intuitively, I would think they're not needed.  . I'm thinking the the gear itself won't be doing anything, however... it appears that setting plate washer helps keep the starter clutch gear pushed in towards the engine.

The starter clutch gear has about 1-2mm play in-out towards the engine, and it looks like that washer helps keep it in place.
I know there is an oil passage on the crank underneath that gear - will there be any pressure loss if it's not kept pushed in all the way?  I'm thinking not, but just want to confirm. 

On the flip side, if I leave the gear and washer in there will they be vibrating a lot now that the starter motor spur gear isn't there to hold them still?

I'm leaning towards it won't be a problem to remove the reduction gear and starter plate washer, but just wanted to confirm with someone who has experience with removing the starter motor.

Picture attached.

Thanks,
Chris

[Don R]

 Is that a low serial number engine?  The reason I ask is, that looks like the early heavy flywheel. And I'm a rabid K0 guy.

[Kickstart]

Is that a low serial number engine?  The reason I ask is, that looks like the early heavy flywheel. And I'm a rabid K0 guy.

I don't know about early... but it is an "earlier" K2.  It had the older style front forks.

Reducing the flywheel weight some is a potential future project.

[scottly]

Chris, remove everything, including the shaft (it doesn't act as locator for the cover; the dowels do that) and the clutch on the back-side of the alternator rotor. The later rotor without the flange will bolt right on, and weighs 1.234 pounds less than the early one. There is a restriction in the oil passage in the crankshaft, so there will be no loss of oil pressure.

[Don R]

 A friend that raced sohc's told me he snapped the end off a crank with the heavy flywheel on it. His point was don't run a high perf engine with one. I'd get a light one, remove the gear and the sprag (starter clutch) parts too. I went the other way, leaving the starter drive and removed the dyno with a ziz wheel and turned it smooth on a lathe. I'm trying to start an 1124 with a hayabusa starter.

[Kickstart]

Argh... you guys bring up a really good point about the heavy flywheel.  Honestly, I forgot about it.  When we rebuilt the engine last year I remember saying that we should really get the flywheel cut down (or replace it with a newer version) but we didn't have time.

And, prioritization wise, yes... saving 1.25 lbs rotating mass is probably a lot more important than saving 5 static lbs from the starter motor.

I was under the impression, that while I heard of the snapped crank issue with the heavy flywheel, it was a pretty remote probability -  even with racing... Maybe I'm taking a much larger risk than I had previously thought?

I'd rather not replace the flywheel right now, as I'm not very comfortable with being able to torque the bolt to the correct valve during reassembly.  In another thread  discussion on the best way to do this if the engine is already put together.  As I recall it was a combination of putting the bike in 5th gear, rear brake, and foot pushing on the kick starter... all at the same time to hold the crank still while the rotor

OK, so I don't need to worry about the starter gear moving around.  I didn't know about the oil passage under the starter gear already being restricted.  Since the gear has an oil seal in it I assumed the gear itself was responsible for restricting the oil.

Scottly, are you sure about the shaft not being needed?  The alternator cover only has one locator dowel as opposed to the shift and clutch covers having two dowels.

[Don R]

 I was thinking there was more than one dowell, is one missing?

[Kickstart]

I was thinking there was more than one dowell, is one missing?

Per the parts diagram there's only one dowel on the alternator cover.  I'm pretty sure I've only ever seen one dowel on the few I've opened up.  I'm thinking the shaft must act as the other locator.

[MCRider]

I was thinking there was more than one dowell, is one missing?

Per the parts diagram there's only one dowel on the alternator cover.  I'm pretty sure I've only ever seen one dowel on the few I've opened up.  I'm thinking the shaft must act as the other locator.

Good point on the locator being the shaft. Probably true, though I've run without it. In my brief tenure at a drag/chopper shop back in the day, I saw 3 cranks snapped off, all on hot street bikes. High RPM downshifts, with lots of engine braking, were often the cause moreso than upshifts.  Not on our racers, but they all had lightened or absent rotors.

[edwardmorris]

Chris, its actually easier to torque down the dynamo rotor if its out of the engine, I torqued (and disassembled) both of mine in my tiny 4" bench vise without issue.

[Don R]

 Good conversation and info.

[Kickstart]

... In my brief tenure at a drag/chopper shop back in the day, I saw 3 cranks snapped off, all on hot street bikes. High RPM downshifts, with lots of engine braking, were often the cause moreso than upshifts.  Not on our racers, but they all had lightened or absent rotors.

Oh boy... OK, so I should be worried about this.  Interesting how 1.25 lbs makes the difference between no issues and snapping a crank.  I just figured the cranks are so large/thick and over-engineered it was a low probability.

Ordered a newer model rotor off of eBay... not looking forward to getting it torqued up properly when I go to install it

Hi Rafi!  ... yes, it's definitely easier to torque it when it's out of the engine... I just don't have time to tear down the engine, nor do I want to take the risk of doing an engine rebuild right now... I'm only two weeks away from an upcoming track day, and then two weeks later will be our first race.

[PeWe]

Alternator job was a cheap "upgrade" for many years ago. Mine got lightened and still charge the battery

[Don R]

 They don't all snap the crank, it's just another possibility. I'm guessing honda reduced the weight for a reason. I'm not sure they were snapping cranks but my friend did, his was a bad to the bone engine though, running within .02 of the 1/4 mile record back then.

[edwardmorris]

Oh? Nevermind, I thought you had it apart. I haven't done much digging yet but apparently there's a motion pro clutch holding tool that helps with installing the rotor at the end of the engine build. I'm going to need it as I'm going to have to install the dynamo rotor AFTER I time my cam on the K3.

[MCRider]

... In my brief tenure at a drag/chopper shop back in the day, I saw 3 cranks snapped off, all on hot street bikes. High RPM downshifts, with lots of engine braking, were often the cause moreso than upshifts.  Not on our racers, but they all had lightened or absent rotors.

Oh boy... OK, so I should be worried about this.  Interesting how 1.25 lbs makes the difference between no issues and snapping a crank.  I just figured the cranks are so large/thick and over-engineered it was a low probability.

Ordered a newer model rotor off of eBay... not looking forward to getting it torqued up properly when I go to install it

Hi Rafi!  ... yes, it's definitely easier to torque it when it's out of the engine... I just don't have time to tear down the engine, nor do I want to take the risk of doing an engine rebuild right now... I'm only two weeks away from an upcoming track day, and then two weeks later will be our first race.

My first experience, I was a floor sweeper in a shop, battery charger etc. The guy rode the bike in, said his battery wouldn't stay charged. And the electric starter quit working.  Wonder why?  Just like with a twisted cam, it will still run.  Pulled the alt cover off and plop.

[754]

 Put a good fitting 6 point box end on it, hit it with a hammer to loosen or tighten. use a strap wrench if tightening with a torque wrench...

[scottly]

Scottly, are you sure about the shaft not being needed?  The alternator cover only has one locator dowel as opposed to the shift and clutch covers having two dowels.

Yes, I am quite sure there are two dowels. The possibility of snapping the crank is somewhat remote, so I wouldn't worry about it if you are close to meeting a racing deadline. However, if you have the tools, parts, and know-how, it's not that big of a job to swap the rotor and remove All the starter parts.