Topic: Maduncle's brat style CB750F - now called "The carb eater"

[maduncle]

You could call today the 'big learning curve' day.

I started to pull the stock footrest sets off the bike and soon discovered how things are held together.

So I learnt that one of the bolts the stock gear mounts to is a full length rod that runs through the engine block and into the bike frame on each side, and it has a short length of thread on each end. It looks like I will need to either remove and modify (by shortening it by 10cm and tapping more thread) or maybe buy the right length of steel rod and make a new shorter one.

The other mounting point is off the rod that holds the swing arm to the chassis, and this one has a bolt head one end and thread the other end. Once again - it will require shortening and rethreading, or replacing.

My question is - are these two rods made of a specific material that is strong enough to work as an engine mounting rod and swing arm mounting rod, in which case do I need to use them and modify them?

Or - can I substitute with stock metal rod that I thread on each end?

All advice appreciated, I can also start to hunt down two of these stock parts so I can modify them whilst still keeping my bike on the road a bit longer.

(Mind you - damn thing would not start again, turns over but won't fire up - and yes it does have a full tank of fuel).

[Raef]

depending on how far they stick out you could just put an equal spacer on each side.

if you are going to modify the existing ones I would pull them out thread one end the required distance and cut off the excess.

Mark

[maduncle]

Yeah, I don't think spacers are a good option as that would leave me with 5cm stubs either side of the bike on the rods, I like your idea of thread one end and trim - that will work for the engine mount, but with a fixed bolt head on the swing arm rod I still need to slide it out, or cut the stock rear set away from it.

[Terry in Australia]

G'Day Cliff, well from memory they're both fine threads and I doubt that you'll have much luck finding threading dies for them, but I'm pretty sure that you can replace them with K series items which are shorter, as they didn't need to pass though those big plates. Cheers, Terry.

[maduncle]

Good point on the thread pitch Terry - had not thought of that.

The manual shows a different swing arm rod on the K to the F, looks like the K one has grease nipples on it, and the F model has a sleeve over the rod - dunno.

I read through the manual this morning on the train on the way to work (as you do), it looks like I can safely slide the lower rear engine mount bolt out safely as the engine is still held in three other points to the frame.

I can then shorten it and tap it with a stock thread.

The swing arm bolt will be a different matter though.

What I am thinking of doing is taking the stock rearset plate off the left side, tapping the swingarm bolt through so it sits proud on the right side, then cut the bolt head off the rod, then pull the right side stock rearset plate off, then tap the rod end and shorten it to suit.

I think I can do all of that whilst the rod is on the bike, as long as I can grip the rod to thread it.  I might be able to hold the rod on the left hand nut whilst I thread it.

[Syscrush]

Nice score on those 'Busa rearsets.  Looking forward to seeing how you get them sorted out and mounted.

[Free Booter]

Still lovin' that seat!

[Terry in Australia]

Good point on the thread pitch Terry - had not thought of that.

The manual shows a different swing arm rod on the K to the F, looks like the K one has grease nipples on it, and the F model has a sleeve over the rod - dunno.

I read through the manual this morning on the train on the way to work (as you do), it looks like I can safely slide the lower rear engine mount bolt out safely as the engine is still held in three other points to the frame.

I can then shorten it and tap it with a stock thread.

The swing arm bolt will be a different matter though.

What I am thinking of doing is taking the stock rearset plate off the left side, tapping the swingarm bolt through so it sits proud on the right side, then cut the bolt head off the rod, then pull the right side stock rearset plate off, then tap the rod end and shorten it to suit.

I think I can do all of that whilst the rod is on the bike, as long as I can grip the rod to thread it.  I might be able to hold the rod on the left hand nut whilst I thread it.

G'Day Cliff, the earlier swing arm pivot bolts had grease nipples either end, the later ones were the same as your F2 bolt, just shorter. If you're leery about removing one bolt then installing the next, just use the new shorter K bolt to tap out the F2 bolt, one comes out, and another goes in. As long as you put a block of wood (or several) under the bike to take the weight you won't have the arse end collapse, if that's your concern.

As I said, I seriously doubt that you'll find a die to match the ultra-fine thread on the swingarm pivot bolt, (which has been case-hardened and hard chromed, so won't be fun to try to thread) but the 10 x 1.25mm mild steel engine mount rod threading die will be easier to find, if not cheap. (unless you buy one on EBay, a wonderful source of almost anything) Cheers, Terry.

[maduncle]

Thanks Terry, I will get on to tracking down a late model K swing arm bolt before I do any more work.

I have not seen one up close so I am hoping it is already threaded both ends, and not capped with a bolt head one end like my F one (which makes testing rearset plates very difficult!).

[maduncle]

Big changes to the bike today.

I went and saw Terry, picked up a swing arm bolt that is shortened and internally threaded, along with some other goodies for the bike which should make it run a little better.

Including a 4 into 2 into 1 exhaust set.



New set on the left, my old set on the right.

I stripped off the stock rear sets, fitted the swing arm bolt and set about making a pair of rear set mounting plates out of 7mm plywood to test fit the 'busa rearsets. I am close to getting the left side working, I need to file out some of the splines on the gear change fitting, it is .5mm less in diameter than the spline on the bike so whilst it would probably tap on with a few hammer blows, I would prefer it to slide on and tighten up on a bolt.

More fun tomorrow, with any luck I will have both sides mocked up and working for the rear sets.

[Syscrush]

I am close to getting the left side working, I need to file out some of the splines on the gear change fitting, it is .5mm less in diameter than the spline on the bike so whilst it would probably tap on with a few hammer blows, I would prefer it to slide on and tighten up on a bolt.

Better to open it up as you plan. 0.5mm isn't a small amount when you're talking about fitting metal pieces together.

[maduncle]

Better to open it up as you plan. 0.5mm isn't a small amount when you're talking about fitting metal pieces together.

Well - I started the day with a careful filing of the inside of the gear shifter attachment, but once I had it at a slide on fit stage, bolted it all up and tested it - it slipped on the spline!

So I went to plan B:

Ground the back off the pin that holds the uni joint to the lever, tapped out the pin, got my stock gear change lever, drilled just the right sized hole, shortened it, tapped in the uni joint from the other fitting and then burred and rounded the back of the pin off once it was tapped into place to make sure it stays there.

Not much to look at, but the smallest parts can be so hard to fabricate in your back shed.



Fitted it to the bike, fitted the linkages and it all works nicely.



So I moved on to the brake side. This was actually easier to do than the gear change side, I copied the mounting positions across from the other template, but I had to adjust one mount hole as the rear sets don't have three mount holes in the same place - the brake side set has a third offset hole but not as offset as the other one.

I made up the bracket, test fitted it with the master cylinder, found a good mounting point for the reservoir and it all works fine (or will - when I bleed the brakes).



You may have noticed that the first bracket was a little 'slimmer'. I will go with the larger second bracket as it will be sturdier and avoid any chance of bend or breakage across the point where most stress is applied. At this stage I am looking at 10mm aluminium for the brackets, with 20mm of spacer between them and the frame, which I may do with 10mm thick spacers cut from the same stock.

next steps:

- draw up the brackets for manufacture.
- extend the wiring on my brake switch.
- consider a new rear brake line (although the stock one does reach).
- shorten the lower rear engine bolt by 53mm and re-thread the end I cut.

And then I will have Hayabusa rear sets on the High Tea Racer.

[Syscrush]

Very nice.  They look like they belong on that bike.

[maduncle]

Very nice.  They look like they belong on that bike.

Thanks - I thought they were a good choice too. I like these rear sets as they have ribbed rubber footrests like the stock CB ones and the 'wing's are rounded so they look a bit like the Honda wing.

[Terry in Australia]

Nice Job Cliff, and I'm glad you sorted the shift lever spline issue, I didn't have the heart to tell you that Suzuki use different size splines than Honda! Cheers, Terry.

[maduncle]

Nice Job Cliff, and I'm glad you sorted the shift lever spline issue, I didn't have the heart to tell you that Suzuki use different size splines than Honda! Cheers, Terry.

Ah thank you master Jedi - your Paduan continues to master the dark side of Honda bashing!

[maduncle]

Slight change of design on the rearset plates...

My optimistic set of drawings using 10mm aluminium plate and 30mm dia aluminium bar stock to make chunky spacers cannot find a local fabrication shop to do the cutting and drilling - so I have switched materials, now using 6mm steel plate and steel tube cut to length to make bolt spacers.

Plus - I will be bolting the plate flush to the bike frame and then spacing the 'busa rearsets off the plate. I reckon this will be stronger as the plate will have more support flush against the frame, and the rearsets mount up on three bolts so they will be strong enough on the spacers.

I have a 30cm x 30cm sheet of 6mm steel plate, now I just need to draw my brackets on to it and see if I can't cut it myself - but can a hand held jigsaw with the right blade on the right speed with lubricant cut 6mm thick mild steel?

Only time (this weekend) will tell folks!

[Retro Rocket]

My optimistic set of drawings using 10mm aluminium plate and 30mm dia aluminium bar stock to make chunky spacers cannot find a local fabrication shop to do the cutting and drilling

Hi Cliff, go see the master Jedi mate.....

[maduncle]

My optimistic set of drawings using 10mm aluminium plate and 30mm dia aluminium bar stock to make chunky spacers cannot find a local fabrication shop to do the cutting and drilling

Hi Cliff, go see the master Jedi mate.....

My master requires time to tackle a K, so I  am on a solo quest as part of my training.

And I have changed thedesign (again)...

... 6mm steel plate brackets, cut and BENT so that each bracket has an offset bent into it to space the rearsets off the frame when the bracket is flush to the frame.

Much stronger and less parts, as I don't need spacers.

Plus it may look more like a stock part once it is painted to match the frame.

If I end up with a good one piece bracket design that mounts Hayabusa rearsets onto a CB750 frame without the need for spacers, I will post drawings here for anyone else who wants to make them.

Or I could even get a batch of brackets made,  get some swing arm bolts shortened and tapped, get some lower engine bolts shortened and tapped - and sell them as a kit!!!

[maduncle]

Three hours of trying to remember how to do an engineering drawing resulted in this:


(I know it is upside down - but then I am in Australia, that is how we draw)

Three seconds with a hot iron resulted in this:

[maduncle]

Help,



I have six exhaust flanges, but as we all know eight is required to do the job.

If anyone has two (or more) they can spare for sale - please PM me!

[Flying J]

Im sure i do but shipping might be crazy, better if you can find them local.

[maduncle]

Im sure i do but shipping might be crazy, better if you can find them local.

Thanks - I eneded up buying a new pair from CMSNL and a set of copperwashers at the same time, and shippng from UK to Australia is cheap compared to shipping from USA.

Meanwhile - I am also looking for a CB450K0 or K1 front end (forks and trees) as my next project requires either that - or a CB750 font end conversion...

[maduncle]

Some progress,

I ended up making a new lower rear engine bolt from 12mm bar stock that I cut to length and threaded. I also fitted my new Venhill rear brake line today (such a good place to get brake lines) and I fitted my 'busa brake light switch, although for some reason the bikes circuit has the brake light always on at the moment - and that was BEFORE I fitted the 'busa switch.

The brackets will be laser cut and bent next week, so I should have this rear set conversion done pretty soon, then I can get the new headers on and measure up for the adapter pipe for my Lossa muffler.

Meanwhile - I am inside my CB450K0 engine now, finding rusty pistons and working on getting them out somehow...

But that's not a SOHC4 project is it? So I will save that one for the Honda Twins forum.

[hapakev]

you may have the running light and brake light wires switched, it will cause the brake light to be always on.  If you have the brake switch set too tight, it will do the same.