Topic: 1976 CB750F - first bike, first build - mild cafe

[riffman12]

So today was productive. Finally got an angle grinder and got to work with the frame modifications. I apologize in advance for anyone who tells me I'm a horrible person for cutting the frame.

The damage. I haven't gotten to it yet, but I will be grinding and sanding everything smooth + painting:








here's what I'm really happy about. I think if I cut about an inch off the front of my seat, I should be able to use the factory rear frame hoop.






You can see here how much I need to cut off to stop it laying under the tank, about an inch. I considered having it just sit under the tank but I think when the tank moves around it will clang around on the seat pat and be annoying




My plan is to put some sort of hooks for the front of the seat to slot into. Then I can use the factory hoop at the rear to bolt some sort of L brackets into the back of the seat pan with flat heads on the seat side. Then maybe even wing nuts so I can take the whole thing on and off quickly. Not totally decided on all this yet.

But I'm just happy I don't need to weld in a new hoop 


Next steps:
- fix my buggered up threads in the rear wheel bearing retainer, get the rear bearings in.
- mount the wheels, get it off its milk crate
- mount my exhaust
- get her running once again

[SOHC4 Cafe Racer Fan]

I spoke with Ian.  If you are interested, the best method for upholstery would be to send him the seat when you finalize the length.  That way the pan will be dead nuts on and the build up for the tank as well.

[riffman12]

sweet thanks. Once I have the seat pan all ready to go I will give them a call.

Quick question. I bought these Hagon shocks, but it looks like they're a little wide for the normal mounting spots. Do I need to put washers in there to take up the extra space?

top:




Bottom:

[GritCity750]

Definitely want to check that you can see light through those pilots!  Compressed air is useful to clear them out after a soak as well.

Float measurement is easiest with the carbs upside down, at an angle so the floats are hanging just starting to touch the needle.
Great resource with picture instructions:  http://www.salocal.com/sohc/tech/carb/asmpg_mgs/flthgt.htm
You don't have to seperate the carbs to change the needle clip position, but you do have to pull away the throttle body to unscrew the tops obviously.
I wouldn't go moving needle yet, start at stock position, middle groove, get main-jet right and idle circuit dialed in and see how it is.

I have a 76F with carpy 4into1 as well, I think you'll absolutely need to jet up a bit, it's a very open pipe.  115's should be good to start, do a wot plug chop and if looks rich start stepping down.  I've been through almost every intake option since i built the bike and have a full set of jets from 105-130, mainly just because i like to play.  I've run open stacks, uni-filter pods, and the stock airbox now with k&n filter & intake modding. I'm actually in the process right now of leaning it back out for the air box.  Just like anyone will find with 5 minutes research, i could immediately feel the throttle transitions are way smoother with the airbox and no turbulent air passing things on the highway.

I currently have 122.5 mains and 42 idles with needle one clip richer from running v-stacks, it's running very rich all around with airbox now obviously.  No black smoke but fuel ring on the plugs is black and sooty and it feels lazy.  I'll be taking them back to 40 idle 118 mains this weekend to see how that is.  Will be interested to hear how yours looks with the 115's.

75/76F is my favorite, looking forward to seeing more of yours as you  progress.

+1 for sure. I run a Carpy Dunstall 4into2 with K&N pods and 118 jets with 40 pilots works well. I picked up a few sets of different sizes of jets from 4into1 and (i think they are about $2.50 each) and played with them until i found the best setup. Once i got it figured out, I replaced them with the OEM Kehhin jets ($4.50 each).

[Gooseman]

Yes to the washers to fill that play in the shock clevis's.  Some shock builders will include shim washers as they're commonly needed.

[riffman12]

Yes to the washers to fill that play in the shock clevis's.  Some shock builders will include shim washers as they're commonly needed.

great, thanks. What about the top? Does that look OK as is?

[riffman12]

anyone know if the top of those shocks look OK? Or if I need some extra spacers in there?

[Gooseman]

Tops look fine to me in the pic as long as they tighten down ok.
Being the gap on the bottom clevis is on the outside of the mount, they definitely don't need a washer behind them.

Only real reason for the washers on the bottom is so you don't bend and weaken the cleavis.

[riffman12]

Tops look fine to me in the pic as long as they tighten down ok.
Being the gap on the bottom clevis is on the outside of the mount, they definitely don't need a washer behind them.

Only real reason for the washers on the bottom is so you don't bend and weaken the cleavis.

hmm so you're saying you don't think I need a spacer at the bottom? Or I need one in between the clevis and the swingarm?


I've started building the seat pan for my upholstery. Got the template all worked out last night. It was a major pain because the seat gets narrower towards the front. Next step is actually cutting it out of aluminum sheet and bending it to fit.

big thanks to CB750 Cafe Racer Fan for the help with this 

[riffman12]

OK so this rear wheel is going to fight me every step of the way. 

So first I had some issues with the wheel bearings. I was tapping in the brake rotor side (the one with the retainer) and tapped it a bit too far so that it smushed up against the collar on the inside. After a lot of swearing I got it to back out a bit until it was just snug up to the collar, but could still move the collar.




but now I have a whole new issue. My brake caliper bracket is rubbing against my brake rotor. The spacing in the rear axle is wrong somewhere. See pics:
 





Here's the rest of what is going on, in case someone can see something that does not look right








As you can see it is nowhere near centered in the bracket. I'm trying to figure out where the spacing can possibly be off. Here's my thinking so far:

1) I am using a wheel from a '79 CBX, but everything else here (axle, spacers, brake bracket) are from a '77 750F.

2) I double checked that the brake bracket was the correct fit, and indeed the CBX and 750F brackets are identical (same part number)

3) I' wondering if perhaps the two little collar / spacers on either side of the wheel were spaced different for the CBX. The part numbers are different.

4) I wondered if perhaps the little spacer / collar is not far in enough, but it pushes up against the bearing, and the bearing has no more room to go in.


I figured that all the Comstars would share the same spacing for everything regardless of bike model. Am I wrong in thinking that?


Here's how it looks on the bike...one day when I stop hitting road blocks like this 




I know it's a bit of a unique issue, but can anyone shed some light on this?

My next step might be buying a full rear axle from a CBX... but I'm worried it won't fit in the 750 swingarm or something silly.

[Jerry Rxman Griffin aka MuthaF'er]

Perhaps you need a 75/76 caliper? Check in with Wilbur aka madmtnmotors. He may be able to compare the 2 calipers for you.

[riffman12]

Perhaps you need a 75/76 caliper? Check in with Wilbur aka madmtnmotors. He may be able to compare the 2 calipers for you.

hmm I don't think the caliper or the bracket are the issue. The wheel, brake rotor, and caliper bracket are all from a CBX. The issue seems to be that little collar / spacer between the hub and the caliper bracket.

so frustrating. I just want to get the wheels on 

[calj737]

The bike is 40 years old. Takes patience to put it back in service. The delta in timing between "wanting" and "having" it done is the critical aspect of why some builds never get completed. Breathe deeply. It will be right soon-

[riffman12]

OK well I ordered a complete CBX rear axle complete with spacers off eBay. Hopefully that helps some of my issues at the back.


My next obstacle is my front sprocket. I ordered a brand new 17T sprocket. Went to mount it and the bolts didn't feel quite right. I figured they were just a bit gummed up from being in the old sprocket. Now it seems the threads weren't quite right and I may have damaged them.

Is that normal for the threads on a new sprocket to be different than the old ones? That seems odd to me.

[riffman12]

OK so here is the latest. I'm hearing from several sources that my '77F swingarm is wider on the left side than my '76F bike. I took these pictures to see if anyone can confirm this.

The only reason I'm puzzled by all of this is that I purchased the bike from someone who (as far as I know) rode it with this frame / swingarm combination and I think he would have noticed if the shocks were crooked.

What do you guys think? I think I am seeing that my left shock kicks out further than my right one.

Ignore the wheel not being quite centered. I've got some axle / spacer / bearing issues I'm working on









PS: Thanks to all that I have been sending PMs to trying to help with this.

[calj737]

Easy enough to confirm. Drop a plumb line from the upper mounting boss and see where it hits the lower arm.

[riffman12]

hm that's a good idea. And just put a spirit level across the top of the bike or something? to make sure everything's level?

[Jerry Rxman Griffin aka MuthaF'er]

Yeah, thats not a F/F1 arm and looks like a F2/F3 from the axle adjuster area. Being that, it is 10mm wider on the left. I had an 10mm adapter and spacer made. When I tried different shocks (3 brands) I discovered the top mount on each is a different width with the Honda shock being wider. I don't know how much difference it will actually make but the angle will be different. Can't do pix now as I'm about to hit the road again.

[70CB750]

What Jerry MF says, it looks like the left shock needs to come out at the top.

[Jerry Rxman Griffin aka MuthaF'er]

10mm offset shock mount adapter



This is in conjunction with the 10mm offset swing arm left side.

Stock shock mounted using the adapter with F2/F3 swing arm. Notice the clearance of the sprocket plate and the arm with this setup. NO clearance using the 75/76 F arm (-10mm offset) and the 77/78 sprocket carrier that is necessary for the alignment with the 77/78 engine.



The Redwing shock and the 'other' shock (forgot the Italian sounding name) are both narrower at the top mount and leave a small space where the top shock mount could move laterally. Washers/spacers should probably be used in this instance.

[70CB750]

I replaced the stud. 

[riffman12]

as nice as it would be to replace the stud altogether, I'll probably go the route Jerry suggested. Any tips on where to get that offset shock mount adapter? Or do I need to get it done custom at a machine shop?


My biggest question now is...why am I even going through all this work to make the wider swingarm work? My engine is the narrower '76F engine, so I feel like I'm trying to force this wider swingarm, custom offset sprockets etc. for no added advantage. Am I right in thinking this?

Scratching my head trying to figure out why the previous owner even installed the later swingarm in the first place... 

But if I go back to  the '76F swingarm:

a) I would need to find and buy the swingarm, powder coat it to match.

b) would my '79 CBX wheel even fit?

[Jerry Rxman Griffin aka MuthaF'er]

Can't say about the CBX stuff vs stock 75/76 F stuff but yes, you would need the 75/76 swing arm if everything else matches it and you prefer not to do the shock mount if you want to do it correctly IMO.

Keep in mind the 77/78 rear sprocket carrier is 10mm wide than the 75/76 so you need to determine which you have.

Make sure which engine/output shaft you have. Flush or offset?

My rear is not back together yet so I MAY be able to help with measurements once I'm home and have picked up my stuff from the coater late next week.

[riffman12]

Thanks again, Jerry. I owe you big time once this is all done.

The annoying thing is that for some reason they put 5 rubber bushings in the rear wheel drive of the CBX, vs 4 in the CB750, so I can't put a narrower sprocket carrier

edit: this is what the CBX carrier looks like:



I wonder if it's possible to machine it down or something...

[Jerry Rxman Griffin aka MuthaF'er]

Naw, wouldn't even consider modding it like that.

The question is - do you need a different sprocket carrier? You really need both 750 rear set ups to compare to/with that one for total width and spacers.