Topic: 72 CB750 almost back on the road

[Casor]

My 72 750 is almost done.  Frame off resto, just started it the other day and it ran great.  Waiting for a couple odds and ends before I complete it. 

[HondaMan]

My 72 750 is almost done.  Frame off resto, just started it the other day and it ran great.  Waiting for a couple odds and ends before I complete it. 

Nice job!
Don't let mine see it, it might get jealous and leave me...

[Casor]

I could not have done it without your book.....I was hoping you would chime so that I could thank you for writing it.  I bought your book when I bought the bike about five yrs ago - it was smoking a little so I knew I would have to do at least the top end.  Your book was very helpful for not only this but for just about all of it.  After we pulled the engine, my fellow rider/assistant said:  "You're not that far away from doing the whole thing" since at that point the front end and rear wheel was off.  So, that's what I did and I am glad that I did it.  It was a fun, relaxing, exciting bike to redo.  As an aside, I put the repainted frame on the engine, not vice versa, the engine being protected and laying on its side atop 2x6 studs that were cut and positioned to accommodate the engine.  I think putting the frame on this way took us about a minute.  Literally, a minute and with no scratches or drama.

Thanks for all your help Mark

[newday777]

  As an aside, I put the repainted frame on the engine, not vice versa, the engine being protected and laying on its side atop 2x6 studs that were cut and positioned to accommodate the engine.  I think putting the frame on this way took us about a minute.  Literally, a minute and with no scratches or drama.

Thanks for all your help Mark

Cool beans! I need to get back to the 74 I started on late last January for a friend. I have the frame and engine painted awaiting putting the frame on the motor. Do you have pictures of the 2x6s and the use of them?

[Casor]

  As an aside, I put the repainted frame on the engine, not vice versa, the engine being protected and laying on its side atop 2x6 studs that were cut and positioned to accommodate the engine.  I think putting the frame on this way took us about a minute.  Literally, a minute and with no scratches or drama.

Thanks for all your help Mark

Cool beans! I need to get back to the 74 I started on late last January for a friend. I have the frame and engine painted awaiting putting the frame on the motor. Do you have pictures of the 2x6s and the use of them?

I didn't take photos of them but easily described.  The eng was supported by its clutch area and the cylinders/head.  Clutch cover was off and I covered the open area with a pc of ply - screwed in place.  Two pair of 4-6" long 2x6's screwed together and a ply base screwed to each of them.  One pair was shorter to accommodate the cyls/head - this kept the eng level when on its side.  3 layers of cardboard strapped to the rt side of the cyls/head to protect the fins.  Cardboard taped over the 2x6 stands and these were then screwed to a large, flat topped wooden dolly cart - offsetting them so they aligned with the clutch and cyl areas.  Eng was placed on the 2x6 stands on its right side.  Another block to steady it under the points cover.  Frame was then carefully maneuvered over and on and the bolts were slipped in and temporarily tightened.  The stands helped with the clearance to get the nuts and plates on the frame.  Took longer to make the stands than it did to put the eng on them and then the frame on that.  Friggen easy.  I would say that you could probably make the 2x6 stands a lot shorter than I did - maybe 2-3" or so.  Just enough to give you access underneath.

[Shtonecb500]

you have a very nice collection.

[Casor]

you have a very nice collection.

Thank you!

[Godffery]

 Look'n Very nice.  And might I say; what an Awesome Rotor & Caliper you have there...!   

[Casor]

 Look'n Very nice.  And might I say; what an Awesome Rotor & Caliper you have there...!   

Yes, that's yours!  I also have stainless lines and rebuilt the master so I hope the damn thing stops better!

[Godffery]

 Look'n Very nice.  And might I say; what an Awesome Rotor & Caliper you have there...!   

Yes, that's yours!  I also have stainless lines and rebuilt the master so I hope the damn thing stops better!

I can't imagine it not.  
If you want to get the max out of it, you could upgrade the master as well, to eliminate the need for the in-line break light switch. That's a bit of a PSI thief.

[Stev-o]

Looks good! Got pics of it with the bodywork on?

[Casor]

 Look'n Very nice.  And might I say; what an Awesome Rotor & Caliper you have there...!   

Yes, that's yours!  I also have stainless lines and rebuilt the master so I hope the damn thing stops better!

I can't imagine it not.  
If you want to get the max out of it, you could upgrade the master as well, to eliminate the need for the in-line break light switch. That's a bit of a PSI thief.

That's an idea I haven't thought of.  I am trying to keep the bike completely stock (or looking so) but as a matter of practicality a different master might be a good idea.  I will see how the thing stops with what I have for the moment since I have changed so much on the brake system and then go from there.

[Casor]

Looks good! Got pics of it with the bodywork on?

Stev-o thank you for the comment.  It was really a pleasure to redo this bike.  It was mostly complete when I got it but it smoked a bit and since I already had the entire front end off, the rear wheel and the eng out, it wasn't that much of a stretch just to redo the whole thing.  The tank and side covers are very nice so I just have to get a few miserable breather tubes before I finish it.  I am also having fits with the rear brake but will figure this out.

For those interested, I have attached a memo detailing the restoration process.

[Godffery]

 Look'n Very nice.  And might I say; what an Awesome Rotor & Caliper you have there...!   

Yes, that's yours!  I also have stainless lines and rebuilt the master so I hope the damn thing stops better!

I can't imagine it not.  
If you want to get the max out of it, you could upgrade the master as well, to eliminate the need for the in-line break light switch. That's a bit of a PSI thief.

That's an idea I haven't thought of.  I am trying to keep the bike completely stock (or looking so) but as a matter of practicality a different master might be a good idea.  I will see how the thing stops with what I have for the moment since I have changed so much on the brake system and then go from there.

Well there is the Master Cylinder from a 77 - 78 750 A, F & K that has a larger piston bore, as well as a built in brake light switch.
https://www.5thgearparts.com/products/1978-honda-cb750k-cb750-cb-750-front-brake-master-cylinder?variant=21617721351

[Casor]

Godffery - from the cursory research I did on the net and in this forum, it seems that going down in size to maybe 12mm is the answer of will help.  I believe that the newer 77-78 master is 15mm - Vintage CB750 sells new masters in this range and say it's better than stock so not sure what to believe.  The stock size if 14mm for my bike.

[scottly]

All of the K models, as well as the F0/F1 used a 14 mm master, and the pressure switch does Not reduce the PSI..
A 12mm master is a good size for a single 38mm caliper.

[Casor]

All of the K models, as well as the F0/F1 used a 14 mm master, and the pressure switch does Not reduce the PSI..
A 12mm master is a good size for a single 38mm caliper.

Thank you for the help!  I need all I can get....

[Casor]

Couple more pics as I near completion.  Only item left is receipt of the rebuilt tach.

Much of this bike is original- the engine case, exhaust, front and rear wheels/spokes, side covers, fenders, controls, fork lowers, electrics.  It even has the original owner's manual and tool kit.  It was complete and unmolested when I bought it.  Major things I did was the disassembly and reassembly of the top end of the engine - new pistons/rings, valves, guide and cam running gear as well as new seals and gaskets of course.  Engine work was done by Cycle X.  Has new fork tubes, new front brake caliper, stainless lines, new rear shoes.  Rebuilt tach and speedo.  I rebuilt the carbs.  All the bolts, nuts and various hardware pieces were replated and had some chrome done as well - headlight ears, brake pedal, exhaust nuts and stubs.  The fuel tank was repainted before I got the bike and it is a nice job.  A very pleasant bike to redo.

[Shtonecb500]

looks lovely my friend.

[BenelliSEI]

Nice looking and great job. My son chose the same colours for his K3!

[Casor]

Nice looking and great job. My son chose the same colours for his K3!

I think that's a good choice - I really like the met olive!

[Casor]

looks lovely my friend.

Thank you!!

[Casor]

Little things I learned along the way.....

If you're taking the bike entirely down, take the frame off the engine with the engine on its side.  Conversely, as noted above, do the reverse when the frame and engine are ready.  Much easier.

If you're just taking the engine out, strip the engine as far as you can with it in the frame and the bike tied down.  Remove the chain tensioner.  Unfasten all the nuts and remove the upper bolts and plates so that the engine is now resting only on the lower aft rod mount and the two forward bolts.  Plug the intake and exhaust ports.  Protect the fins with cardboard strapped or taped around them all.  Strap an 8' 2x6 to the back of the head/cylinders with the strap going around the 2x6 and around the front of the head/cylinders and back to the 2x6.  Screw in a cross mount of a short piece of 2x6 to each end of the 2x6.  Make sure this is sturdy.  Run a strap around the 2x6 going underneath the engine and up the other side back to the 2x6.  Tight!  The 2x6 assembly should be mounted to the engine asymmetrically - the long end out the left side of the bike.  This will give the guy on the left some room to get the engine through and out of the frame.  The "T" handles on the 2x6 will give you some way to maneuver the engine out and it is a good idea to have your landing zone right next to the bike and perhaps a few inches below the lower rail on the frame.  This was a 3-guy job for me but 2 guys could do it.

Carb clamps - the ones w/o the flanges go on the rubber boots connecting the airbox to carb.  Put small washers on the screws to keep them from distorting the thin metal of the clamps.

Remove the lower part of the airbox when installing it in the bike up to the carbs.

The brand new stock Honda air filter's foam seals are too hard.  They will leave you a gap in the housing once installed.  Replace one side of these seals with a soft stick-on strip seal from the hardware store.

Rear brake - when reassembling - make sure the dots on the ends of the fore and aft splined shafts absolutely line up properly with the slots on the levers.  Also, the brake shoes may look good but they probably ain't.  It doesn't take much wear for them to be undersize and throw off all the lever relationships.  This gave me fits - once I changed the shoes and lined up the dots, the world was a happy place!  Lube the pivot points with Staburag heavy grease that won't fly off or go anywhere but where you put it.

https://cnc-specialty-store.com/grease-lubrication/kluber-isolflex-nbu-15-50-gram-tube?gclid=Cj0KCQiAuJb_BRDJARIsAKkycUnKG9JtLFLmpJMVrytz89esXGuc34UD7FmmHsrlVuegeRW9HyVujwsaAkhXEALw_wcB

Change all the rubber pieces you can get to depending upon the scope of your job.

To remove the rear wheel, take the master link off the chain and slide the wheel and axle out the back end of the swing arm.  Safety wire your master link after going back on.

Straighten out the aluminum cable ties in a smooth jaw vice.

If you're doing a resto and will be replating hardware, use Evaporust in an ultrasonic cleaner to take off rust and corrosion.  Really works.

Run an additional ground from the seat lock assembly to the back of the engine - I used the bolt holding down the carb drain tube bracket.

Read my restoration notes PDF above on the first page for other tips.

[Casor]

Have had the bike on the road for about 150 mi and it's running great.  Couple of issues I need some advice on since I don't know the 750's that well

1)  Fr Brake is squeaking like mad under braking.  Would caliper lube help and where?  Driving me crazy!  Bike stops pretty well however.  Using NOS Honda pads
2) Loudly clunks into first gear at rest.  When I have some forward motion, it's a lot quieter.  I did not replace the clutch pack since they appeared OK to me and the clutch is adjusted per the manual.  But the lever engages the clutch at the farthest end of the lever's travel.  I have a mm or so free play in the lever and it feels right and the clutch does not slip when engaged.

Any help?
Thanks
Rob

[HondaMan]

Have had the bike on the road for about 150 mi and it's running great.  Couple of issues I need some advice on since I don't know the 750's that well

1)  Fr Brake is squeaking like mad under braking.  Would caliper lube help and where?  Driving me crazy!  Bike stops pretty well however.  Using NOS Honda pads
2) Loudly clunks into first gear at rest.  When I have some forward motion, it's a lot quieter.  I did not replace the clutch pack since they appeared OK to me and the clutch is adjusted per the manual.  But the lever engages the clutch at the farthest end of the lever's travel.  I have a mm or so free play in the lever and it feels right and the clutch does not slip when engaged.

Any help?
Thanks
Rob

That 1st-gear 'clunk' is telling you that you did it right! That's what these do. It happens because the gears in this tranny are about 50% bigger than they needed to be (and in all similar versions after 1980) because Honda was afraid of a big, visible public failure (like blown open cases?). All that mass, and the looseness between the disengaged dogs on all those gears, get synched when you drop into gear, and that mass pulls the clutch plates into full slip, which the oil assists. It will usually clunk a little between each gear when it is fully warmed up, a unique marque of this bike.

The brake: any brake pads made by EBC squeak, period. The only other ones that don't also do not stop in the wet, at all.
Look closely at the pucks to see if there are tiny bits of brass embedded in the pads: if not, get some that look like that instead of those you have. These good ones are called 'sintered' pad material and will squeak only about 1%-2% as much. In the meantime, you can try some other things (that won't work much), like cutting an "X" across the faces of the pads with a hacksaw (deeply, like 2-3mm deep) to reduce the frequency (pitch) a little bit. You can also spray (and let dry overnight) some of the anti-squeak spray from the auto parts stores. If you can find one, you can also install a thin nylon ring (like a thin washer) on the moving-puck side, at the dome on the back of the moving puck, that just barely spaces the metal surfaces apart. The idea of this is: the nylon will absorb the squeak that happens as the puck is lightly applied, because under heavy braking it usually stops vibrating. In my experience this works, but I had to make my own in trial-and-error trips for a month. If you can find a genuine NOS Honda brake pad (either or both sides) from eBay (check with JTMarks, he might still have one or two) that will last most of a lifetime. I am only on my second set, as 150k+ miles.