Topic: CB750K6 -76 project back to life with more updates

[PeWe]

Good news about primary chains!
Slack only 65.4mm despite almost 28.000 km of a abuse!
Min 80 whp, most of the time ~90whp with good torque, last time +100whp.

They were a little bit less than 65mm direct after installation when new, engine had not run anything.

The CCC chains really are stronger!!
I thought slack could have been +67mm due to the extra torque of 1000cc.

This change my plans.  I have enough to do anyway.

I'll not pull the engine, only head and cyl block to replace base gasket.
Probably another head going in. I'll might get a "racing" cam chain tensioner with white gliders instead of rubber wheels in a stock tensioner.

I have measured many times to get a higher value, but not.
Parallax error  (photo in an angle) on photo that does not show 65.4mm as it is.

[PeWe]

Replaced alternator and shifter cover gaskets today.
Yesterday new gasket on oil pan. Green Honda quality gaskets.
Next on engine is replacing base gasket and head when a 392 head is refurbished and improved. Chamber volume tested and verified with my old K2 head.

[Joe Deleon]

Hello everybody! I wanted to say that I have a set of 69 CB750 sand-cast gauges that Im selling, if anyone out there is interested please reply to my message

[PeWe]

New rear tire and drive chain with sprockets went on today

- Metzeler Roadtec O1 again, but wider this time, 120/90-18.
- Chain DID 530 ZVM-X
- Sprockets 17:48.

I saw my Service notes from earlier this year when changing rear tire about the chain that then looked to survive 2 rear tires more, +10.000 km.
Wrong, chain was really bad after less than 4000 km!   Risky chance to let bike run on Dyno. I warned the Dyno guy about the chain and avoid snappy throttling

My mistake to change lube, from my much used well working Motorex Chain lube to Maxima Chain Wax that had got good reviews.

I wonder what made it that good on reviews!
I saw rather soon a red rusty dust around front sprocket creeping outside

I understood too late that the wax was no good lubricant. Only a fluid chain cover. Case around front sprocket covered by a thick waxy goo that needed lots of degreeser and scrape the sh!t off.

Motorex Chain lube to be used, always. I'll see after 25.000 km.

I need to remember to lube the chain on my K2 with good lube, not the bad Maxima Chain Sux.

Will rivet the chain tomorrow. Master link is mounted with x-rings and side plate. Just to squeese it in place. There are spacers to not tighten too hard before riveting it. Hollow link this time.
Easier than my old DC chain with solid link.

[andy750]

Per
I was never too happy with Maxima Chain wax. I switched to Motul and found it cleaner but still effective. Rear tire looks good!

[PeWe]

Hi Andy,
OK, Motul makes chain lube too, good to know.
How it lubes the chain and sprockets most important, less visible dirt on rear wheel is not on the list. Possible to wipe off when needed.

I'll try to wear the new tire more evenly next time, knees closer to  the asphalt

I use reinforced hose this time, really thick. Like a tire inside the tire

[seanbarney41]

Hi PeWe...another chain lube suggestion for you.  PJ1 Black I have found to be very good.  Spray it on when the chain is warm from riding(ideally, it works good on a room temperature chain, too),  it then congeals to more of a thick, sticky grease that flings off very minimally, but lubricates maximum!

[andy750]

I use reinforced hose this time, really thick. Like a tire inside the tire

I use Michelin Heavy duty tubes which are very good. What did you get?

[PeWe]

I use reinforced hose this time, really thick. Like a tire inside the tire

I use Michelin Heavy duty tubes which are very good. What did you get?

Same I guess.
Michelin Reinforced for Motocross...

[PeWe]

Hi PeWe...another chain lube suggestion for you.  PJ1 Black I have found to be very good.  Spray it on when the chain is warm from riding(ideally, it works good on a room temperature chain, too),  it then congeals to more of a thick, sticky grease that flings off very minimally, but lubricates maximum!

Good to know. I'll see if available here.

[PeWe]

One more detail...always good with an extra master link when riveting.
This time too hard riveting so part of the soft swelling part cracked and fell off.

But, I had 3 extra master links ordered with the chain

Another thing about the bad Chain Wax, I got thick tar like blobs of sticky black wax on tools, floor....
Had to clean tools, bike, floor and myself with naphta.

[PeWe]

Tire comparison.
4.0-18 installed earlier
120/90-18 installed a few days ago.
The latter tire swell more outwards from rim.

Let's see how long it will survive with handling  as good as the old tire that was very stable when crossing lanes with heavy markings between them. Indents in asphalt hardly noticed. Typical wobble starter.

[MauiK3]

Is that a stock style rim?

[PeWe]

Yes, D.I.D  2.15" as sold by all aftermarket sellers.
I bought a Honda rim once, only difference except for a higher price was a Honda label on the DID paper wrapping. Made in Indonesia as the other today and minimum 10 years back.

[PeWe]

Another tire arrived today.
90/90-19 is not that narrow as I thought!
I have used 100/90-19 on this bike before which was too much for fork, fender, rim.

The bike need wider rims, that's for sure!
2.15-19 front, 3.0-18 rear.

2.75 a rare size when looking around. It fits 120/90-18 tire.
130 can be next.
Wider tire might live longer.

Only aluminium alloys found.  I need to find a rear hub. Front hub on the shelf.
Rear wheel need to be redone. Off with the new tire that is too wide for 2.15" stock rim.

[PeWe]

Replaced oil lines since the old leaked, visible after oil change. New oil floaded under the frame. Probably the crushwasher with extra rubber seal as Yamia sell, rubber that did not seal and caused a leak when cold. It leaked oil earlier this year when riding too.

I had new black $$$ lines that entered to ensure no leaks. Alu washers only this time. The black lines look much better and not as bulky as the old ss lines.

[PeWe]

Got an old rear hub from a UK seller today. Less than a week shipping, 5 working days!! 
For my wheel project. Wider alu rims for the wider than stock tires. 90/90-19 and 120/90-18.
Next time 120/80-18 rear.

130/80 would look fine too. Tight fit to chain cover, though.

Lucky to get a low mile hub. Marks after spokes more or less rust only, very small marks dented the alu.

Cush rubbers included that look and feels OK after a quick check!

No cracks found on brake lining that is really rusty, but no visible wear after brake shoes that leave a higher edge.

I have grinded some. Will grind all rust away.
After that brush, grind all alu before polish. I have new SKF extra sealed ball bearings to mount in this rear hub and my extra front hub.

I'll order new rims after new year. If order from UK, VAT and customs will add on the so the UK VAT must not be added.
Rims delivery time is around 6 weeks so I had no chance to get them before BREXIT anyway.

Another shop in Belgium claim he has Morad rims, I need to investigate first.
2.15-19"
3.0-18"

[andy750]

Tire comparison.
4.0-18 installed earlier
120/90-18 installed a few days ago.
The latter tire swell more outwards from rim.

Let's see how long it will survive with handling  as good as the old tire that was very stable when crossing lanes with heavy markings between them. Indents in asphalt hardly noticed. Typical wobble starter.

I am interested in this as Ive always found the 120/90-18 on a stock rear to square off pretty fast resulting in non-ideal cornering.

[PeWe]

Hello Andy,
I have seen that too. I have therefore started a new wheel project with wider rims.

I have the hubs. Now the boring bearing replacement. Stinking old grease when heating the hubs before hammer out the bearings.

I was a little bit too quick mounting the 120 tire on my stock sized wheel. This tire size was much cheaper than 4.0

I got the enlightening  idea thanks to another thread where wider rims were up.

See charts below.
Rim vs tire size .
Tire angle on stock rims. The height is the interesting detail.
90/90-19 and 120/80-18 are very close to stock heights.

Thanks to the rim vs tire chart I realized the tire rim combo often recommended is not OK. Too wide tires.

I have looked into my CB750 shop manual. No 100/90-19, 120/90-18 mentioned anywhere, only 3.25-19, 4.0-18.

I think this is from a time when there were very few tire sizes made. Tires will work, not fall off, but way wrong.

100/90-19 front.
Too wide for 1.85 rim.
90/90-19 is also a wider tire than stock, will probably work better but still in need of wider rim, 2.15.

120/90-18 rear.
Way too wide for 2.15 rim. 2.75 is the ideal but not common. 3.0 works too.
Next rear tire after the 120/90 will be 120/80 which match stock height much better.

So that new rear tire will be taken off and remounted on another wheel.

I think the rims will be Morad valanced rims or similar.

This will be a good upgrade on this bike. Tougher dressing.

My stock K2 however, will always get stock tires.

[PeWe]

Another small step.
Floor worker....
Rear hub bearings are off

Front hub, rubber seal sat really hard followed by a fight with the retainer that I hammered off with a chisel. Difficult to hold the hub.
Dremel grinded off remaining thread bumbs where punched. I did not drill enough making hub to look like a cheese.

Threads excersized with old retainer and valve lapping compound until the new retainer was easy to fully thread on.

Lapping compund on surfaces for the brake discs after a file grinded off some marks.

Used an old disc as grinder with fine compound, valve lapping style. Both sides until surfaces where flat and free from stick outs.

Hammer out old bearings on front hub next.

[Smowzer]

It's incredible seeing the progress of this bike- I have the exact same model! I have the US version, so main differences I can see so far is the engine covers, kick lever, carburetor style.. really interesting to be able to note these differences. I too am in the process of a rework on this one, I'm nearing the end of the wiring process now and am hoping to be finished by the end of January. I'll try my best to keep up with this thread. Best of luck!

[PeWe]

Thanks! The modifications of this bike has been ongoing for decades.
All those parts you mentioned are all aftermarket.
The engine covers are old. New of very similar design can be found on Internet, Thailand. https://www.motolanna.com/ourshop/prod_3225027-Set-Engine-Covers-Finned-Billet-CNC-Alloy-CB750-SOHC.html

The difference between US and my version is rear fender with  lamp, K1 style. Blinkers also K1 style.

[PeWe]

Worked in my warm garage, 24C a little bit too warm.
Changed fork oil.
I measured the amount of old oil when draining it, catched when pumped the fork up-down until no more came out. ~200cc!

I had done as the German made progressive springs specified last time, 160mm from top, completely collapsed fork without springs.
Always the K0 fork recommendation.
Except for Honda CB750 Shop manual where this K6 fork should have 155-160cc.

Fork has been rather OK the last years, except for a little bit soft. Sag when straighten bike up from parked on sidestand.

Sag fixed today too, washers under the fork caps. 4.6mm filled up the fork pipe  over spring, fully stretched fork.

One of the washers on each side reused old washer for rear shocks upper mount.

Filled 160cc in each, Motorex 10W-30 fork oil that looked as new despite a really old bottle!

I'll see if it will wobble in high speeds next season. Fork feels better now. Washers cured the sag.
Now with tank off, let's see with +20kg tank with fuel + me!



I looked for new copper washers since the old had leaked a little, found a set of chromed plugs with washers from Yamiya. Good to have parts in stock.



Lifted front until fork was fully extracted.

[PeWe]

Continued to hopefully improve the carb boot clamp assembly.

I used wider clamps last time that squeeze over the entire spigot area, not only on the end where the relatively sharp spigot ends.

I have since then had an idea to fill the boot groove with nylon strap to ensure it will squeeze where needed.

Cut and pre formed the 7.6mm wide straps to make assembly easier when actual. After base gasket replacement, (thinner and cure the oil leak).

No marks at all in the new Honda bagged boots after these clamps, only around 1000km done.
Bottom photo: NOS K0 boots packed on plastic bags with old labels, no bar code. Different rubber back then. I bought that set 1989.

[PeWe]

I checked my K2 that also have 9mm wide clamps.
Not a mark!
These were packed separate in Honda bags.

The very much cracking ones that looked exact as Honda were packed in a set of all 4 in one bag with an aftermarket reprinted Honda label.

I remember that the cracking boots had to get their clamps retightened very shortly after some test rides when clamps screws where rather loose.

Below K2 boots with 9mm clamps, not deep marks yet. It will get straps under clamps too.