Topic: CB750 K2 engine + bike project, frame will come

[PeWe]

Primary hub to be sent to Germany for cush rubber replacement. Riveted installation.

I’ve only seen the cush rubbers held in by the little nubs. Riveted?

This is the primary hub inside engine. The entire assembly is riveted together. Rubber pucks inside.

CycleX and a french solution bolt it together after rivets are removed, rubber pucks replaced.

[grcamna2]

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[Terry in Australia]

Got the thumb out and finally cleaned the frame. (After 2 years)
Degreaser sprayed everywhere, pressure washed with warm water afterwards.

My plan to sand frame smooth and spray with 2k rattle cans has changed to visit a professional shop.

Let them sandblast frame, swingarm and battery holder. 2k paint. Prime and glossy black. The shop need clean parts

This frame will not be a new CB750 build. It will be the frame for my brown K2 mostly stock that will get new identity with uncut frame.

The brown K2 will get other tank set in freedom green metallic and the engine in this thread. Most likely 890cc.

I'm thinking seriously about finally building a K1 Per, I have a couple in pieces in my garage and think I have a frame that's been repainted that I can start bolting parts to. I just need to keep in mind that I'm gonna have to empty out my patio so we can use it for our Christmas Eve BBQ, so might not be able to start until after Christmas. A new bike project is very exciting though!

[Don R]

 I bought a no numbers diecast motor for my candy blue green bike so it's 836 can go home to the K4 frame it was built with.
  When I took it apart, the M6 threads that stripped were fitted with 1/4" X 20 bolts. The four threads under the nickel washers had 5/16" allen head bolts. I plan to helicoil the 6mm threads but might just leave the four head to block holes as they are. It would take a pretty big m6 insert to fill that size hole and the head would probably need sleeves in the holes also.

[Terry in Australia]

I bought a no numbers diecast motor for my candy blue green bike so it's 836 can go home to the K4 frame it was built with.
  When I took it apart, the M6 threads that stripped were fitted with 1/4" X 20 bolts. The four threads under the nickel washers had 5/16" allen head bolts. I plan to helicoil the 6mm threads but might just leave the four head to block holes as they are. It would take a pretty big m6 insert to fill that size hole and the head would probably need sleeves in the holes also.

That sucks Don, I understand that the US is still using non-metric sizes so I suppose (but don't know) that metric screws are harder to find, but it's a pain in the arse when someone decides that he's gonna undo all of Honda's work. I've got to strip the engine down on the K1 project, as expected the top end is off and the bottom case is full of dirt, so I'll need to strip it right down to the last nut and bolt, hopefully they'll all still be metric.  

[PeWe]

A K1 build will be nice.
The soecial gauges might be tricky to find unless you have a pair.

I have different sizes of Wurth time-sert thread inserts.
- First step has same size as a std helicoil type. 6.1mm drill
- Next step is called Big-sert and fits when the time-sert is coming up. 7.3mm drill

- Then another size, self cutting. No special tap needed, only an M6 bolt with a distance threaded on to it.

I bought cheap version from China that look exact as the Wurth except for the color, shiny grey instead of Wurth yellow. 9x1mm, drill 8.2-8.6mm. Work fine for the inner cam holder bolts.

I used this size in a head earlier in this project. See in the beginning.

- There is another size after that as well. 10x1.5mm 8.7-9.4mm drill.
This need some meat around it.
I lock them with Loctite 272, red high temp.

If a thread is really vandalized and not soace fir big-sert. JB Weld and later std time sert might help. Or glue time sert in place if there us anything that can hold it in place.

My K6 ported head had a repaired thread for cam stud cyl 2.
Not much meat around it. It got self cutting 9.0mm, reinforced with JB Weld.

[Terry in Australia]

A K1 build will be nice.
The soecial gauges might be tricky to find unless you have a pair.

Thanks Per, I have a K1 speedo and tach on my K2 bitsa but they need restoring so I'll probably send them to Marcel in Holland unless I can find some better ones. I have a feeling that I have another set somewhere, but can't remember for sure. I have pretty much everything else though.

[PeWe]

I have NOS gauges to my K6, but they look too nice to be used
My working original speedo show all km it has done since the very beginning.  Some km ridden when speedo cable has been broken.

A new speedo will delete the history.
A new build on parts can have  a speedo at almost 0.

[MauiK3]

Metric fasteners are easy to find here, all grades and materials.
As we all know, most "American" autos and trucks are a bewildering mix of metric and SAE fasteners.

[PeWe]

I ordered thread tool sets and inserts from Thread Doctor in USA.

[PeWe]

One step forward today.
Started to prepare cases for paint.
I have pressure washed the cases + paint remover a few months ago.
Focus on the inner oil passages that could have had blasting media inside.
It was some media outside after the pressure wash. 140BAR spec washer with warm water. Sprayed various chemicals inside before.

Today scratching off old Permatex sealer that has run inside. It comes off rather easy so important to get it off.

Plan to paint cases within a few days so it will get time to cure before engine assembly.

Primary hub to be sent to Germany for cush rubber replacement.
This engine has CCC HD prim chains. K7 gear box, under cut 2-4. CycleX super rods.
It will get 890cc. I have an idea to give it to my K2 this spring.
Another year adjusting carbs! This year Smoothbore 29. I have old notes so I'll might get it right rather soon.

I need to decide cam too.
- Megacycle 125-20 (like KH F)
- RC295
- DP315
- Action Fours SS-1 (Good working modest profile. Nice to valve train )

It depends on compression too, not that low.
Old stock rockers might not like the higher lifts.

[SOHC4 Cafe Racer Fan]

Nice recipe of parts for that motor!

[PeWe]

Nice recipe of parts for that motor!

Yes, difficult to not do it
Parts gathered during some years.
If I get it together this spring so I can swap engine in my K2, it will get the deeper sounding Lotus Root 4-4 my blue had a few years ago.

I have had thoughts that the blue K6 should get 4-4 again since it look really good with it.  But it runs really well with the Hindle 4-2-1.

Everything starts with some leftover parts. Then buy the missing when finding them. It suddenly grows to another bike.

[PeWe]

One step further, cases finally looking better with paint. I used same as on my other 2 bikes engines, Motip Engine paint , aluminium.
It is rather durable and easy to respray where needed if needed. Very close to stock Honda color.

I covered the lower case with alu foil wrapped oil pan.
I'll let it cure a few days. Maybe some areas that need an update with paint when flipping cases

[grcamna2]

Per,the cases look good.  Will you now heat-cure them in an oven ?
Did you ever spray paint a cylinder head or cylinder block fins with silver engine paint?
I want to ask you:what type of silver engine paint had the required rating to keep it from burning-off the fins ?

[SOHC4 Cafe Racer Fan]

Per,

That color looks spot on to factory.

[PeWe]

I have used that paint before. I did not cure paint in oven, I let it dry for a while before assembly. Final cure when running the engine.

It is not like high temp color for exhaust that need  high temperature to cure at all, not being sticky.

I have used same paint on cylinders and heads. It handles the temperature fine.
It is specified for 150C.

It is very close to stock color. My K2 case had good stock paint in the starter motor compartment. Did not paint it and saw no difference where I have painted after it had dried.

I know people using thick 2k paint, Mercedes I think. That paint is very durable but paint look thick, engine get a very smooth surface like it has been dipped in a barrel of paint.
No  imperfections on case surfaces. The manufacturing marks, burrs that make it to look stock.

[grcamna2]

I have used that paint before. I did not cure paint in oven, I let it dry for a while before assembly. Final cure when running the engine.

It is not like high temp color for exhaust that need  high temperature to cure at all, not being sticky.

I have used same paint on cylinders and heads. It handles the temperature fine.
It is specified for 150C.

It is very close to stock color. My K2 case had good stock paint in the starter motor compartment. Did not paint it and saw no difference where I have painted after it had dried.

I know people using thick 2k paint, Mercedes I think. That paint is very durable but paint look thick, engine get a very smooth surface like it has been dipped in a barrel of paint.
No  imperfections on case surfaces. The manufacturing marks, burrs that make it to look stock.

Thanks PeWe 

[PeWe]

I did some more painting with cases together. Front and rear where needed. The underside of front, case bearings markings and the entire rear.


Next day I used heat gun to warm up the cases now sitting together.
Tape and plugs removed before heating.

Heat gun into 4 holes for sleeves, 3 holes on left side for transmission and the bigger opening for clutch.

Alternated into all, 10 second in each until the cases were warm, almost too hot for fingers like after a ride. It took appr 15 minutes.
Cases stayed warm for at least 30 minutes.

I'm sure paint will cure to a harder surface and will survive assembly and engine installation better.

Paint color look better and closer to stock when cured.
Photos soon after painting

[denward17]

Looks great PeWe..

[PeWe]

Looks great PeWe..

Thanks, fully agree.
I need to get the thumbs out and send primary hub to Germany for cush rubber replacement.
Missing part is a circlip for later clutch.
https://www.cmsnl.com/honda-cb750k6-four-european-direct-sales_model14384/circlip-external_90602371000/

I think this will fit, snap ring
DIN 5417.
Model SP40
https://simplybearings.co.uk/shop/p20115005/Major-Branded-SP40-Snap-Ring-to-Suit-40mm-Outside-Diameter-of-Bearing/product_info.html

Groove dia in shaft is 38.0 mm, 1.6 mm wide.
Above site spec tab look hopeful.
The ring might be available at a local Wurth shop since Wurth has DIN 5417 SP40 on internet.
.

When these are fixed, assemble the lower end. I assemble cyl studs and top end in bike, probably clutch and side covers too.
Easier to lift alone. Bike has frame kit.

Pull the existing engine need some tools, good ideas using a jack or 2

[BenelliSEI]

Those cases really look great!

[PeWe]

Those cases really look great!

Thanks!
I like them too.
Hopefully no surprises when assemble all things.

Stock studs sat in when I bought the cases. Test asssembly with crank checking bearing clearances and crank rotation when crank bolts tightened with 25Nm. Plus all covers mounted too.

A stray parts build have som check points.

[BenelliSEI]

Those cases really look great!

Thanks!
I like them too.
Hopefully no surprises when assemble all things.

Stock studs sat in when I bought the cases. Test asssembly with crank checking bearing clearances and crank rotation when crank bolts tightened with 25Nm. Plus all covers mounted too.

A stray parts build have som check points.

PeWe..... I call that a “Mix & Match” build. Can create some surprises!

[PeWe]

Those cases really look great!

Thanks!
I like them too.
Hopefully no surprises when assemble all things.

Stock studs sat in when I bought the cases. Test asssembly with crank checking bearing clearances and crank rotation when crank bolts tightened with 25Nm. Plus all covers mounted too.

A stray parts build have som check points.

PeWe..... I call that a “Mix & Match” build. Can create some surprises!

I hope the K7 trans will work. K final shaft has K7 gear.
But it should be fine.
When paint has cured harder, I'll can start.