CB750K2 - Identifying Parts

[Biggles07]

Hi all, I recently purchased a nice, fairly un-restored UK CB750K2 in gold. But it has some features that I either can't reconcile or don't understand. I'm wondering if the gurus out there can help:

1. I've had the carbs done but I have 2 pipes coming form the mid-line of the assembly that I don't understand. See pic. I'd love to know what there're for!
2. My left fork ear has a square hole in it. Its empty - what's it for?
3. The L/H switch gear has an additional momentary press button mounted underneath the assembly. It is not wired to anything. Again, anyone know what it's for?
4. The bike has 'UK-style' lower handlebars (which I like) but the cables are clearly intended for the higher US-style bars. I've sourced shorter throttle cables, but the shorter upper brake hose is eluding me. Any ideas on the precise part number and possible sources?
5. Finally, the PO spray-painted the engine cases and cylinders silver in-situ (small over-spray evident). What was the original state of the barrels & cases? Painted or plain aluminium?

Very grateful for any help with this. Thanks in advance, Simon

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[JamesH]

Hi all, I recently purchased a nice, fairly un-restored UK CB750K2 in gold. But it has some features that I either can't reconcile or don't understand. I'm wondering if the gurus out there can help:

1. I've had the carbs done but I have 2 pipes coming form the mid-line of the assembly that I don't understand. See pic. I'd love to know what there're for!
2. My left fork ear has a square hole in it. Its empty - what's it for?
3. The L/H switch gear has an additional momentary press button mounted underneath the assembly. It is not wired to anything. Again, anyone know what it's for?
4. The bike has 'UK-style' lower handlebars (which I like) but the cables are clearly intended for the higher US-style bars. I've sourced shorter throttle cables, but the shorter upper brake hose is eluding me. Any ideas on the precise part number and possible sources?
5. Finally, the PO spray-painted the engine cases and cylinders silver in-situ (small over-spray evident). What was the original state of the barrels & cases? Painted or plain aluminium?

Very grateful for any help with this. Thanks in advance, Simon

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Hi Simon - I may be able to answer some of these..

1) Mid-line pipes are vents for the fuel bowls (they vent to atmosphere). They run from small elbows that fit into no 2 & 3 carbs bodies, and exit up over the top of the air filter.
2) Square hole if for the rubber moulding that holds the US spec 'buzzer' unit - which most people discard (I suspect your's is long gone, hence the vacant hole)
3) LH switch 'underslung' button is to silence the item in #2 above lol - just leave it disconnected.
4) A UK spec CB400F upper hose does the trick - DSS sell pattern parts here: https://www.davidsilverspares.co.uk/CB400F-SUPER-SPORT-FOUR/part_189733/
5) Engine cases would have ben painted 'cloud silver' by Honda from the factory.

James

[Biggles07]

James, thank you so much. Very helpful. Interesting that my bike (which is definitely a UK machine registered in July 73 in Hull) has what appears to be US spec parts. Still, after 49 years its maybe not surprising! Someone has definitely changed stuff at the front end over time. I'm going to gradually get it back to original, but riding it is more important as the weather improves! Thanks again, Simon

[Nurse Julie]

Welcome to the forum Simon. I'm away at the moment but if you need any up close and personal photos of UK K2's, just shout as I have a couple at home.

[Biggles07]

Thank you Julie.

Supplemental re Cloud Silver for engine cases: what sort of paint should one use (I'm thinking that a VHT paint might be best?), and are there any tips on sourcing it and the best method of applying it?

Again many thanks in anticipation.

Cheers Simon

[Nurse Julie]

Thank you Julie.

Supplemental re Cloud Silver for engine cases: what sort of paint should one use (I'm thinking that a VHT paint might be best?), and are there any tips on sourcing it and the best method of applying it?

Again many thanks in anticipation.

Cheers Simon

Simoniz SIMVHT31D is the best we have ever found both for colour match and finish on all of our own and customers engines. As with anything though, a good outcome is all down to the prep. The engine has to be fully stripped and prepared as the VHT needs air curing and oven curing.
It's available from ebay. You will need about 2 cans to do a full engine. Read instructions carefully and do exactly as it says in the instructions.

[Biggles07]

Thank you again Julie.

Great advice. I have a complete S/H engine that'll be the basis of a full rebuild this spring. It'll get the 'Simonize' treatment! I'll post my results once its in progress.

Cheers Simon

Simoniz SIMVHT31D is the best we have ever found both for colour match and finish on all of our own and customers engines. As with anything though, a good outcome is all down to the prep. The engine has to be fully stripped and prepared as the VHT needs air curing and oven curing.
It's available from ebay. You will need about 2 cans to do a full engine. Read instructions carefully and do exactly as it says in the instructions.

[PHILIP2908]

Re painting engine with VHT paint
Don’t make the mistake I did. I had the engine out of the frame to replace the head gasket and thought I’d spray the crankcases and upper part of the engine with a VHT silver paint. I though the heat from the engine would be enough to cure the paint. WRONG !!
It works OK on the barrels and the cylinder head which get nice and toasty but not hot enough on the crankcases. Consequently, any drop of petrol from the carbs results in the paint falling off. Looks a bit messy now.
The only way is to spray them and then cure in the oven.
When I restored a CB750 K2 back in 1990 or thereabouts, I sprayed the crankcases in Ford Cortina Silver Mist and it looked good, had a bit of shine and most importantly stayed on. Wish I'd done that this time round.

[Biggles07]

I will be able to paint it while completely disassembled….the only ‘wrinkle in the paint’ will be Mrs F’s attitude to the use of her oven……

[Martin6]

Interesting comments on VHT engine paint. The case of my K6 was previously resprayed with VHT, then leaking carburettors removed plenty of the paint. Not enough temperature to cure the paint.

Once I've got the old girl reliable (🤞), I'd like to do something about that, without removing the engine. I've previously had very good results by using cut up pieces of sponge to apply paint, avoiding overspray.

Can anyone recommend a suitable paint for the engine case?
- It must get pretty hot in places, especially behind the exhausts, but not enough to cure VHT paints. 
- is it matt silver?

Thanks.

[McCabe-Thiele (Ted)]

My BiL painted his Fireblade  engine in situ with a great result.
It will air dry & cure over an extended period.

http://www.sohc.co.uk/index.php/topic,28517.msg268028.html#msg268028

.https://www.frost.co.uk/vht-cast-iron-engine-enamel/?gclid=Cj0KCQjwmdGYBhDRARIsABmSEePCbaToXB0usEPUkOpLCJlcM6IJMXOzWiGj0maZBRi7auTU2W44CSAaAoV7EALw_wcB

[Martin6]

Possibly, I wonder whether a watercooled fireblade engine might get more even heat distribution, to cure the paint. That might be fine for the front of the engine by the exhausts, but it is cooler around the starter/ gearbox area and that is where the VHT hasn't stayed put, on mine.

[McCabe-Thiele (Ted)]

Possibly, I wonder whether a watercooled fireblade engine might get more even heat distribution, to cure the paint. That might be fine for the front of the engine by the exhausts, but it is cooler around the starter/ gearbox area and that is where the VHT hasn't stayed put, on mine.

BiL just left it for 3 months to self cure at shed temperature.

Once all the solvent has evaporated it is cured - baking or similar just speeds up the process he claims.

[Martin6]

👍