Topic: Build of CB750 K2 1975 - Europe had K2 until 1975 - Engine started feb 17 2019

[johno]

Bike looking nice, hope it sounds nice !
Interesting to see the difference in cranking pressure between the two pistons, thanks for showing that.
Do you know what the difference in comp ratio is ?

PeeWee I notice you don't let the grass grow under your feet , since the covid thing you have inspired me to start work on a couple of old 750 projects I haven't touched for a couple of years.
cheers Johno

[PeWe]

Thanks Johno. (Check Terry's Kawasaki build thread. No grass grows there, he is very active 

I have no CR numbers of the K7 (392) pistons. I think the K7 head's chambers were larger than previous K heads.
I have read they could have a little bit more CR, but maybe in a head with larger chambers.

 This can explain the big difference I have seen.

Here a big difference in CR.
Old CI 61mm K std pistons 140-150PSI
K7  CI 61.5mm pistons 170-180 PSI.
This with same head (K6), and cam K7/K8.

It must be a cheap way to get a little bit extra on a stock bike.
CruzinImage K7 piston kit cost $120USD.
I'll order another set for my old cylinder this bike had.
https://www.cruzinimage.net/2017/08/17/77-78-honda-cb750k-k7-k8-0-5mm-over-size-pistons-set/

Good idea to order their cheap clutch plates too.

[PeWe]

I have had charging issues again. I had last year, installed a voltmeter to keep control while riding. I saw how the voltage could suddenly drop and come back again. I changed regulator and battery which fixed it then. 3000 good km.

Problem again this year. Charging voltage is 13.5-14.5V without headlight on. When on it drops  2V. At idle below 12V.

OK direct when switching off headlight.
I have measured the currents between battery and plus cable when ign switch on, killswitch in/off, headlight on.
All numbers match the connected loads. I forgot all 4 small bulbs in gauges that takes 1.5A extra.
I had thoughts about current leak in right handlebar switch which can be a future risk for a fuse melt down.

NOS switch ordered. It look different with PLH. Reflector has parking which is welcome for daylight riding. LED parking bulb is bright. My K6 has that.

To this switch a small left hand light on/off switch needed too. The bike will become closer to as it was back in the days.

I have increased the core gap on regulator from 0.7 to 0.9mm.
This did not help either.

Remembered thst I have a better looking alternator cover, complete with generator windings.

So I did a quick swap when working from home during my lunch break
No problem to remove left side covers. Not much oil leak despite it has been parked on side stand before.
Alternator cover leaked a teaspoon, gear shifter cover much more, maybe 2 table spoons of oil.

I had a short test ride. A rain storm stopped me and the shining clean bike I just have washed after another rain episode making it dirty by the road splash.

It look promising so far. I need a 150km ride to be sure.

Good to have spare parts, just swap and test. My K2 engine project can get another.
My rolling K2 is well worth a better looking cover and hopefully functional charging system.

Regulator need to decrease voltage, it spiked up to 15V or more. To be adjusted 1/4 turn counterclockwise.

At the test ride I got another reminder, clutch started to act bad a few rides ago. Jerky take offs as if metal plates were warped. Clutch sticks together after a few hours parking.

Good to get that done and more. I'll change the steel basket too. It sits too loose and rattles LOUD at idle.

I talked to a friend that has a lot of old CB750 parts.
He will dig out around 3 baskets I can test. I want one with tight fit and much less rattle.

I have prepared with a set of new discs from CruzinImage and cleaned a set of the alu parts too. Filed the jagged edges after steel discs. I think the old parts are OK.



Alternator cover is an upgrade.


Clutch job started after the ride.
A set of new clutch fibers are soaked in oil


This type of basket, but tighter fit

[PeWe]

Got a better clutch basket today. Took my old basket and an extra clutch hub to a friend and could compare the tightness of several baskets splined fitment to hub shaft

Got one that slided on without heating it with no play.

Found out late that the old crappy gasket had residues needed to be scraped off.

It got a new good Honda gasket that will not stick glued to surfaces, no problem to remove cover several times with same gasket.

It got a new CruzinImage clutch.
It idles better and clutch work smooth and fine at the test ride.

[PeWe]

Serviced the rectifier today. I forgot to do that at the build.
The ground connection at the bottom was very corroded.

Grinded the surfaces and added an extra ground wire to battery.
I read about it in an older post by Hondaman.

Fixed the contact surfaces for ground cable in main harness attached via a screw to seat lock holder bracket to frame.

[PeWe]

This bike has got relays too. Relieve right handle bar switch from current, use thicker wire from battery to headlight relays. Lo and Hi. Auto mini relays hidden in headlight bucket.

Switch activate relays now

Ignition  got a relay too, almost no current at the kill switch.
Relay sit beside charging regulator. Black/white wire before fed the coils, now feed the relay which switch on 12V direct from battery via a thicker wire.

I had added some extra ground wires from battery( -). Thicker.
One to headlight bucket for relays and Hi/Lo, for rectifier and for ign coils relay.

2 hanging fuses of 10A each
Lo/Hi and coils 12V close to where 12V wires are connected, the starter relay/solenoid where battery 12V is connected .

Battery - has an x- mas tree

Below  pics before all wires strapped to frame, away from carb 2 throttle arm and easy tank attachment.

[andy750]

Very impressive Per on the wiring! I could use a few relays on my K2 as well. Have you considered a MotoBatt battery with 4-terminals - makes it a little easier to fit it all on.

cheers
Andy

[PeWe]

Hi Andy,
I had thoughts about relays for a while to avoid "higher" current thru the handlebar switches. I saw some voltage potentials at the black- green in headlight bucket compared with battery.

Much thicker wires and additional thick ground cables must improve as it did on old cars.

I have a cheap GEL battery that work OK.  I recommend the smaller Mini Auto relays, half size than my std Auto relays K6 has. But those have sockets with wiring.

The mini has the flat connectors direct to relay pins. Important to use isolated versions. No shorts even if they become squeezed or contact with metal

I'll build a rectifier as done in the $6 rectifier thread to improve charging at lower rpm.

[PeWe]

Charging system is now very stable. Connected the voltmeter between the gauges to coil 12v feed direct from battery via relay. 
Adjusted max voltage to 14.1V which is recommended for GEL batteries.

More adjustments making bike to run better
- Main jets: i got the impression that the new pistons could have use for more fuel at higher speeds. 120 tested. Again verified to be too rich.

Engine reacts as my K6 Mikuni carbs on too rich mains. Full throttle at higher speeds as 160kmh, here roll off a little and hear/feel the rich "brrrrlllrrrlllrr" sound.

So 115 back in.

I drilled the emulsion tubes to cure a hesitation at low lift when taking off. The smallest hole closest to main jet drilled, 1.0mm drill. Both holes (1 hole on each side)

I think I could have drilled next hole too. I need to verify for a while, drill hole wider has no return.
This helped the hesitation and reduced severe exhaust bubbling sound when warm at throttle offs/idle. (Air screws could not fix it).

[PeWe]

Adjusted the Ikon shocks to highest position.
This is a much better riding height. Too low cause pain in hips.
Damper at softest, 1.
Only test with this setting was with wife today on a 320 km trip.

Handling feels OK too. Steering damper is not yet on, maybe it will. I have an old one on the shelf, hopefully not leaking.

Not much left to adjust. I can do an ignition fine tune.

[PeWe]

Bike feels more stable now. It was OK before, like removing vibrations sideways.

[MauiK3]

The paint looks great!

[PeWe]

Thanks!
It start to live in the sunshine.

Clear has orange peel. I'll sand and polish when it has got scratches in need to be removed. Thick paint despite warmed up the 2k rattle cans.

I guess you have seen the commercial for Peugeot 3008 SUV. Very often brown metallic, this color. I saw one in the sunshine May 2018 on a holiday in Spain.

[PeWe]

This bike will get a frame swap coming winter.
A not cut frame.
Edit: No, not this winter

So it will get another plate.

[PeWe]

Close to a ride today!

Syncronisation of carbs, adding straps under inlet rubber clamps to protect the rubber against the clamp's jagged edge.

And finally lubing drive chain with good chain lube took longer time than planned, sun disappeared.

Syncronisation of stock carbs PITA!
I'm now used to change needle heights and syncing the Mikuni TMR's that are much easier and done really quick while stock CB750 carbs are irritating.

The connection on carb 2-3 sit really tight. Fuel hoses must be rerouted for removing the plug screws, adding pipes for carb tune hoses and back with the plugs again WITH alu washer on all.

The bench sync was rather OK, not much off. But now is the sync done.

It need a good clean another day.

A ride tomorrow?

[seanbarney41]

Pewe, i recently bought honda oem carb clamps from yamiya.  I think honda has made a new batch after being nla for some time.

[PeWe]

Thanks, I'll check that.
Hopefully better screws than the old Honda x screws that were too easy to damage.

 I had some old clamps that fell apart in early 80's. The Honda carb boots were harder back then.
No problem with the jagged hose clamps.

Anyway, that type of clamp is better for the rubber.

[seanbarney41]

Yeah, Pewe, it's still the same old screws.  I have found they are ok for the job if you make sure to use a good fitting screwdriver or JIS driver.  Or just replace screws with a nice stainless allen head capscrew and a washer.

[PeWe]

Time to search for that type of clamp, but more robust that must be available in correct diameter range and width.

[Terry in Australia]

I bought some narrow hose clamps on Ebay Per, work heaps better  than OEM crap, and cost a fraction of the price. Stainless steel too so they don't turn to sh1t after a couple of years.

[PeWe]

Smooth surface inside as stock type?

[seanbarney41]

Terry, post a link to those clamps.  I have never been able to find anything better than oem crap!  I think Ekpent has a source too.  Maybe he will turn up and post.

[lash]

These clamps are awesome!
https://www.aircraftspruce.ca/pages/ep/clamps/oetiker.php

[PeWe]

Important to not overtighten the clamps too.
The later Honda rubber is softer than original from 70's-80's, the end of inlet spigot is rather sharp. Risk it will crack where the spigot ends.
This is how the rubber cracked on my K6 last summer.
On that one I'll use wider clamps with the pre-shaped and cut straps with smooth side towards rubber filling the groove and not tighten that hard.
12mm Clamp cover all over the spigot from head and out. I'll see how that will work. Carbs also in a slightly different angle to ensure no bending forces.

My old by age hardened beyond use carb boots purchased ca:1983 have small marks from my clamps, but not much.
The stock carbs strapped into boots, no other support since it had pods. No bouncing carbs. minimum 40.000km that way.

Same clamps on when my rubber boots cracked really much om my K6 after less than 3.5 years of use (25.000km), happy to not melt a piston or 2.

[Terry in Australia]

Terry, post a link to those clamps.  I have never been able to find anything better than oem crap!  I think Ekpent has a source too.  Maybe he will turn up and post.

I couldn't find the ones I bought Sean, so I just did a search for "40-60mm hose clamps", (I measured the OD on a hard old inlet rubber and it was 47mm) and found lots. These ones are in the US, and for 13 bucks for 10 clamps, you couldn't go wrong.

https://www.ebay.com/itm/NORMA-01266704050-000-0541-Hose-Clamps-40-mm-60-mm-X-9-mm-W4-Pack-of-10/264806746873?hash=item3da7b64af9:g:~g8AAOSwS51ejxov