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

[PeWe]

Pistons arrived from Cruzinimage. Ordered from the webpage www.cruzinimage.net.
Very nice support and good shipping. I could not resist to order a cheap pack of clutch plates too.
Later 392 pistons.
To be bored in September. I hope I'll get time for breaking in same month.


I know, pistons to be oriented with dot forward.

[PeWe]

I got the idea to change head this weekend if the "government" does not have other plans

K6 head that will look as a 1975 bike's head. The K1 head that is used now is a little bit smokey, no ex seals. Also good to be sure about the cylinder and pistons used now.  If only head smokes or if the pistons/ bores are guilty too.

Head got a layer of paint today where most visible. Cam studs thread holes sealed with JB weld to ensure no leaks that way. Studs are virgin in head and sit tight so they should not leak.

The oil pump might be replaced too when pipes are off. A refurbished pump with MessnerMoto rotors going in.

[PeWe]

No oil leak from head so I had to investigate why! I checked compression before. All 4 150 PSI without carbs

Head gasket had kept it dry.

I had to scratch the residues off the cylinder and vacuum clean it. Currently waiting for head gasket to sit flat so O-rings will not creep under it.

A really good fitting flat gasket is worth some extra. This time a cheap one as before.

Now a little bit Permatex avaition and a little with Loctite gasket spray 3020 on outer spots making gasket flat before enter the other head.

When beer is slowly done, head on.

[PeWe]

Head tightened 27Nm (20 ft lbs).
Torque it again tomorrow morning and see if the nuts will move.
I got extra grinding job for longer type of cam chain slider. Lift head since it could not go on when slider hit the tight narrow head. After some grinding, on with it.

Strange,
I was sure that all K6 used the long one. This head must been shipped on a bike with the short one I was sure was for earlier engines.

[PeWe]

K1 head replaced by refurbished K6 head.
Oil pump replaced by refurbished pump with Elan's kit + MessnerMoto's rotors.
New carb boots. New Denso X24ES-U plugs. New oil and filter. Extra oil dumped when pump removed.
Bike back to ready for a ride. I started it and let it idle for a minute or two. Sounds fine.

[seanbarney41]

Top notch work as always, PeWe!  Looks fantastic.  How about a little ride report on those Heidenau tires?

[Terry in Australia]

Looks great Per, good work! Is that the stock length rear fender? It looks longer than the one on my bike? Cheers, Terry.

[PeWe]

Thanks guys!
The tires are fine with right look for these bikes. Handling is good too. I'll continue to use them.
Heidenau K44 3.25-19, K36 4.0-18.
 My K6 has same rear tire, will get Heidenau front at next change, tire is waiting.

The photo make fender to look longer, wide angle camera mode on my phone.
It is a NOS K1fender from DSS to get correct holes for rear light used for all K2 and K6 to 1976. All K2 and later spares are for the larger US light with extra holes

This time easier to get the air box on. I understood after reading other posts about it and Terry's description about box stacks that the carbs must sit a little bit upwards to make everything to fit so the carb boots are oriented for that. Air box easier to press in place too.

[PeWe]

Test ride after work was fine except for dirty carbs in need of cleaning. Pilot circuit or emulsion tubes or both. Remove them and clean. The carbs have had this problem since a week or 2.

I initially blamed air screws but understood after some adjustment that the problem must be dirt.

It ran better after a few minutes on 7000rpm on 5:th gear, 17:48 gearing. Mains going bigger from 110 to 115 can work.
Not smokey as before head change.
Bike got an oil cocktail based on a mix of 2 mineral and 2 synthetic oils:
1 L (bottle) Spectro 20W-50,
~0.8L Motul 3000,
~0.8L Motul 7100,
 ~0.4L Red Line 20W-60
Home made Semi synth

Neutral easy to find when warm.
Motul 7100 smells very aromatic when warm.

I hope I can clean carbs right avoid additional filters.

[andy750]

PeWe I am using Motul 5100 semi-synth if you can get it.

Great documentation as usual and looking forward to ride report. Good luck with the carbs.

cheers
Andy

[PeWe]

Hi Andy,
I have tried Motul 5100. My K6 like Red Line 20W-50 synth better, much smoother gearbox.

My K2 has Spectro Heavy Duty 20W-50 mineral. But clutch sticks extra much so I started to mix it with synthetic oils.

Last change some oil leftovers in the cocktail.
Per

[Terry in Australia]

Beautiful work Per, and your carb issues inspired me to reach deep into my Redneck K2 build budget and buy new repro carb intake rubbers and airbox rubbers, assuming that I might need to pull my carbs off at least once after installing the engine, as is usually the case after a rebuild.

[PeWe]

Both bikes have carb issues now.
My K6 has overflowing, leaking no 2 carb.after pilot jets uograde. All float bowls off  at the moment.
Leaking bowl is one thing I have fixed before when gasket sit wrong, now floading and leaking. I'll make another try of bowl fitment and make sure float is not blocked.

My K2 hopefully enough to take off bowls, air screws, emulsifier tubes and pilot jets, spray clean it with chain clean which is a very good multi cleaner stronger than carb clean. I hope no blocked air jets in need of taking off air box.

 I'll blow the system with compressed air thru all holes after spraying with chain cleaner.

[Terry in Australia]

I don't think I've ever seen chain cleaner Per? But then again, I dont think I've ever cleaned a chain on a road bike, I've cleaned tbe mud off the chains on dirt bikes back in the day, but not in recent years. I was gonna just use the hard old rubbers on my carbs, but I'll give the old girl a birthday, I broke my special carb installation tool awhile ago, and these special tools don't grow on trees.....

[PeWe]

I have not used the chain cleaner I ordered by mistake ( thought I ordered chain lube) for the chain. I found it was very useful when cleaning dirty alu parts as the carbs, alternator cover etc.
First time Motorex chain cleaner, a must have in the garage.
www.motorex.com/en-us/moto-line/chain-care/chain-clean-spray

I found cheaper brand when ordering tubes and could not resist to add 3 cans for $3US each to be used as a multi cleaner. A9 chain cleaner.

Chain get naphta sprayed richly and a few minutes later massaged by  140-145 BAR pressure washer with warm water. The golden color will then shine again from former oily black.

[PeWe]

I found today that aftermarket crappy pilot jets had cracked inside carbs. I need to lift tank, remove carbs and up on the bench upside down taking out the broken tips if the crappy pilots with a little bit to wide tip. The part sitting in carb is aroun 5 mm long

4into1 crappy jet. I read that someone had broken one when order. I did not realize how except tighten it too hard. I know now. Stay away from that crap!

Most likely no problem to take the brass crap out, the bad extra work to remove carbs.

**** My blue K6 needed some care too ****
I fixed leaking no 2 carb to find misfiring issues when starting it. Changed plugs,. new NGK D8EA.

Edit:
I have changed carb setup to match the very well flowing 4-2-1.
Earlier setup for 4-4 with much higher back pressure and easier to tune low throttle lifts

[MRieck]

I found today that aftermarket crappy pilot jets had cracked inside carbs. I need to lift tank, remove carbs and up on the bench upside down taking out the broken tips if the crappy pilots with a little bit to wide tip. The part sitting in carb is aroun 5 mm long

4into1 crappy jet. I read that someone had broken one when order. I did not realize how except tighten it too hard. I know now. Stay away from that crap!

Most likely no problem to take the brass crap out, the bad extra work to remove carbs.

I fixed my blue leaking no 2 carb today to find ignition issues when starting it. I'll change plugs to start with, use old ones.

Next investigate ignition wiring that can have a bad connection somewhere.long time ago bike had ignition issues. Loose HT lead and bad HT lead a year or 2 before.

Many times aftermarket stuff just isn't worth it.

[PeWe]

Especially these. I was prepared for not exact INSIDE size, no problem as long as all 4 are equal.
2 cracked and blocked inside.

 Carbs off and a risky job drilling the sh!t out and some blow job from all directions.. I drilled all 4  just for sure to get exact same size on all. 2mm drill, max 1-2/100 mm bigger than the lower part of the hole were this part of the pilot jet sit.

Started bike and it idles fine

The hole for pilot with brass residues.
All 4 had very tight threads so I did not notice the obvious brass cracking. The not broken ones were tight as the broken ones

[PeWe]

Had a test ride yesterday. The K2 runs nice and even again.

[Terry in Australia]

And it looks pretty good too!

[PeWe]

Thanks Terry. I like the brown more and more, it look really good in the sunshine with its sparkling metallic.

Perfect cruiser for my woman sitting behind, she like the smooth running bike in almost legal speeds

[PeWe]

Oil mix feedback:
The clutch and gearbox feels fantastic!
I noticed today when taking it to a bike clubs Wednesday meeting eating burger outside town that the clutch had not sticked at all after been parked. Last time it was running was 4 days ago. I started it and shifted from neutral to 1 without clonk or jerk. Silky smooth. When stopping with warm engine, neutral is very easy to find!!

This is the mix! (I wonder if Red Line assembly lube is involved in the smooth running gearbox and good clutch? Only cam bearings and some on the lobes when I changed head, not much.

Bike got an oil cocktail based on a mix of 2 mineral and 2 synthetic oils I have used earlier separate.
1 L (bottle) Spectro 20W-50 (mineral) (This oil only, clutch really sticked together, dragging clutch despite rocking clutch apart)
~0.8L Motul 3000 20W-50 (mineral)    (Not smooth running gearbox with this oil only)
~0.8L Motul 7100 10W-50 (esther synth)   (Rather smooth gearbox with this oil only)
 ~0.4L Red Line 20W-60 (esther synth)   (This oil mostly in mix with Red Line 20W-50: Very smooth gearbox with this oil, I did not like the very thick sludge like oil when drained oil pan after last summer, when I upgraded the oil pump in my blue K6)
Home made very good Semi synth !!! 

All together work fine!
I'll try 1 bottle of Spectro + 1L 7100 (smells nice when warm) + 0.6L Red Line 20W-60 next oil change. 2.6L is the normal amount of oil needed when change oil + filter.

[RAZZ]

Hi Per

Interresting Oil mix - Have you seen the Gulf Classic 50 Oil ? 2400 ppm zink - i have tested for 900 km now ( Stock engine)and it is good [IMG]https://uploads.tapatalk-cdn.com/20190725/15ee14d85fb452117d5a7cc2187c5645.jpg[/https://www.billigbilpleje.dk/pi/Gulf-Classic-motorolie-20W-50-5-ltr_2639736_146960.aspx?gclid=EAIaIQobChMI0frJ2cnP4wIVhZ-fCh2cLAIVEAQYASABEgL53PD_BwE


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[RAZZ]

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[PeWe]

That is a single grade for larger bearing clearances,  right? Like old UK Norton's and Triumphs from the 50's
Cold start might be tough for a CB

I can find Gulf Classic 20W-50 for old cars with extra zink.

Spectro and Red Line have also high amount of zinc.  2200-2500 something. Motul must have less to match modern bikes with cat, maybe around 1000.
Both my bikes have fresh oils so I can't change until next year

I have mixed Red Line synth with a cheaper synth to make my Red Line stock to last longer. Q8 SBK Racing 10W- 50. In my K6 that need good oil. Runs harder
Gearbox not that smooth as my last mix in the K2.

I think "Racing" oils have more zinc.

I need to do the same once more to verify if Assembly Lube was involved.

Update:
The following starts,  gearbox was less smooth and clutch can stick a little. Back to a normal good working oil.
I'll continue to mix oils for this bike. (My K6 will get Red Line only)
- Spectro mineral for the zinc,
- a little bit Motul 7100 synth for the nice smell!
- Q8 SBK racing for the synth spec and save my Red Line.