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

[MauiK3]

Nice looking project, following.

[PeWe]

A small update:
I finally got my thumbs out and sent a box with 2 primary hubs to Germany for cush rubber replacement. 1 early, 1 late.

The later for this build that will get a later clutch with double metal disc.

I have to check the head I intend to use. Measure all chamber volumes and shapes.

Use an old 836 head gasket, model clay in chambers and press the 67mm pistons down until contact with gasket and see all prints are equal.
No too close areas as I think it might be here and there, especially one chamber in need of massage for these pistons domes. Squish areas might not be perfect, hopefully eaqual on all 4.

After that do the crank. Remove stock rods, alternator with starter gear. Replace oil seal and assemble again as it sat before.
Mount the CycleX Super rods after all clearances are verified with plastic gauge.

All this before the return of the primary hub so bottom end can be done.

No known missing part yet except for clutch basket circlip to late primary hub shaft, on its way from Netherlands. Found a used one.

Photos will come

[PeWe]

Got the hubs back today. New cush rubbers inside snd riveted together. My K6 with >100whp runs with primary hub restored by same shop since 2017. https://fourever-classic-parts.de/index.php?option=com_content&view=article&id=26&Itemid=31

One late, one early. Late will enter this engine.

I need to do the head before bench will be full with engine.
Measure chamber volumes and make all equal.

Then remove stock rods from a crank and assemble CycleC Super rods.



Oil hoses also from another person in Germany today. I sent old and very ugly, got them fresh back!
Found that service on German CB750 forum acfew years ago. My K2 has  oil hoses from him.

[grcamna2]

The company does very nice work on the crimps of the oil hoses 
Did they also replace your cush drive rubbers in the clutch hub ?

[PeWe]

Cush rubbers replaced by Fourever-classic-bikes.

Oil hoses/lines done by a private person, Peter Boxdorfer.
Found on the German forum
http://www.cbfourclub.de/
Börse + model

There are various people that offer to sell some upgrades.

Here sending the old to him and get fantastic looking back. The outer material look close to stock.
The black variant repells dirt and easy to clean.

My brown K2 has a set.

[grcamna2]

Excellent sources you have found 

[PeWe]

Did a chamber vs piston dome check today.
JE 890 12.5:1 pistons that I have tested with the head summer 2021.
Head loose on cylinder without head gasket. Rotated crank to verify if it ran free wich it did not. Head lifted.
Verified where, grinded chambers where hit until good with 1:4 and 2:3.

Next was plug mangling, ground straps pressed to zero gap. Double plug washers fixed that.

Tested with different cams. Megacycle 125-75, 125-20 and DP 315.
Too high compression with all, pinging included even when DP 315 ran on less lash than specified, 0.10/0.15 instead of 0.3/0.3 mm causing a huge overlap.
This with Honda stock base gasket and thick fiber head gasket.

I got an idea to mill piston domes 2mm off wich will let plugs go free with at least 1 mm clearance.
This will reduce compression hopefully enough.

I hope it will be in the good area with  0.02" RCS base gasket and thick fiber head gasket.
I have thinner head gasket if compression can be pumped up later on. MLS 0.03"
Then use double plug washers just for sure.

Today double checked chamber volumes and made som clay play with pistons to see squish and clearances.

Old used 65mm fiber gasket as clearance and guide pistons. Chambers are 65mm wide.
Pistons dome dia 63mm at its bottom.

Chamber 1-2 are a little smaller  (ca - 0.25cc) and have also a little less clearance. Thinner clay.

I'll give them a massage with flap wheel where clay were thinner.
Pistons not exactly centered as when running in an engine but will show anyway. Chamber 1-2 had thinner clay around, mostly valve sides.










"Racing type" valve cover with bolts holding cam holders down is a good head tool. Easy to align head before measure chamber volumes with fluid. Adjust the bolts and level it.


Need to get another cover for bike

[BenelliSEI]

Per..... I tried to find Peter B. on the forum and failed. Can you send me or post his email address? I’ve got several sets of old hoses and would like to send him a one.  What’s he charge? Thanks!

[PeWe]

If clicking on the name on the CB750 sale forum
peterboxdorfer@t-online.de
This is same adress I used 2018 and a few weeks ago.

He take 90Euro for a set (alu washers included )plus return shipping.
He only make lines you send to him to make an equal setup, hose lenghts.

The alu fittings look wonderful too. Maybe vapor blasted or a fine glass beed.

I did 2 sets just for sure.

[PeWe]

Another head caring day. Best to do what I can when at it.
Started to remove some small scratches on mating surface. Not first time that head is massaged on that bench.

2 rounds of grit 240 papers followed by 1 round of grit 400.  MLS will like the surface.

Earlier small adjustments of chambers where clay indicated closer to piston domes.
Now only chamber 1 that differ, 0.15cc less. Inlet valve not that recut as the other.

Head restored several times with different valve/guide setups. 1 in valve sit higher.

I have measured a stock head that differed much more, between  22 to 22.9cc.

Tested to use double washers under plug. Affected volume very little, not worth the struggle.



I measured the distance between guide seal and valve keeper groove to be sure about clearance with high lifting cams.
11.5 mm so there are good clearance.
My cams have around 10mm lift as most.

I know the consequence when distance is 9.6mm and cam at running lash is ~9.8mm.
Huge oil consumption after a few thousands km. Higher revs make it to happen earlier, seal lips will be damaged.

Old stock head I have has 9.2mm distance.
A more/deeper cut seat will increase distance.

Important to modify stock guides installing them deeper, cut new groove for stopper circlip.
In this head CycleX Iron guides for higher lifting cams.

K valves have crazy high groove for keepers. 1.5mm less towards seal would help.