Topic: 69, 69 and another 69 - CB750 projects

[Terry in Australia]

When compression is that high is there and engine temperature issue?

I haven’t noticed it on the K0 Steve, but my Kawasaki Z1-B with the 1103cc Moriwaki race pistons gets really hot, really quick, hence the oil cooler I installed recently. An oil cooler on the K0 would probably be a good idea in summer at least as I have one on my K2, but as most of my riding is in the country there’s not too much stop/start city traffic to make it overheat.

[Salman_z8]

Those bores all look pretty good to me mate, but as you've already said, measuring the ring gaps will give you a good idea, try measuring them at the top and down an inch, then down another inch on the thrust surfaces (front and back of the cylinders, the sides won't show as much wear) and of course slide a feeler gauge betwixt piston and cylinder in each bore.

I was building my K0 around the same time you were kicking off this thread and had similar issues, busted cases (chain damage) that I repaired using a torch to heat the bent pieces which I carefully tapped back into place and used JB Weld to fill. I used second hand CB77 pistons with stock size 61mm rings that I bought from a member here several years ago in bores similar to yours. Two years and over 3000 trouble free miles later, I still ride it most weekends in warm weather and it's probably my favourite bike. I'm looking forward to following your efforts!

Before:

K0 by Terry Prendergast, on Flickr

Two weeks ago:

K0 Thursday 20 October 2022 5 by Terry Prendergast, on Flickr

So, received the set of rings and looks like the end gap as it sits is right about 16 thou.
As it runs and seats, probably will open up a bit, but i think i am pleased with that.

The question now is, should i hone more to clean the top ring grove completely, or leave it where i have it now.
Its there, i can feel it, but doesnt catch real bad.

[MauiK3]

Are you saying you can feel a ring hanging in a groove in the cylinder?

[Salman_z8]

I honed quite a bit of it already, but yes some is still there.
A few posts ago, there are some pics posted of the cylinde r

[Salman_z8]

Are you saying you can feel a ring hanging in a groove in the cylinder?

You can see it in this one

[Stev-o]

Are you saying you can feel a ring hanging in a groove in the cylinder?

You can see it in this one

If you can feel it with the "fingernail test", it needs to be addressed.

[Salman_z8]

Are you saying you can feel a ring hanging in a groove in the cylinder?

You can see it in this one

If you can feel it with the "fingernail test", it needs to be addressed.

Any trick to cleaning it out with the three stone ?
I dont wana damage the bore more than it already is

[Salman_z8]

Lets just say i am not proud of what i did.  :'(
My impatience got the better of me.

Needless to say, i smoothed out the ridge wear some more, but now my ring gap is at 18thou at the top, first 15mm of the more and then tightens up to tight 16thou.

Yes i have ruined a decent bore, i am aware

[Salman_z8]

Keep in consideration, these bikes will never see lots of kms, may be a few rides a year, 1000kms perhaps.
I am going to deck the head, so that will add some compression.

For sure there will be blow by.

As long as it doesnt smoke, and doesnt pressurize the crankcase to unmanageable levels.

Any thoughts ?

[Salman_z8]

Seems like the bike sat under a pine tree for a long time, all covered in sticky pine sap

[Salman_z8]

The yammy front end is gone

[Salman_z8]

Internal engine has all the correct pieces

[Salman_z8]

Had the case built up.
And brazed the alternator cover, there was a big chunk missing

[Salman_z8]

To this,

[Salman_z8]

While waiting on new primary and cam chains, and seals, i decided to strip the tank.
The emblem mounts were bondo’d up, and also some crazy dent repair on the right side, ( not much of a repair )

[Salman_z8]

This is where i am at

[Salman_z8]

The bottom end is together now, i installed the clutch as well.
May be i’ll polish up some covers next.

Handle bars cleaned up good, so will be reused.
Will use the turn signals, and rear fender ( huge dent i removed as best i could )
Rear rolled rim will get replated spokes, and reused.

I have a couple sets left of k1 fork lowers, those with new tubes, tapered bearings, will complete the front.

Tail light bracket is bent, probably got rear ended in its life, so will replace that.

I should be able to save the wire harness.

However this tank will not be used on this bike, as i have a full yamiya set in candy red already sitting in boxes.

The goal is to save and reuse as much parts as i can, even if some parts are less than perfect.

Normally i just get new production rims, but since i am using the original rear, i will use a matching used front rim with replayed hardware.

Do have a k1 fender, and a k0 yamiya seat, so that will go on this build.

[Salman_z8]

I get distracted easily, so i was staring at the head and decided to quickly pop a couple valves off to inspect guides.
Seem ok, i will put in new valves, get the seats cut. Probably deck it around 10 thou.

Head has ports ground and cleaned up on the intake side. So thats exciting.

[Salman_z8]

Meanwhile, staring at this, and wondering what to do next

[Salman_z8]

Should i also open up the rd top end, and then also start on the water buffalo petcock gasket, which starting weeping all of a sudden.
It never ends

[Stev-o]

Should i also open up the rd top end...

Why do you want to open it up?   When was the last time it was running??

[Salman_z8]

Should i also open up the rd top end...

Why do you want to open it up?   When was the last time it was running??

Piston rattle. It runs fine, just a noisy top end.

[Salman_z8]

Bottom end, ready to receive the top end

[Salman_z8]

Decided to just go ahead and get it bored to 1st OS.
New pistons rings, etc

[Salman_z8]

Another shot of the new pistons