CB550k1 US Import - UK registration

[Trigger]

Looks like it has been blasted. A nice looking head is not always a good head 
Just looked through my records and the last 26 heads that i have worked on needed new valve guides, due to being worn or cracked .
Go back 15 years and you could always pick up a workable head. A lot have cracked valve guides and bent valves because of the rockers bending them when the owner forces on the rocker cover.

[K2-K6]

Agree that surface on that one needs light skim too  general gouging from, looks like, someone trying to clean off gasket especially around the tunnel for camchain.

Also the sealing rings around the cylinders has corrosion pits where the fire rings clamp to resist the compression of each cylinder that wouldn't give a reliable face for new gasket to work with. The one with blue zip tie looks the most credible, but others less so.

Assessment of both to see if valve guides are in tolerance would be initially a decent start point.

[K2-K6]

Looking through the heads posted earlier, I felt this one was potentially the most honest from Looking at the photos only https://www.ebay.co.uk/itm/275635167268

Bearings and most threads look good, gasket needs cleanng off, combustion temps (colours of chamber) look quite good with #1 a bit rich.

Obviously, what's inside is not checked but looks like it's from a reasonably run engine.

Doesn't anyone sell those with their cam cover pair at all ?

[Sesman]

One thing. If that head has been blasted I’d be carful to remove the camshaft bearing oil gallery bungs and make sure the gallery is squeaky clean. Trigger may may able to advise how these are removed and replaced?

[juitz]

Thanks all, I'll take the head and cylinder block to get skimmed together.

Cylinder rings have some very slight pitting, can you machine these surfaces? Is there a spec I can point to?

[Sesman]

Cylinder rings? Or do you mean the cylinder bores?

[McCabe-Thiele (Ted)]

I did wonder what was meant as well Phil. I suspect he means the top of the liners.

[juitz]

This bit?

[McCabe-Thiele (Ted)]

Not sure if its how they are machined from new to mate up where the seal rings in the head gasket fit or if its a contact mark?

[Sesman]

Ah, the squish band. Just remove any high spots and smooth them removing as little material as possible.

[K2-K6]

Yes, the squish band as Sesman notes.

It's there from original casting mould and not really machined generally.

Function is to "squirt" the unburnt combustion charge towards the spark plug site just as the piston comes up to compression. The spark has already fired (btdc) the mixture, the flame front should be making it's way out radially from that point, the squish accelerating the unburnt towards that front to improve combustion speed/complete burn.

It notably should not have any sharp edges in that critical zone as they may go over temperature and promote pre-ignition firstly.

In reality here, the area will be reduced slightly as the head will move closer to the piston after skimming, meaning that you can gently "dress" this area to clean it up with a rotary abrasive as you've got a little excess material to play with after that skim. Technically you should do the same to each one to match across the four cylinder to keep equal combustion.

[juitz]

Made it to the camshaft - ok or not ok?
Pitting on the valve lobes?

[Laverdaroo]

I'm no expert Dave but I'd be looking for a new one if it was me but like I say, I'm no expert. Thats quite excessive in my book but somebody should be along soon with a bit of 'better earnt knowledge'.

[K2-K6]

That first photo of peak load site seems to scupper it if left that way.

Some here have had good repair and regrind by Newman cams that may be an option for you. Thats if a decent replacement is not readily available.

Some used one's will equally have problems, it's by no means certain that you'll be able to buy one that's perfect. 

[juitz]

I'm no expert Dave but I'd be looking for a new one if it was me but like I say, I'm no expert. Thats quite excessive in my book but somebody should be along soon with a bit of 'better earnt knowledge'.

Cheers Roo - I'm leaning towards a replacement but any second hand ones seem to have the same issue.

Did peruse other threads and seems like some people have not had issues with pitting as long a sit doesnt get worse.