Chocolate Valve Guides? Strange CB500 Head?

[Seabeowner]

As the weather is yet again grotty, I have back on doing my DK special 1978 550K. Showed 21000 ish miles and the bores seem to back up that sort of mileage and have even left most of the bottom end together as the primary chain looked OK. (surprise!) I have noticed that in general though that the finish of the bike does no compare with my 1971 500.
There have been one or two Easter Eggs, but started tidying up the head. The exhaust valve guides are absolutely shot. I’ve had 500s with double the mileage and that were near absolutely fine.  Inlet guides are ok and, by feel, I would use. Exhaust guides get progressively worse from 1-4.
On 4 valve stem is 5.43 and the guide opens up to 5.95 at the ends!
I saw on a post here trigger mention k-liners. Would they be suitable? Could probably get a drift made up to extract, but am wary of getting in too deep.

[Trigger]

K-liners on valves under 6mm are a problem, just use replacement valve guides .

[Seabeowner]

What is it about 77,78 bikes? Is it another feature of the lean running carbs?
Presumably new guides at £25/ea + labour will end up at near £200.
Anyone have a spare head pre 77?

[kevski]

£200 would be a good price.

[MrDavo]

When I lived in Lancaster, I bought a Triumph T100 cafe racer (from John McGuiness' dad, a proper rum Arthur Daley type, complete with sheepskin coat and rusty Transit) that turned out to have home made valve guides apparently made from brass, which wore oval.

This led to two things - constant plug oiling, which caused me to break my hand when I lost my temper and punched the bike when it ground to a halt (well I was only 17), and me filling my mum's house with oily smoke when I put the head in the oven, without degreasing it, to get the guides out.

[Trigger]

£200 would be a good price.

£200 is too cheap, as when a head is heated to drive valve guides in, the valve seats sometimes go a little out of shape, so I always regrind the seats and skim the head 

[kevski]

£200 would be a good price.

£200 is too cheap, as when a head is heated to drive valve guides in, the valve seats sometimes go a little out of shape, so I always regrind the seats and skim the head 

That's why £200 would be a good price, my Zthou head refurb cost in excess of £600 but it's a lovely job and new stainless valves.

[matthewmosse]

I've had a couple of k3s from '78, no issues with the valve gear wearing and they were mega rough examples that had  suffered a lot of abuse. It might be that by '78 a Sohc Honda was getting long in the tooth so new owners were possibly a bit less carefull running them in..... I have a few spare cb500 and 550 heads, but by the time I've stripped them down to inspect the valve guide wear to see if it's any better than yours it would be a big investment of time, I think at some point I really must make a valve compressor jig as my proper valve spring compressor doesn't fit the 550, and my improvised g cramp and bit of gp100 fork leg with cut out takes an age to strip a head down. Also I have no records of what age bikes they are from.... most interesting one is one that has needle roller camshaft bearing conversion. On my collection of spare heads it's these bearings that are most often worn. I do have a cb500 head that is low mileage ( according to the breakers who sold it me, engine looked very fresh ) but it has 8 bent valves ( tensioner let go) so probably needs the same fix... keep us posted on the outcome.

[Seabeowner]

Been mulling this over Matthew. I'm ashamed of my valve spring compressor. It was bought for a car or maybe a Triumph bike and as the Honda valve springs are smaller O/d it has a couple of bits of metal attached to bodge it.
Back to the problem in hand. I also have a externally very rough looking 500 head. Peeling black paint/dirt, broken/bent fins, exhaust stud threads butchered, and the like. Think done 42k. Have removed the exhaust valves and they are fine!
Just shows it would often be cheaper to get another head or even a compete engine than replace valve guides.
So will look keep looking for another as I have 6 months. Anyone?

[kevski]

Been mulling this over Matthew. I'm ashamed of my valve spring compressor. It was bought for a car or maybe a Triumph bike and as the Honda valve springs are smaller O/d it has a couple of bits of metal attached to bodge it.

I have a valve spring compressor for a car i use on my bike heads, mine has not been bodged, it has been adapted to suit various heads though.

[Seabeowner]

Resurrected this as I got round to getting another head for my 550K and the valve guides look good.
But in looking for a new head I came across this CB500 head on ebay.com. Says it came from an early 71 CB500.
What are those four bits in the oil bath under the camshaft? Oil drillings? Was it ever standard?

[Bryanj]

Never seen anything like that on any 500/550 before. All 500/550 heads are the same its the rocker cover that was modified

[jon stead]

Here’s a recent shot of my 500 head.

Surely you want a “puddle” of oil for the cam lobes to splash around in? Oil drain holes would prevent this splash lubrication.

[AshimotoK0]

I will dig out my 3/71 head tonight and photo it to compare

[AshimotoK0]

Checked my 3/71 500K0  head and it's the same as the strange one you bought ...so mystery solved