Skimming Cylinder Head surface to Remove/reduce pitting

BarrieC

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Guys a very straightforward question, which i cant find a straightforward answer too.

I have some pitting on the alloy sealing surface of my cylinder head - its not major, but i can feel my fingernail against the steel part of the combustion camber (only just). I believe that skimming by 0.2mm will, if not totally remove, will greatly improve sealing capability.

The question is: How much can you safely remove from an XS650 head, running standard pistons etc, before you run into timing and worse potential piston and valve interference

Thanks

Barrie
 
Hi @BarrieC

I had mine skimmed/resurfaced. Unfortunately I can’t tell you how much they removed but I can give you a phone number to call where I’m sure they can tell you?

Daniel.
 
Hi,
I cant at the minute, setting up a new Laptop (Arrgh) to be honest any photos don't give a clear idea, you have to see it from all angles
Anyway, my initial thought was that this would be ok as it is and the gasket would take up the minor pitting. However, trying to do this right so.........

Again, in peoples experience am I safe to go to 0.2mm? or only 0.1mm? either way it will improve sealing (the head is not warped)
as far as i can tell the head has not previously been skimmed

I just need to know a safe limit I can go to,

Thanks

Barrie
 
Hi @BarrieC

I had mine skimmed/resurfaced. Unfortunately I can’t tell you how much they removed but I can give you a phone number to call where I’m sure they can tell you?

Daniel.
Hi Daniel, that could help, i'm not getting very far with this question (particularly on the UK forum!) did you have the head skimmed due to pitting of the surface? and of course it runs great now?
Thanks
Barrie
 
Hi Daniel, that could help, i'm not getting very far with this question (particularly on the UK forum!) did you have the head skimmed due to pitting of the surface? and of course it runs great now?
Thanks
Barrie
Hi Barrie,

I never post on the UK Facebook group.

I had mine done as I was having the valve seats cut, valve guides installed & reamed so just wanted to get things as flat and smooth as possible, like you’re asking, I don’t imagine they would of taken off very much at all, but like you say just enough.

Search for Roland Alsopp’s in Chobham, that’s who did my work.

Daniel.
 
measure your head now.

Find spec of what it should be and see where your at.

.2mm should be safe, but only go as far as need be to get it flat but you can’t know if it’s safe unless you know what your starting with.

A thinker head gasket can be used if need be.

You got a mill? Or you plan on taking it somewhere?

Might be easy enough to break out the glass and sandpaper to run some figure 8s.

Photos would help a lot.
 
measure your head now.

Find spec of what it should be and see where your at.

.2mm should be safe, but only go as far as need be to get it flat but you can’t know if it’s safe unless you know what your starting with.

A thinker head gasket can be used if need be.

You got a mill? Or you plan on taking it somewhere?

Might be easy enough to break out the glass and sandpaper to run some figure 8s.

Photos would help a lot.

So, bit of a stupid question, but I have no real idea, how to see where it is now: how is the depth of the combustion chamber measured to obtain valve piston clearance?
here is a photo, but believe me this makes it look a lot worse than it is. Regarding the milling, its going to a shop, I would expect to be able to get them to start at 0.1mm and go to 0.2mm if required - setting up being the longest part of the job.
I believe the Athena Gaskets are the thickest - my set came from a (far as I understand) reputable company in the UK called Yambits, head gasket is made by Interface- says made in the USA, not sure if that is a plus point?
 

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Piston to valve clearance is normally only a concern if "decking" the cyl. or head by more than a few thousandths or if installing a higher lift camshaft. It is normally measured assembled by placing Plastigauge or some putty on top of the piston and rolling the motor - then disassemble to check clearance.

On a close to stock motor the only concern is flatness - the generally accepted spec is <.002", measured on a surface plate (plate glass, etc.). Can be brought to spec by #400, #600 grit sandpaper on the surface plate and moving the cyl. or head in a figure-8 pattern.
 
Hi JP, so the pitting is no real issue and not a reason to have the head skimmed? "decking" is not a term i'm familiar with can you clarify please?

Thanks

Barrie
 
Some pitting is normal on these old bikes. That (in the pic) looks bad enough that I'd be attempting to improve it via some surfacing - nothing too aggressive - to see if it'll clean up: plate glass, 400 grit taped-down, then 600 and even pressure as possible.
 
"decking" is not a term i'm familiar with can you clarify please?
Term in engine building for removing significant material via milling machine with special fixtures, etc. Used to change combustion chamber characteristics and compression ratios: extreme hi-performance stuff
 
You could take it to a machine/engine shop and have them evaluate it. I'm a backyard mechanic and tend to try to do most things myself:banghead:

It is possible you could get it good enough DIY IMO. Was the head gasket leaking before teardown?
 
The question is: How much can you safely remove from an XS650 head, running standard pistons etc, before you run into timing and worse potential piston and valve interference
Thought I'd better read the book; and to finally answer your initial question;)
img031.jpg
 
If your head was mine I’d see what I could do to clean it up myself first.

If you can’t get a sheet of glass, I’ve found a big “marble” tile from HD works just as good and it’s only a few bucks.

400 grit wet/dry tapped flat on the tile.
Water
Dykem the sealing surface
Lay it flat, enough pressure to move it only, run it in figure 8 pattern, spinning it 90deg in your hands every 10 figure 8s so you make sure your never putting too much pressure in any one spot.

I’d probably start at 5-6 sets of 10 and see where it was as.

If flat, smooth it out with 600 doing the same thing as above.

That would be my take on it.

Pj gave a lot of good insight.
 
Thanks Guys,
Unfortunately, this arrived to me as a basket job, literally!
The engine had been stripped, vapour blasted and then painted in horrible gloss black - that has all gone now. Came with new pistons, rings, pins set and new camchain. Bores have been honed and measured within tolerance.
At the time the crank appeared ok, i did not notice that at some point it had been dropped and one small end was out of round. So it has new conrods, big end and main bearings and the bottom end is back together.

short question, long answer, I have no idea of the state of the engine prior to teardown. judging by the receipt for the gasket set (which I have slung) was stripped 25 years ago!
I am determined this bike is going to run again.

PJ, when you mention about backyard mechanic, something springs to mind.

In 1987 I stripped and rebuilt an ex Police R80/7 Engine in a backyard with a table lamp, no special tools, and a Haynes manual
In 2019 I stripped and rebuilt an R65, I needed lots of new tools, hours of research and probably changed a lot of things that did not need doing.

In 1991, I got a basket case XS650, I rebuilt that from the crank up, with nothing more than a Haynes manual and a bit of advice from Tony at Halco tuning, it ran fine for the 3 years I had it.
There must be a moral there, either that or a lesson for me!

Not being used is a Mirror topped small table (mirror fixed to wood), probably ideal for the initial measurement to gauge flatness,

Thanks

Barrie
 
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Thinking out loud here
English is not my first language
But Pitting is that not small spots with deeper surface.
Warping is a larger surface being out of plane.

A flat surface glass or marble and some mark paint can find out if the surface is plane as mentioned above.
Assuming small spots What can happen .. If leakage shall happen it needs to get there and get further

if we are talking 0.1 ..0,2 mm .. I would consider not doing anything except perhaps the slight touch with the
carborundum paper As above .. I dont believe 0.1 can be that much .Heat expansion and imperfect seating of cylinders and head and so.
The gasket shall also take up something.

Taking it to a shop milling can cause more damage than do good . Cost $ 100
If it goes wrong later leaking Without the milling one can take the engine out and do it then.
Feel free to correct if I am thinking wrong here.
It also matters what kind of rebuild
 
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