G5 no compression

[vigo]

Gents, a few weeks ago I bought a non runner that had lost compression. Investigation revealed 1/4 inch play in exhaust push rod, sticking valve? Head off revealed the copper gasket had been pinched and was distorted by escaping gas. But that's not why I'm writing, a layer of metal is missing about 3/8 long on the rim around the head dome. This is not a gas seal area as the copper gasket sits outside of the damage. The damage reveals what seems to be a different metal beneath and I would like to know how the head is constructed. Unfortunately Ican't see how to attach pics in forum.Anyway the head is back on with good compression.
Any wisdom appreciated.

[Eamonn]

Unfortunately Ican't see how to attach pics in forum.

For instructions see this topic:
http://www.jampot.com/forum/viewtopic.php?f=53&t=12424

[Martin.S]

The head casting is 100% aluminium alloy apart from the valve seats .
Cheers

[Ozmadman]

To attach a picture start writing your message as I am doing, look down underneath the message box and you will see a tab " upload attachment" CLICK ON THAT AND ANOTHER BOX WILL OPEN, click on the "browse" tab to get your picture off your PC or whatever, make sure it isn't bigger about 250kb or about 640 x 480 pixels, click on the picture and the name of the picture will appear in the box below the browse tab. Hit add file and then submit

[cfaber]

Is it possible that this different metal is lead? Remember, these bikes ran on leaded fuel and it did build up everywhere on head.

[Duncan]

Could it be the valve seat?

[clanger9]

Lightweights have a hardened exhaust valve seat that looks like it's made from phosphor-bronze.
They vary in size and it looks a bit like a repair (but it's not, that's how they came from the factory...)

Here's a photo of mine:

IMG_2370.jpg

Here's another one (off eBay). In this case, the hardened seat material extends all the way into the head gasket area. Looks strange, but apparently normal:

s-l1600.jpg

[Ozmadman]

and here's mine

[Martin.S]

It was only the later heads that had the bronze type seat - mine have two steel seats.
Cheers

[vigo]

Gents, a few weeks ago I bought a non runner that had lost compression. Investigation revealed 1/4 inch play in exhaust push rod, sticking valve? Head off revealed the copper gasket had been pinched and was distorted by escaping gas. But that's not why I'm writing, a layer of metal is missing about 3/8 long on the rim around the head dome. This is not a gas seal area as the copper gasket sits outside of the damage. The damage reveals what seems to be a different metal beneath and I would like to know how the head is constructed. Unfortunately Ican't see how to attach pics in forum.Anyway the head is back on with good compression.
Any wisdom appreciated.

Thanks for the interest. That ebay head pic posted by clanger9 is similar to mine and I'm now convinced the exhaust seat is what can be seen exposed.The bike is now back together and I had it running. Let's see if it stays together.
The valve lifter was out of commision from previous owner, no cable.
Now here's probably a daft Q but why don't I need a valve lifter when booting my 850 Commando but this G5 has one?

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