Cu head gasket

[Lorenzo]

intake valve and brass brush;

IMG_20210708_204255.jpg

this is how the valve lap looks:

[Lorenzo]

...and a little surprise, proof that the head had been leaking in at least one place:

[bitzz]

That valve need to be ground. You can see a ditch where it sits on the seat.
You need to accurately measure the piston and bore to decide if you can re-use them.
If you're holding a piston with 40 year old rings, you replace the rings, at least.

[Lorenzo]

Thanks for the reply.

Allthough the valve might look scored, I can assure you that what you see is only a streak of carbon, after only a provisional cleansing;

viewed with a lens, they do not exhibit scores nor they are pitted.

About the rings, okay, should be standard procedure, to change them, after all those years, even on an hedge trimmer, but we don't know if they are that old, after all the engine has been opened before, and knowing how to judge them regardless of age, is not a bad thing.

All I wanted to know, if there has been some kind of blow-back or else;
they are going to be measured as a matter of course, together with the bore (a bore gauge is on its way) and the piston, along with a lap of the valve seat, as you mentioned, and a hone of the bore.

[Lorenzo]

Pistons are in the 70.45mm (2.77in) range, against the limit of 71.880 mm (2.8299 in) so a rebore and new pistons is overidue I guess.

[Lorenzo]

Marking and tracing the copper sheet.
It's gonna be head and base.

[Lorenzo]

[Lorenzo]

Time to countour and hone

[Lorenzo]

suits fine...

[Lorenzo]

Base gasket paper mockup (no model)



back to the drawing board...

[Nessism]

Are you going to use the rubber cam chain tunnel seal? And based on the size of the stud holes, I presume you have some seals for those too?

[Lorenzo]

As I said, I'll go without rings and if it seeps I'll put them on, but I think they won't be necessary.

[Lorenzo]

Looks authoritative

[Lorenzo]

Now, before I can get the bike to be started, I need to sort the carbies, but before of that, there is something bugging me, I've been though three choke cables since I had the bike (six years) and was wandering if you have some advice on the feasibility on turning the command from cable operated to "link" operated, below tank and coming off the left hand side(?).
Thanks

[Rich82GS750TZ]

Depending on the year and model, the "stay" function of the choke cable when you pull up the knob in the center of the steering head (some models), or push the thumb lever under the left hand control (other models) is built into the top-side cable end connection. You thighten or loosen the holding power of the choke cable with adjustment there. If you remove the cable, you would either have to hold the enriching circuit shaft pulled out, with your left hand, while holding the clutch lever in with your other left hand, while pushing the start button with your right hand, then holding the shaft out while the bike warms up, or fashion some type of device to hold that shaft out as the bike warms up, then push it in as needed. At least, that's how I imagine it. Someone here must have done such a thing in the past. Have you tried using Advanced Search in the archives?

Here's one such thread I've found by using Advance Search, entering the key words Choke Cable Elimination, and changing the search criteria to Title Only (this is very important, and the only way to get meaningful search results)

https://www.thegsresources.com/_forum/showthread.php?258936-Choke-cable-elimination&highlight=choke+cable+elimination