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Half Moons MUST Be Replaced???

  • Thread starter Thread starter aaaaaaaaaachooo
  • Start date Start date
A

aaaaaaaaaachooo

Guest
Hey guys ~ planning on doing my first valve check & adjust.
Wondering if the half moons must be replaced if they still look like they are in good shape. I have the tappet tool, gasket, and feeler gauge on the way....

Didn't realize the half moons MIGHT need replaced as well.
I will be checking every 4,000 miles on my '82 GS750TZ.

Is this something required each time you pull the valve cover?!?!
Thanks in advance! :)
 
It really depends on how well they come out in the first place - sometimes I've replaced them and a couple of times I was lucky and didn't need to.
 
cowboyup3371 said:
It really depends on how well they come out in the first place - sometimes I've replaced them and a couple of times I was lucky and didn't need to.
Click to expand...

In the pictures I'm seeing on a valve check, the half moons don't look like they are even removed during the process.
What would you recommend as far as checking them?
Pull them out and inspect/replace?
If so, do they need to be sealed back down with something?
Leave them be?

Appreciate the input as I'm new to the process.
It seems easy enough, just want to do it right. ;)
 
You typically don't need to replace them unless they have shrunk or cracked. Use some Ultra Black silicone or Three Bond sealer on the curved area of the seal and bond it in place. As long as the flat section is flush or sits a little proud of the gasket surface, you should be fine. If they are stuck in the engine and not leaking, leave them alone.
 
Nessism said:
You typically don't need to replace them unless they have shrunk or cracked. Use some Ultra Black silicone or Three Bond sealer on the curved area of the seal and bond it in place. As long as the flat section is flush or sits a little proud of the gasket surface, you should be fine. If they are stuck in the engine and not leaking, leave them alone.
Click to expand...

Very informative. Thank you sir! :D
 
What Nessim said... but you could tell that couldn't you? If they're out I would just see if they're still pliable or not. If they're hard they might have shrunk some, best to replace them as they're cheap.
 
What Ed says. One of mine stuck to the gasket when I removed it once and the other times I could see they were visibly torn.
 
I love the Ultra Black for such uses. Like was said, a little smear on the curved surface of the head AND ( for me anyway ) the half moons. I let it set up about 10 minutes or so to get more sticky than slimey and then set the half moons in place. Use a straight edge to get them setting pretty level across the flats in relation to the heads gasket surface.

A little proud is good in that when the cover seats it will squish the RTV nice and leak proof.
 
Its a misnomer that the half moos " shrink". They are metal plugs that are rubber coated. What happens is the metal gets squished so many times and they get loose. Yes they can be picked up with a magnet..i discovered this myself when one stuck to my pencil magnet on the bench.
 
Last edited:
chuck hahn said:
Its a misnomer that the half moos " shrink". They are metal plugs that are rubber coated. What his the metal gets squished so many times and they get loose. Yes they can be picked up with a magnet..i discovered this myself when one stuck to my pencil magnet on the bench.
Click to expand...

Ha! Did not know that! Of course rubber still shrinks, gets hard, and cracks whether it's wrapped around metal or not. I guess the metal limits the distortion of dimensions that come with age.
 
true that Allie. But my surmation is that even though the rubber coating looks fine and undamaged, its more the metal base is squished and we all know that its not gonna be spinging back. Its squished and thats that in the end run. Yes the new gaskets thickness does press them down again, but maybe a bit less than if they were new. Thats why i like the Ultra Black as a stop gap for them.
 
A mechanic I know always replaces them because they are cheap and a failure means he has to redo the work for free. For home use, he told me to reuse them if the rubber is still pliable and not chewed up. Add a bit of black goo like Chuck suggests and they should be OK.

Jim
 
Thanks for the replies everybody.
I did the valve check/adjustment today.

Old gasket was destroyed (glad I had a new one).
However, the half moons were in great shape.
Utilized some gasket sealant, and it was good to go!!!
 
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