Cylinder Plugs (little semi circular rubber bits in side of head)

[bill_face]

I've got a 79 GS550E. There are 4 of these semi-circular plugs.Two in each side of the head next to the camshafts. I'm just wondering if they benefit from some gasket sealant around them on rebuild?

I don't currently have any gasket sealant and would rather not wait for postage or venture out to get some for 4 little smears. However, i imagine they are perhaps not as pliable as they once were...

Cheers

[Nessism]

Yes. Sealer on the curved portion of the plug is recommended. If the rubber is shrunk, and the plug undersize now, it's best to replace them.

[bwringer]

I generally use a wee squidge of case sealer on used half-moons, not RTV.

If I really, really didn't want to bestir myself that day, sure, I'd try them without any goos or elixirs; as long as there's some sort of small compression factor when you tighten the bolts, you should be fine. As long as they stay in place, any leak would be very minor.

And if it doesn't leak, you've successfully saved yourself the trouble of donning trousers and shoeing yourself that day.

Some of us have taken to installing them backwards, with the flange on the inside so they can't squirt out (this has happened a few tiems). This is generally what I do, and it's worked well so far.


Edit:
As Ed states, if they've shrunk, I'm afraid you'll have to venture forth... try test-fitting one with the gasket and valve cover to see if there's a comfortable amount of compression.

Also, new half-moons are often challenging; sometimes they are a little large and sit too proud of the surface to the point that it's hard to compress them flush. And sometimes they tend to squirt out of place or leak at the corners.

[bill_face]

Thanks for the advice chaps. They seem to be pretty plush so I'll venture out for some goo

[bill_face]

I generally use a wee squidge of case sealer on used half-moons, not RTV.

What is case sealer?

[Grimly]

What is case sealer?

Threebond, Yamahabond, etc.
For these, I use Hylomar.

[bwringer]

What is case sealer?

One good example, ThreeBond 1184:

https://www.z1enterprises.com/yamaha-xs650-3-bond-1194-gasket-sealant.html

This stuff remains very flexible and stretchy, sticks very tightly to metals (but can be scraped and peeled if needed), and doesn't form balls like RTV.

It's mostly used when joining crankcase halves. It is not an RTV; RTV does not belong anywhere near a motorcycle engine.

Sometimes it's sold under the Yamaha name as Yamabond #4. Yer friendly local dirtbike shoppe should have some on the shelf.

Handy stuff to have around.


I've also used this Permatex #2 sealant for field repairs; things like sealing torn gaskets, popped half-moons, etc.

https://www.permatex.com/products/gasketing/gasket-sealants/permatex-form-a-gasket-no-2-sealant-3-oz/

The main advantage is that it's easily available at absolutely any US auto parts shoppe.

It's a thick, black tar-like glop that never hardens all the way. It can seal gaps, stays pliable, and resists oils and gasoline. Messy, but very handy and available anywhere, and can be cleaned off later without much trouble.