NE gasket set, do I need thicker o-rings?

[SteveW]

Just doing the base and head gaskets on my 650. Got a gasket set from Silvers NE brand.
Wasn’t there something on here a while ago about using slightly thicker o-rings instead of those in the kit?

[Bryanj]

Original gaskets contained asbestos and because that added strength were thinner, idealy a slightly thicker O ring at the head gasket would be better with new stylr thicker, non asbestos gaskets.

[SteveW]

Thanks Bryan, the existing o-rings are 5 x 2.4. Would 5 x 3 be okay?

[Seabeowner]

Hondaman suggested an imperial size I think that I converted and noted down as 5.6 x 2.38mm. The actual oil feed channel I measured as 4.83mm.

[SteveW]

wouldn't I need thicker than the standard 2.4mm?

[Trigger]

It all depends on the thickness of the gasket so, measure it up and work the size out 

[Seabeowner]

Hondaman suggested an imperial size I think that I converted and noted down as 5.6 x 2.38mm. The actual oil feed channel I measured as 4.83mm.

Going back to this that O ring appears to be 7/32 x 3/32. And not terribly different from the 5 x 2.4 mm that is on the p/l. Just measured a few bits. The location in the top of the block (two old blocks) 1.11mm and 0.99mm (perhaps that ones been skimmed). Three old removed head gaskets (probably all aftermarket) 1.23mm, 1.24mm, 1.29mm. Two new head gaskets, 1.24mm, 1.09mm.
How much do the gaskets compress, how much do the relax when remove, who knows?
So quite a range. Taking the max location depth and the max head gasket thickness would be 2.4mm!  Best case would be 2.08mm
There are many intermediate sizes available, so and 2.4mm looks not enough, but it is often the source of leaks if you don't get it right.

[SteveW]

Measured my original head gasket today and bang on 1.2 mm. new head gasket measures 1.29 mm so I’m thinking of using a 5 x 2.5 o-ring instead of the 5 x 2.4.

[Oddjob]

Was the original unused or used?

[SteveW]

Used.
Bugger, just realised. More confused than ever now.

[Oddjob]

I have a brand new unused head gasket, genuine Honda, for the Cb500K, I could measure that if it helps.

[Bryanj]

Depends how oldit is Ken, supposedly thickness changed when asbestos was removed and that was some time ago

[Oddjob]

It's an original Honda one Bryan, full top end kit, in that green flat packaging they used to do back in the 70s. I have 2 of them IIRC plus a couple of the bottom end kits as well. I also have a couple of aftermarket kits lying around, must see if there is a difference in between the 2 head gaskets whilst I'm up in the loft, can't recall whose makes the other kits are but Noburo or something sounds familiar. Kits are 40 years old now.

[SteveW]

I have a brand new unused head gasket, genuine Honda, for the Cb500K, I could measure that if it helps.

If you don’t mind that would be great. Thanks

[SteveW]

I've just measured the new o-rings in the new gasket set.

The originals are 5 x 2.4 mm, these are 5 x 2.0 mm. So with the gasket being 0.1 mm thicker and the o-rings 0.4mm thinner that's 0.5 mm under size.

I'm not risking fitting these 0-rings, I'm ordering some 5 x 2.5