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

[Seabeowner]

Other relevant things:

Has the head been skimmed, the depth of the location will be less.

The size of the hole in the head gasket.
May affect The room the O ring has to expand into, May/may not be concentric with the location in the head. Mine vary from 10.8mm to 11mm

O ring sizes available. I found:
5.0 x 2.4,  5 x 2.5,  5 x 3.0
5.23 x 2.62
5.3 x 2.4
5.5 x 2.4,  5.5 x 2.5,  5.5 x 3.0
5.6 x 2.4

How much is recommended as the maximum to compress O ring.

[Bryanj]

Head skim wont matter as its flat but block skin would as there is a recess

[Oddjob]

Just measured the head gasket thickness.

Genuine gasket out of top end set, difficult to measure as Honda put some sort of sticky layer around the hole and it has the effect of sort of bubbling the surface a little but 1.4mm is my best measurement.

My aftermarket kits were both NP ones, Royal Industries NP18004 to be exact. the kits were mixed together but 2 head and 2 base gaskets along with 2 sets of Orings etc, only one of which included the ones for the head oil gallery in question, no sticky layer around the opening, unlike the Honda one but both measured around 1.4mm as well. If anything I'd say they were slightly thicker than OE as they did measure thicker at times, both measured 1.5mm depending on how you read the micrometer.

All the kits were from the 80s maybe even earlier, late 70s maybe.

[SteveW]

Thanks for the info guys. Pretty sure my engine has not been apart before, I only did the top end because the valve stem seals had failed. I had no other leaks.

I’m just glad I measured everything, if I had used the gasket set with the o-rings supplied I’m convinced it would have leaked.

I’ll post up my findings once I have the thicker o-rings and it’s back together.

[Seabeowner]

Head skim wont matter as its flat but block skin would as there is a recess

Yes, got right in the earlier post, meant block and typed head. Dunce.

[davidcumbria]

Reviving an old thread because I’m in exactly the same quandary. Hope you see this Steve. What size o rings did you fit and have they been ok ?

[SteveW]

5 x 2.5 and they have been perfect. Done about 500 miles and zero leaks.

[davidcumbria]

Thanks that’s good to know. Are they nitrile or viton and how thick was the gasket before compression?

[SteveW]

Gasket was 1.29mm, original bang on 1.2.

Picture is my order from Simply Bearings, they are Nitrile. I went for the stronger shore rating of 90.

[davidcumbria]

Thanks. My vesrah gasket is 1.4MM thick so an extra 0.1mm thicker than yours. Ithink it makes sense to go for the stiffer 90 shore ring given what’s going on with pressure and heating and cooling. I’ll ditch my cheapo eBay rings of that size and buy the same as you since there is good evidence it works  but the o ring has an even bigger gap to fill with my vesrah gasket. Any problems and I’m going to go original.

[Oddjob]

I kept wondering why his head gasket measured 1.2mm when mine, from an original top end gasket set, measured 1.4mm and I spotted the reason in post number 1. His is a CB650 not a CB500/550.

Different gasket so most likely a different thickness, odd though that it still used the same oring.

[SteveW]

I’ll be doing the top end on my 550 over the winter so I’ll put up the measurements from that one as well.

[Trigger]

A lot of Honda head gaskets have two different thickness. You have the old asbestos type and the non asbestos which are the thicker type.
Always measure up what you have and work out what o'rings are needed for a good seal