Honda-SOHC
Other Stuff => Misc / Open => Topic started by: SteveW on October 20, 2022, 03:56:59 PM
-
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?
-
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.
-
Thanks Bryan, the existing o-rings are 5 x 2.4. Would 5 x 3 be okay?
-
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.
-
wouldn't I need thicker than the standard 2.4mm?
-
It all depends on the thickness of the gasket so, measure it up and work the size out ;)
-
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.
-
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.
-
Was the original unused or used?
-
Used.
Bugger, just realised. More confused than ever now.
-
I have a brand new unused head gasket, genuine Honda, for the Cb500K, I could measure that if it helps.
-
Depends how oldit is Ken, supposedly thickness changed when asbestos was removed and that was some time ago
-
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.
-
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
-
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
-
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.
-
Head skim wont matter as its flat but block skin would as there is a recess
-
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.
-
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.
-
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.
-
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 ?
-
5 x 2.5 and they have been perfect. Done about 500 miles and zero leaks.
-
Thanks that’s good to know. Are they nitrile or viton and how thick was the gasket before compression?
-
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.
-
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.
-
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.
-
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.
-
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 ;)