Does this result in a leak visible outside the engine? Where should I be checking, please? I used a David Silver gasket set (Vesrah, I think) and put it back on the road before I saw your advice.
The leak that occurs begins around the 2 oil ports at the back of the cylinders, on either side of the cam chain's tunnel. Most of the time it takes 500-1500 miles after a rebuild before it appears: if the cylinders were milled down 0.010" to compensate for the new head gasket, it takes longer, like ~4000 miles for it show up. Since most aftermarket gaskets don't have the extra goo that Honda used in the head gaskets to forestall this sort of leak, the O-ring must work better than it did OEM, so I make them 0.2mm thicker (like the head gasket is) than OEM and also mill the cylinder deck 0.22mm (0.010"), which puts those O-rings at near maximum seal tightness for the 60 PSI pressure there. (If you squish an O-ring beyond 25% of their cross-section they tend to have short lives and can split).
With aftermarket head gaskets and the standard 2.2mm thick O-rings, it appears first in the center of the front of the engine in most cases, because of the tilt of the top end. Eventually it also starts showing up just above the cam chain tensioner body in the back, That's why these 2 spots are always so wet in these engines: it is common with the OEM engine after 50k miles and 40+ years when those 2 O-rings got hard and stopped sealing very well. It's worse with thinner oils, and high-detergent oils can bring it about more quickly as they dissolve the goo Honda put on the head gasket itself.
On engines that live in places like Arizona, Texas, South Africa or Iraq where it's pretty hot, the OEM head gasket lasts longest with this extra sealing added. They are getting hard to find, though. My last one of those went to a 750F1 in Iraq in 2011, still doing well (fingers crossed!). In the aftermarket gaskets I've had the best luck with the Vesrah, which is why you'll see me mention them often for the 750.
