Sweating cylinder heawhat looks like

Other places to check for drips.

The rocker end plates

The rocker end plate bolts

The rocker cover/cap gaskets

The rocker cover/cap studs and nuts ...especially the big single rear bolt.

The rocker oil feed washers

The spark plugs sealing washer

The head bolts nearest to the roil eturn tunnel from the inlet rocker area.

The oil return tunnel itself. Is it blocked?

On my 99/650 engines I found the most common sources of oil leaks were the rocker end plate bolt due to the coarse thread and lack of meat for the bolts to screw into. I used some silcon goo on the bolt threads and small annealed copper washers under each head to sort this.

The rear rocker cover cap was another regular dripper. This needed more goo on a new gasket plus a copper or aluminium washer under the domed nut to sort the drips there..

My low pressure fed 99 head never leaked at all ,then I found out that it was running almost dry. I converted the tank parts to jubilee spec and am now slowly making gradual steps back towards standard oilways sizes to try to achieve a compromise between leaks and a quiet valve gear.

Hi Ron, I've seen silver painted heads (I have an old spare one) but never imagined it was done to seal them against porosity but you could be correct, which is a pity as if this is the reason, I have a worthless cylinder head....

One way to test for tiny air (gas) leaks is by lathering up your cylinder head, when it was cold, with a soap solution and shaving brush (not too much though) then start the engine and rev the engine for a few seconds. Any source of a leak will be revealed by large bubbles being created....Jet wash or hose off after test.

Without a photo of the "oil sweat" I can't say for sure but sometimes fuel "blow back" from the carbs can accumulate as they get drawn back from the carb mouth by the swirling air passage eddies at the rear of the head. This picks up dust and then looks like an oil build up......

Les

Might be worth contacting Ultraseal Slough. They vacuum seal porous cylinder heads. Check all other possibilities first, to avoid needless expense.

Most of us painted the heads silver to clean them up, no vacuum blasting back then!

I have never heard of an 88/99 head being porous, not that it's impossible. Chase up all the other possibilities before blaming the head casting. Solid copper head gaskets are prone to gentle oil seepage on occasion. I have reverted to the standard composite ones. The other oil leak checker I have heard mention of is spray-on talc. Don't know if you can still get it. This assumes your bike is immaculate in the first place before testing. Wouldn't work for my bike.

Never experienced a porous 99 head myself but anything's possible. As Gordon suggested get yourself some crack detector developer, which is like spray on chalk dust and is around £10 a can from fleabay. You need to make sure the head is totally degreased and clean either by spraying with the crack detect cleaner or suitable brake cleaner. Apply a light dusting of the developer around the suspected area and take the bike for a short run.

The source of the oil seepage should be immediately apparent. My money's on one of the rocker end plates, although I did have an Atlas head that weeped oil between the 3rd and 4th fins from the bottom, just to the rear of the RH spark plug. This is where the internal drilling is for the inlet valve oil drain.

I use the crack detector kit all the time, not only for it's prescribed use but for tracking down those hard to find oil leaks.

Good luck