I just replaced a head gasket and ground the valves on a 1983 Nissan Truck. I now have an oil leak that only happens when it is driven. I left it idle for about 1 hour and do not see and oil leak. If I drive it even a short distance I have oil all over the bottom but no place where I can see it coming from. I also had the front cover off, could that be where it is coming from?
Have you looked at the transmission and differential?
The front cover could well be where the oil is getting out. There is a lot of lube oil going onto that timing chain and it gets slung everywhere.
One way to find an oil leak like this is to lightly (1-2 psi) pressurize the crankcase with all the known air exits taped up i.e. PCV valve access, crankcase air vent, dip stick, etc. Then listen with an vacuum hose to your ear at all the seams where a leak could be. You will hear the ‘rush’ as air enters the hose. Then by appling a light vacuum you can draw sealant into the leaking area and possibly reseal it without having to tear the engine apart again.
Hope that helps.
In my experience the front cover is the (searching for right word) ah, most likely place for a otherwise correctly performed headgasket job.
Don’t let my assesment stop you from verifying the source of the leak.
Any head milling going on? this would offset the timing cover,it may also need milled. Front covers always were a problem for me on early BMW 4cyl and 6cyl.
Have you checked the side of the cylinder head where it mates with the engine block on the passenger side of the truck? (about halfway back)
These trucks used a camshaft oil pressure port that was located very close to the edge of the head, block, and head gasket. Oil leaks were very common from this area and especially if the head was not inspected for warpage, head bolts were not retorqued, etc.