what exactly is valve recession?
ive heard it being used but not known what it exactly is.

When the hot burning gasses pass over the exhaust valves, the additives in the gasoline are supposed to cool the mating surfaces of the valves when they close. When there is not enough
cooling to the surfaces, it sort of melts away the valve seat surfaces. A couple of years ago my nephew asked me how the valve adjustment could get looser as the motor ran on his Harley
Davidson but the adjusters were still tight and hadn't been loosened at all. I told him that he was using unleaded gas and the seats were eroding away. He didn't believe me at first but he
had to buy new heads. Datsuns have bronze valve seats and they are usually not a problem with unleaded fuels.
THIS A IS DIFFERENT PROBLEM. One problem I had with my 1200, I bought a HAYNES REPAIR MANUAL a few years after I got the car. It listed valve lash as .010 cold for both intake and exhaust
valves. On a long trip, I burned a valve. I had it repaired and later, it burner another valve. After replacing valves five different times, I found a DATSUN TECH MAUNAL that listed the lash
as .010 for intakes and .012 for exhausts. I never burned another valve.

> THIS A IS DIFFERENT PROBLEM. One problem I had
> with my 1200, I bought a HAYNES REPAIR MANUAL a > few years after I got the car. It listed valve >lash as .010 cold for both intake
and exhaust >valves.

Hi,

My Haynes "Owner's workshop Manual" and Clymer's "datsun repair manual" has listed a 0.014in lash. With an hot engine.

Can both be right?
(It's probably accurate to tune it cold... any opinions?)

daniel

Valve lash DECREASES when valves receed.

the cold clearance(lash) setting is to get the enging running, as you cant get it hot after youve just stripped it down ect, the cold setting provides a means of getting
the engine started, and when the enging is warmed up to operating temperature the hot clearance can be checked. it is more accurate to check/tune while hot on a datsun.

Yeah Chris, I learned a lot about the valves then. Also compression, the head was shaved a bit each time the head was off. The compression went up enough to need octane boost to
keep the detonation away after the last time it was done. LOL
And I was also a big dummy when I said the valve lash slackened on my nephew's Harley. They did tighten up. That was a few years ago and it was the second time I had encountered
that problem. The first was on an MG midget.

I checked the valve lash on my A12 after I discovered that the exhaust lash being set at .010 cold was too tight and was causing the valves to burn. When I set them at .010 In. and .012
Ex. cold and checked them after the motor had warmed up, they were at .012 In. and .014 Ex. The exhaust valves just weren't sitting on the seat long enough to cool properly and they would
get too hot. This is the limiting factor in valve adjustment as you will want the lash as tight as possible to get the full use of lift and degrees on the cam lobe but loose enough to give
the valve enough time to cool itself. Every motor is a bit different and has its own quirks. Sometimes it takes burning and breaking parts to find the optimum settings for your particular
motor to get its full potential from it. I found mine on the A12 motor the hard way.