I am having leakage on the intake valves of my new Dart heads and valves on my small chevy when shop air is applied into the compustion chamber threw the spark plug hole.

I believe that if I had of lapped the valves there would of been no leakage.

Is it recomended that valves are hand lapped like the old days?

I have seen the same amount of leak on the exhaust side of high milage engines with no problems, but will a leaky intake valve cause back fires?

When cranked over with the starter with no intake mainfold and a little wd 40 down the intake port I can see a puff of mist when cranked back out of the intake port.

This worries me, but there is no cranking pressure diference between leaky valve cylinders and non leaky cylinders.

To start, you need to pick up a simple leak down checker.  You don't need a high dollar unit, Harbor Freight has a nice little cheapy that works just fine.

As to lapping valves...The current state of the art in high performance racing valve jobs say NO.  If I have taken great pains to cut the seat angles in the heads and valves to very precise angles and widths, then I am not going about sticking a great gob of grinding compound and whacking about with the valve and simply destroy hours of tedious work.

Having said that, it has on occasion been necessary, usually in the field or as a temporary 'fix' to lap the valves, <ever so lightly>, to get by for a race.  On the dyno, lapping the valves by hand as opposed to precisely cutting them, shows a distinct drop in torgue and hp!!!

Not to say I haven't lapped a bunch of valves/ball valves in my day, just saying that the machines that do the job are a lot more precise today.  Heck, I used to seat the valves in my flatheads with a big mallet...worked too.  I don't think I would do that on one of my Lotus engines, though.

It seems that this thread is over but I have one thin to add that seemed was missing.  Each valve seat needs to be ground to ensure the guide and seat are concentric to one another.  In my experience in Industrial Engines lapping w/ fine compound was acceptable but not to correct a major problem.  I was also taught to vacuum test each valve seat after assembly was completed.  Do manufactures rely on accurate grinding? Yes, but they calibrate at specified times and they also use cutters and not stones so they do not have any grinding dust.

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