Is some degree of blow-by just normal?

[Grover]

A while back I was burning oil pretty quickly and seeing puffs of smoke out of the back quite regularly. A leak-down test showed the piston rings were perfect but that I had leaking going on in the valve stems. So, I recently rebuilt a head and put it on there. During a drive today I noticed some smoke coming out the rear after sitting at a stoplight for a minute or so. Out of curiosity I then found an open stretch of road and took the car up to about 5,500 rpm, let off the gas for a couple of seconds, and then reaccelerated. Sure enough, a pretty sizeable puff of smoke burst out the tail pipe. Is this "normal" or indicative of something more concerning?

[johnhup]

How long ago was it rebuilt. How many miles? When my motor was first rebuild I had a little blowby, but after a few hundred miles or so it settled in quite nicely.

[winstontj]

What did you do to the head? Were the valves and guides replaced or just the seals?

[Grover]

The rebuild was done all of 100 miles ago. The valves were reused but I believe all the other parts were new.

[winstontj]

Seals should keep the oil out but if the guides/valves have too much play that could be an issue. Did you measure everything up?

Give it 500 miles and re-check. There is still a break in period where you'll burn some oil before things seat up for the long haul....

good luck

[jetboy]

yeah, before things sit right, you got 300-500 miles of break in time. go drive it a lot and worry if it keeps on after that.