Leaky valves?

[ramwing7]

Did a leak down test on my 305 and heard air leaking out of the left side carb. So I've disassembled the head and lapped the daylights out of the all the valves and seats. Upon reassembly I squirted compressed air into the intake and exhaust ports and I still get tiny bubbles at about 30 psi.
So, what's next? Do I hunt up someone to regrind the valve seats or what?
If that's the case, any suggestions, precautions, etc.?
thanks.

[G-Man]

Are the valves & the seats in the head free of pitting?

G

[SMBH]

The old trick to checking for the valves seating ok with the valves fitted with springs, was to up turn the head and fill the area full of say white spirits lamp oil or something that will not evaporate leave for say 24 hours and see if any has leaked down the guides try placing the upturned head on some paper then you will see any leaks.

[ramwing7]

The valves are not pitted, so I tried another approach. I stuffed dry rags into the intake and exhaust ports, turned the head upside down and put in water to the top. Waited 2 hours and I only had one wet rag. So I figure to lap the leaking valve some more until it holds water and then put the head back on and do a leak down test.
Sound like a plan?

[G-Man]

Yep - sounds like a plan.

Any chance that the leakiy valve has a bent stem? Try swaping it for the good valve if you cannot get it to seal.

G

[ramwing7]

Yep. Thought about that. Gonna check it out.

[squeaky99]

Hi Guys. With regards leaky valve , water has too high a surface tension to be a good eliminator of leaks(unless the leak is real bad). When testing valve/seats mark the seat with a hign carbon pencil at 4 points, 90 degrees apart. Insert the valve and turn it no more than 90 degrees. If you have scored all 4 pencil marks then you have a perfect seal. Engineers blue can also be used. Sounds like you have either a bent valve or the valve/seat is worse than you think. Recutting is the only option, other than hours of grinding.[/quote]