Valves do not deal tight after cleaning and lapping

Tiny
LYNCH890
  • MEMBER
  • 1989 AUDI 80
  • 2.0L
  • 4 CYL
  • 2WD
  • MANUAL
  • 150,000 MILES
I took the cylinder head out for valve seal replacement and discovered that the cables had excessive carbon deposit, so I decided to clean and lap them by hand with a professional lapping compound.
After everything was done and assembled it was time to do a leak test by pouring gasoline on the valves with the cylinder head upside down. To my bewilderment the gasoline went right down past the valve edges in no time. I leaned over to take make a visual inspection and sure enough there was about 1mm gap between the valve head and the seat. I could literally see light coming through the gap from the intake/exhaust ports.
Now I know that it couldn't have been my mistake, for I lapped the valves with a lapping stick by hand.
This sure seems a mystery to me. What could have happened here?
Is it possible the previous owner to have done a lapping or resurfacing which could account for this?
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Monday, February 11th, 2019 AT 1:14 AM

3 Replies

Tiny
SCWICKEDSTANG
  • EXPERT
Hello,

Did you make sure to put the valves back to the cylinders they came from? This is important to do because they do not wear evenly. The way to remedy this is to lap the valves to cylinder head with valve lapping compound. I have managed to get a lapping tool into a drill and lap the valves this way. It does the job a lot faster and easier. I hope that this helps.

Thanks,
Alex
2CarPros
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Monday, February 11th, 2019 AT 4:03 PM
Tiny
LYNCH890
  • MEMBER
Yes, I made sure each valve went into the place it came out of.
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Tuesday, February 12th, 2019 AT 1:11 AM
Tiny
SCWICKEDSTANG
  • EXPERT
Hello again,

That's great. My suggestion to you would be to get the valve lapping tool, or a suction cup device into a drill and go about lapping them that way. I have included the valve seat and valve measurements in the diagrams below. I hope that this helps.

Thanks,
Alex
2CarPros
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Tuesday, February 12th, 2019 AT 1:54 PM

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