Valve lapping

[Let'sgoflying!]

What is your goal when you lap a valve which has been leaking?
If you need more details, propose a situation/engine, this is a broad question.

Are you bandaid-ing it to keep it going til the soon-to-be-required cylinder change?
Are you doing a temporary fix, and expect to do it again within 100 or 200hours?
Are you setting it right and if the engine is managed well from that point, you could get another 500hrs without intervention?

What are reasonable expectations with valve lapping?

 

[Tom-D]

What are reasonable expectations with valve lapping?

Depends upon what you started with..
Was the valve warped?
Was the seat pitted ?

Simple lapping often doesn't work.

 

[Clark1961]

I’m not going to google this one for you my liege. Only time I’ve done it is on newly rebuilt heads after the valve grind. Heard of it being done for repair by some of the old guys...

 

[Checkout_my_Six]

the goal of a field lap job?....to get it to seal and make pressure. They are temporary at most. I'd expect a few hundred hours before it needs it again....or the leakage progresses enough where the cylinder has to come off.

 

[nrpetersen]

I understood lapping as a way to analyze the contact pattern to see that it shows reasonable valve head alignment and correct contact. The amount of material removed is trivial.

 

[Tom-D]

I understood lapping as a way to analyze the contact pattern to see that it shows reasonable valve head alignment and correct contact. The amount of material removed is trivial.

you can use it as an indication of what the problem is. Lapp a little bit, to find out that this ain't going to work.
Then it becomes, is the cylinder worth a new valve? is the seat pitted? is the cylinder's bore worn out?
Boring over size, replacing the seats and guides, pistons and rings, is often more than a new cylinder assembly. (if they re available) some times you don't have a choice.