lapping valves and seats necessary?

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Belgian1979
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lapping valves and seats necessary?

Post by Belgian1979 »

Hi,

I'm wondering if this is still necessary. The shop did my heads and tested the valves sealing, but some say that you still need to lap them with paste. Thanks.
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Re: lapping valves and seats necessary?

Post by rebelrouser »

I usually only lap a valve to see where the valve is sealing on the seat, how high or low. Or you can slap them and see the mark on the valve. As far as sealing a seat with lapping compound, I don't think that is necessary, if you have good equipment. I check seats with vacuum, if the valves hold a vacuum, then they will hold compression. I always vacuum check new heads as I quite often see seats that leak from the factory.
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Re: lapping valves and seats necessary?

Post by 1972ho »

Just get some Prussian blue and check for 100 percent contact and call it good but if a valve job was done they would have already done that and lapped them.
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Re: lapping valves and seats necessary?

Post by Alaskaracer »

My head guy laps them VERY LIGHTLY, but just to check seat contact.....NOT to help them seal.....
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Re: lapping valves and seats necessary?

Post by Walter R. Malik »

I certainly won't lap valves with that "road gravel" valve lapping compound you get from the parts store.
I use 400 grit "Clover" polishing compound.
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Re: lapping valves and seats necessary?

Post by allencr267 »

Are they a mirror finish?
Can't get any smoother then that.

Some materials won't, but that's their problem.
//
Magic marker/sharpie/whatever to see where they're mating.
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Re: lapping valves and seats necessary?

Post by 1980RS »

Walter R. Malik wrote: Sun Dec 04, 2022 12:10 pm I certainly won't lap valves with that "road gravel" valve lapping compound you get from the parts store.
I use 400 grit "Clover" polishing compound.
I used to use that stuff, now I use gritty tooth paste. Works great.
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Re: lapping valves and seats necessary?

Post by PackardV8 »

Haven't seen anyone in this century lapping valves with grit compound.
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Re: lapping valves and seats necessary?

Post by digger »

PackardV8 wrote: Sun Dec 04, 2022 4:06 pm Haven't seen anyone in this century lapping valves with grit compound.
Not seen YouTube? Plenty seem to think that a VJ and guides that have done 200k just needs some cheap paste and spin the valve until they mate
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Re: lapping valves and seats necessary?

Post by 1980RS »

digger wrote: Sun Dec 04, 2022 5:24 pm
PackardV8 wrote: Sun Dec 04, 2022 4:06 pm Haven't seen anyone in this century lapping valves with grit compound.
Not seen YouTube? Plenty seem to think that a VJ and guides that have done 200k just needs some cheap paste and spin the valve until they mate
That's the Honda valve job :lol:
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Re: lapping valves and seats necessary?

Post by PNEguy »

In the shop I was involved with....Using a VGS20 seat cutter, we would ocassionally see things like a Honda cylinder head exhaust seat need a slight touch up with laping compound. Those Honda valve seats were some hard stuff!
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Re: lapping valves and seats necessary?

Post by modok »

This is a very annoying question.
I'm not interested in insulting people who do things old ways.
VINTAGE speed is about re-living the past, so, that's ok. If people lapped valves in the 60's then maybe you want to do that too and see what it was like.
If you are just trying to do a GOOD job, and lapping IS necessary for you, please get better tools, is my opinion. Your wasting your time not having the right tools.
There is no advantage to grinding a groove in the valve face at all. Introducing abrasive is not good either, requires yet more cleaning.
If you cannot grind a seat good enough to run use a old valve for lapping if possible and keep refacing that valve again and again, if there is no other way.
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Re: lapping valves and seats necessary?

Post by digger »

What are people using to clean the nasty stuff out of the pores ?
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Re: lapping valves and seats necessary?

Post by Belgian1979 »

Thanks. Overwelmingly clear that it's not needed.
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Re: lapping valves and seats necessary?

Post by David Redszus »

Did you grind the seats or cut them?

Are the valves and seats concentric?

A very slight lapping will reveal seat contact width and concentricity.

But ultimately, I always rely on a vacuum seal test.
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