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Valve lapping
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3rd generation View Drop Down
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Joined: 09 Oct 2025
Location: Iowa
Points: 8 		Post Options Post Options   Thanks (0) Thanks(0)   Quote 3rd generation Quote  Post ReplyReply Direct Link To This Post Topic: Valve lapping
    Posted: 18 hours 23 minutes ago at 8:25pm
I’m sure this has been long discussed if lapping is needed. I just had hardened seats installed and valves ground. Personally I trust modern machining for a good seal. How many of you still lapped valves with hardened seats?
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steve(ill) View Drop Down
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Joined: 11 Sep 2009
Location: illinois
Points: 88803 		Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 17 hours 24 minutes ago at 9:24pm
always a good idea to get a finish lap.. if nothing else, to CONFIRM it is correct..
Like them all, but love the "B"s.
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Joined: 12 Sep 2009
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Points: 8694 		Post Options Post Options   Thanks (0) Thanks(0)   Quote SteveM C/IL Quote  Post ReplyReply Direct Link To This Post Posted: 16 hours 26 minutes ago at 10:22pm
Can't hurt? When seats and valves are ground/cut correctly it's not needed.
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DrAllis View Drop Down
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Joined: 12 Sep 2009
Points: 22211 		Post Options Post Options   Thanks (0) Thanks(0)   Quote DrAllis Quote  Post ReplyReply Direct Link To This Post Posted: 15 hours 13 minutes ago at 11:35pm
HELL  NO !!     Ask yourself this: do you think GM or FORD for example take the time to "lap" valves and seats after their modern and expensive valve grinding equipment has just mass produced hundreds of cylinder heads a day ?????? NOPE.
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Points: 8 		Post Options Post Options   Thanks (0) Thanks(0)   Quote 3rd generation Quote  Post ReplyReply Direct Link To This Post Posted: 9 hours 56 minutes ago at 4:52am
Bluing would confirm a fit. I do think it’s a method appropriate many years ago and has stuck in the minds of some. My search has yet to convince me it’s needed. The hardened seats will do more for longevity than any lapping could provide.
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Joined: 08 May 2020
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Points: 1449 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Les Kerf Quote  Post ReplyReply Direct Link To This Post Posted: 7 hours 28 minutes ago at 7:20am
When Grandson and I used my 100 year old Van Norman valve grinder and my Chinese-made seat cutters from Amazon to do a valve job on Mr Cato's Model C Allis-Chalmers head with the sloppy valve guides and cast seats, why yes, we most certainly felt it appropriate to hand lap the valves. Tongue


Edited by Les Kerf - 7 hours 26 minutes ago at 7:22am
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Points: 3587 		Post Options Post Options   Thanks (0) Thanks(0)   Quote AC7060IL Quote  Post ReplyReply Direct Link To This Post Posted: 2 hours 46 minutes ago at 12:02pm
You could easily have it vacuum tested to expose any possible valve/seat fit leaks.
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steve(ill) View Drop Down
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Points: 88803 		Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 2 hours 18 minutes ago at 12:30pm
lapping it for 30 seconds would give you an idea of the seat and verify that all is well.. Just a quick test.
Like them all, but love the "B"s.
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Joined: 08 May 2020
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Points: 1449 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Les Kerf Quote  Post ReplyReply Direct Link To This Post Posted: 12 minutes ago at 2:36pm
Originally posted by DrAllis DrAllis wrote:

HELL  NO !!     Ask yourself this: do you think GM or FORD for example take the time to "lap" valves and seats after their modern and expensive valve grinding equipment has just mass produced hundreds of cylinder heads a day ?????? NOPE.

Lapping valves after having been done correctly on modern equipment does no good and may reduce longevity by a small amount.

I do not own such modern equipment Big smile

It would be difficult to prove the difference on a vintage Allis-Chalmers tractor.
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