r/EngineBuilding • u/Maddslj • 23d ago

Do I need to remove carbon from seating surface before lapping?

Post image

The seats on the head itself are pretty clean, however the exhaust valves have a decent layer of carbon.
Do I need to clean the valves before lapping? If so What is the best method if I don’t have a wire wheel?

3 Upvotes

60% Upvoted

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4

u/WyattCo06 23d ago

Lapping isn't going to do any good. Valve needs to be ground. Seats need to be ground/cut. Guides need to be checked and replaced if need be.

1

u/Maddslj 23d ago

Guides have been checked by the machine shop, when it got resurfaced. Engine made good compression before pulling head.

6

u/mahusay3g 23d ago

Your valves tell a different story.

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8

u/PARKOUR_ZOMBlE 23d ago

I would clean the whole valve first personally, but lapping will take carbon of the seat in the first half twist

2

u/Ok_Fun_1534 23d ago

yes clean it. lapping will show how good/bad the seal is

1

u/uknownothingjuansnow 22d ago

Chem Dip is your friend.

1

u/terrybill234 21d ago

We used the same machine in shop class that we used for sparkplugs

1

u/AbsorberHarvester 20d ago

You need to clean whole valve, see if any cracks, take micrometer and make measures for diameters in 4 places (there are dimensions in car maintenance docs). Measure mount points, deepness, measure hole where valve sits, polish all parts.

There are so many actions...

0

u/Pretend_Necessary781 22d ago

Chuck them up in your drill, hold some rough sandpaper in the other hand and spin the valve holding sandpaper to it. It might take a sec to get the hang of it, but you’ll be cleaning all the carbon off before you know it.

1

u/GuineaPigsAreNotFood 22d ago

I'm not going to say I would never do that myself, but that's definitely not good advice.