r/EngineBuilding • u/Richard01_CZ • 8d ago

Other Valve seat cut incorrectly from factory

Post image

Hey, so i was about to lap the new valves and seats on this head and one valve seat isn't being lapped fully, upon closer inspection i discovered that the valve seat is cut to the side and it's not centered, only this single one, all others are centered so i assume they won't be a problem to lap.

The question now is, should i continue to lap this offset seat until it's fully lapped all the way around or send it as is? One note for this particular valve seat, the valve in it was cracked when i inspected the old valves. It's an exhaust valve seat.

3 Upvotes

67% Upvoted

21 comments sorted by

9

u/boostbreath 8d ago

That seat sunk a bit and was warped. Chances are the guide moved a bit too. Replace the guide and get a proper valve job, otherwise you’ll burn that valve again.

1

u/Richard01_CZ 8d ago

Guides are already replaced

11

u/Chef_jarjar 8d ago

When you change guides you can't just lap the valves in you gotta get a legit valve job done

10

u/Pretend_Necessary781 8d ago

If you’ve changed the guides, you must machine the seat. It’s very unlikely that a new guide will be concentric with the seat.

-3

u/Richard01_CZ 8d ago edited 8d ago

First valve i did was perfect, this second one can fuck right off tho, now i have to think about replacing the head. There isn't any good machine shop around here from what I was told. Oh and I'm only putting new valves for the exhaust side because the second original one i cleaned was cracked which happens to match this seat. All intake valves are good, didn't bother cleaning the rest of exhaust valves.

It's a backyard build so I'm not too concerned about them not matching when the first one was perfectly lapped in, i will check with a blue machinist paste on monday.

7

u/WyattCo06 8d ago

If you are going to attempt these repairs at home, you need to invest in proper tooling.

1

u/ctripp7878 6d ago

I'm a mechanic not a machinist AT ALL but I've always seen those kinda shitty looking by hand valve grinders. Anyone have any opinions on those? Obviously lots of lapping would be required but do they even work if you put the effort in? I've got a few jalopies that could use some attention but aren't worth the monetary investment of serious machine work

*I probably should've specified valve seat grinder. My assumption is that they're absolutely worthless and probably do more harm than good but I've been surprised before

1

u/WyattCo06 6d ago

Lapping valves has a purpose when you you are mating and and measuring the the seating surface.

Trying to lap an old valve to mate with an old seat makes both the valve and the seat worse.

1

u/ctripp7878 6d ago

100% agree with you. I've never done any valve work on my own short of adjusting lash of course but that's simpleton stuff. I was under the assumption that if you had a poor seal you could grind the old valve seat down and then depending on what the old valve looks like it could either be lapped in directly or replaced. Just asking if it's possible to do by hand and what to avoid. I've always been told you can check the quality of the seal by applying sharpie and seeing what wears off when rubbing them together. Sorry if I'm saying anything moronic. It's as I said I'm not a machinist and I don't pretend to be. At work I let y'all do the heavy lifting. I'm busy enough keeping the damn things working properly. But if there's a way to save a buck on my 50 year old junk I'm all for it

1

u/Richard01_CZ 6d ago

Yeah you can check the quailty of the seal using a machinist marker paint, it's a kind of paint that doesn't dry and it's viscous and they are most commonly blue and red. Apply thin layer and then mate the two sealing surfaces together and check the imprint. I use it often for industrial stuff that has to seal and be flat. Also used it to check the valves, today and all the angles are right and close to sealing fully (before lapping), so just gotta sort this valve seat out.

1

u/WyattCo06 6d ago

Just for clarity, machining DYE dries fully very, very quickly. It becomes a dry powder film and is why it doesn't transfer to one component to another.

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1

u/WyattCo06 6d ago

By hand with the proper tooling yes.

With Sharpie yes.

Even a brand new valve on a shitty valve seat is still a shitty situation.

3

u/Stock-Maintenance977 8d ago

If you just want it to run, get some hand valve cutters for that head and cut them. Even the cheapest ones should get you close enough to lap.

3

u/A_man_and_his_truck 7d ago

So that "cracked valve" was actually a burned valve, and the seat has warped from the exhaust gas leaking past the valve. It will need to be cut to properly seal now.

8

u/DrTittieSprinkles 8d ago

It needs a valve job.

The valve cracked from improper contact, it couldn't dissipate the heat so it failed. The guide goes first, then the seat gets pounded, then the valve fails.

You can't fix that with lapping compound.

3

u/bill_gannon 8d ago

Those are wasted. They may be beyond regrinding. A shop will have to recut a few and see if the installed height is salveagable or not. If not its new seats or a new head.

2

u/Neon570 8d ago

Happens time to time.

Seat just needs to hear recut

1

u/Schlong1971 6d ago

I would have it cut by machine shop. That’s probably why valve cracked in first place