Valve lapping: Am I doing it right?

[invader_star]

This is my first attempt at doing a fine lap job I just curious as to how much lapping is necessary to get a good seal going. Once I got my suction cup to stick without slipping, I ended up with these results.


Should I do a little more lapping so that the seat is smooth all the way around? Or is this more or less where you want to be? I wasn't sure, and didn't want to grind the valve too far down since it was pretty smooth. Thanks fellas

[georgeb]

Seat looks pitted. I always thought they had to be ground first, then hand lapped.

[hotfordcat]

Old way was hand lapping. I would suggest a machine shop at this point. If cost is a concern, you can continue the old way, but that might not get you the best job.

[91mcnasty]

I always just throw the valve spring and locks In, cycle them up and down a couple times, then pour gas in it and see if she leaks!!!

[invader_star]

Bummer. This was a junkyard pickup. A really nice head with only 147k on it, but as a result it was sitting for a bit. The valve seats had a little rust on them. Cost is unfortunately an issue, so I guess I'll be lapping for a good while. I'll definitely test the seal with some break cleaner. Plenty of that, heh.
The valve seats are supposed to be totally smooth then?

[zoe60]

I'm no machinist, but if you lap down the seat far enough the valve may end up ground too far. Like I say though I don't know anything.

[FestYboy]

that valve has been ground too far, you're looking at new seats/valves for that head, sorry.

[zoom zoom]

I just recently had a 3 way valve job done on a 16 valve bp and it cost 117$ with valve grinding, head milling, and valve stem seal installation.

[invader_star]

that valve has been ground too far, you're looking at new seats/valves for that head, sorry.

Nooooo way, ugh. Does that mean that this head has had a valve job in the past, perhaps? They looked about the same before I started lapping them... I'll have to post some photos of the other valves tomorrow. Noooo

:'C

[FestYboy]

the valve seat may be able to be saved, but that exhaust valve lap surface is way too wide to be serviceable.

[invader_star]

That's encouraging, at least. I have two other heads with valves still in them. Could I potentially take the valves from another and lap them to fit? I really can't afford to buy brand new valves for this project.. also , what is the worst thing about using valves that are this far down? Is it just really poor compression that leads to other things breaking or what? I don't really know what worn valve seats mean in the big picture.. If I were to use valves ground down this far, but had a perfect seal, what would happen?

[Movin]

The interference angle is lost. Take the bare heads and valves..your extras too, to a
machinist, and see if he will cut you a deal since they are apart. The contact surfaces
cannot be corrected by lapping but a machinist can likely help you.

hand lapping was done after grinding because the grinding back then was
not as accurate as now. Lapping worn out or damaged stuff was not done successfully
back then either!

[invader_star]

I suppose I might have to take my valve reserves into the shop and see if I can have something worked out. I got a photo of the other valves that came out of the head I'm working on. All of the lips look pretty large... do you think these valves have been machined before?

What is the interference angle, and what does it control? I'm trying to learn what some of these things mean. I'm not looking for a "yeah you can probably use them" I actually want to know how this affects the engine as a whole, haha.

[Movin]

I don't have the actual specs but will give some general info. The valves in your pics
need ground real bad, probably there first time as the face of the valve still has some meat between the seat area and the face. Okay to grind. The valve grinder will likely grind the festy valve at 45 deg. You can see the seat area and it stops close to where the grinding stops, just back a little. We are talking about the area closest to the top of the valve, that is where the sealing takes place. If it is too close the sealing area will get hot and burn. your valves are just right in this respect, just wore out.
The valve seat will be cut in 3 angles, the middle angle is the sealing one. The other two are used to locate the sealing surface on the valve right where your are. The middle cut of the valve seat will be cut at 44 deg, an interference cut that will
put a little more pressure on the combustion side to create a positive valve seal.
If you lap this surface it will very quickly show a narrow ring on the valve face at the combustion edge, right where yours is except narrow. On yours you can see the entire width of the 44 deg seat cut worn into the valve. It can't chip carbon any more so
the pitting starts that you see in your valve pic. A tight valve guide will keep the
surfaces working as they should.

Thermal dynamics are really interesting and the hottest part of this situation is the outside edge of the valve. Cooling takes place the long way to the valve guide, and the short way through this seat contact. The amount and location of seat contact greatly affect the temp of the valve, ping, detonation, how good your gasoline has to be all kinds of things. increasing or decreasing the interference angle affects all these things..so this angle and the location of it on the valve are a juggling act to compromise the rebuild into the best assemble for the application.

seals, designed amount of oil to be consumed here at the guide, type of oil, sodium cooled or not, valve lash and lobe profile of cam, percent of maximum power averaged for this application, expected coolant load, all are not discussed here but could be to argue the exact location of these variables into the ideal valve grind.

Take them apart, clean them up, assemble them, lap a tiny bit if you must but let a knowledgeable valve grinding artist set you up with a good solid foundation...a valve grind!!!

All you really need to know is how to recognize good work, how to give the information properly to get what you want back.

[sc72]

Valve job

Thanks for taking the time to explain what a multi angle valve job is and what it does. It was a good read.