Matt Harwood

Valve lapping

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I'm working on a Ford flathead and pulled the aftermarket aluminum heads to replace them with original aluminum heads. As long as I'm in there, I'm wondering if I should lap the valves. I don't know how many miles the engine has on it, but it's been rebuilt at some point as it has been bored .030 oversize already. I've been doing some reading about valve lapping and while there are some schools of thought that suggest that it's good to improve sealing, there are others that say it doesn't do anything but check the quality of the valve job before the engine is assembled.

 

Any thoughts? Tips? Hints? I don't care a whole lot about the engine, but I do care about doing any job right and as long as I have the thing apart I figure I may as well do it right and practice a skill that I might need in the future.

 

What do you think? Lap the valves?

Edited by Matt Harwood (see edit history)

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I check the seats and valves to see if they both have a clean, even-width contact ring. If they do, lapping isn't needed. If the contact ring gets narrow, or darker in some areas, I lap (or grind, then lap) to bring them back to an even, clean contact ring.

 

Paul

Edited by PFitz (see edit history)
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What do the chambers look like ?

How many miles since she's been opened up ?

You going to wire brush the top of the block ?

Might as well while you are in there.

Any cylinders running rich / lean ?

You can use "blue die marker' on the valves and give them a spin to see the width of the seal.

 

Got pictures ?

 

Mike in Colorado

 

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Well back in the day, if I had access to the valves, I lapped them. Period.

 

Why? Because if a valve leaks a little it isn't making contact with the seat. Contact with the seat, and the water jacket below is what cools the valve. If it doesn't cool between firings, it might burn. If it burns, the engine isn't going to stop missing and shaking until it has a valve job.

 

Less than perfect valves can be "lapped in", despite what some folks may think. The contact area will be too wide, but that is better than the alternative.

 

Bad rings can be lived with, with some mechanical sympathy and attention to the OIL. The engine probably won't even run noticeably different, unless you are checking with a stopwatch. Bad valves make a bad car that no amount of tuning will help or even improve.

 

Edited by Bloo (see edit history)
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4 hours ago, Matt Harwood said:

I've been doing some reading about valve lapping and while there are some schools of thought that suggest that it's good to improve sealing, there are others that say it doesn't do anything but check the quality of the valve job before the engine is assembled.

 

Actually, both are true. A tiny bit of lapping with light compound on a fresh valve job before assembly should make a thin even line around the valve and seat, out in the middle of the newly ground surface, and NOT right at the top or bottom.

 

On the other hand, if one is "cleaning up" an old valve job, because the engine is apart, or just replacing one burned valve, it is quite telling that Clover Compound used to come in a double-sided can with coarse grit in one side and fine in the other.

 

If it didn't clean up instantly with fine grit, then one would go to coarse grit and grind until there is a nice gray line around both the valve face and the seat, and then switch to fine to smooth it up. The line will be too wide, but if it is still out in the middle of the valve face it will be fine. If it is way up on top, it is time for a new valve.

 

There is a particular action you use with a lapping stick. You do not just go round and round. Go back and forth a bunch of times, lift, turn a few degrees, back down, back and forth a bunch more times. Repeat until the line goes around all the way on both the face and the seat, and until there are no pits that will allow gas to escape under or over your newly lapped seat. There will be pits. The location is what matters. You have to wipe all the compound off in order to see your progress, because the compound is the same shade of gray as the line you are trying to make.

 

adtin186a.jpg

 

Edited by Bloo (see edit history)
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I did this just today, motorcycle only four valves. I like doing it. After the valve setup is apart this doesn't take long and, as said above, gives you a good look at the condition of things. One old book I read once said you're listening to the "tone" of the lapping. It's a satisfying task.

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Are the valves adjustable?

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3 hours ago, DonMicheletti said:

Working on the valves of a Ford V8 flathead is a giant PITA if it is as original

Well, there is that..........

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4 hours ago, DonMicheletti said:

Working on the valves of a Ford V8 flathead is a giant PITA if it is as original

Aftermarket adjustable lifters are an excellent investment!  Cad flatheads' stems pose the same trim-the-valve-stem issue in a valve grind, and there was a factory tool (J-1055?) that was no more than a T-shaped piece whose elngth was that of a collapsed hydraulic lifter.  Before that tool was reproduced, I used two inside mics, one set at X (length of collapsed lifter) + 0.030 and another at X+0.070, for the pump-up range.

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Hello Mark,

 

As others have said I would look to see if the valves are seating evenly and have enough seating width. Lapping works great but only if its done correctly.

As you no doubt know there are a lot of vehicles out there that have been poorly lapped causing more problems than it cures.

 

Here is one of the new valves for my Wisconsin showing one of the lapped valves and width of the seating area. In this case

the valves were new but I had to lightly dress the seats using an old valve seat grinder setup and pilot which worked great.

With the seats its critical to dress the stone to the correct angle often and go very lightly!

 

Then I lightly.... again lightly.... lapped each valve by hand using just the bare minimum of lapping compound. The problem

is when people use too much compound and or lap too much or try to use lapping to fox a bad seat. When your lapping the

compound tends to thin out near the outer edge and seat of the valve and its very easy to end-up with a concave seat and or valve.

 

A little bit of layout blue and a few seconds twirling the valve will tell you what the seating area looks like.

 

 

847080403_photo1(5)a.jpg.1e0fd59c888943d6d8405d25de6aac24.jpg

Edited by Terry Harper (see edit history)
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I also have used a red or black magic marker, painted both the valve and seat, put the valve in and turned it back and forth about a quarter turn with light pressure. Then removed the valve and looked at the shiny area of contact. Be carful with the lapping compound, any not thoroughly cleaned out will cause excessive wear if it gets into the wrong area.

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