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DIY Guru
96 Ranger-stock
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Discussion Starter #1
How to lap a valve

The subject head is a Chevy LT1
The procedure will be the same for any cylinder head.

First thing to do is remove the Valve locks, retainers and springs.
Second is to clean the valves of carbon, oil and deposits.
I prefer the valve face to be ground to remove all pitting to insure a good valve to seat seal.
Most machine shops will grind the valve for a dollar or two.

The tools needed will be a lapping tool and valve lapping compound.
There are different brands, grits and bases. Even colors.
I use permatex water base fine grit. Grey in color.



Place a fair amount on your finger tip.



Then bead it around the valve face.


Next is slide the valve back down the guide and seat the valve.



Once the valve has made contact with the seat, stick the lapping tool onto the valve and spin the tool back and forth with both hands. You will feel and hear the valve grinding compound “crunching”. At random intervals lift the valve up so more compound will work down on to the seat. Appox.10-15 seconds.


Remove the valve and wipe clean and inspect the valve face, It should have a gray, or whatever color your compound is, line all the way around the face. IF not the valve is bent and should be replaced.

Next wipe the seat in the head clean, and look to see the same line around the seat, If you see areas on the seat that are not the color of the lapping compound, Load the valve again and lap some more till you have a perfect color line all the way around.

If you lap several times and the seat line does not come in, the head is severely warped and the seats are distorted, The head should go to a machine shop to be fully checked and have a valve job preformed If you have a good solid line around the seat, then clean all traces of the lapping compound from the valve and head and reassemble the valvetrain..
 

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If you don't mind, could you explain (in full or partial detail) what, why, and when to lap valves?

Not so much for me but for anyone reading. Plus your threads are like sitting in a classroom for a lesson lol.

As a matter o factly it would be great to do that for all your threads.
 

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DIY Guru
96 Ranger-stock
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637 Posts
Discussion Starter #3
If you don't mind, could you explain (in full or partial detail) what, why, and when to lap valves?

Not so much for me but for anyone reading. Plus your threads are like sitting in a classroom for a lesson lol.

As a matter o factly it would be great to do that for all your threads.
Lapping a valve boils down to one basic reason, checking valve to seat contact.

Reasons you do this vary, could be checking for a warped or bent valve, a distorted seat, checking the seat width, or cleaning carbon off the valve seat.

Anything that will keep the valve from fully seating and sealing.



I started doing these years ago to help inform the new guys, I always get questions on how this is done or how that is done, also what to look for in your local shop and what to avoid.

The big thing being belt surfacers.

Are there better ways or just other ways some of the things I write about done? Yes, but these are the ways I learned and do daily and have little to no issues with.
 

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To enlighten myself and my other comrades. Would you need to lap the valves after a valve job has been preformed? ive heard both arguments. I would like to hear your take on the subject.
 

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97 honda coupe
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To enlighten myself and my other comrades. Would you need to lap the valves after a valve job has been preformed? ive heard both arguments. I would like to hear your take on the subject.
Whenever i cut my valves i put a light smear of lapping compound on my valve and lightly rotated it. Reason i did that was to make sure that the contact point was in the correct location on the valve face and seat. This was of course after using the Prussian blue and everything looked good.

Usually though i could just lightly slap the valve in a couple times as long as the face of the valve was a fresh cut and get a good idea where the cut was at on the face of the valve, and adjust it from there.
 

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96 Ranger-stock
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Discussion Starter #6
To enlighten myself and my other comrades. Would you need to lap the valves after a valve job has been preformed? ive heard both arguments. I would like to hear your take on the subject.
That is a solid question, and no really steadfast answer.

It boils down to what equipment is used to do the valve job and the care the machinist takes when doing the work.

Now with the old school Souix or black & Decker stone grinders, along with the newen seat cutter sets, yes I would say it is almost mandatory that the valves be lapped in.

This is due to to wear on the stone, and just how hard the powder metal/sinter metal seats are in aluminium heads.

Both of these style seat grinders were designed for the cast iron head with flame hardened seats.

Stone seat grinders need constant dressing of the stone angle, every set oer two to rid the stone of grooves cut into it by the seat. ( search ebay, Valve stone)

Now when you have a good head shop, T&S, Serdi, DCM among others, they run a 3 angle carbide cutter. (search ebay, serdi cutter/blade)

It cuts much more accurate, seat width is the same from seat to seat, seat run out is minimal.

No matched with a good valve grinding machine, I prefer a dual 3 ball chuck set up (Kwik-way SVS2) Lapping is is almost nill. the only real time it is done, and not really every valve gets it, is if a burr is left on the seat form build up on the blade.

Another decent cutter is the "Mira" cutter, commonly found with the Petterson DCM head shops. this is still a 3 angle cutter, but the blades are about 3 to 4 times as much as a serdi style blade.
 

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So what I usually do is attach a silicone vac line to a power drill and use that to pull the valve into the seat to lap it. I don't run the drill very fast and do reverse the direction. My thoughts are the pressure pulling the valve using the vacuum (or any other type of correct ID line) line from the seal side is more consistent and even than using the sucker stick on the other side.

Like so (you don't see the reversal in this video): Thoughts?

https://www.youtube.com/watch?v=g5dc_JTvQUA
 

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DIY Guru
96 Ranger-stock
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Discussion Starter #8
If you have to lap a valve for more than 5-10 seconds, to get the line to come in, something is off and the valve need ground or replaced, or the seat is distorted and needs cut.

If the seat to valve contact is too wide the valve cools to fast and you get deposit build up, too narrow and the valve gets too hot and it will burn thu.

Either method works, I have done both, I prefer the spin stick.
The valve will have the same amount of "wobble" due to guide clearance. You can tighten that up by applying a touch of wheel bearing grease to the valve stem before pushing it thu the guide.

The vid is set to private.
 

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97 honda coupe
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7,611 Posts
So what I usually do is attach a silicone vac line to a power drill and use that to pull the valve into the seat to lap it. I don't run the drill very fast and do reverse the direction. My thoughts are the pressure pulling the valve using the vacuum (or any other type of correct ID line) line from the seal side is more consistent and even than using the sucker stick on the other side.

Like so (you don't see the reversal in this video): Thoughts?

https://www.youtube.com/watch?v=g5dc_JTvQUA
If i had room like on d-series heads i would just clamp down on to the valve stems with the power drill jaws and let the valve barely seat and run the drill at 1/3 speed. This is a good idea though for valve stems that are recessed, ill have to use that next time.
 

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Would you need to lap the valves after a valve job has been preformed?
I was going to ask the exact same question; but it appears the answer was received. I've always personally left the lapping up to heads without newly cut valve seats or a new valve job. But I guess there can be arguments for either side.
 

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96 Ranger-stock
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Discussion Starter #12
Good vid.

If you think of the seat as a funnel, the valve is going to ride where it is going to ride unless the guide is so wore out it is like throwing a hot dog down a hallway.

The 45* seat angle is going to force the valve centered.
 

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Sometimes I'll use a sharpie to draw lines evenly spaced around the valves on the seating surface. When they are gone evenly, you're done. I have used the drill and tubing method but I prefer the stick, you can actually feel what you are doing.
 

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I use that permatex fine grit aswell and it doesnt leave a glossy/polished smooth finish, it looks dull almost, is this no problem?

Mind you this is the only grit I have used, but Ive never had a damaged head or a head that needed excessive grinding, just a few seconds on the drill each valve to be sure the contact surfaces match and make a perfect contact ring, is the surface finish of the sealing area such a big deal or is this one grit fine enough?
 

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96 Ranger-stock
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Discussion Starter #15
I have tried a few other grits over the years and still come back to it. as long as the valve seals all is well.
 
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