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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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PostWhore, The AFDB is on a lil tight.
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thanks for the how tos I read them all. Do you have your own machine shop? or work for one?
 

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Just be advised that some engines specifically say to NOT hand lap the valves. I think the IDI diesel I'm currently building say to not lap the valves.

With the modern tools available for machine work now, I didn't think anyone still hand lapped valves anymore.

But still good information and thanks for posting this and the other "How To's". :thumbsup:
 

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Discussion Starter #5
@Splattered.. Yes I do own a machine shop, I have started posting "how to's" so people will be more informed on what is going on in the machine shops, and what equipment is being used.
NOT all machine shops are set up the same, some still use equipment that was made back in the 60's which will not do the best job on todays modern heads and blocks.

@1995 Coguar RX7... Thanks and your welcome!

@94 Daily Driven 4.6l.. That is a rare instance, but true.. But it dose make me wonder why they have it like that....
 

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Discussion Starter #7
I have not posted all that many, I have just started in the past few days. But as I do more I will be sure to post them here for you
 

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I lap every valve with very fine compound, its a good way to catch valves that are not cut perfectly straight (about 1 out of 100 even when brand new) I also caught it when I dropped a pilot and it bent ever so slightly.
 

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Discussion Starter #9
I seldom have to lap a valve, unless I am doing a performace valvejob and want to back cut the valves, or doing a "patch job" for a used car lot....

With the seat and Guide machine I use, and the valve grinder, I have not had issues with valve to seat seal, but to be sure I still vacuume check each cylinder, and as long as I achive 27 in of vac (or more) I have no problem letting it out the door.
 

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I have found the vacuum test only works good on thick stem valves. You only need the slightest amount of contact to seal via vacuum. The fine paste I use won't change the seal as the seats and valves are so hard, it only shows the contact pattern on both parts.
 

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Discussion Starter #11
nick, I will agree to a point, the small dia stem valves 4.5mm and such, the valve spring pressures can and will "pull" the valve head in to a false seat.

I did not metntion, I will vacuume check before I install the springs.

I use a TnS system 2000 head shop that is a didjial level with the 3 angle carbide inserts.
 

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Man, that brings back some memories...

I used to build motors for foreign cars and after a three angle cut I always lapped the valves by hand like that. I always looked to make sure the contact width was equal across all the intake and exhausts.

I haven't done a valve job like that in years though.
 

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I've only done the hand lapping a few times, but a friend of mine said he uses a cordless drill on the valve stem to spin the valve with compound on the seats. Anybody ever heard or done such a thing? I personally can't see why a valve would need quite that much "lapping"... lol
 

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Discussion Starter #14
@NetKeym... if they are that bad .. and need lapped that much, the seats should just be cut, and a full valvejob performed...

but yes, I have heard of people doing it like that....
 

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Can you post picks of a bad valve too?
 

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nice write up, im just wondering what you do about stem height issues? when you grind a valve you take off .003-.006 off of the valve and i dont know how much you take off the seat when lapping, but it could be more than you think?? on heads with no adjustable rockers it could be bad... just wondering how you measure and cut the valve stems?
 

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cool stuff BogusSVO, Im actually an engine machinist myself but dont spend a lot of time on heads as much as i do with the bottom end of the engines, the odd time i will cut a seat, grind a valve and check clearances and heights tho, again nice write up :cool:
 

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Discussion Starter #20
flatblack.... I used to do bottom ends, bore blocks , resize rods n such..But I ended up in the head departments most all the shops I worked at. I never much did like block work.
 
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