Why do you lap in valves

paulkish

Premium User
I always thought valve seat was either right or wrong and non destructive bluing was used to check how they seat. I don't understand wearing out a valve to see if it seats ok?
 

jake17j

Member
you are insuring that the valve and seat are true thru the entire mating surface. look at it as more of a fine polish instead wearing of the parts
 
Every valve/valve seat is a tad different. You never just throw a valve inside a motor that was in another motor. You want to make sure there is not one bit of air leakage inside the motor itself. You will loose compression and a loss in compression means a loss in power.
 

Gillem

New member
Interesting question. Some seat cutting machine tool mfg will tell you not to lap i.e. Serdi. Some engine builders, not necessarily kart engine builders, can see flow numbers change between lapped and not lapped valves. Just food for thought.
 

paulkish

Premium User
edit:

Thanks for the replies. Some go one direction and some go the other. When ever that happens it means there's more discussion needed to settle it or to learn exactly why one way and why the other.
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I was curious about what kind of responses I would get from the question.

In general when we check out an engine shop were thinking about having work done and we see valve lapping compound where they do heads, we won't take them any valve work.

I thought if a valve seats right it's right and lapping is not needed. I see using bluing or a sharpie pen on valve and seat to see if it's correct and where they meet on the valve and seat, but you never lap valves in. I thought all lapping valves does is cause them pre mature wear. Is what I wrote why some would not recommend it? I agree it's not needed if the valve seats ok.

I use to be pretty good at doing a stepped valve job. But it's been so long ago I don't remember any angles and don't remember how to run a machine to do it. I taught how to do it and it was a pride thing to be able to have it perfect. Now what they do is horrible. Just throw them in an automated machine and grind the heck out of them. Heck the customer doesn't know any better and only expects a few servicing's, before they can get additional bucks out of them. Same with boring, nobody wants to take the time even if you want to pay for their time, just hog it out and make more later sooner.

and... as usual I'm not saying what I said is correct, it's what I remember which is often flawed. ... :(
 

Freezeman

Premium User
Well Paul I think you are flawed and incorrect. You say ''Now what they do is horrible" and "nobody wants to take the time even if you want to pay for their time"
You speak as if you have used or seen all the people that do this type of work and have come to the conclusion that all of them are just out to make money while not providing a quality product.
In General, if you are always experiencing bad customer service you might consider that you may just be a bad customer.
 

paulkish

Premium User
"In General, if you are always experiencing bad customer service you might consider that you may just be a bad customer."

Good Point.
 

PD Power

New member
edit:

Thanks for the replies. Some go one direction and some go the other. When ever that happens it means there's more discussion needed to settle it or to learn exactly why one way and why the other.
_______________


I was curious about what kind of responses I would get from the question.

In general when we check out an engine shop were thinking about having work done and we see valve lapping compound where they do heads, we won't take them any valve work.

I thought if a valve seats right it's right and lapping is not needed. I see using bluing or a sharpie pen on valve and seat to see if it's correct and where they meet on the valve and seat, but you never lap valves in. I thought all lapping valves does is cause them pre mature wear. Is what I wrote why some would not recommend it? I agree it's not needed if the valve seats ok.

I use to be pretty good at doing a stepped valve job. But it's been so long ago I don't remember any angles and don't remember how to run a machine to do it. I taught how to do it and it was a pride thing to be able to have it perfect. Now what they do is horrible. Just throw them in an automated machine and grind the heck out of them. Heck the customer doesn't know any better and only expects a few servicing's, before they can get additional bucks out of them. Same with boring, nobody wants to take the time even if you want to pay for their time, just hog it out and make more later sooner.

and... as usual I'm not saying what I said is correct, it's what I remember which is often flawed. ... :(
Easy PK......
Tlhere are still guys around who know how to do valve jobs.
What you want is a sealed valve, and don't worry how they got there.

I do not invite people into my shop area for that exact reason.
Not in the business of giving lessons....just sealing valves nice and tight.
Of course....that is just one of many critical procedures in/on the head.
 

paulkish

Premium User
"What you want is a sealed valve, and don't worry how they got there."

Thanks Paul, I don't know what else to say, what you said is just a good way to explain it.



... but though I think your correct... there's no way I'll repeat it to my son. He'll reply. "That's total bull .... , It's either right, wrong or shoe maker job.".
 

flattop1

Dawg 89
I would say most lap valves because they do not have either valve grinding and or seat cutting/ grinding equipment.
In a flathead specificly , a home mechanic is installing new valves in an experienced block. they also use a compound which is very coarse for similar reasons. After purchasing a neway seat cutter I was amazed at the time and effort I wasted doing it old school.
 

CarlsonMotorsports

Premium User
I think it makes a difference with what equipment you are using as well.
A Serdi VGS machine is considerably more accurate than the Neway kit. It's also what, 100 times the cost?
I see guys using worn stones in a Sioux style valve seat grinder and you end up with seats with grooves. = NOT GOOD.
I've seen plenty cut improperly with carbide cutters as well. = NOT GOOD.
Now, if you take the time to "lap" the valves with fine lapping compound after you have ground/cut the seats and valves, you will get a better finish (and better flow.)

Another thing to consider is the valve seat material. (ie Beryllium Copper seats cut very easily with carbide cutters and can most certainly leave a lip/edge if not extremely careful to reduce pressure when finishing.)

I'll absolutely agree with your son though Paul, in that if it's done right, it's right = no need for lapping. With that said, I'm guessing that most kart engine builders (Briggs) have less than high dollar equipment for cutting valves and seats and certainly less experience than your professional (big) race engine shops at doing valve work. As long as they are checking/lapping with a very fine grit compound, I see no harm in it and can actually be beneficial to a less than perfect cut/grind job.

Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cuts
www.CarlsonMotorsports.com
765-339-4407
bcarlson@CarlsonMotorsports.com
 
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