To lap or not to lap

Hi,

at risk of sparking a storm here, I will be grinding seats and installing new valves and guides. I typically grind as speced in the manual. Who here then laps them versus leaves em be? I have heard both ways.

Bill
 
I don't have grinding equipment, so I send the heads and valves out for grinding.

They don't get the springs and retainers. I put them on after getting the heads back.

I do lap. That makes the contact area visible. I can see if the grind was done properly, check the stem clearance, put the seals on, and not have to guess if everything was done right.
 
It is like this,if you buy a $20,000.00 Big block they lap the valves, so I do too.
 
That is something the machine shop should do.

I can mike the valve stems, if bad I will send new valves with the head when it goes in.

If the guides are obviously bad, I specify they replace them. Otherwise I request they be checked, and replaced before the seats are ground.
 

Lapping is a hangover from the bad old days. Where the mechanic did not have access to proper valve and seat grinding equipment . They made do with a stick, suction cup and some abrasive compound.
 
"Lapping is a hangover from the bad old days."

Well, apparently NOT, guess some guys still second guess the results of the machine shop services they paid BIG bucks for and want to make things better!

Who are we to judge?
 
I would lap any valves. No matter how well they are machined you could put brand new valves in a brand new engine and would still benefit from laping them. It's simple to test the valves if they really need it or not. Take a sharpie and mark the seat on both surfaces and spin them as though you were laping them and see if there is uniform wear on the marks.
 
I use lapping compound to clearly mark the new seat so I can see exactly where it is and if it needs to be narrowed. For that purpose it works great, just as Prussian Blue is used to check mesh-pattern on hypoid gears when setting them up.
 
(quoted from post at 21:20:10 01/26/18)
Lapping is a hangover from the bad old days. Where the mechanic did not have access to proper valve and seat grinding equipment . They made do with a stick, suction cup and some abrasive compound.

Not really. In the old days you would "freshen up" an engine by lapping the valves and re-ringing the pistons. No grinding was ever involved.
 
In response to the guys that put dye on seats and go to the trouble to mark up, take the fresh ground valve and snap it into the seat, it will leave a nice mark on the valve so you can test the margins. No need to go to any additional trouble. I always grind new valves, find that they are sometimes off a little from setting.
 

I always lap the valves I grind...I've noticed that my favored machine shop I send heads to lightly lap the valves on their cylinder head overhauls too. I thought that it was standard procedure!
 
Using lapping compound clearly marks the new seat and will show imperfections, if they exist, that you sometimes cannot see
without. Just takes a little extra effort.
 
(quoted from post at 22:38:25 01/27/18) Using lapping compound clearly marks the new seat and will show imperfections, if they exist, that you sometimes cannot see
without. Just takes a little extra effort.

So does Prussian Blue, or a simple series of pencil marks, WITHOUT adding NASTY grit!

NOT sure why you would expect to see "imperfections" in a valve or seat ground with decent equipment by a reasonably skilled operator... can you go into more detail as to why "imperfections" might exist, JDEM?
 
Yes, pits in the seat. Very common in older equipment. Especially with induction-hardened seats (no inserts). If you have
not seen such a thing, then I assume you have not done a lot of valve-machine work on older blocks or heads.

Also the case of being able to accurately see a seat in case is needs narrowing. As to using Prussian Blue instead? I
already mentioned using it instead. So obviously I agree.
 
(quoted from post at 10:08:13 01/27/18)
(quoted from post at 21:20:10 01/26/18)
Lapping is a hangover from the bad old days. Where the mechanic did not have access to proper valve and seat grinding equipment . They made do with a stick, suction cup and some abrasive compound.

Not really. In the old days you would "freshen up" an engine by lapping the valves and re-ringing the pistons. No grinding was ever involved.
I thought that is what I said ?
 
You can see pits in the seats with a good light and eyes, give the valve a good snap down, it will leave a mark in the valve so you can see the margins.

No need for any dye or other stuff.

I hate grit and extra work.
 
. A few pits here and there on the valve seats or cylinder walls never did any harm . As long as the vast majority of the of remaing surface was true .
 
when i was in class many years ago in the seventies... we were taught that the interferance angle , a difference of one degree between valve face and valve seat was for faster valve seating . no need to lap valves. that is basically an obsolete procedure. never have seen or done valve lapping on a properly done valve job. the valve face is marked with a marker then snapped into the seat. this will show exactly where the seat is positioned on the valve. do you know how many hrs. you can stand there and spin the valve in the seat with compound and you wont see much for results. obsolete procedure. and no its not standard procedure.
also a new valve needs to be trued up on the face, just because its new dont mean it will seat good.
 
Obviously not "obsolete" if some people still do it. The question from the incipient post is not if it is necessary. Question is if anyone does it. I do. So do many others. I already stated why I do it. Just as a good marking compound. I find it works for me better then an ink pen or Prussian Blue.
 
I have New-Way cutters which do not require lapping due to the 46 degree angle but I lap to gauge where I'm at with the valve job.
 
I guess it depends what you were taught, back in 91 when I was at trade school they had us face valves with a cutter set, then cut the seats and lap them in to the head. The local "Good" machine shop that closed down after the owner retired would always lap the valves before they put things together to. I watched his guy do a head I was picking up that wasn't quite finished when I got there one day, It had new valves/guides fitted and the seats cut.

If I had a head apart here and the seats/faces looked a bit off with some pitting I'll give them the old paste and spin freshen up to if the customer won't spend big money on a rebuilt head on some old junk Belarus or something like that, as long as it starts those guys don't like spending money.
Regards Robert
 
I think lapping is like an insurance policy. It might not be needed but might sometime or other save the cost of a early tear down.
 
It depends on who your boss is. I was taught in 1955 in US Army Engine Rebuild school to never lap a valve. Then I started to work at a IH dealer in 1958 and boss says, we lap them in after refacing the seats. Later years, I just took it upon myself to quit lapping them. A interference angle and a good slap on of the valve on the seat to look for the mark, and so it goes.
 

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