# valve lapping



## scooby (Nov 10, 2021)

Still working on putting together howell v4..  Valve cages are phosphor bronze, valves are stainless steel.

Made valves and seat cutter without changing compound rest angle so they both angles should match.

I have a few questions:

1) What compound should I use for lapping? I have really fine diamond paste (yellow&green), and some timesavers lapping compound.
2)Does the lapping compound need to be cleaned off the valve cages/valves after lapping?
3)What is the procedure for lapping valves? Do them by hand, half turn cw, half turn ccw, lift off seat, rotate, then repeat?

Please keep answers simple cuz I'm stupid.. 

Thanks


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## kf2qd (Nov 10, 2021)

Lapping compound is an abrasive, and if left in place will migrate and cause all kinds of wear. As small as those valves are you want to use some very fine compound.


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## Brian Rupnow (Nov 10, 2021)

I machine my valve seats to have a total included angle of 90 degrees. I machine the valves to have an included angle of 92 degrees. That means that I get a line contact between the valve and it's seat at the top part of the valve seat. I use 600 grit aluminum oxide lapping paste, and after coating the contact surface of the valve I pull the stem of the valve with hand pressure against the seat and spin it back and forth between my finger and thumb. I generally spin it back and forth about ten times, then releasing pressure I turn the valve about 45 degrees and repeat the back and forth spin under pressure another ten times. I go thru that routine about ten times. Then I remove the valve, and scrub the surface with liquid dish detergent under a running tap of warm water. I clean any remaining grit from the valve seat with a cotton q-tip. My valves are turned from cold rolled steel. My valve seats are brass.


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## David Shealey (Nov 11, 2021)

I was taught, decades ago, that one should NEVER lap valves to correct ANY misalignment! I have only used fine lapping compound lightly to insure the seating is even. never to remove any appreciable material.   The reason I was taught this is that if you use lapping to correct bad seating, then when the exhaust valve head gets hot and expands, then it will seat on the tiny amount of unlapped area, and that on the inside of the valve seating area, exposing the cold seating area to the exhaust gas and promote seat burning.


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## bluejets (Nov 12, 2021)

Many times on small engines a wack with a hammer and a brass drift is enough, forget the lapping.


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## simonbirt (Nov 12, 2021)

bluejets said:


> Many times on small engines a wack with a hammer and a brass drift is enough, forget the lapping.


Interesting, this is the way we seat balls in non return valves. 

I found that the valve seal on my Farm Boy was much better after its first run- same principal I imagine.


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## Steamchick (Nov 12, 2021)

Fundamentals: Proper machining and grinding are processes that remove metal to get "the perfect shape" we need.
LAPPING the surface (as described by Brian) is removing he "peeks of machining" from the  metal - thus improving the surface finish of the MACHINED surface.... You cannot LAP a surface to be "in a better place" - and using a coarse grinding paste under a valve to try and correct an "OUT-of-TRUE" seat will never work properly. You will get an "Uncontrolled" and "Worn" seat that isn't good from an Engineering perspective, even if you can get it to seat "well enough" for running.
It is a BODGE - by innocent amateur mechanics who have not been taught the "proper way" to get a narrow, controlled circular seat that will be wear resistant (due to the nature of the material surfaces and precision of mating concentric to the axis of the valve), good for heat transfer (cooling of the valve) and good from day 1 (Already correctly made so does NOT need the seat to be "run-in").
The WHOLE aim of "good manufacture" is GOOD MANUFACTURE.
Enough rant... Shoot me if you disagree... (It is Human Frailty that causes the masses to rise up and destroy knowledge, or for the "Top Bullies" to keep knowledge from the masses... KNOWLEDGE IS POWER! - Let's use it wisely.).
K2


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## simonbirt (Nov 12, 2021)

Steamchick said:


> Fundamentals: Proper machining and grinding are processes that remove metal to get "the perfect shape" we need.
> LAPPING the surface (as described by Brian) is removing he "peeks of machining" from the  metal - thus improving the surface finish of the MACHINED surface.... You cannot LAP a surface to be "in a better place" - and using a coarse grinding paste under a valve to try and correct an "OUT-of-TRUE" seat will never work properly. You will get an "Uncontrolled" and "Worn" seat that isn't good from an Engineering perspective, even if you can get it to seat "well enough" for running.
> It is a BODGE - by innocent amateur mechanics who have not been taught the "proper way" to get a narrow, controlled circular seat that will be wear resistant (due to the nature of the material surfaces and precision of mating concentric to the axis of the valve), good for heat transfer (cooling of the valve) and good from day 1 (Already correctly made so does NOT need the seat to be "run-in").
> The WHOLE aim of "good manufacture" is GOOD MANUFACTURE.
> ...


Having revisited this, I wonder if what is actually happening when things improve after a run is the valve stem is bedding in, thus allowing the valve to fully close. I found when testing on my Farm boy that just pulling the valve stem made for better compression. It is now very good and will hold compression for a minute or more.


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## Steamchick (Nov 12, 2021)

I suggest that the valves should be lapped so they properly seal "as new" . I have never done tiny valves on models, so only speak from my apprenticeship (over 50 years ago) and motorcycle and car engine "hobby" work since then. All valves are lapped so no petrol leaks when the intake or exhaust port is filled - and any leakage checked on the combustion chamber side after 5 to 15 minutes.
When cutting seats on "refurbished" cylinder heads, we had 2 angles of cutter or grindstone, 45 plus/minus 1/2 degrees. Seats were cut to have an equal width of each, then when the 45 degree valve was lapped you always got a fine line of lapped-polished surface. About 20 to 40 thou width was good. Lapped surfaces were checked/examined by eye with a jewellers loupe.
Perhaps models are simply too small to have the double- angled seat cutting process? Brian's post above is the best advice.
If your valves don't seat perfectly as new, but settle down after a short run, then I suggest the surface is a bit rough and able to be smoothed by running. Valves do 2 things. They hammer seats, and they rate and wear the seats truly circular.
Lucky you for holding pre sure as well as you say.
Enjoy modelling!
K2


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## kwoodhands (Nov 12, 2021)

scooby said:


> Still working on putting together howell v4..  Valve cages are phosphor bronze, valves are stainless steel.
> 
> Made valves and seat cutter without changing compound rest angle so they both angles should match.
> 
> ...


I use tooth paste as a lapping compound. Do not know how it compares to manufactered  lapping compounds.  
I clean the tooth paste off completely whenthe lapping is done.
mike


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## Brian Rupnow (Nov 12, 2021)

The engines I build all require at least "some" compression to start and run. I find that if I can get the valves close enough that they mostly seal, the engine will start. Once the engine starts and runs for 10 or 15 minutes there is a remarkable rise in compression. I use cold rolled steel to make my valves and brass for my valve cages. My theory is that once the engine runs, the steel valves will actually "form" the softer brass seats until they seal tightly.


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## Steamchick (Nov 13, 2021)

Brian, I think that there may be 2 elements to increasing compression, piston blow-by the main reason, with a much lesser degree of valve seat leaks. But the brass and steel combination will have some bedding-in, by "hammer" if the springs do not keep the valve train "connected" so the cams lower valves onto seats. But that will be noisy! And some bedding-in of valves takes place as gases "clean the surfaces", and when they rotate. Are your valves "petrol tight" when assembled? - If so I expect "no blow-by compression loss" through the valves.


simonbirt said:


> Interesting, this is the way we seat balls in non return valves.


I have just assembled 2 hand water-pumps: I.E. 4 non-return valves. Sealed perfectly WITHOUT the application of the hammer on the balls. But I only tested 1 on a boiler - steam test at 42psi... The other is for hydraulic testing and exceeds 100 psi against a bit of rubber held against the end of the outlet pipe. Couldn't do that with leaking balls!
On my boilers, I used to tried the "hammer" method, as explained in a book on valves, but found a bit of precise machining of the seat worked every time with new balls...
I recognise forging as a process with its proper place, but IMHO not for seating poppet valves. - And for those who say "that is what happens in service when valves close" - I retort that with correct and cleverly designed cam profiles for durability, the valve will be lowered onto the seat by the cam-action, so "hammer" stresses are very small: just the difference between the speed the cam allows the valve to be travelling at just before the tappet clearance opens. Otherwise engines would be incredibly noisy, and would not last very long at all!
The problem I have with the hammer, is that if the valve is anything less than perfect any "out-of-perfect" shape will be impressed upon the seat, so the seat will not work well when the valve rotates in service (as it must). Whereas the "precisely made" circles of valve and seat made on your excellent and expensive machines will allow for rotation of the circular face of the valve to retain a seal against the concentric and circular seat...
I wonder where the "engineering" and "Machinist" are with your unspecified hammers being used without calibrated arms and certified drifts? - IMHO... that is?
Oh, my "humble opinion" is based on working as an engine design Engineer in a car manufacturer... and I now call myself an "amateur" as I no longer practice professionally. I therefore cannot offer anything but advice based on the best of my expertise.
K2


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## rutzen (Nov 13, 2021)

I found that I couldn't get good compression on my Rumely until I re-machined the seats to a very narrow edge,  no more than a few thou.  I lightly lapped them in with metal polish.  The compression has improved a lot since I've done more running. Oh, and I chucked the valves in the 4 jaw independant with a dial gauge to get them running dead true to re- machine them.  The first try I used the 3 jaw and it just wasn't good enough.


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## Steamchick (Nov 13, 2021)

kwoodhands said:


> I use tooth paste as a lapping compound. Do not know how it compares to manufactered  lapping compounds.
> I clean the tooth paste off completely whenthe lapping is done.
> mike


Hi Mr Woodhands, Toothpaste is used by diamond polishers to polish those hard bits of rock, and they call it "jewellers' rouge". I understand it is a calcium mineral so it is about the same hardness and chemistry as tooth enamel, or marginally softer than the enamel so it doesn't wear it away. Yet softer materials will "lap" harder ones - like your steel valve parts - though I cannot explain "How". Though I advocate using proprietary lapping compound, as this is calibrated for grain size (relates to surface finish), and will lap valve seats much quicker than toothpaste. For a final finish, I have used metal polish - for brass or silver or aluminium or toothpaste. Yet with my limited expertise I cannot decide what is best... so the car gets just Lapping Compound, the motor bike a final "Brasso" polish after lapping. Model valves, being so small. probably appreciate the extra attention of toothpaste for that "gleam" when you smile when it runs...!

K2


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## propclock (Nov 13, 2021)

Just my experience , A very narrow seat width is the key for
not perfectly precise, not manufactured ,home made model engines.  I learned this the hard way. One of my earlier engines
was the Hoglett.  It has a cast iron head with no valve cages.
I cut with a miniature valve seat cutter , a 45 degree  face  .
how wide ? not sure but looked good by eye ~25-30 thou. 
The valves were made from solid in one chucking to maintain
concentricity.  Leaked like a sieve.  Or just simply A LOT !
I lapped with all the above suggestions. Of course the seat width
kept getting wider.  And the leakage kept getting worse.  WHAT?   If you used blueing  or magic marker  to check the seating ..... perfect.   I finally decided that the wide seat due to
physics beyond my comprehension, crop circles in the metal?
Was the culprit.  So I was forced to make 2 more valve seat cutters. As in automotive practice. a 30 and 60 degree cutter.
with the new very narrow  45 degree seat width. "presto" perfect!
Yea presto that was 2 days of work.  So now I leave valve seats
and valve cages as cut  as in 90 degrees  Sharp edges, a light lap or with tooth paste/ or   brasso or time saver  does the trick.
The wack method also works.  Just my 1.414 cents worth.
It has saved me a lot of time on the many engines to follow.
PS got my HMEM  stickers yesterday Yea!


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## Steamchick (Nov 14, 2021)

On "Wide versus Narrow seats". The Engineering is so simple that having learned it as a young-un, I believed everyone knew this: The pressure of the seal must be greater than the pressure of the fluid, for the seal to work. As you have a fixed spring on the valve, say 1lb. and a fixed area of seat - say 0.01 sq. in. the pressure it will seal is 1lb / 0.01sq.in. = 100psi. But if the seat is wider, - say an sealing area of 0.1sq.in. - then the pressure it can seal is 1lb / 0.1sq.in. = 10psi....
In other words, twice the width of seal is half the pressure it can take, or 10 times width of seal is 1/10th the pressure it can take.
I'll let you have a think about your valves and springs and then tell me that "poppet valves have pressure helping them seal"... 
OK It is a bit more complex, but your experience of "narrow seats sealing better" is the simple solution. And "proper Engineering" is that simple. Solving problems. Which is what you did to overcome your "crop-circles". (But you do need to use a bit of brain).
Enjoy!
K2


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## scooby (Nov 14, 2021)

I'm going to make my valve cages over again. 

The turned parts are made from the bar on right, which I got from speedy metals, it says its SAE 660 Bearing bronze on receipt.

The round stock on the left is from from McMaster-Carr. I had searched for phosphor bronze on their website and it showed me 544 bearing bronze (it also says in description that is also know as phosphor bronze)

My question is, is one better than the other for making the valve cages?


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## Steamchick (Nov 14, 2021)

544 hardness = Hb 85, but 660 hardness = Hb  65. (Not so hard).
544 is also higher tensile strength etc. So that should be better... Annealing temp. >900 deg. C. So should be OK for exhaust temperatures....
K2


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## stevehuckss396 (Nov 15, 2021)

Bronze of any kind will be fine. Most people use brass.


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## tornitore45 (Nov 18, 2021)

Another reason why wider seats do not work is that we are not dealing with perfect geometric surfaces. It gets easier to "find" a sneak-by path between to imperfect conical surface as the "contact" width increase.  There is more opportunity for the deviation from the ideal geometry to go in opposite directions and create a gap.
I have transitioned to no machining of the seat, too much risk of the tool to be misaligned, off center and cocked.
Leve it sharp and give it a light tap.


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## Bob Telep (Nov 18, 2021)

Steamchick said:


> On "Wide versus Narrow seats". The Engineering is so simple that having learned it as a young-un, I believed everyone knew this: The pressure of the seal must be greater than the pressure of the fluid, for the seal to work. As you have a fixed spring on the valve, say 1lb. and a fixed area of seat - say 0.01 sq. in. the pressure it will seal is 1lb / 0.01sq.in. = 100psi. But if the seat is wider, - say an sealing area of 0.1sq.in. - then the pressure it can seal is 1lb / 0.1sq.in. = 10psi....
> In other words, twice the width of seal is half the pressure it can take, or 10 times width of seal is 1/10th the pressure it can take.
> I'll let you have a think about your valves and springs and then tell me that "poppet valves have pressure helping them seal"...
> OK It is a bit more complex, but your experience of "narrow seats sealing better" is the simple solution. And "proper Engineering" is that simple. Solving problems. Which is what you did to overcome your "crop-circles". (But you do need to use a bit of brain).
> ...


That is not quite correct.  You are confusing the area of the seating surface with the area based on the valve diameter.  Let's say you have a poppet valve 1.00 inch in diameter at the seat (neglect the width of the seat for a moment.  This yields an area of 0.785 sq. in.  This is the effective area of the valve.  With the valve closed, the force on the valve due to pressure is F= P*A where A= 0.785.
It could be argued whether the effective area is calculated using the inner or outer diameter of the seat.  A "perfect" valve and seat contact would suggest the effective area be based on the inner seat diameter.  Since nothing is "perfect", the effective area would be based more toward the outer seat diameter.
Of course the width of the seat does affect the unit pressure of the sealing surface, and narrow seats will have higher conformity and thus better sealing potential.


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## GreenTwin (Nov 18, 2021)

Reading this post is most confusing, but definitely thought provoking.
I hope to build a model IC engine one day, so I pay attent to things like valves and valve seats.

Steamchick seems to be saying that the pressure a valve can seal against is linearly proportional to the valve seat area.

Bob T seems to be discussing the force generated on the valve via pressure applied to the top of it?

Steamchick mentions pressure as a function of the valve spring.

I am not sure we are all comparing apples to apples, at least it is not clear to my feeble mind.

We do know that an intake valve with a light spring, such as the non-actuated ones typically found on hit-and-miss engines, will lift off its seat on the intake stroke, and be sealed to its seat upon the compression stroke.
The force on the seat, and the pressure from below that the valve can seal against, is related to the pressure being exerted on the top of the valve, regardess of valve seat diameter, ie: it is an upper pressure vs lower pressure thing, or the differential pressure between the internal cylinder pressure and atmospheric pressure.

The valve spring is intended to assist the valve to the seated position, not generate the force required to seal the valve (for an IC engine).
For a safety valve on an air tank, the converse is true; the spring on the safety valve determines the pressure at which the safety valve will open.

The exhaust valve springs on hit-and-miss engines are many times stronger than the intake spring, and the exhaust valve is forced open via the cam/pushrod/rocker.
The force exerted on the exhaust valve by the spring is for the purpose of quickly closing the valve, and preventing any valve bounce (I think).
Again, the exhaust valve spring is not sealing the valve on the seat nearly as much as the pressure from above the valve.

No doubt if there were no pressure above the valve, then the spring force would dictate how much pressure the valve could retain, which I think is what steamchick is saying.
But the dictating forces in an IC engine are from internal cylinder pressures; valve springs just act to close the valves after they open.

This is all purely hypothetical, and not based on anything other than what just popped out of my head, but this would seem to be logical.

.


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## GreenTwin (Nov 18, 2021)

I have seen people seat a ball valve on the seat using the method mentioned, which was tapping it with a hammer.
I don't have any experience with IC valves, other than lapping lawnmower valves that get pitted and burned.

I think the key for the "tapping with hammer" thing to work is that the valve and seat are very close to being exactly round and concentric.
A valve or seat that is not concentric would only seal in the position where it was tapped with the hammer, and if/when the valve rotated, it would no longer seal.

When I have lapped lawnmower valves, they tend to become oblong I guess due to heat/distortion, and you can see where the compound begins to cut on about 1/2 the valve surface before gradually spreading to the entire valve surface as the lapping process progresses.

Lapping using the method that Brian Rupnow mentioned is the way I have always done it, using progressively less coarse compound grit.
If the valve and seat (lawnmower) has only light pitting, I start with 600 grit compound.

It may also be true that a light hammer tap will align the valve with the seat.
I have not built any IC engines yet, so I have much to learn and verify.

.


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## Steamchick (Nov 19, 2021)

Bob Telep said:


> That is not quite correct.  You are confusing the area of the seating surface with the area based on the valve diameter.  Let's say you have a poppet valve 1.00 inch in diameter at the seat (neglect the width of the seat for a moment.  This yields an area of 0.785 sq. in.  This is the effective area of the valve.  With the valve closed, the force on the valve due to pressure is F= P*A where A= 0.785.
> It could be argued whether the effective area is calculated using the inner or outer diameter of the seat.  A "perfect" valve and seat contact would suggest the effective area be based on the inner seat diameter.  Since nothing is "perfect", the effective area would be based more toward the outer seat diameter.
> Of course the width of the seat does affect the unit *pressure of the sealing surface* _(This is what I am talking about - K2)_ and narrow seats will have higher conformity and thus better sealing potential. - _Correct_.


And here's where I disagree, being pretty sure I am not confused. The force applied to the _sealing surface_, divided by the _Area of the contact face sealing surface_ becomes the "EFFECTIVE PRESSURE WITHIN THE SEALING SURFACE".  This must exceed the fluid pressure - otherwise molecules of fluid will pass the seal. Initially, the pressure on a poppet valve is only derived from the spring pressure, but this does increase as the fluid pressure on the "whole effective area" acts on the valve, as you explain, but unless the initial seal is formed by the spring force and valve-face to seat-face geometry, the valve will leak. Having designed equipment that had to be "hermetically sealed" and having re-designed elastomeric seals that initially proved inadequate, I had to "learn the rules" - professionally.   
I apologise if my explanation was mis-leading. I was trying to explain why larger width of lapped surface of the valve seats always leads to leakage of the valve. Oft misunderstood by seemingly "clever mechanics" who think a wider seat (lapped surface) will seal better (I have met many!). There is also a correct comment about conical misalignment - which is a root cause of leakage when valve stems and valve guides wear.
As you explained
Green twin is correct : "
"the key for the "tapping with hammer" thing to work is that the valve and seat are very close to being exactly round and concentric.
A valve or seat that is not concentric would only seal in the position where it was tapped with the hammer, and if/when the valve rotated, it would no longer seal. " - which is why I do not advocate "hitting" poppet valves in any circumstances. Any mis-alignment is likely to lead to distortion of the relationship of valve head to stem alignment. This means that when the valve turns (as it will) the valve will then naturally become mis-aligned and of course will then leak.
Of course, there are always 2 limits in design, Max and Min. We have considered "minimum seat pressure" - ergo "maximum seat area" but the materials and temperatures involved also affect the "minimum seat area", as a seat that is "too narrow" (in the case of both the poppet valve and the pressure vessel safety relief valve) will naturally deform as the yield point of the "weakest" material is exceeded, to become large enough to withstand the maximum forces on the sealing surface (forces derived from the closure spring plus pressure differential upon the valve head). (This is clearly seen when a valve acts upon an elastomeric seal in compression - the elastomer can take up a set due to material creepage with time and pressure. I saw this on equipment after many years of service where elastomeric face-seals were well distorted to the point of leaking, as a result of compression set. But that was a complex problem that needed re-designing.).
Enough said. (Most models are made, and happen to work without the engineering needed for "sustainable and profitable industry").
K2


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## scooby (Nov 19, 2021)

I got the valve cages made, the ends are at 90 degrees..





I then put a valve in a cage, held the end of the valve in a collet, then by hand held the cage and spun it against the valve back and forth a few times, lifted cage away from valve, rotated, then repeated a few times. I didn't  put any lapping compound on it but it did make a small bevel 





If I tested valve this way with a mighty-vac, what amount of time for it to go from 30inHg to no vacuum is decent?





I made a way to test it with putting air pressure through  spark plug, but that was with cages I had build before, and they were loctited in the head already. I want to test them before they get loctited. That's why I figured I'd test it with the mighty-vac


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## scooby (Nov 19, 2021)

I think testing it with the mighty-vac this way won't work, because if I pull the valve away from the cage, it still very slowly loses vacuum, because the small hole the valve slides in provides somewhat of a seal.


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## Steamchick (Nov 20, 2021)

Pressure decay takes a lot of calibration to get right. (from what I learned in industry). The simplest procedure (not "best?", just something you can maybe do "at home?) is a simple calibrator: Using a needle valve (fuel valve from an Aircraft model shop, that normally fits into a 2-stroke aero engine intake - or something?). Take the valve "fully closed" and monitor pressure decay from pump "ON" => vacuum valve closed time to plus 30 seconds  - or 5 mins - or whatever interval suits so you get  (say) 20% vacuum pressure drop: Then repeat the check, just cracking the needle valve to admit air so instead you get (say) 40~50% vacuum pressure drop. Then you can say "you have a leaker!".  That gives you 2 conditions that define an OK and No Good condition for your testing. - I was taught by the guy that commisioned many Helium-leak-test stations for various car parts, and pressure-decay testers.
Pressure decay wasn't perfect though, but fast and effective for production, where less than 6 failures per million parts were allowed. But it needed daily/shiftly calibration against the OK and NG parts, "to be sure to be sure". (The parts held after 1 calibration until the next calibration was confirmed OK - it is an OK "end" calibration check that proves the batch OK for shipping, not the "start" calibration check.). 
OR: Assemble the valve into the valve seat body, held by the spring, and introduce a drop of petrol, or other thin fuel, into the valve body so you can see if any fluid leaks past the valve. Just don't smoke while doing this one! You can assemble parts, then black with a candle flame before testing with fuel. The carbon dust shows-up the fuel leak a bit easier than "shiny metal"... Talc may work as well... But extinguish the candle before opening the fuel can! An "eye dropper" or pipette can aid putting a drop of fuel into the valve body...
It works well for car engine poppet valves... 
I have lots of "stupid ideas"... just tell me what works and what doesn't!
K2


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## minh-thanh (Nov 20, 2021)

Simple trick to check valve and seat that I learned from my father a long time ago (I learned a lot of knowledge about engines, mechanics.. from my father, for me he is a master)
  Make sure valve and seat are clean.  .Hold  the valve in the seat by hand or spring, pour a little kerosene or similar liquid or water into the IN or EX, . After about 10 seconds, look at the valve and seat contacts (Or use paper towels to wipe them) : if they are dry that's good enough
 Or another way: put a little kerosene on the contact, and use compressed air about 1 bar to blow into the IN and EX, if there are no air bubbles in the contact, the valve and seat are fine.
  I usually check the valve and seat this way and they are always fine
  I did it both ways: Lapping valve with seat, and closed the valve to the seat with hammer
But for me, the Lapping valve with seat is always the first choice !


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## scooby (Nov 20, 2021)

Would this stuff be good to use for lapping and is 320 grit ok?


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## Bob Telep (Nov 20, 2021)

Steamchick said:


> And here's where I disagree, being pretty sure I am not confused. The force applied to the _sealing surface_, divided by the _Area of the contact face sealing surface_ becomes the "EFFECTIVE PRESSURE WITHIN THE SEALING SURFACE".  This must exceed the fluid pressure - otherwise molecules of fluid will pass the seal. Initially, the pressure on a poppet valve is only derived from the spring pressure, but this does increase as the fluid pressure on the "whole effective area" acts on the valve, as you explain, but unless the initial seal is formed by the spring force and valve-face to seat-face geometry, the valve will leak. Having designed equipment that had to be "hermetically sealed" and having re-designed elastomeric seals that initially proved inadequate, I had to "learn the rules" - professionally.
> I apologise if my explanation was mis-leading. I was trying to explain why larger width of lapped surface of the valve seats always leads to leakage of the valve. Oft misunderstood by seemingly "clever mechanics" who think a wider seat (lapped surface) will seal better (I have met many!). There is also a correct comment about conical misalignment - which is a root cause of leakage when valve stems and valve guides wear.
> As you explained
> Green twin is correct : "
> ...


Thank you for the response.  We are in agreement that a narrower seat will tend to seal better, but not for the same reasons.  Given all else the same, if the form of the valve & seat contact surface are 'perfect' ie  zero geometry deviation, 100% contact, smooth surface, etc., a narrow and wide seat width will both seal equally.  Since nothing is 'perfect', the narrower seat will tend to have a smaller leak area, plus the higher unit loading will provide additional conformity.
I mean no disrespect on your many years of practical experience.  I think we will just have to agree to disagree.


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## f2dantonio (Nov 20, 2021)

kwoodhands said:


> I use tooth paste as a lapping compound. Do not know how it compares to manufactered  lapping compounds.
> I clean the tooth paste off completely whenthe lapping is done.
> mike


I was using tooth past too for lapping pistons and liners,crazy amount of work,but great finish and not harmful  after even little cleaning...


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## kuhncw (Nov 20, 2021)

Scooby,  what leakdown times did you measure with your Mighty Vac?  

Chuck


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## scooby (Nov 20, 2021)

with valve closed against valve cage, around 5 min..
with valve pulled away from cage around 2.5 min..

The rate at which it leaks seems to be more at the start (more vacuum), and slows down as it goes towards normal air pressure


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## kuhncw (Nov 20, 2021)

It looks to me like your valves seal very well.


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## scooby (Nov 20, 2021)

so to get the loctited cages that are in the head now (green loctite), I have a heat gun and a propane torch, which to use to heat it up before I try and press the old cages out?

After I get new cages installed, I can perform pressure test by putting air through spark plug hole and listen for leaks, any thoughts on how much psi I should put to it?


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## GreenTwin (Nov 20, 2021)

scooby said:


> Would this stuff be good to use for lapping and is 320 grit ok?
> View attachment 131154


300 seems a little coarse, but as I mentioned, I have not built a model IC engine yet.
I have only done valve work on lawnmower engines.
I guess the proof is in the pudding though, and if you tried the 320 grit, and it worked well, then no need to find 600 grit.

Brian Rupnow had problems with his valves seating until he got some 600 grit lapping compound.

Does anyone have any data on the life of narrow vs wide valve seats?
Seems like a narrow valve seat would be prone to wear, since the force would be concentrated in a much smaller area on the seat?
Maybe it is a non-issue on a model IC engine.

There must be a sweet spot for valve seat size.
I guess the height of the top of the valve dictates the seat size?
A taller valve top could have a longer face at 45 degrees or whatever angle is used.

.


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## kuhncw (Nov 20, 2021)

scooby said:


> so to get the loctited cages that are in the head now (green loctite), I have a heat gun and a propane torch, which to use to heat it up before I try and press the old cages out?
> 
> After I get new cages installed, I can perform pressure test by putting air through spark plug hole and listen for leaks, any thoughts on how much psi I should put to it?



Scooby,

I recently removed Loctited valve cages from an aluminum cylinder head by making a punch that fit the ID of the cage.  I heated the end of the punch to a dull red, then used the punch to transfer heat to the cage and press the guide out.  

As to pressure testing your valves, 50 psi should be good.  A cheap stethoscope with the sensor removed is handy for finding leaks. 

Chuck


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## Brian Rupnow (Nov 20, 2021)

Here's a little more to add to the mix. In automobiles, the only way valves are able to get rid of some of the heat of combustion is direct contact thermal transfer. This essentially means that automobile engines need contact over a wider area between valves and  the valve seats to shed heat. For our small engines heat is not nearly as large a problem, so an almost "line contact" between the valve and the valve seat is acceptable.


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## scooby (Nov 20, 2021)

I made this to press it out, pin will keep things centered, and the ID slips over top of valve cage and od is small enough to go through hole in the head






I was gonna use the lathe tailstock to press it out


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## Steamchick (Nov 21, 2021)

Scooby, You need to chemically degrade the loctite to relase the parts. Use a bit of a bar of household soap to mark some lines on the aluminium cylinder head,: these will tur black when the cylinder head is hot enough - and to avoid overheating anything - and the loctite should have been adequately burned to non-bonding chemicals. Either hot air gun or flames are OK.... differential expansion (of course) will affect the fit of parts so a press to dismantle is safer than a hammer! (I use my 4" engineers' vice, as it is a screw-press in application). But make suitable supports for cylinder head and pins for the valve seats.
K2


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## scooby (Nov 21, 2021)

so if I understand correctly your saying rub soap on the head? Do I focus heat on the head around the cage, on cage, or both?


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## Steamchick (Nov 21, 2021)

Yes, the fat in the soap will char with the alkali..... at somewhere around 200 to 250C. (I think!). This is above the char temperature for the loctite. Just warm the whole job, not any specific zone.... (I reckon. You'll soon tell me if I am wrong!). As I don't have your head and valve seats I can't try it for you..... hot air gun should be fine....
Take care whatever you do.
K2


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## scooby (Nov 21, 2021)

1 down, 7 to go...


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## Alec Ryals (Nov 21, 2021)

Not supposed to lap valves use different angles like 44x45


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## scooby (Nov 22, 2021)

Tried using toothpaste, but I think I'm gonna try this:   McMaster-Carr
and then use toothpaste if needed.

When using toothpaste, how often do you do wipe off/clean from valve and put new toothpaste on it? After a couple minutes of lapping?


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## JohnBDownunder (Nov 22, 2021)

For what it's worth, here in OZ some of us use "Gumption cleaner". It's a mildly abrasive household cleaner that rinses out / off with water. 
To be fair, some use various grits of lapping compound be it a diamond or carborundum grit.
Personally, I use the Gumption cos I'm cheap and it's in the laundry cupboard. Probably replenish it a bit less frequently than toothpaste and it works for me.
John B


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## minh-thanh (Nov 23, 2021)

Hi  scooby !
The first  : make sure the valve and seat are "relatively "concentric
Use a grit size of about 600, 800... this depends on the surface of the seat and valve when you do it. The time for this lapping is also more or less depending on the surface. For me, this step only has the effect of "shaping the contact surface" of the valve and seat . So it doesn't take much time and, again it depends on the surface
 If, when the above step is completed,   lapping valve and seat  with a size smaller  : 1800 or 2000 or ... . Just these 2 steps are enough
 If the valve and seat have very few leaks, use toothpaste
 The above steps do not need to change the material used for lapping often, just change it when it "feels" like it is no longer effective. With toothpaste, only change it when it starts to change color
A question : is this your first   IC engine ?


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## David Shealey (Nov 23, 2021)

Steamchick said:


> Yes, the fat in the soap will char with the alkali..... at somewhere around 200 to 250C. (I think!). This is above the char temperature for the loctite. Just warm the whole job, not any specific zone.... (I reckon. You'll soon tell me if I am wrong!). As I don't have your head and valve seats I can't try it for you..... hot air gun should be fine....
> Take care whatever you do.
> K2


You do not need to "char" Loctite to seperate parts.  Loctite will soften (it is a polymer), and make it easier to separate parts at a much lower temp.  I have removed many parts, bearings, bushings, screws and nuts, by heating just enough for the Loctite to soften and make removal easy.  Never to a point where anything would char.


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## scooby (Nov 23, 2021)

I've done some other of Jerry Howell's engines. Beamer stirling, Bill 1906, and Powerhouse. I've spent much more time working on the v4 then the others and want to make sure I get everything right instead of dealing the the disappointment of a non-starting engine. I get much more enjoyment out of making things rather than putting things together. Give me a blueprint dimensioned correctly, and I'm happy.

My heads were dirty so the soap will help clean them anyway


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## scooby (Nov 23, 2021)

How do you quote someone and and put it in your reply? I tried clicking on the persons quote, and wrote in the box on the bottom, and nothing shows up when I post


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## minh-thanh (Nov 23, 2021)

First: "quote"
Then " insert quote "
 After :




And. : 
You can delete some  in " quote "


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## scooby (Nov 23, 2021)

minh-thanh said:


> First: "quote"
> Then " insert quote "
> After :
> View attachment 131251
> ...


This is only a test..


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## scooby (Nov 23, 2021)

damn I just got the 600 grit delivered, Got the 12 oz jar instead of 2 oz jar by mistake


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## scooby (Nov 23, 2021)

Tomorrow I'll have some of the higher grit lapping compounds (2oz this time)

Right now the ends of the valve cages are 90 degrees (bored the inside of them and when pulling out of hole used same boring bar to face end of it)

Do I use the valve seat cutter I made and do a couple hand turns to get a small bevel on the cages and then apply the lapping compound to the valve?

Or do I NOT use valve seat cutter and just use lapping compound on it? (I tried this on a test pieces and I get a line of contact on valve)





I've been using isopropyl alcohol with a q-tip to wipe off the lapping compound to clean the cages and valves. Should I be using liquid dish soap like mentioned before to clean this compound off or can I just use the isopropyl alcohol or mineral spirits to clean the compound off?

I really do appreciate all the help you have all provided me


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## minh-thanh (Nov 23, 2021)

Hi !





						Ford 300 Inline Six
					

The model's rocker cover is pretty similar to the drawn steel original but was machined from a block of 6061 aluminum. A significant difference between them is the original cover attached to the head with seven hex bolts around its perimeter, while the model's cover will be held down with three...




					www.homemodelenginemachinist.com


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## Steamchick (Nov 24, 2021)

I should use spirit initially, then soap and water. An ultrasonic cleaner ($20) is cheap and effective to clean these things well with a drop of detergent in the water bath. Uten 600ml Ultrasonic Cleaner Timer Jewellery Coins Cleaning Machine With Basket  | eBay
K2


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## scooby (Nov 24, 2021)

minh-thanh said:


> Hi !
> 
> 
> 
> ...


If drawing calls for a .015 seat, is that .015 dimensioned at A, or at B?









Steamchick said:


> I should use spirit initially, then soap and water. An ultrasonic cleaner ($20) is cheap and effective to clean these things well with a drop of detergent in the water bath. Uten 600ml Ultrasonic Cleaner Timer Jewellery Coins Cleaning Machine With Basket  | eBay
> K2


When using an ultrasonic cleaner, do you  clean parts every time you change grit size, and how long do you keep in the ultrasonic cleaner for?


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## Steamchick (Nov 24, 2021)

4 mins Ultrasonic is OK. Every time you change grit.


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## scooby (Nov 24, 2021)

Previously I had not cut seat in cage, just put 600grit lapping compound on valve and lapped. This made a single line of contact on the valve.
I re-cut the 45 deg on test valve to get a fresh surface. Then used valve seat cutter to make small bevel on test valve cage (still don't know if A or B is right from previous post). I put on the 600grit lapping compound and moved valve back and forth against cage about 10 times, lifted off, rotated and repeated a few times. That made a line of contact like the first time, but thicker. Are the lines of contact supposed to be noticeable on the valve after lapping, or is the 600 grit too course to start off with


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## Brian Rupnow (Nov 24, 2021)

600 grit will leave a visible contact ring completely around the valve face. Using toothpaste for lapping might work if you live long enough. --The "grit" in toothpaste is about 2000 ---Fine for teeth, rather useless for steel.


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## scooby (Nov 24, 2021)

I was gonna work my way up from 600 to 2000


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## TonyM (Nov 25, 2021)

If concentricity is ensured by the machining process with a decent surface finish then grinding is a waste of time and effort.  The seat and the bore are machined from the same end without removing from the chuck and the seat and stem are machined without removing from the chuck. I have only found it necessary to lap valves on old(full size) engines where the seat or the valve has been replaced or re-cut or where there is some pitting.


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## minh-thanh (Nov 25, 2021)

scooby said:


> If drawing calls for a .015 seat, is that .015 dimensioned at A, or at B?
> View attachment 131276


the word "seat" or "valve seat": it says it all !


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## scooby (Nov 25, 2021)

ok I'm going to loctite new valve cages in and re drill intake/exhaust paths. Will test with pressure through spark plug hole like before.


TonyM said:


> If concentricity is ensured by the machining process with a decent surface finish then grinding is a waste of time and effort.  The seat and the bore are machined from the same end without removing from the chuck and the seat and stem are machined without removing from the chuck. I have only found it necessary to lap valves on old(full size) engines where the seat or the valve has been replaced or re-cut or where there is some pitting.



Happy Thanksgiving to you all


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## Steamchick (Nov 25, 2021)

The intention of lapping valves is not to make an eccentric valve align with the seat, but to improve the surface finish of the machined surfaces. If the machined surfaces are a fine finish and high degree of concentricity, then the seat will be perfect as machined. But when grind - stones are mounted on a mandril to grind the seats in industrial applications the ground surface is too coarse and needs lapping to get a finer surface finish. My opinion is that 1000 grit is OK, but that is only because that is the finest grit I have...
My Moto Guzzi workshop manual gives seats machined at 89 degrees internal angle and valves at 90 degrees internal angle, then intersection of the 2 cones is lapped to 0.5 ~ 1mm wide. But that is on valves 28 ~ 30mm diameter.
Hope this is of some use?
K2


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## RobConway (Feb 11, 2022)

Hi,   What did you end up doing @scooby ,   Valve seat cutter or valve and compound grind on a square cut seat.

Im glad i read your post as i was amazed I  could hold vacuum when the valve was off its seat (using my brake bleed pump) same as you.


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## scooby (Feb 12, 2022)

RobConway said:


> Hi,   What did you end up doing @scooby ,   Valve seat cutter or valve and compound grind on a square cut seat.
> 
> Im glad i read your post as i was amazed I  could hold vacuum when the valve was off its seat (using my brake bleed pump) same as you.



I used valve seat cutter and made a very small seat, haven't lapped them yet. The plan is to lap with the highest grit lapping compound I got, put in ultrasonic cleaner, then test with pressure using thing I made.


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## RobConway (Feb 12, 2022)

Thanks,   For now think i will re-make and install the valve cage without seat as i wont to move on to the inlet manifold and need the valve cage in place.    Later ill make the cutter and do some testing before cutting the seats.


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## scooby (Feb 12, 2022)

I made the valves first, then without moving lathe compound, turned the seat cutter so the angles will match


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## Alec Ryals (Feb 12, 2022)

scooby said:


> I used valve seat cutter and made a very small seat, haven't lapped them yet. The plan is to lap with the highest grit lapping compound I got, put in ultrasonic cleaner, then test with pressure using thing I made.


Lapping is not necessary if the valve seats and valves are done correctly


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## Steamchick (Feb 13, 2022)

Hi Alec, fair comment, except to get those perfect mating cones takes a bit more expertise than some amateurs can achieve. Moi aussi!
Engineer's blue proves the surfaces before and after lapping.
E.g. Slip gauges stick together because of perfect surfaces, but I can't file that well to create such.
K2


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## simonbirt (Feb 13, 2022)

On the Seal that I am building at the moment the valve guides are shown with a sharp edge and a 45 deg valve face, Haven’t made them yet, so unable to comment on how well they will seal ( very confusing sealing things on a Seal). I imagine than when lapped there will be a very narrow seat. The valves are only 3/16’ diameter or there abouts.


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## scooby (Feb 13, 2022)

The reason I am going to lightly lap is to get a better surface finish and thus perhaps a better seal. It seals right now, but not as much as I think it should


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## RobConway (Feb 13, 2022)

I assume if we can achieve good concentricity and a reasonable seat now,  the running-in process beds in the seats after the first few runs ?


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## minh-thanh (Feb 14, 2022)

scooby said:


> The reason I am going to lightly lap is to get a better surface finish and thus perhaps a better seal. It seals right now, but not as much as I think it should


 
My way :
Use a magnifying glass to see the surface of the valve and seat
   At the position of the valve and seat contact circle : No more scratches or similar caused by machining
   Even a very small scratch or blemish will affect the sealing
Lapping with large grit size until No more scratches or similar caused by machining, then lapping with small grit to perfect the surface.


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## Steamchick (Feb 14, 2022)

Keep the seats narrow. Check with Engineers' blue that you have full contact of the valve on the seat. Don't lap, unless the Blue shows a gap.
K2


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## minh-thanh (Feb 14, 2022)

Steamchick said:


> Don't lap, unless the Blue shows a gap.
> K2


 
If the surface machining of the valve and the valve seat is perfect - it depends on the machine, the tool.....
   That is not possible for me. I try to make the surface of the valve and seat the best I can but they are not completely sealed
I lapping them because I need them sealed -* really sealed*
  I don't like : "They get more sealed when the engine is running"
    Of course this is how I usually do it
If I could machine the valve and seat well enough to seal, I wouldn't need lapping


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## gbritnell (Feb 15, 2022)

OK here's the straight information! First let's compare a couple of things. If you do a valve job on a full size engine with proper tooling that's rigid and accurate then you most likely will get a good seal right from the start, but not always. So let's say you have (just for comparison sake) a .001 gap on a 2 inch diameter valve. Not good but not bad in numerical terms. Now let's say that you are building a miniature engine with adequate tooling  and you end up with a .001 gap on a .375 diameter valve/seat. That's a huge leak! I have built my share of  I.C. engines and I'm here to tell you that the times I have had a perfect seal right off of the machine is maybe 3 out of 16 on a v-8 engine. That's not to say that they can't be sealed with a little lapping but there is no comparison between full size automotive valve machining and model engines. When machining valve seats in a head or block  I never cut them on the mill, too much chance for error between concentricity  and angularity.  Going back to automotive practice I use the valve guide as my alignment guide for cutting the final seat. I make a cutter with a pilot  shift that fits the valve guide snuggly (a couple of tenths) and turn it by hand to cut a seat which is generally no more than .025 wide depending on the size of the valve/seat. Even with this I usually have to lap a touch to get a perfect seal. To check the seal I make a tapered tube which I wring into the port so I can use my vacuum gauge on. I also put grease around the valve/guide area so that no vacuum is pulled past the valve stem.
I will say that lapping can't and won't make up for poor machining but with model engines it's almost a necessity!


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## Bentwings (Feb 15, 2022)

minh-thanh said:


> My way :
> Use a magnifying glass to see the surface of the valve and seat
> At the position of the valve and seat contact circle : No more scratches or similar caused by machining
> Even a very small scratch or blemish will affect the sealing
> Lapping with large grit size until No more scratches or similar caused by machining, then lapping with small grit to perfect the surface.


Traditional valve lapping compound always seemed coarse to me. Ibyhinknitbbreaks down as you use it. I marked the valve seat area with blue dykem then lapped the valves to show the seat area. I used magnifying glass too. You could se scratches but they were more like something you would see using fine wet or dry paper it gets better as you use it . We had the palm stick as well as a crank thing usually the little seal surface was nearly polished . We then put the springs on and  poured a little alcohol or acetone in if it didn’t leak all was good.   Since it was a back and forth motion there were no directional fibers. Even after a hard nitro run the seats were highly polished or burned. Aluminum heads had very hard seats but still polished nicely


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## minh-thanh (Feb 16, 2022)

Bentwings said:


> You could se scratches but they were more like something you would see using fine wet or dry paper



Yes , you are correct . The surface of the valve and my seat are similar
  But I'm talking about scratches....caused by machining 

  The lapping valve and seat can be fast or slow, just one time or many times depending on the surface of the valve and seat when machining - of course concentricity is necessary.
  (concentricity between valve and seat on my engines: I don't know how precise it is but it can be called enough)
   With me, most of the leaks between the valve and the seat (between the needle and the nozzles in a diesel engine) are from scratches or the like due to surface machining - Lapping is my best choice


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## Bentwings (Feb 16, 2022)

minh-thanh said:


> Yes , you are correct . The surface of the valve and my seat are similar
> But I'm talking about scratches....caused by machining
> 
> The lapping valve and seat can be fast or slow, just one time or many times depending on the surface of the valve and seat when machining - of course concentricity is necessary.
> ...


Almost all of my valve machining was don on with valve grinding equipment valves were easily regroups or checked for concentricity just by chucking them in the grinder seats were done with seat grinder and variety of stone wheels there were various grits available. I turned a few valve in the lathe but not many . Most automotive valve finishing today is done with special cutters in a milling machine or dedicated machine lapping is a final finishing process just to get the very best seal . Valves go everywhere but straight when they get hot . Spring pressures are so high today it’s a wonder there are not more dropped valves .


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