Valve Lap

[apogeecustom]

I'm not finding much in the way of searching, so I'll ask.
I see a lot of mention about valve lapping, and I can see by a Google search that it is meant to make sure the valve seats well against the casing.
I haven't seen much in the way of technique on this forum though. How far do I have to go with this? There is a nice video here http://vimeo.com/3209398 and I wonder if something like this would be OK to do. Looks easy enough

[Steve]

The method I have used is even quicker and easier than that hot glue trick. I took an allen-head cap screw and put a piece of rubber hose over it that was rather tight, and chucked it into my cordless drill. The hose only needs to extend far enough past the screw to ensure that the screw does not touch the valve. Put come compound on the valve or the seat, put the valve in place, press against the head with the hose. Use your finger to lift the valve off its seat a bit, then start the drill. Let it come down lightly on the compound and let it spin for a bit. Control the seating pressure with your finger on the stem.

I also found that it works well to put the head on a table saw for this procedure. You can just hang the head over the edge to get the outer valves, then extend the table a bit to hold the outer end and reach the inner valves up the middle. To help you visualize this, take a look at the first minute of my video that shows how to change valve seals. Of course, you will want to have the head turned the other side up to do the lapping.


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[chef1366]

Don't forget the clean up all the lapping compound.

[SqDancerLynn1]

It is very important to clean the compound off as Chef said. If you are going to use your table saw as a work bench, AT least put a piece of plywood over the top to protect it..

[Steve]

It is very important to clean the compound off as Chef said. If you are going to use your table saw as a work bench, AT least put a piece of plywood over the top to protect it..

If you look at my video, you will see that I used an old, folded-over beach towel.

That allows a 'droop' under the working area.

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[old_chopper]

Once more, make sure you get ALL the compound cleaned up. It is abrasive and loves to eat piston rings and cylinder walls! I bet it would also take a bite out of some bearings if given the chance. Did I mention cleaning up the compound? Make sure you do.

[Ponderosa]

Don't forget...

Make sure you have a good surface on both seat face and valve face. I do it the old fashoined way, have my old suction cup stick, less compound thrown.. Don't forget to get some blueing for checking your seat surface...

[sk843143]

valve lapping is not just to make the valve seal agenst the seat......
it is part of a prosses in cutting new seats and refaceing valves .....
after you cut the seats (takes some precision tools and special equitment)
then recut the face of the valve so that it has a 1 deg diference in angle to the seat example the valve face will be cut to a usualy 45 deg angle and the part of the seat that it will contact is usualy a 46 deg angle.
when you lap the valve are makeing shure that both the valve and the seat are concentric to eachother ........ (it doesnt take long to wear out that 1 deg interferance and then the surface that seals is roughly .030" wide )


if you lap in an old valve you are increasing that surface to say .040" this dosnt sound like much till you do the math ..... if you have a 100lb valve spring ...(just to make the math easy) and fig how much pressure is on the sealing surface (and therefor the sealing capasity of the valve ) taking a 1" valve the diff in surface pressure would be in the relm of 3422lbs (i just woke up so my math could be skewed but the princibles still aply)

in short if your not resurfacing both the valve and the seat then lapping does no good...... if your woried about valve seal then use a vacume pump ( small hand pump from auto store) seal the combustion area with the valves both exhaust and intake compleatly asymbled and see if you have any leeks if you dont dont worry about it .... if you do disasimble clean and recheck.......... hope this is was clear and understandable.......

[Ponderosa]

Knew it...

valve lapping is not just to make the valve seal agenst the seat......
it is part of a prosses in cutting new seats and refaceing valves .....
after you cut the seats (takes some precision tools and special equitment)
then recut the face of the valve so that it has a 1 deg diference in angle to the seat example the valve face will be cut to a usualy 45 deg angle and the part of the seat that it will contact is usualy a 46 deg angle.
when you lap the valve are makeing shure that both the valve and the seat are concentric to eachother ........ (it doesnt take long to wear out that 1 deg interferance and then the surface that seals is roughly .030" wide )


if you lap in an old valve you are increasing that surface to say .040" this dosnt sound like much till you do the math ..... if you have a 100lb valve spring ...(just to make the math easy) and fig how much pressure is on the sealing surface (and therefor the sealing capasity of the valve ) taking a 1" valve the diff in surface pressure would be in the relm of 3422lbs (i just woke up so my math could be skewed but the princibles still aply)

in short if your not resurfacing both the valve and the seat then lapping does no good...... if your woried about valve seal then use a vacume pump ( small hand pump from auto store) seal the combustion area with the valves both exhaust and intake compleatly asymbled and see if you have any leeks if you dont dont worry about it .... if you do disasimble clean and recheck.......... hope this is was clear and understandable.......

Knew someone would get to the tech here.. We used to grind both valve and seat, then lap, many different types of grind also, three angle, ect.. In the old car days we would use a the width of a match as a guide to measure seating area after lapped. Another way to check seal, is to assemble and fill each port with solvent, or a #1 Diesel, look for leaks.. But blueing the face and checking for contact usually does the trick.. Tip, a small amount of blueing goes a long way, you may find it in the darndest places after a typical job...LOL Had a friend who washed his hands before he went to the head, almost went to the doctor the next day thinking he had contracted some strange disease from his girlfriend.. His girlfriend had NO sense of humor once he figured out what it was....LOL

[Macmatic]

I'm sure there's an easier way to do this, I wish somebody would share it with me.

Quote from the video.

Here ya go! Don't use a magnet, use something like a popsicle stick or any non-magnetic pokey and use a dab of sticky grease on the outside of the keeper too. This sticks it to the...stick and you can just press it in place and side the stick away. Bearing grease seems to work fine for me.

I haven't done valve one on a bike yet but I've done probably a couple hundred on small engines and dozens on cars. Works like a charm and no fighting the magnet!

/\/\ac

[Calvin Blackmore]

I thought valve cutting with engine specific machine tools was the proper way to do a valve job on these bikes?

thought it made for a smoother surface and so on. less prone to wear better seating etc.

I meen the things do spin about do they not