Topic: Valve lapping leak test - alternate method

[Lavis500]

So I've been looking for the appropriate length of time for the valve lapping leak test.  I've let it sit with kerosene in the ports with a fresh, clean shop towel folded underneath the head, and it will hold for about 5 maybe 10 minutes.  After that you can see a small drop forming.  Is 5-10 minutes fine?

I also found this: 

HOW TO Check Valves for Proper Seating on OHV Engines

Is this actually an acceptable method of testing?  I suppose it makes sense, but want a few opinions before I do this and button it all up.  I'd rather ask too many questions than put it all together and miss something.

[dave500]

that fella is optimistic hoping the valve will pound its way into seating,im surprised he didnt belt it with a hammer to seat it,sheeezz,bent valve head or warped seat,try inverting the head and filling the combustion chambers to check leakage,should be zero leak,a leak like he showed will only get worse with running as the hot combustion pressure "blow torches"its way across the sealing area.

[Lavis500]

In the comments on the video somebody asked why he didn't keep lapping the valves.  The star of the video said that he did lap the valves again afterward and the valves had a good seat after that.


FWIW I did the light test and I get no light, but I suppose that means nothing to the Old Timers here on the forum?

[dave500]

he also said it went out to another shop to have the seats cut?and thats how it was returned? shame,shame shame!

[Lavis500]

So if I'm understanding you, it shouldn't matter how long I leave it sit?  It shouldn't leak after 5 minutes or 5 hours?

[dave500]

correct.

[MCRider]

that fella is optimistic hoping the valve will pound its way into seating,im surprised he didnt belt it with a hammer to seat it,sheeezz,bent valve head or warped seat,try inverting the head and filling the combustion chambers to check leakage,should be zero leak,a leak like he showed will only get worse with running as the hot combustion pressure "blow torches"its way across the sealing area.

yup. I've always filled the ports with solvent, rather than the combustion chamber. A little easier perhaps to see the drip in the chamber, if there's a leak. And I'd agree. Should be no leak regardless of time.

[Lavis500]

**le sigh**  Oh well.  I'll be spending all of tomorrow lapping valves, too.   There are worse things I could be doing, I suppose.

Of course, it doesn't help that engineer's blue is seemingly impossible to find around here.  I've heard of making lines with pencil and checking for a smear, but I'm not so sure that it sounds as accurate of a method as the real stuff.  Of course my wife (who has a boatload of art supplies) has all of Prussian blue packed up at her parents' house...   

[Lavis500]

yup. I've always filled the ports with solvent, rather than the combustion chamber. A little easier perhaps to see the drip in the chamber, if there's a leak. And I'd agree. Should be no leak regardless of time.

This method appealed to me because I could put the shop towel beneath the head and see the leakage right there.  Also I could see where around the valve it was leaking.

[dave500]

try some thick graphite pencil?the valves must be tight,the graphite might give you an idea,apply firm pressure as you do it,dont forget horspower is lost even through weak valve springs with good seats,and those "weak" valve springs are impossible to compress between your thumb and forefingers with two hands.

[Bodi]

A magic marker works like machinist's blue. The solvent in grinding compound dissolves it but if you put a really thin coating of fine compound on the valve and mark the seat, a quick turn of the valve will show the contact ring. Same for the valve, in reverse. Using a spot of paste made from Comet and water will do the same without dissolving the marker ink.

[MRieck]

That exhaust seat looks like crap and the valve is sunk as deep as the Titanic. Awful work.

[Lavis500]

I want to say that when I took these valves off my head a year ago that I measured the free length against the specs in the book, but I don't honestly remember.  Let's face it:  I've slept since then.     Will measuring their free length to see if that is in spec to the factory manual tell me if they are good?  Or is spring strength only able to be tested with the loading reference they provide?  How does one go about testing that?

[Lavis500]

Well, the seats pass the sharpie/fine grinding compound test.  However, they still don't hold kerosene.  I guess this means I have weak springs.   Here I was hoping I'd be able to finish her this weekend.  I guess I'll have to pack up the old girl without finishing her and leave the country without hearing her roar.  I don't have the time to wait on new springs to come in...  **sigh**