Checking valve sealing after grinding

[Paul J.]

I had a valve job done on small valve '61 heads. Back in the '60s lapping after grinding was standard, however the machinist said nothing had to be done with the valves just put them in. A friend who has been racing for 50 years said lapping was part of "do it right" and to check them afterwards by putting solvent in the head and see if it leaked out after sitting overnight. After lapping them I put paint thinner in the combustion chamber, because I thought it would be the easiest way to check, with light weight springs installed, and it leaked very shortly out the ports. I installed the regular springs and put the thinner in the head and it leaked into the combustion chamber very shortly.
Should the valves seal better than this or is this normal? The archives show that there are different grades of valve grinding compound. Perhaps I need to go to a finer grade of grinding compound? My 30 year old jar of Balkamp #765-1524 compound does not specify a grit. In years past I have used this compound but just installed the heads as I never thought of testing them.
Any thoughts are appreciated. Thanks.

[David B.]

Re: Checking valve sealing after grinding

Paul,

I hand lap mine and then test with blue machinist's dye. Dye the valve seat portion, let it dry, then turn the valve lightly and check the pattern. Once you see a good seal all the way around, it is done. Then, it should hold liquid overnight. I use WD-40 for the test. A good seat will hold it overnight. Check the underside for leakage, not the combustion chamber side, as there will be some evaporation which should not be confused with leakage.

Dave

[Paul J.]

Checking valve sealing after grinding

Thanks for the info Dave. How long should it take to get a good seal doing it by hand? I show a 1/16" strip around the valve but evidently that does not mean it is enough grinding. Do you leave the compound on the valve so it can cut into the Dykem? Are you saying to put the liquid in the combustion chamber and look for liquid leakage on the stem end or put liquid on stem side and look for liquid leakage in combustion chamber? Does it really matter? It is easier to put the liquid in the combustion chamber and check ports for liquid. What force is required on the valve to seal it for the check? Is a large 1 1/4" socket be sufficient or would light weight(5# - 15#) springs be better?
Paul

[David B.]

Re: Checking valve sealing after grinding

Paul,

You're very welcome.

It should not take much lapping ( one or two iterations of lapping each valve) to get a good seal on newly ground valves and seats and you don't want to overdo it because it can affect the tolerances for the width of the contact sealing portion and for the valve edge. I use Permatex water mixed compound (part #34B). A nice thing about it (vs. oil based) is that you can add a few drops of water to it if needed if it gets old and dry, and it cleans up easily. It can be used on both hardened or regular seats, and it even works well with stainless steel valves. I use an old fashioned hand lapping tool - the kind you spin with your palms with the suction cups on the ends - nothing fancy. I think I have better control and feel with that than with a drill type tool.

For the dye checking, I coat the valve seat with dye and put a small diluted amount of compound on the valve. Then I turn the valve with some light pressure maybe 30 degrees or less back and forth just a couple times to remove the dye and create a pattern (ring) on the seat. When you pull the valve out, the seat should look clean all the way around on the contact ring area. If it doesn't, there is a part that is not sealing. Don't go all the way around with the valve with this test because it can give misleading results if you do. This is also a good time to measure the contact width in the pattern to make sure it is within specs for exhaust and intake. I can email you some pictures of what the dye pattern should look like if it may be helpful.

For the leak checking, I temporarily install the valve springs (without the seals), making sure that the compound has been thoroughly cleaned everywhere so it doesn't interfere with seating/sealing. Clean and blow out the valve guides and oil them before inserting the valves.

I keep the head upside down and level and put some WD-40 in the combustion chambers (no need to fill with much - just cover the entire valve shroud area). I like WD-40 because it doesn't evaporate very much and if it can't get through, I figure nothing else would. (I don't think you should test with light springs or weights.) Then look for leakage in the intake and exhaust runners. There should be no leakage. If it leaks, there are a number of things to check that I can follow up with you directly if needed.

Feel free to send me an email direct on any of this. I hope it seals well on the first try!

Dave

[Paul J.]

Checking valve sealing after grinding

Dave
I would appreciate the photo. I just finished lapping some more and the intakes leak within a minute and the exhausts were holding but I quit for the night so I will check them tomorrow. Therefore I would appreciate your input on the leak checks.
I will email you about this also.
Paul

[Mark #28455]

Still living in the stone age?

Problem number one - you just introduced a source of grit into your engine - make sure you clean it out well including the valve guides - any compound left behind will make the stems wear out much faster.

Problem number two - leaking liquid overnight has little bearing on a running engine. Your engine at 3000 RPM only has about 1/200 of a second per combustion stroke to actually leak anything. Like ring end gaps, it gets a lot of bench racing time but means little in a running engine.

Problem number three - the high end racing shops will use a dial indicator to verify valve seat concentricity with the valve stem, not load the engines with foreign substance.

Mark

[Paul J.]

Re: checking valve sealing after grinding

Good info Mark.

[David B.]

Re: Still living in the stone age? - Not Hardly!

Mark,

I disagree:

- the heads are obviously off the engine and they will be cleaned before assembly, so no foreign substance is being introduced into engine wear

- a good valve seal does matter - it's best to check/resolve any potential valve seal issues before the heads are installed

- dial indicators are used to measure guide tolerance and seat concentricity, they are not used to measure seat sealing and cannot be used to do so, they cannot provide assurance against a bent valve or warped valve head against leakage

While the majority of machine shop finished heads will function acceptably for normal use without checking, testing, or lapping, I wouldn't put a set of heads on that did not prove to seat/seal properly on the bench first. If you feel that is "stone age", you should let Voegelin ("Guide to Engine Blueprinting") and Monroe ("Engine Builder's Handbook")know. They need to know to eliminate that guidance from their books.

From The E/B Handbook, p.93: "If you want to be sure the valves seal before you run your engine, there's an easy way to do it. ... using Kerosene, fill each combustion chamber and let the head sit.. preferably overnight. If [it]empties, or is lower.. you know a valve leaked. You will have to redo that valve or seat. If you find a leaky valve, check with your engine machinist on remedying the problem." also "[Concerning Lapping] racers and specialists do it regularly as a check."

From Engine Blueprinting, p. 88: "[Valve lapping] will provide the best possible valve seal, and allow you to check the workmanship of your machinist."

And, I do measure and fit the end gap on my rings too. If you disagree on the importance of ring end gap and performance, you better tell GM to eliminate their specifications for it. They must need to brought out of the stone age as well.

Dave

[Greg L.]

Re: Still living in the stone age? - Not Hardly!

Here's my two cents....

I agree with Mark on all counts BUT, I use David's methods because I'm not a high end precision machine shop. My valve grinder and seat grinder is probably as old as the heads that I repair so I use the "valve grinding compound step" just to be sure...

I used to use the "leak down check" 20 some years ago for the heck of it on a few heads until my dad told me to stop wasting time... He was an old GM mechanic from the 60's and they never did that check...ever, on flat rate. I would "waste" lots of time re-lapping valves, trying to get the "weeping" valves(I used gas) to stop and this was with valves that had really nice lap patterns too! There was no real world or seat of the pants, what ever you want to call it, difference from the "leaky" valves to the "sealed" valves. Now I would tend to think that with todays modern equipment AND a skilled operator that you would be able to get a "perfect" seal as machined. You can be sure that new production engines don't get the blue dye test...

One thing that I can not over stress though is to make sure that ALL of the valve grinding compound is removed!!! I had one failure that I'm sure was due to some compound being left in a guide or on a stem because I had one guide out of 16 near perfect guides fail a few hundred miles after a valve job. It wore really bad, really quick and was all chewed to heck when I took it out.

My guess is that if you are truely getting a nice seat pattern then your valves will seat just fine once placed into service.

[Dick W.]

Re: Still living in the stone age? - Not Hardly!

Greg, I have done many heads and valves on a Sioux machine that I guarantee is older than I am. (and there are those of you that thought that the only thing older than me was dirt ) I found that if you keep your stones dressed, had a 1° interference fit, and took your time to do it right, the valves did not leak. Where you get into problems is with guides that are worn out and you cannot get your pilot as square as it needs to be, or with guides that are not clean. Take your time.

[David B.]

Re: Still living in the stone age? - Not Hardly!

Greg, Dick,

I agree with all of that. I too have a very old Sioux seat grinder, and a not so old valve grinder. I dress the stones carefully, and use a succession of grits, to end with nice surfaces. Also, I have a nice selection of .001"+, etc. oversized pilots for guides that are a little worn as Dick pointed out.

As for what happens after that...

If I were in the business of doing "flat rate" work (which I am not), it could reasonably be considered finished at that point. And, that is a generally acceptable industry standard, especially with the newer precision seat cutters now available in many machine shops. The valves will normally tend to seat fine with some wear in unless there is the unlikely event that there was such bad work that it distorts the valve head in doing so.

But, since I have the time, interest, and take enjoyment in work on my heads/engines, I do all I can to make sure it is best it can be, even if it might be considered a waste of time in a production shop. I think this is consistent with what Greg said, and it seemed like what Paul was looking to accomplish.

Different perspectives for different situations. Meanwhile, a lot of valve grinding compound does get sold every day,

Dave

[Mark #28455]

Do what you will

I spent some time in a shop that built high end BB engines - you know, 8000+ RPM toys - and you would be surprised at the amount of "lore" in engine building that has been shown not to matter! As for checking a valve for being bent, when refacing the valve use the dial indicator, it should be obvious. As for the grit in the engine, we used a sonic tank to clean the parts. At home I have to settle for a pressure washer - even after 30 mins of repeated scrubbing and sudsing, you would be surprised how much crap is still there! At the shop, they wouldn't even allow "scotch brite" in the door for just that reason.

Like I said, do what you want and be happy, but I don't think you have hit upon some great secret that has been "forgotten" as new technology comes into play. Consider ring end gaps for instance. Did you realize that a gap as large as 0.050" does not lose any significant power over a gap of 0.026" in a BB engine? I bet that leaks a whole lot more kerosene than the valves.

Mark