 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / May 2006valve lapping how-to
How long should I spin a new valve when I'm lapping it in? In the past I just spun it 30 seconds or so back and forth and all around until it seems to fit nice and smooth. Is that good enough? anybody know the pros or cons of water or oil based lapping compound? -supa > How long should I spin a new valve when I'm lapping it in? In the past > I just spun it 30 seconds or so back and forth and all around until it [quoted text clipped - 4 lines] > > -supa One method that is easy to use for checking the valve seating is to remove it after lapping and wipe the cylinder head seat and the valve face very clean, then use a No. 2 graphite pencil to mark radial lines on the valve face about every 1/4 inch (like a wagon wheel). Then without using any compound, lap the valve again. Just a few seconds of spinning should suffice. Now take the valve out and look at the markings on the face. The pencil marks will have smeared only where the valve is contacting the seat on the head. You are looking for a nice even thin line that is well centered on the valve face. You can even use a dial caliper or precision machinist's rule to measure the thickness of the seating area and compare to the repair manual specifications for that engine, to see if it is correct. If the seat contact area is not centered or not the specified thickness, there are methods to correct that. They involve grinding the seats with various degree angled stones. You would do best to leave that up to an experienced machinist. I have never used water based valve grinding compound so I have no comparison to offer you on that one.  SignatureKevin Mouton Automotive Technology Instructor "If women don't find you handsome, they should at least find you handy" Red Green > How long should I spin a new valve when I'm lapping it in? In the past > I just spun it 30 seconds or so back and forth and all around until it [quoted text clipped - 4 lines] > > -supa I've been told that most modern engines shouldn't need to have valves lapped in, that the machining is precise enough that a little touch up is all that should be required. That said, you can check your work by putting some Dykem (machinist's blue dye) on the seating surface of the valve, inserting the valve into the head, giving the valve one sharp rap with a hammer, and looking to see if you have a nice even transfer of the dye from the valve to the seat. I have no input on water vs. oil based compounds. Before you go too nuts you ought to roll the valve across a piece of flat glass to check for wobble. If you have a dial indicator set it up so that you can rotate the valve in its guide and check for head concentricity (i.e. wobble that isn't evident to the naked eye but still might be a problem.) good luck, nate >How long should I spin a new valve when I'm lapping it in? In the past >I just spun it 30 seconds or so back and forth and all around until it >seems to fit nice and smooth. >Is that good enough? When you take the valve out of the seat, you should be able to see where it was ground down during the lapping process, and on both valve and seat these marks should go thoroughly all the way around the circle. Jasper > How long should I spin a new valve when I'm lapping it in? In the past > I just spun it 30 seconds or so back and forth and all around until it > seems to fit nice and smooth. > Is that good enough? You should be able to tell the contact area by just looking at the pattern of the grinding compound on the valve and seat. Also after clean-up the area that is ground (where seat and valve mate) should have a texture that looks different (sort of matte finish) then where it wasn't ground. -jim > anybody know the pros or cons of water or oil based lapping compound? > > -supa > How long should I spin a new valve when I'm lapping it in? In the past > I just spun it 30 seconds or so back and forth and all around until it [quoted text clipped - 4 lines] > > -supa Don't spin the valve. Turn it only 1/2 to 3/4 of a turn. Otherwise a high spot can give you an erroneous trace. I use a magic marker (less messy than machinist layout dye) to color the valve and the seat before lapping. This gives a much clearer trace of the valve to seat contact. I also use oil based compound and like the others never used water based. Valve lapping went out with the Ford Flathead engine...... Engine builders and engineers long ago realized that when the engine fires up, the valves and the valve seats - being two different materials - expand at different rates as they rise to normalized combustion chamber temperatures where they most-often operate, so the valve does NOT seat itself on the room-temperature, lapped-in portion anyway. Combustion chamber temperatures are much higher than the ambient room temperature at which lapping takes place. The relationship between the valve and the seat at room temperature if far different than it is at normalized combustion chamber temperatures where everything is heated to normal operating temperatures. Just do a good, multi-angle valve job. Having said that, I prefer the oil-based lapping compound over water-based when I am doing engine-turning on aluminum plates in my milling machine. It makes less of an oil/water mess on my machine. > Valve lapping went out with the Ford Flathead engine...... Hmmm. First I hear of this. Where have I been? <grin> But seriously, I like to stay up on current technology and industry practices. It is sometimes difficult to keep up with changes because I seldom do any live repair work anymore, and I have to follow text book procedures. If I understand you correctly, you are saying that machine shops no longer lap valves in after re-facing or replacing them. I will have to take your word for it until I find out otherwise. Thanks for the information. Any other machinists out there concur with this? BTW, I'm not talking about race type repairs, but just good old commuter car repairs. Kevin > Engine builders and engineers long ago realized that when the engine fires > up, the valves and the valve seats - being two different materials - expand [quoted text clipped - 14 lines] > when I am doing engine-turning on aluminum plates in my milling machine. It > makes less of an oil/water mess on my machine. I used to wipe the face of the valve lightly with prussian blue paste, drop the valve on the seat rotate the valve to wipe the compound on the seat , take the valve out clean it and drop it back in turn it and look at the contact on the valve face, worked on my 9 second Hemi SS car.( All this done as a final check step after the valve job) >> Valve lapping went out with the Ford Flathead engine...... > [quoted text clipped - 36 lines] > It >> makes less of an oil/water mess on my machine. >> Valve lapping went out with the Ford Flathead engine...... > [quoted text clipped - 8 lines] >Any other machinists out there concur with this? BTW, I'm not talking about >race type repairs, but just good old commuter car repairs. I last worked as an automotive machinist in 1969. We were taught then that a three-angle cut with stones was all that was needed. Of course, you check the seating accuracy with the lead-pencil method already mentioned, but lapping with compound has been considered kind of a quaint anachronism for quite some time. Lapping also defeats the purpose of cutting the seat angle one or two degrees different from the valve face. > >> Valve lapping went out with the Ford Flathead engine...... > > [quoted text clipped - 16 lines] > Lapping also defeats the purpose of cutting the seat angle one > or two degrees different from the valve face. I can see that. Makes sense to me, but our text books still teach lapping after the grind. Learn something new all the time. I feel kind of silly for making my students learn how to hand lap a valve. I still have to teach it though because it is a required part of the curriculum, but I may not put much emphasis on it if the standard industry practice is to avoid the lapping. SignatureKevin Mouton Automotive Technology Instructor "If women don't find you handsome, they should at least find you handy" Red Green Kevin <kmouton6@cox.net> wrote in article <oRneg.50946$9c6.15531@dukeread11>... > I can see that. Makes sense to me, but our text books still teach lapping > after the grind. I taught Vocational Automotive Technology at the secondary level for 10 years - leaving the political B.S. behind in 1984. Even brand-new texts - due to bureaucratic decision-making at the publishing houses - continue to carry forth many "old grandpa" tales regarding automotive service and maintenance.....I'm sure you could point out several of them from your current texts. No offense intended, but many publishers rely primarily on teachers for their technical updates - teachers who have been far-removed from the day-to-day roiutines of the industry for many years. Some teachers seem to believe that lapping valves is, somehow, a near-religious experience - a right of passage to automotive service and repair. That plus it can be made to keep the kids busy for hours - a "makework" situation. When I was teaching, I used to often say, "The problem with education is that it is run by educators - not business people." Yeah, THAT made me popular, all right! I'm surprised they don't still suggest the carrying of a chamois to strain fuel. I was in charge of curriculum development for my own program, and could substitute newer, more commonly accepted information for obsolete information anywhere I chose. My main goal was to make sure my students were prepared for entry-level employment in the industry - using currently accepted industry practices. The fact that I was also required to maintain a volunteer advisory or "Crafts Committee" composed of people from the automotive business, went a long way towards de-bunking textbook errors. Valve-lapping is one example. At a monthly meeting after my C.C. had taken home textbooks to review, my automotive machine-shop C.C. member stated that it was no longer common industry practice to lap valves.....which I already knew having come into teaching right out of the automotive service and repair trade. That went into the minutes of the meeting with supporting statements from the others, and from that point forward, I no longer had valve-lapping as a task page in my Trade Analysis.......although, I would still often mention the concept just as "nice to know" information. > Learn something new all the time. I feel kind of silly for > making my students learn how to hand lap a valve. I still have to teach it > though because it is a required part of the curriculum, but I may not put > much emphasis on it if the standard industry practice is to avoid the > lapping. If you REALLY want to understand exactly how un-common lapping valves is, in my area, in MANY wholesale (professional) auto parts stores - such as NAPA, Carquest, etc. - lapping compound is a special order, while in MANY retail (DIY) auto parts stores - such as Pepboys, Auto Zone, etc. - it sits there for the DIY who learned from his grandfather that you MUST lap valves. I know, because I still buy it occasionally to do engine turning on aluminum. "Cheating only means that you take winning seriously." - Red Green > If you REALLY want to understand exactly how un-common lapping valves is, > in my area, in MANY wholesale (professional) auto parts stores - such as [quoted text clipped - 5 lines] > I know, because I still buy it occasionally to do engine turning on > aluminum. I keep a tin of it around for a little extra "bite" on problematic screw heads... :) nate Signaturereplace "fly" with "com" to reply. http://home.comcast.net/~njnagel >> If you REALLY want to understand exactly how un-common lapping valves is, >> in my area, in MANY wholesale (professional) auto parts stores - such as [quoted text clipped - 11 lines] > > nate And it does work damn good for that! But that's the only use I've found for it in at least 20 years. Bob >> Valve lapping went out with the Ford Flathead engine...... > [quoted text clipped - 12 lines] > > Kevin The OP asked for help about lapping valves, not if it was still done. Valve lapping was with us long after the demise of the Ford flathead, but most machines shops no longer do it. A shop that has done much work for me uses a vacuum device to ensure that the machined fit is air tight. >>> Valve lapping went out with the Ford Flathead engine...... >> [quoted text clipped - 14 lines] >> >The OP asked for help about lapping valves, not if it was still done. Information that is no longer commonly recommended would qualify as "help about lapping valves" in my book. >Valve lapping was with us long after the demise of the Ford flathead, but >most machines shops no longer do it. For good reasons. >A shop that has done much work for me uses a vacuum device to ensure that >the machined fit is air tight. A much better approach. Don www.donsautomotive.com >>>> Valve lapping went out with the Ford Flathead engine...... >>> [quoted text clipped - 32 lines] > > Don Who said it was no longer recommended? That a machine no longer does it is a sign that's not economical, that's all. For the DIYer or a shop that relies on older machinery, it's still a viable way of checking valve seating. Chas Hurst <hurst1@comcast.not> wrote in article <XbednRVG4K2XtefZRVn-og@comcast.com>... > Who said it was no longer recommended? That a machine no longer does it is a > sign that's not economical, that's all. > For the DIYer or a shop that relies on older machinery, it's still a viable > way of checking valve seating. Using "Dykem", Prussian Blue, Magic Marker, even soft pencil marks will all check valve seating while not destroying the one-degree "interference" that was set up when the seats were ground at 30° and the valves at 29°....nor will any of these methods create a much rougher surface compared to what the machines left on the sealing faces of the valve and seat. And, such methods are really only good for checking seat seal location - not its ability to seal well. As a matter of fact, roughing up the mating surfaces almost guarantees more leakage than the near-mirror-smooth sealing surfaces left by the machines. Spinning the valve will, actually, hide any imperfections. A high spot on the seat, for example, will leave a line scribed all the way around the valve, while a high spot on the valve will do the same to the seat. It is entirely possible to have a valve seating on two high spots that shows a complete ring around the valve and seat due to spinning the valve on the seat. Current technology of creating a vacuum to check the seal seems to be best. Chas Hurst <hurst1@comcast.not> wrote in article <NoWdnbY0f79gjufZRVn-qQ@comcast.com>... > The OP asked for help about lapping valves, not if it was still done. Sometimes, the best "help" is to recommend not doing something......or to point out that it is no longer "standard practice." > Valve lapping was with us long after the demise of the Ford flathead, but > most machines shops no longer do it. So once a machine shop has set up a standard 29° valve face and a 30° seat for a knife-edge fit, why would *anybody* encourage someone else to go ahead and destroy that fit by lapping their valves? And, per an earlier request, we're not even talking about a racing three-angle setup...... > A shop that has done much work for me uses a vacuum device to ensure that > the machined fit is air tight. As do many shops...... I used to sell the Mity-Vac hand vacuum pumps, and I still have a few samples laying around in my shop cabinets. A friend of mine who rebuilds 20-or-more Ford Flathead engines every year, spotted my leftover samples, and after I explained what the various pumps were set up to do, he just could not let it rest until I sold him the one with the cups for checking valve seal. Here's a guy in his 70s who is not afraid to keep up with the times. He, too, no longer laps valves in. |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.