Dr. Frankenstein
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I've got the KZ400H LTD engine back together, and it went very well, but for some reason I woke up this morning thinking of valve lapping vs grinding vs cutting. I lapped in the valves for the bike and it went pretty well - I put about an ounce of alcohol into the valve ports when I finished each one and only got a very slight bit of wetness spreading out of one, so I figure it'll run, but ideally there shouldn't be any escaping. The seats looked like the surface of the moon when I started, and I finished with a nice gray ring around the seats and valves. I was only pressing the valve into the seat with my fingers when I added the alcohol, so I figure the springs will hold them much more securely - but when it comes to refinishing the valves and seats, what are you guys doing/using?Fwiw, what I do when lapping is put some valve grinding paste at four points around the valve itself, stick the valve through its hole and attach a bit of fuel line to the valve stem, and attach that to a shank that I have in my battery powered drill. I then pull the trigger and rotate the valve with the dressing on it at moderate speed, gently pressing the valve into its seat with my fingers and periodically lifting the valve off the seat as it rotates in one direction, then reverse it doing the same. This way I get a nice even ring around the valve and seat, and it takes far less time than hand-rolling those suction-cupped wooden hand grinders - which tend to come off anyway - plus you can hear when the valve smooths out in the seat. Then I take a Sharpie, color in the seat and re-do it to make sure all the Sharpie is rubbed off by the valve, which shows me whether the valve is making even contact with the seat. If not, I do it again until I get the Gray Ring of Success.I haven't yet ground or cut any valve seats - I haven't really had to, lapping has worked just fine for me - but the thought is there; power is produced in the head, after all - but is anybody on here taking it to the Next Level and grinding and/or cutting valve seats? What benefit is there to grinding over lapping, and cutting over grinding? I've heard about the Sioux grinders, and Mike Nixon goes on at length about how crappy that system actually is here: valve seat tools www.motorcycleproject.com - or is all this getting outside of the realm of most garage mechanics?
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Hand Valve Lapping Needed?
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(Automotive)
(OP)
8 Feb 07 15:20I am having leakage on the intake valves of my new Dart heads and valves on my small chevy when shop air is applied into the compustion chamber threw the spark plug hole.
I believe that if I had of lapped the valves there would of been no leakage.
Is it recomended that valves are hand lapped like the old days?
I have seen the same amount of leak on the exhaust side of high milage engines with no problems, but will a leaky intake valve cause back fires?
When cranked over with the starter with no intake mainfold and a little wd 40 down the intake port I can see a puff of mist when cranked back out of the intake port.
This worries me, but there is no cranking pressure diference between leaky valve cylinders and non leaky cylinders.
(Automotive)
8 Feb 07 16:22To start, you need to pick up a simple leak down checker. You don't need a high dollar unit, Harbor Freight has a nice little cheapy that works just fine.As to lapping valves...The current state of the art in high performance racing valve jobs say NO. If I have taken great pains to cut the seat angles in the heads and valves to very precise angles and widths, then I am not going about sticking a great gob of grinding compound and whacking about with the valve and simply destroy hours of tedious work.Having said that, it has on occasion been necessary, usually in the field or as a temporary 'fix' to lap the valves, , to get by for a race. On the dyno, lapping the valves by hand as opposed to precisely cutting them, shows a distinct drop in torgue and hp!!!Not to say I haven't lapped a bunch of valves in my day, just saying that the machines that do the job are a lot more precise today. Heck, I used to seat the valves in my flatheads with a big mallet...worked too. I don't think I would do that on one of my Lotus engines, though.Rod
(Electrical)
8 Feb 07 16:23After grinding valves and valve seats, the sealing will not be perfect and any leaks will result in hot combustion gasses quickly eroding the valves. Laping the valves is required to guarantee a seal. Alternately, the valves can be given a hard hit on the head (big brass drift and a big hammer).
(Automotive)
(OP)
8 Feb 07 17:10Thankyou for the info,
I am going to try something before I pull the heads, the head gaskets are about $65 cnd. a peice.
If I apply air, remove the spring and chuck the stem with a drill motor and spin the valve against it's seat with wd 40 to keep it from getting hot maybe I can lapp them in without compound or removal of the head. If a hammer works I would asume this might work.
I have had no reply from Dart yet, I feel I will get more help from this site then the manufactur.
As far as leak down what is the allowable limit on leaking valves? Maybe I am over reacting and they will take care of themselves in a few hours of operation.
(Mechanical)
8 Feb 07 17:11Mike Halloran
Pembroke Pines, FL, USA
(Automotive)
8 Feb 07 19:17<off topic> Mike, have you ever had to work under/for an architect that thought he was an engineer?
sreid.
That's the way we did it when I started building engines.
That's the way it is still done in some shops for street.
That's the way it is done at 'shade tree' racing, for sure.
That's NOT the way it is done in the top level pro shops.
That's NOT the way I do it on my Mini or my Lotus, I'll let my log books and finishing record speak for itself.
Rod
(Mechanical)
8 Feb 07 19:59The trouble with being a mechanical engineer is that _everybody_ thinks they understand what you do, and can do it better.I've done one valve job, without lapping, just like Chevrolet said. I think the trick is to let the valve and seat grinders 'spark out', so the generated surfaces are circular. It takes a little extra time. It worked fine for ~200,000 miles.The strange little valve in my example was unguided. Given the eccentric load applied by a coil spring, and the clearances in the assembly, it could _never_ have worked as designed without lapping.
Mike Halloran
Pembroke Pines, FL, USA
(Automotive)
9 Feb 07 14:35Mike.
Make no mistake, I ment that I do not systematically lap the valves on my race engines, at least that's the initial setup. "S*** happens" so there are no 'absolutes' in racing.
I have, on many occasions needed to use that little green can of lapping compound to effectively seal valves in machinery, air compressors and, yes, even an old engine or two. All that, however, does not change the reasoning behind 'not' lapping a cylinder head that I have spent two days setting up properly. It's all about time and money, bottom line, is it not?
Rod
(Automotive)
13 Feb 07 14:26Evelrod, any comments on what you allow as a maximum leakdown figure? Street or race, from your experiences?
(Automotive)
13 Feb 07 16:55Obviously, I shoot for zero!
As a practical matter, however, I seem to be ok with less than 5% on a fresh engine. Most usually come in at well below 5% after one warm up. As a general rule, the leak down remains fairly low for the first couple of sprint race weekends then I see some degradation in the #4 exhaust valve for this particular engine. I'm working on getting better coolant flow to that end of the cylinder head. Better, but not good enough, yet. Somewhere, post race, >10%/<20% on any one cylinder and I will freshen the valve job...that's probably too soon, I see my competitors at ~20%, but I'm to anal for that much.
I did run a dyno test pre and post race, VARA enduro of June at Willow Springs...approx 5 hours engine time...the leak down was 3% pre and 5%-5%->5%->10% post race. Comp ck was same pre and post but the dyno showed a loss of 3hp at rpm. That's not a biggie, but this is my hobby these days and if there is 3hp to be had, (to paraphrase Jessica Simpson) "I want it!"
Rod
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(Automotive)
(OP)
14 Feb 07 21:36Thanks for the input.
Dart got back to me and said that the valves will self lap in themselves and not to worry.
(Mechanical)
22 Feb 07 13:02I'd put some bluing or magic marker on the seats and rotate the valves with hand pressure to test for 360 degree seat contact.
I never know what I'll find until I look and measure it myself.
It is usually much easier to discuss and resolve manufacturing defects when the parts are new and have not been run
(Automotive)
28 Feb 07 02:57There are hundred of theories "how to" lap valves is best way, but lapping is not "old days" stuff.Especialy if You change guides.Proper seat angle cut makes 90% of job in best way.
(Automotive)
28 Feb 07 14:22Sorry, but if your changing guides and 'lapping the valves in', your are absolutely doing it the "old days" way. All your missing is perhaps a 'large hammer' to seat the valves!
I would hate to think of the mess that the OEM's would create with a policy of 'hand lapping valves' in all their new, high tech engines! We would be back to the days where 'valve jobs' were needed every twenty to fifty thousand miles and it was extremely rare to see an engine go 100,000 without major repair!!!
Rod
(Automotive)
5 Mar 07 21:25Funny stuff. Well it is the year . And guess what?If you are a machinist, yes the same old technology still applies. Believe me aerospace machining still involves "lapping". And if you were to purchase special gauges and standards I'm sure you would not want them unless they were lapped.So gentlemen lapping is the way to go if you want closeness.
(Automotive)
6 Mar 07 14:44dicer
For gauge blocks, ok. I'm not a professional machinist.
For automotive valves (to which this thread pertains), I must respectfully disagree. As I previously posted, a 'simple' light lapping in of a low time engine cost three hp. No biggie, but why waste three hp? I don't mind the extra hours it takes to make the valve seats perfect. I've been present at some pro NASCAR engine shops and I can guarantee the valves on those engines were not lapped in prior to dyno testing.
Rod
(Mechanical)
7 Mar 07 18:53"I don't mind the extra hours it takes to make the valve seats perfect. I've been present at some pro NASCAR engine shops and I can guarantee the valves on those engines were not lapped in prior to dyno testing."
Hi Evelrod,
Would you expect carefully prepared valves to leak air as described in the original post?
Thanks,
Dan T
(Materials)
7 Mar 07 21:06Um, a big difference between gauge blocks & automotive valves is that the latter work over a wide range of temperature, even with exhaust valves much hotter than the valve seat, due to the angular geometry.
Gauge blocks ordinarily are used for an absolute dimension at a fixed temperature, e.g., 25 oC.
Lapping perhaps improves room temperature sealing but has an adverse effect when things heat up.
(Automotive)
8 Mar 07 01:08"Lapping perhaps improves room temperature sealing but has an adverse effect when things heat up."
And with a machined finish that wouldn't also happen?
Actually I somewhat agree with what you say kenvlach, but I would take it a bit farther and say no matter what the method of finishing the seats and faces there will be inconsistances due to heat stresses. Lapping with the correct media, would assure a better cold fit than without.
(Automotive)
8 Mar 07 02:01Lapping would make the sealing of a conical pair of faces /worse/ if there is thermal expansion.Think about the shapes.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
(Automotive)
8 Mar 07 13:42Dan T
No. I think all this comes down to 'workmanship'. All theory aside, the man on the 'mike' is the determining factor, IMO.
Greg
A little logic is always helpful. It is an uphill battle to convince (why I try, I do not know) folks that just because lapping the valves in has always been done that it is the correct way and not 'just a crutch'. Thanks.
Rod
(Automotive)
9 Mar 07 11:29Good point Gregg.
(Mechanical)
10 Mar 07 17:19So, carefully and nicely machined valves and seats are likely NOT to leak during a compressed air pressure test.
This makes me extra suspicious that the manufacturing workmanship of AlkyUser's heads is in serious question. I'd take them apart (keeping parts identified for identical reassembly) and check out the valvestem-to-guide clearance, seat runouts and concentricities, including putting some bluing or magic marker on the seats and rotate the valves with hand pressure to test for 360 degree seat contact. That also can be used to test seat width and if the seating occurs in the outer third of the valve seat, both of which can be pretty profoundly effect set performance and life, and have little or no effect on sealing when brand new.
(Automotive)
11 Mar 07 11:27waste of time evelrod?:) Its one my favorite jobs - angle cut and valve lapping.Im not a billion dollar industry shrick to apply to high tech machines to do elementary bussines.I'd treat lapping as a higiene.
(Automotive)
11 Mar 07 16:30Ebola, (interesting handle, hey?)
I'm just a hobby builder these days and retired to boot. I have lots of time to waste it seems. You don't need mega bucks or high tech machines to turn out quality valve jobs. Talent, experience, skill...qualities gained from doing this for 50 years will help. As I said, I lap the valves in street engines or when a problem arises in a race head that needs fast attention...no problems. However, what we are talking about here is a high dollar set of RACING heads and in that context, I just do not accept anything less than perfect if I am given a choice.
Tmoose
I usually "test" a valve (if something is suspect after a leak down ck) , not so much when it's fresh, but later, after run in with a vacuum cleaner and a stethoscope. I'm not sure what you mean by compressed air. I use engineers 'white' marker to ck the seats, less messy.
Evelrod...(appropriate handle, hey?)
(Electrical)
13 Mar 07 13:06Does anyone know how valves are seated in brand new engines? Do manufactures rely on accurate grinding of valves and seats?
(Mechanical)
13 Mar 07 18:21For decades, Chevrolet has recommended ground valves against ground seats with a 1 degree difference in angles, so they nominally seal only at the outer diameter of the seat. That's what's in their service manuals. I assume they do something similar in production.
Mike Halloran
Pembroke Pines, FL, USA
(Automotive)
13 Mar 07 20:42Does anyone know how valves are seated in brand new engines? Do manufactures rely on accurate grinding of valves and seats?I used to have the job of hand lapping the valves on those engines which had failed their compression tests on the dyno.I imagine these days that everything is cut to size and no lapping is done, but must admit, have never wandered over the road to check.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
(Industrial)
8 Apr 07 21:05It seems that this thread is over but I have one thin to add that seemed was missing. Each valve seat needs to be ground to ensure the guide and seat are concentric to one another. In my experience in Industrial Engines lapping w/ fine compound was acceptable but not to correct a major problem. I was also taught to vacuum test each valve seat after assembly was completed. Do manufactures rely on accurate grinding? Yes, but they calibrate at specified times and they also use cutters and not stones so they do not have any grinding dust.
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