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Join Date: Apr 2005
Location: Co. Carlow, Ireland
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Do new valves need grinding?

This might sound a bit of a dumb question, but do brand spanking new valves need cutting/grinding?

I was planning on reusing my exhaust valves and I sent them off to the machine shop for bead blasting and regrinding, but unfortunately they've been lost in the post by our splendidly incompetent Royal Mail (which is unfortunately what we have to use here in the UK). Now I'm wondering if I was to order brand new ones would I need to get these ground too? I don't know if new ones come precision cut ready for use, or if they come slightly oversize for grinding down or something?

Thanks for your help, and sorry if this sounds a bit of a naive question!
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Old 06-01-2005, 01:53 PM
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Not a dumb question, I wondered this myself when I was starting out. They do not need any grinding, they are ready to use when new. Too bad your old ones got lost!!
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Old 06-01-2005, 02:56 PM
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I would recommend a quick grind just to make sure it's sitting flush against the seat. Only takes 2mins with a bit of paste and a rubber stick
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Old 06-01-2005, 03:42 PM
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Typically you'd want to 'lap' them to check for contact area /location. You would use 'lapping compound' (strangely enough) available at most parts stores. Stick the valve in with just a little dab of compund on the face and use a 'lapping tool' (a small round wood handle with a suction cup) to attach to the valve.
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Old 06-01-2005, 03:59 PM
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Lapping or grinding of new valves is NOT recommended anymore. Check with your supplier to be sure. They sometimes come with special coatings that are ruined by grinding or lapping. Grinding new valves is not recommended because the factory equipment is so much better than any machine shop grinders that the concentricity cannot be maintained. In other words you will make them worse. True lapping is not recommended because it will cause the valve to become unseated when it heats up. The grooves made by lapping no longer match when the valve heats up. The valve guides should be replaced and the valve seats recut.

Last edited by snowman; 06-01-2005 at 04:20 PM..
Old 06-01-2005, 04:17 PM
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I concur with Jack. This recommendation has been around for awhile. The seat contact pattern moves up or down depending on the seat and valve face diameter as well as the width of both.

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Old 06-01-2005, 04:33 PM
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I stand corrected!
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Old 06-01-2005, 05:36 PM
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strangely enough a small ammount of lapping is allowed on used valves. I do it just enough to see where the seat is, ie just enough to mark the surface, but not to lap them togaher. I am not certain that even this proceedure is a good idea, but I do it. If really concerned you can use markum or a magic marker to accomplish the same thing without lapping the valves at all. In fact it is a required step to assure that the valve and its seat are concentric.
Old 06-01-2005, 06:59 PM
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Thanks for the advice guys.

I posted a question a while a go about lapping valves when I thought I'd be reusing my old ones (before they got lost in the post) and the general consesus seems to be that its okay to do it just to check they seat okay, but not to remedy anything. I didn't have a clue about new valves though - sounds like they won't need it, which is good.

Thanks again for all your advice and replies.
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Old 06-02-2005, 01:40 AM
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I use reground valves to lap the reground seats with fine lapping compound (to check for concentricity), and then install my new valves.
Old 06-02-2005, 08:35 AM
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With new valves I would stick to a majic marker or blue dye like Markum for checking concentricity. Coat the valve with color and spin it back and forth, just like lapping. Look and see if all the valve is covered by seat. Clean, and then color the seat, repeat the process and see of the seat is clear, ie contact over the entire contact points. If so every thing coposetic. It may not seem necessary but you MUST do it both ways. This is also an "acid" test, ie it is much tougher than valve grinding compound.

Last edited by snowman; 06-02-2005 at 08:26 PM..
Old 06-02-2005, 08:23 PM
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See if your machine shop has a gauge to test the valve face concentricity like this one:
http://www.goodson.com/store/template/product_detail.php?IID=562

The spec for a new valve face should read under .0005" runout, a decent job at a local machine shop should be no more than .0008"
If the shop does not have a way of checking the valve face runout choose someone else.
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Old 06-02-2005, 09:44 PM
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Using a dial indicator and a homemade v block you can make your own concentricity tester, no big deal. The test using blueing or a magic marker is just as good, although you don't get an exact number as a result.
Old 06-02-2005, 10:38 PM
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