Valve seat tools

Tips and Recommendations from Guru Mike Nixon

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mikenixon
Early 'Wing Guru
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Valve seat tools

#1

Post by mikenixon »

Recently, I heard from someone who wanted to talk cylinder head and valve work. Though I have posted on this subject before, it occurred to me someone might find my reply interesting.

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On lapping, well, I am not trying to be rude, but let's turn the question around. You asked why not lap, and I'll ask...why? Why do it? If you have done a good valve job, there is no need to lap. In fact, you will be degrading, undoing, much of your hard work. That is answer number one. In my mind, lapping at its very best is not part of a valve job but a very poor substitute for it. Answer number two is another question. If you understand the what and why of valve recession, why then would you do a procedure that hastens it, and actually produces it where there was none to begin with? Makes no sense to me. Now though I avoid lapping, my friend and colleague Nigel Patrick (five-time consecutive ProStar champion) very lightly and faintly laps to check contact and concentricity. Just a few strokes. And that makes sense, in a way. He doesn't do it to improve the seal, only to confirm it. But even there I have to ask -- why? Why substitute the traditional Prussian Blue to do this job, with lapping? With him I think it's just habit born of many many years. No harm. Third answer: 70s Japanese valves are plated. Why defeat or harm that plating by abrading it? I can't say this strongly enough: though OEMs countenance it, lapping is a hack procedure best avoided and with virtually nothing to commend it.

On the subject of the different cutters/stones, I break it down like this:
two categories of tools
1. dead vs. live pilot
2. multi vs. single point

1. dead vs. live pilot
dead pilot = pilot stays stationary, fixed into guide, while cutter or stone rotates
a dead pilot is never and cannot be concentric w/seat, thus seat machining of seat is not concentric
all pilots are either tapered, expanding, or loose fit
tapered and expanding pilots definitely cause non-concentricity -- no way around it
guides, whether worn or not, will not hold tapered or expanding pilots concentrically
(loose fit pilots are not by definition dead pilot)
where found: black and decker, sioux, Kwikway, neway
live pilot = pilot rotates as one with cutter or stone (either as part of handle or bolted to it)
a live pilot self-centers, as accurate as valve itself, making seat machining more concentric
where found: OEM hand-turned cutter or stone sets, serdi, mira, hunger, newen

2. multi vs, single point
sub-categories within the two categories above
multi point = cutter touches seat 360 degrees
cutter or stone, by design, can only follow original seat's level, contour
if seat or guide have shifted, cutter or stone can't correct that, only follow, conform
seat that has started not perfectly perpendicular to valve ends the same way after cutting
this will produce poorly-sealing seat
where found: OEM hand-turned cutter or stone sets, all powered stone type, neway
single point = cutter touches seat only at single point
cutter doesn't follow seat level, doesn't conform
if seat or guide have shifted, cutter does not have to follow, it re-levels the seat
its registration is to the guide, not to the seat as in multi-point systems
result is corrected level, accurate, beautiful seat, best possible seal
heads that always have shifted seats thus do poorly w/multi-point: Honda CBX1000, early DOHC fours
where found: serdi, mira, hunger, newen

The bottom line in the two types and the two sub-types is where is the tool "registered", that is, what is its datum point, its reference? A tool whose cutter registers to the guide is intrinsically more accurate than one that registers to the valve seat. Single-point systems register to the guide, multi-point to the seat. Simple, eh? I wish this were all there was to it, but there are complexities, compromises.

You will conclude that the best tool is live pilot, single point. But this is true only if you have $30,000-40,000 to spend on the tool. From a practical standpoint, it's easier to reach target quality spending reasonable money with a multipoint tool centered on a live pilot than it is with a single-point tool live pilot system (live pilot is assumed in any case, there just is no good reason to use a dead pilot system).

In short, if money is no object go Newen, the ultimate computer-controlled, rigid, accurate single point live pilot system. If however as is usually the case money is a consideration, hand-operated live pilot multi-contact (stones) is best. But in any case, note that live pilot is preferred. Always.

Also note that although economy hand-held versions of the Serdi and some of its clones (three at last count) are available, reports are that the quality doesn't approach the conventional floor models of the Serdi, and I can attest to that from my own experience. The promise in this theoretically best combination, the hand-held Serdi Micro or the Mira, just doesn't play out, mostly due to the lack of rigidity in these economy models that bolt to the cylinder head's gasket surface, and turn by a wobbly hand crank. Thus my recommendation of multi-point live pilot, which interestingly enough is exactly what the Big Four made available back in the 60s and 70s.

I think you have missed the point re live versus dead pilots. It is the very fact that the dead pilot *doesn't* move that makes it inferior. It can't possibly correctly center, as noted above. I.e., not moving is a disadvantage, not an advantage. What does the valve itself do? It self-centers. Thus a pilot that does the same as the valve does is an advantage as far as the influence of the pilot on the finished work goes, though there are other considerations.

A dead pilot can't hope to center in the guide, if it is taperered or locking. Thus the cutter, which will attempt to center on the seat anyway, is nonetheless influenced by the non-eccentrically positioned pilot, and that can never be good as it simply compounds error. That is, the multi-point cutter already is thrown off by its registering on the seat, then thrown off even more by the influence of a crooked pilot. This is exactly what is wrong with the Neway system. It's doubly inaccurate. On top of this and of little consideration in this discussion, the finish left by Neway is very poor. It looks from your pix like you're doing very good work, especially considering you're using Neways. But I wonder if you have ever vacuum tested Neway cut seats. It will be disillusioning.

Remember the pilot does not register the cutter in a multipoint cutter system. The cutter itself does, which is the multipoint system' only, and huge, drawback. The pilot only comes close to registering in a single-point system. And while that is certainly true, there is a rat in the basement. Even this is not completely reliable. In a single-point system the pilot doing the registration is only theoretical. Registration in single-point is somewhat dependent on the floating mechanism, whether in the cutter drive (small Serdi models) or in the floating table (large Serdi models). But to be fair, single-point does rely heavily on guide registration.

The dial tool you're referring to is a dial indicator configured to measure seat concentricity. Two versions of it that I know of are available from firms that cater to cylinder head work.
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NGW folks, hope you found this educational. :)
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