Originally Posted by Magnetoman
Originally Posted by Hillbilly bike
One advantage is the Newan can greatly reduce valve seat runout that most machinists in a shop cannot do...So the guide clearances on my Triumphs and A10 are .008 on intakes and .0012 on the exhausts. ... Single axis valve machines can be knocked off tolerance by a hard spot on the seat insert. This may be not noticed by a less skilled worker...
(You missed a zero on the intake -- I'm sure you meant 0.0008").The Newen and a ball head cutter in a mill both rely on a pilot to keep the cutter Concentric with the guide. However, a big advantage of a Newen machine for valve seats in a production environment is separate profiled carbide cutters aren't needed for each engine since it has a single-point cutter and uses CNC to create any desired seat profile. If a Toyota head is done after a Ford head, instead of the downtime needed to change cutters (and the cost of maintaining a large inventory of cutter shapes), all the operator needs to do is pull up a different profile from the machine's memory. As for the "hard spot," that strikes me as a marketing, rather than a real, advantage given the quality of seats from major manufacturers.

Interestingly, old school runout gauges used 0.001" indicators, which was fine for old school recommended runouts of no more than 0.0015"/inch (i.e. 0.0026" for a 1¾" valve). Because I can do a lot better than that with the tooling on my mill I found a gauge that is missing its indicator in order to modify it with a 0.0001" indicator. You are only able to work to better than 0.001" if you have instruments that measure to better than 0.001". Such a "precision" runout gauge is available from Goodson for a mere $615. Again, though, it takes me a lot longer to accurately cut a seat than it does someone with a machine like a Newen.

Addendum: I wonder what guide clearance and seat runout someone would get if they took their Triumph head to a "typical" machine shop to have the work done. Hillbilly bike cites real performance advantages to having the job done to modern standards, but are most shops using those standards, or older ones?

And the problem with this is the same one I have with the mythically perfect "machined from solid billet " CAD parts, is what ends up happening is the shop owner puts a $ 10/hr dullard on the end of the machine to recover the costs as quickly as possible because the machine can not make a mistake, till it does, but the operator who does not know any better keeps on feeding new parts into the machine & pressing the buttons turning good parts into scrap, some thing I have seen countless times in industry.
Or he puts a $ 50 /hr technican on the end so prices himself right out of the market because the number of customers who are willing to pay the same for a valve guide machining as a replacement heat ( remember we are talking about old British motorcycles not F1 race engines ) would be pretty close to zero.
And that is assuming that some one has programmed in the specifications for a 1943WM20, a 1973 B50MX or even a 1928 Ariel all of which would be very doubtful .

And of course we are now going in the endless circle.
Precision costs money and the cost rises exponentionaly with every order of magnitude
So then the costs have to be weighed against the benefit in one of those things accountants & political lobbyist love, a cost benefit analysis .
Do I want a bike that will go just fast enough to outrun the local police & occasionally win a drag against my circle of peers ?
Am I happy for it to self destruct just so long as I can be the fastest on the night ?
OR do I want it to run for long distances with a mean time between failures that could only be dreamed of when the motorcycle was new
Or do I want to ride a "Budget Brit" for the minimum outlay & maximum fun ?
Will the fine precision last long periods of storage or will cams. cam followers. bearing races & rolling members end up either corroding or Brinneling due to not being used , or valves sticking due to corrosion from lack of lubrication cause by lack of use, let alone things like stiction caused by oxide growth over time , and of course wear from actual use itself negate the fine precision used in the remanufacture ?
Right down to the question is turning an old production bike into something that would have cost 5 years wages back in the year it was made so would have never actually been made, is being true to the ideal of riding a historic vehicle or are you really just making a hot rod without the extensive body work changes.

All very personel questions that will have a different answer from each & every one of us so none will ever be universally applicable.

Then when talking about precision in the orders of 0.0001" or the implied +/-0.00005 just how accurate will that actually be be when the simple act of touching the part or even measuring the part can cause enough temperature change to affect the reading so of course those reading will need temperature compensation and at that level of precision the difference in the thermal properties of the actual different grades of steel come into play let alone the temperature of the workshop & the presence or absence of any breeze that may be in there and the temperature of said same breeze and of course the temperature rise caused by the maching process itself regardless of what type of cooling is used .

Does a valve seat that is 0.010 wider than it should be really affect the performance of the engine ?
Well to all effects & purposes the answer is no. There is probably a point where there will be insifficient clamping force to prevent leakage but at what seat area ?
In theory it will transfer more heat & cause the valve to run colder than it should and reduce the sealing pressure so make it more prone to leaking ,,, in theory
The burning question is does it make any difference in practice in the actual engine, so a 13:1 dope burner running at 10,000rpm probably but a 7:1 street bike, not likely and a 6:1 SV no way ?
A valve guide true to 0.00001" is fine, but the valve does not heat uniformly nor does it expand uniformly and of course we can all appreciate that the stem itself will become conical from the effect of thermal expansion so the cold assembly precision can quickly vanish at operating temperatures