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Shim for setting valve clearances (steel hardening question)

Shim for setting valve clearances (steel hardening question)

Shim for setting valve clearances (steel hardening question)

(OP)
Hi!
I've done some work on the seat of an engine head, and now i can't find any shim that can i use for setting the valve clearances.
The clearance is set by a 11.5mm in diameter diameter shim that is placed just under the bucket, between the bucket and the valve stem.
The minimum shim that i can find is 2.00mm. I'd suppose that it's difficult to find shim under this value because this shims seem case hardened, and under 2.00mm the core can be too brittle, and can split in two under the load of the valve stem (6mm stem loading something like 60/70kg at max rpm, spring load + inertia).
I need some 0.95 /1.00mm shims, so i must find a way to machine them by my own.
I know that the tip of the valve is hardened at least at 53 hrc.
I've think about grinding the shims and get them nitrided, so that the core will be untouched.
Someone have a suggestion for me?
Really thanks!!!

RE: Shim for setting valve clearances (steel hardening question)

You should take a look at Precision Brand, they as well as others have 1.00 mm feeler gage stock.  You could also look at hardened drill rod, key stock, or even flat stock to get your required 11.5mm thickness.
The majority of feeler gage stock is through hardened.

http://www.precisionbrand.com/ProductsCatalog/PBPCategories.aspx

RE: Shim for setting valve clearances (steel hardening question)

(OP)
Really thanks for the suggestion, really quite interesting! I'll take a look on the whole site if i can find something that can be good for me!
Only a note, 11.5mm is the diameter of the shim, the thickness must be 0.9.
I've fear that using full hardened shims it can broken due to be too brittle...
The original one's don't have the dark gray color that is common in oil threated steels (as the oil add hardness, but also made it more brittle), but is light gray.  

RE: Shim for setting valve clearances (steel hardening question)

Measure the surface hardness of a factory shim.  Then gently grind it down to your required thickness.  Measure it again.  If still hard, have it checked for grinding checks via liquid fluorescent mag. particle (Magnaglo).  If the ground surface is softer, nitriding should be able to restore it.

Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all.
Rudyard Kipling
 

RE: Shim for setting valve clearances (steel hardening question)

(OP)
I have some britemor 4455 and a wood light, i'd suppose it will suffice. A case hardening is possible on a 1..5 diameter, 2mm thick shim? I'm thinking about this, but i'd suppose that it's quite difficult to obtain a precise case hardened on that small part...
Else i can use normal tool steel/drill rod to made my own shims...
Unfortunately i don't have access to an hardness tester...

RE: Shim for setting valve clearances (steel hardening question)

A good nitrided case can be as thin as ~.005", so a .080" shim would be no problem.  Any "white layer" should be removed by lapping, not grinding.  You'd probably need at least a steel like 4140 to get a good hard case.  But there is another way.

Get a piece of pre-hardened S7 tool steel drill rod.  You'll have to grind it to size, but if you do it gently you probably won't crack/heat check it.

S7 is a VERY tough tool steel, even at ~Rc58.  Your shim stresses are probably pure compression, with little or no bending.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein  

RE: Shim for setting valve clearances (steel hardening question)

(OP)
This are really useful infos :) Really thanks!
Mmm, but the oem shims, that are 2.00mm, and surely are heat treated/quenched, can have an hardened layer that leave intact the core of the steel?
Because on the net i've readed that this shims must be only case hardened, but i don't imagine how is possible to heat treat a 2mm shim without through-hardening it...
The shim is acually interested by compression and friction with the valve stem (under 60/70kg of load), and 'sometimes' (hopefully not too often :) )  by some hammering caused by the lifter not following the cam profile, this situation must me avoided, but i prefer to not have a shim split in two due to a miss-shift...

So do yuo suggest S7 over A2 or O1 hardened rods? Surely, i must search them through hardened, so that the core (the the valve stem will sit) will have the same hardness of the surface.

Really thanks for your precious help!!!

RE: Shim for setting valve clearances (steel hardening question)

For your application, S7 is a good choice--better than A2 or O1.  Prehardened S7 should have a hardness of ~Rc52-58, and I doubt you'll be able to break one no matter how high you try to spin the engine.  BTW, what engine is involved?

Wear-resistant parts that have bending stresses (such as gears) are best made from case hardened steels.  If you don't have such bending stresses, a tough through-hardened tool steel should work fine.  You have to determine if the stresses will be pure compression or not. If not, then a case hardened steel is the way to go.

BTW, this is all elementary mechanical engineering----.

  

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein  

RE: Shim for setting valve clearances (steel hardening question)

(OP)
I know that is elementary mechanical engineering, but i don't have made any study on this area... And i'm learnig something in this days, as i've this throuble :)

The engine is a Subaru EJ20...

Bending must not be an issue, the shim on the other side is 'attached' due to superficial tension of the oil to the bucket,plus the shim is quite lightweight, so i'll doubt the the valve hit the shim at any angle.
But, why S7 is more reccomended that A2 and O1?
And how hard is turning pre-hardened s7 steel on a lathe?

Really thanks!!!

RE: Shim for setting valve clearances (steel hardening question)

Can you send a DETAILED photo or drawing of the parts on BOTH sides of the shim?  You must be sure that no or minimal bending stresses are involved here.

NO, you shouldn't attempt to turn/machine hardened S7 in a lathe.  It should be GROUND to size with abrasives.  A good machine shop should be able to do this for you.

S7 is a very well known shock-resisting tool steel.  O1 is a "simple" tool steel that is not expensive, but it not very shock or heat resistant--not that you need much heat resistance.  A2 is an air-hardening tool steel for complicated shapes, etc.  It does not resist shock as well as S7.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein  

RE: Shim for setting valve clearances (steel hardening question)

(OP)
This isn't for sure my best drawing, but must be quite clear how a typical shim underbucket works:

http://img52.imageshack.us/img52/6969/immagineqk.jpg

If you prefer, i can upload some photos.
The shim is the black thing just placed under the bucket, and over the valve tip, and it must be chosen to obtain a play between the cam and the bucket of 0.20mm on the intake and 0.25mm on the exhaust.
During the closing of the valve, the bucket 'CAN' be separed from the top of the stem, due to the inertia of the bucket itself. But the cam has a part of the profile that is at constant velocity to gently accelerate and decellerate the whole thing and slowly clear the 0.20mm play before the ramp.
The bucket will go up and down in it bore, and the valve in it guide.
The work of the bucket is remove the side load exercised by the cam lobe, and transmit only the vertical movement to the valve.
The spring let the valve to close, acting on the retainer.
The shim will surely stick on the bucket, due to the surface tension of the oil, that is present everywhere.
The bucket have a little extension of 0.5mm where the shim sits.
The original shim present little wear where the valve tip sits. The other side has no wear.
The tip has a diameter of 6mm, and the shim itself 11.5mm

Ok, they can ground it, but how they can cut the shim?
60hrc seem to be qute hard... In any case, i can ask in some machine shop...

Please, let me know if you need som other info :)
 

RE: Shim for setting valve clearances (steel hardening question)

Here's what *I* would do, assuming this  is *your* engine and a broken shim isn't going to cause you to lose a million dollar race or strand you in a Siberian winter.

Have a machine shop gently surface grind factory shims to the thickness you need. Make sure they only grind ONE side!  Check the ground surface for heat checks, and install the shims with the ground side against the bucket--NOT the valve tip.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein  

RE: Shim for setting valve clearances (steel hardening question)

(OP)
Yes, this was also an idea that i've had, but would be nice to be able do my own shims :(
So do you think that in this application a prehardened s7 stell isn't good?

RE: Shim for setting valve clearances (steel hardening question)

A prehardened S7 shim will most likely be stronger than a factory shim, but you cannot turn it on a lathe.  You also have to order/buy the material, then have it ground to fit.

By using a factory shim, all you have to do is have someone surface-grind it down.  Do you have a surface grinder?

Where are you?

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein  

RE: Shim for setting valve clearances (steel hardening question)

(OP)
I've not access to a surface grinder, but surely i can get someone to grind them for me. I've 'only' direct access to a firends lathe and mills, both cnc and manual.
I'm from italy (and my english isn't that good :):) )
 

RE: Shim for setting valve clearances (steel hardening question)

Your English is far better than my Italiano, and I spent 6 years in Milano (1998-2004).  What citta are you in?

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein  

RE: Shim for setting valve clearances (steel hardening question)

(OP)
Ahahah, you was here in italy? Nice! :)
I'm from Asti (well known in the world for our wine, and for the 'Palio of Asti'), it's 60km from turin, and about 150km from milano...
And, where you live now?

RE: Shim for setting valve clearances (steel hardening question)

I live near Phoenix, Arizona.  Worked at Ansaldo/Camozzi in Milano, for my company here in Arizona.  Take a look in Photobucket.  My ID there is a word I made up while I was in Italy--it's  Benesesso--ha ha!

 

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein  

RE: Shim for setting valve clearances (steel hardening question)

(OP)
Mhauuaua, Benesesso :):):) You have learned the most useful words needed here in italy!!! :):)

So, you have also visited Asti!

I'll hope that you have nice memories about my nation/city :)

RE: Shim for setting valve clearances (steel hardening question)

Yes, I love Italy!!!  Best 6 years of my life.  Met some great people and visited many places.  I lived in a small town between Como and Lecco (Rogeno).  I am good friends with the 5 or 6 time Italian champion in F2D model airplane flying (combat).  

What is your job (work) in Asti?  I retired from the largest nuclear power plant in the US one year ago.  My job was metallurgical failure anaylsis, corrosion problem solving and material selection.

We built 6 new large steam generators in Milano--the largest ever made anywhere.  They don't make nuclear-related stuff that big in the US anymore.  Each one weighed 800 tons, and cost $30,000,000 (~20,000,000 Euros).

You are awake very late tonight!

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein  

RE: Shim for setting valve clearances (steel hardening question)

(OP)
I've tryied to buy a 4ch model helicopter, but it need much patience that what i have :) After it has crashed a couple of times on some walls, i've abandoned :) And that was after a lot of hour on the simulator! I'snt the right hobby for me, i'll prefer engine tuning :) I'm mading all by myself a 500bhp impreza, after years that i study on complicated car books, specialized forums, etc :|
In any case, for work i'm a computer programmer (.net laguages, mainly vb.net and asp.net, but also sql and js), but i know also a lot in networking (cisco ios programming, complicated server configurations, security, network configurations,etc) and computer in general (virus removal, assistance,etc). I work in a little office (as emplyee), and every day there is something new to do :p
I know also about electronics (it's what i've studied at school), and in the last years i've developed a passion for engines and mechanical stuff :p

I not know much in nuclear stations, but searching on wikipedia they say that the biggest steam generators made weighted about 800tons, might be are speaking about the one's that you have worked on :)
You work must be quite interesting, and higly specialized!

I go always late to bed, else i've not time for my passions. When i'm not at work, i'm in the garange, or on the pc searching something, or studying on books, or mading some small extra works for moneys, like repairing electronic stuff, pc assistance, mechanical works (mainly works for friends that made by a mechanic will costs too much, or that wasn't sloved by others).

But now it's time to go to bed, only 4 hour of sleep :)

RE: Shim for setting valve clearances (steel hardening question)

The following link is provided only to show that annealed S7 is apparently available:  

http://southerntool.thomasnet.com/addtocart/tool-steel-2/tool-steel-round-bars/ts-s7rrt?&plpver=1005&itemids=10036&qtys=1&type=order&prodids=3001038&oln=&PcValue=

If not available, you can buy it prehardened then anneal it or have it annealed.

Grinding the desired shape from prehardened S7 is not very practical although it can be done.  Turn the desired shape on your friend's lathe using annealed  S7 then quench and temper to HRC53 to match hardness of the valve stem.  for the prototype, you can use S.S. foil to wrap the shim for protection against oxidation while you torch heat treat then temper in your kitchen oven.  If this sounds like an approach you want to try, myself or another here will provide you with more detailed instrutions to accomplish the quench and temper.

If you intend to produce in quantity, you will want the shims heat treated in a vacuum furnace or protective atmosphere furnace for best results.

RE: Shim for setting valve clearances (steel hardening question)

(OP)
Mmm, i have an infrared thermometer, and also a 1000°c type k temp reader, and i can buy a poldi hardness tester quite cheap...
I don't need to do a big quantity of shims, only a set (also for future regulations).
Surely isn't the best setup, but can be ok for made my own?
Until now i've excluded to do myself the heat treatment, for fear to made more damage than benefits...

RE: Shim for setting valve clearances (steel hardening question)

Another possible deterrent is that although the S.S. wrap is readily available at least here in the US from suppliers like McMaster-Carr or MSC it is not cheap.  About $100 MSC order number 00049957 but this would probably be a lifetime supply for you.

I do not have heat treat info readily available as I thought for S7.  Some of my info is at work and I am home for a week.  If someone will provide the austenitizing temperature, quench medium, and approximate tempering temperature, we can walk him thru the process.  If you obtain the hardness tester, you can measure the as-quenched hardness and then someone can give you an appropriate tempering temperature.  Your oven might not be hot enough for the tempering operation but you can re-wrap the shims in the S.S. Foil and use the torch since you have the infrared thermometer.

You will want to make a few heat-treat test samples so as not to waste your precision made shims as you hone your heat treat skills.  The test samples can be made by simply parting off the bar stock in the lathe to the approximate overall thickness of the shim say 1-1.5 mm to signify the mass in question.  Practice the heat-treating process on the samples by wrap in foil, clamp a heavy piece of angle iron in a bench vice and lay the sample on the angle iron.  Now heat the iron from underneath using your oxy-acetylene torch but of course measure the temperature of the foil.  The mass is so little that I will guess 5 minutes at the austenitizing temperature will be adequate but let us see what some others might suggest or maybe agree.
 

RE: Shim for setting valve clearances (steel hardening question)

(OP)
I've access to some wood/carbon stove, that must reach quite high temperatures... I can pack them in the steel foils with the type k sensor inside, and mading a sort of support for choosing the best height inside the stove for finding the right temperature, can this work?
So i need a bar of s7 annealed steel, the hardness tester and the ss foil?
I've done a fast search for the foils and i haven't found nothing... Maybe i need to do a more deeper search...

Quite interesting that this things can be used to harden any type of steel, in case i need this in the future...

RE: Shim for setting valve clearances (steel hardening question)

I will get you a link for the MSC company order number 00049957.  This part number I found in my hard copy catalog.

Quote:   ...can this work?

Yes if the k sensor is what I think.  It's a thermocouple?

RE: Shim for setting valve clearances (steel hardening question)


Here is the link:

http://www1.mscdirect.com/CGI/GSDRVSM?PACACHE=000000121109343

Item #: 00049957 Mfr: Select
Non Catalog Item  See Available Substitutes (I don't know what is meant by this but you can call the number below or try to oder online)


24"X50'X.002" STAINLESS TOOL WRAP
Please call Customer Service 1-800-645-7270 for help

Price:     $174.95 ea   (My catalog is 12 yrs old so the price has jumped)
 

RE: Shim for setting valve clearances (steel hardening question)

(OP)
Hmm... but it's in america, and i must add custom duties...
Else, this will be fine?
http://www.stephensgaskets.co.uk/StainlessSteelShim.html

they are in uk, so no custom...
0.002", 6" x 60"
304 steel would be good?
And is also quite cheap...

And, yes, they type k is a thermocouple :) Can handle up to 1000°c, but i'd suppose that i need to stay a little bit lower than this, something like 940/950, right?
Plus i need to buy the poldi hardness tester:
http://cgi.ebay.co.uk/poldi-hardness-tester_W0QQitemZ200421387609QQcmdZViewItemQQptZUK_Measuring_Tools_Levels?hash=item2eaa0bad59
Isn't that nice, but i hope to get at least a bit accurate reading...

Plus the bar itself (that with a bar i can made LOADS of shims)...

But... How i can get a 940°/950° temperature???
I't sufficient on a stove, might be loaded with bbq carbon? I've never tought how many °C can be inside on a stove! :)

RE: Shim for setting valve clearances (steel hardening question)

(OP)
I've found this:
www.precisionshims.com.au
They have quoted me 6.00AU$ per shim (in any measure that i want)...
Plus 20$ of shipping!!
Seem quite cheap...
Are the only one that i've found that made shims on order...
For a set of 16 i spend 96+20+some custom duties (say 25%), and i pay near 150AU$, 93 euro. Near the price of the hardness tester. But if after 30'000 miles i need to redo the shims (for wear in the valvetrin components), i need to spend other 93 euros, and i'm quite in pair with the costs of the whole setup for mading my own shims...
What do you think about???
I'm quite excited to do this work (and learn how to do it) :) Might be my friend with lathes and mills isn't that enthusiast... lol :)

RE: Shim for setting valve clearances (steel hardening question)

Duuhh -- I did not think to look for "shim" stock and here we are talking about SHIMS of all things.

Probably the spendy stuff I linked for you is 304 S.S.

So yes the .002" SS shim should work fine for foil wrap.

I have never actually used this method but I suggest you will want to fold it over the part twice -- the second fold at 90 degrees from the first -- to result in only two edges for the foil to be sealed by then folding each one of those edges close to itself like about 5mm while pressing down on the package to remove as much air as possible.  Then with a roller or hammer flatten the sealed edges firmly to make a tight seal.

Yes your type k will allow for proper temp range.  Someone on this forum will answer the correct austenitizing temperature etc.  Are you familiar with the Iron-Iron Carbide phase diagram?  If not you will want to do so because it is a beautiful thing and you will see the Austenite phase range displayed and begin to understand what you are doing and why.

Quote:  But... How i can get a 940°/950° temperature???
I't sufficient on a stove, might be loaded with bbq carbon? I've never tought how many °C can be inside on a stove! :)

How do you suppose a Blacksmith does it?  You might NOT even need a little bellows but maybe yes or could be a hair dryer.  The valve shim will be protected from the air atmosphere and will be isolated from the BBQ carbon because of the SS foil barrier.  Otherwise your valve shim
if exposed to the carbon would become surface carburized and brittle.

You seem pretty sure of yourself to win a low bid on the hardness tester.  Good luck!
 

RE: Shim for setting valve clearances (steel hardening question)

I think you are on the right track in buying the shims from Australia.  When you order them get some extras, a bit thinner than the ones you use in the engine.  Then, as the valves slowly (you hope) sink into the seats a little deeper, you'll have thinner shims ready to use.

In a high HP engine I like to set the clearance on the exhaust valves a little more than what a stock (unmodified) engine is set for, because your exhaust valve temperatures may run a somewhat higher.

As for attempting to heat treat S7, you may find it requires a lot of care to do it correctly.  S7 has a lot of carbon, and C will be lost from the surface if oxygen is present.  That will cause a softer surface which you do not want.

Yes, the use of SS foils can work, but you may need practice to get it correct.  The first temperature you must reach, and hold for ~45 minutes, is ~950 deg C.  Then you must cool the parts in air, while still in the foil, of course.  When they get down to ~60 C, you must reheat them to at least ~250 C for 1 hour, followed by air cooling.  Then put them in your freezer for a few hours, followed by reheating back to 250 deg for another hour, at least.

Then you need to accurately measure the hardness, which will leave a tiny hole--unless you do it on extra pieces.

Finally, use some very fine silicon carbide sandpaper (~280 grit or finer)and using a flat glass plate, rub them on each surface to be sure they are still flat.  Good luck with your fingertips trying to hold a 1 mm shim!

Here is a link to some S7 HT info:

http://buffaloprecision.com/data_sheets/DSS7TSbpp.pdf

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein  

RE: Shim for setting valve clearances (steel hardening question)

(OP)
Mmm, buying shims befor have actually measured the right clearance not seem to me a right approach, as on an engine with age the valves can settle deeper on the seats, but also the cams/buckets will wear out... Who knows what of the 2 will win? Acually isn't rare to find some with less and some with more lash than reccomended... Too many variables...

Surely you know that setting more valve clearance you are wasting cam timig, only 0.05mm of more lash is like wasting something 5° of cam opening time (depending on the cam profile)... I'll prefer to widen a bit the exhaust seat for better cooling the head of the valve, and maybe imstalling bronze valve guides (that helps to remove heat from the stem of the valve).
I've tryied to remove 0.05mm of lash on a fiat fire engine (that have HUGE clearances, something like 0.40mm on intake and 0.50mm on exhaust) and the difference was noticeable.

So you discourage me to try to get my own shims made and heat threat them?

What do you tink about that poldi hardness tester?
I'm always ethusiast when i can try to do something new, and learno to made things, but sometimes i'll admit that for made a good job the equipment will cost too much for an hobbist :(

RE: Shim for setting valve clearances (steel hardening question)

From a Poldi website:

       "Poldi type Impact Hardness  Tester  is not designed to replace the tensile strength testing machine or standard hardness tester. The accuracy of this hardness tester may very sometimes to the extent
+/- 10% as against the more accurate table type standard Hardness testers. However, the Poldi Impact Hardness Tester has the advantage of easy handling and greater flexibility. This is very important, especially for testing heavy specimens who cannot be taken to table type hardness are extremely costly eompared to Poldi tester and require greater skill to operated properly."

I think I'd spend more time getting your engine running well than trying to HT your own shims.  If you're at 500 HP you must be turbocharged, and turbo'd engines like lots of good tuning.  I have a 250 HP turbo'd engine, but it's not in a car.  It's a Hayabusa motorcycle that weighs ~230 kg without me on it.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein  

RE: Shim for setting valve clearances (steel hardening question)

(OP)
Thanks.

RE: Shim for setting valve clearances (steel hardening question)

I was hoping the Poldi was NOT an impact tester.

Maybe you have a friend who works someplace where they have a hardness tester?

If you find that making your own shims is your only viable option which sounds like it might be the case then Metalguy's comments trigger some other thoughts:

Quote:
"Then you need to accurately measure the hardness, which will leave a tiny hole--unless you do it on extra pieces."

Yes you should have some extra pieces as you would make some anyway for practicing the heat treat process.

I do not think you will have a problem with decarb.  There simply will not be enough air (O2 molecules) to accomplish this if you do a reasonable job of collapsing the foil package around the part(s) in the sealing process.

Quote:
"Finally, use some very fine silicon carbide sandpaper (~280 grit or finer)and using a flat glass plate, rub them on each surface to be sure they are still flat.  Good luck with your fingertips trying to hold a 1 mm shim!""

Good point Mguy.  Might need to make an eeny-weeny holding device to accomplish this.  Which brings up another point.  These magnified pictures or 3D computer models that we deal with, often fool us when it comes to working with the real article.  When machining these shims on the lathe, you will need to make the boss, then part off the shim with slight excess axial material length at the larger diameter.  Then you will need a fixture to hold the part by the boss while facing off the excess material on the face opposite the boss.  The boss is too small to provide sufficient torque resistance while facing the opposite surface.  Therefore you will need to also clamp axially against the shim with a live center in the tail stock.  This will leave a small tit at the center of the shim to be removed with a convex needle file.

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