Shim for setting valve clearances (steel hardening question)

[masterx81]

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!!!

 

[unclesyd]

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

 

[masterx81]

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.

 

[Metalguy]

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

 

[masterx81]

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...

 

[Metalguy]

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

 

[masterx81]

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!!!

 

[Metalguy]

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

 

[masterx81]

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!!!

 

[Metalguy]

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

 

[masterx81]

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

 

[Metalguy]

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

 

[masterx81]

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?

 

[Metalguy]

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

 

[masterx81]

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 )

 

[Metalguy]

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

 

[masterx81]

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?

 

[Metalguy]

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

 

[masterx81]

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

 

[Metalguy]

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