another valve shim swap story/observation

This has probably already been hammered a hundred times but for those who are having their first go at it right now here is my experience.

I read the threads and looked at the pics on this site and they were awesome and I thought I was ready to go. So when my tool showed up today I was excited to go pop out shims. So I positioned the notch where I needed it and pointed the cam away from said notch and bolted the tool down and to my dismay - I could not for the life of me grab the edge of the bucket. Dang! I tried for ten minutes until it occurred to me to turn the cam until IT pushed the valve bucket down and THEN bolt the tool in place - then rotate the cam - WALLAH! I was able to pop the shims right out. Yes ... I am an idiot. But just in case there is another idiot like me out there perhaps you can learn from my experience.

I'm sure when Fitz did his awesome pictorial he never in his wildest dreams imagined someone could be as ignorant as me so he never mentioned pushing the bucket down with the cam.

One more thing, I know the subject of grinding shims has been discussed and it has been discouraged in case the shims are only "case-hardened". But has anyone actually done the metallurgical study to see if that is in fact the case?

I happen to work in the R&D lab of Bendix Brakes and have access to the equipment to examine them. I think I will cross-section one of my shims to see if they are "thru-hardened" or only "case-hardened". That way those of us who have access to precision grinding equipment can grind our existing shims to specific thicknesses.

The main reason this interests me is because the shims are only available in .05 increments and that is the whole tolerance that we have to work with. So in other words, say you have a valve with .0762 clearance with a 290 (2.90) shim. To take that valve to the high limit (which is where I want it since they are going to wear down as they "wear in") I would need a 282 (2.82) shim. But my choices are only 285 or 280. The 285 puts me in the middle of the limit which is ok but I don't want to be doing this again anytime soon 'cause I like to ride my motorcycle and not work on it. But if I go with the 280 that puts me over the high limit by .0254.

I don't happen to like these choices. I think the shims should be available in .025mm increments. Since they aren't (or maybe they are and I just don't know about it), I would like to see if the shims are thru-hardened and if they are I will grind them to the sizes I want.

Now as for the down side I can see to this, the shims would have to be thoroughly demagnetized after grinding. If I have any doubts about that, then all bets are off and I will be ordering my shims from our dear friend Chacal.

 

My $.02 which these days isn't worth much.

Isn't the valve clearance check interval is 5,000 miles?

How much do you ride?

Even riding every day 12,000 miles a year like a car average you'd check twice, change the few that need it and be done with new ones. They shouldn't wear that quickly or the tolerance, shim thickness incriment and/or service increment would be different. In spec is in spec.

Just because you can doesn't mean you should.

I'd be interested to know though if they are hardened through.

 

Just fit the next size smaller & don't stress.

 

Just put them in spec and don't stress.

Once in spec, they don't change hardly at all once the motor has a few miles (past 10K or so.) The last time I did the '81, NONE of them needed to be changed, even the one that's close to tight so my log book say to "keep an eye on it."

 

"Aftermarket valve shims exceed the maximum of the Apparent Rockwell Hardness "C" scale, and average 47.0".....hopefully this info will be of use to you.

 

You would grind the side that has the numbers, and it wouldn't matter if you wore thru the "hardness" layer, as it's away from the cam, but, you need to grind it "square" perfectly, because don't these things rotate??

Am I the only person that uses a piece of 12/2 household wire to hold the valves open ??

 

No TTRide, you aren't.....I had a bear of a time getting my tool to hold on the #3 exh and had to resort to using my trusty wire. Like some others, it's not my favorite method but when all else fails, it does work and it works easier then ANY tool I've ever used. I just hate shoving anything under a valve.....something just doesn't feel right about it.

jeff

 

OK, here are the results of our metallurgical analysis: THEY ARE CASE HARDENED! That means we CANNOT grind them!

We performed a hardness test and confirmed that the hardness is as Len said Rc 47 min. We took three readings and the hardness varied between Rc 50-52 (slightly harder than the min. spec.).

Then we cross sectioned the shim and examined the micro-structure. The micro-structure indicated a "nitro-carburizing" which means that their case-depth consists of a "carburized" layer and a "nitrided" layer. The nitrided layer is the super hard layer that the cam lobes ride on. It is only about .0002" (that's .005mm). I did not make a mistake. It is not .002" but .0002" thick.

Right now we have the camera disconnected from our electronic microscope so I am unable to grab the pictures. We kept the sample and when we have everything reconnected I will take some pics and post them here for future discussions (because I am sure someone will ask this again in the future).

If these were thru-hardened like I had suspected, it would have been a very simple procedure to grind them to size. Tool and die makers regularly hold these tolerances so that would have been no problem. But with the depth of case that we are looking at we would grind right through the nitrided layer which would render the shim worthless.

Ok, best wishes and thanks once again for all the help gentlemen. I have benefited immensely from the people on this board. I have very little to offer compared to many of you. Thank you so much.

 

You have just contributed greatly; this is an issue that has been debated at length, but without sound scientific evidence.

You have now confirmed what some of us knew, but had no hard proof of.

Thank YOU.

***"hard" proof*** oops, I made a funny!

 

Just put them in spec and don't stress. [bigfitz quote]

I disagree, if the reading indicates a shim right at the extreme outer range of tolerance, fit the next SMALLER shim & enter in the log book 'no need to check for at least 6000 mls'

 

Thanks to all for your input into helping me to keep my bike running.

Fitz, you have no idea how much your posts on this site have helped and motivated me. Thanks.

TtR, I consider you my friend even though we are on opposite ends of the country.

Chacal, your input, help and parts are always right on the money.

Wiz, what an awesome resource you are to this board.

Iwin, I will take your advice and Fitz' advice and just fit the shims to put them in spec and not worry.

 

Thanks Micro,
But again, why can't someone grind the "bucket" side of the shim, if they had the ability to do it "square" ??

 

Time,
"square" is the easy part. Slap it on the surface grinder. Turn the mag table on and buzz off as many tenths as ya please. One side will be parallel to the other. VERY parallel.

I agree that if you left the ground side down the case hardening being gone wouldn't be an issue.

also in response to your above comment, the valves, springs and buckets all rotate around because of a touch of cross angle ground into the cams. The shims don't do much rotating in their seats though they certainly could. I think that's more a side effect than the intent.

The reason *I* wouldn't do it is that they need to be at least a little chamfered and that's a whole extra fixturing that's kinda a pain.
These shims are listed as "not chamfered" however the inside of the bore in the buckets ALWAYS has at least some amount of radius in the bottom. It is literally impossible to cut a perfectly sharp inside corner. However once you grind the shim it WILL have an extremely sharp outside corner.
The proverbial square peg, round hole.

What would happen is that the sharp corner would ride high on this radius and with wear would pretty rapidly press in. That'll make the clearance ya check initially pretty useless and make the shims stuck in there absurdly tight the next time they need to be fished out.

I'm with Wiz as far as it goes regarding not minding being just outside spec on the loose side. The difference from one shim to the next is .0019"
Two thousandths of an inch... literally an RCH. Out of spec by say, half that is not going to induce valve slap or excessive cam wear as would being loose by say, ten thou.

Regarding Case Hardened vs through hardened... I have no literature or resources one way or the other on it but if I were trying to make such a part I would certainly spec that it be only case hardened. Metal is more like wood than we commonly or intuitively think. It has internal stresses and when you subject it to various conditions these stresses come to light. Sometimes I imagine a lattice-work of random criss-crossing springs of different sizes and orientations. Heat treating makes the springs stronger.
By leaving the core softer than the surface you reduce the propensity for twisting and warping A) in the heat treating process and B) in subsequent heat cycles of use in a motor.

In seeing this case hardening issue pop up repeatedly I've thought about doing my own hardness test. Drop a known weight from a known height onto a punch on the shim and measure how deep a dent it makes. Then grind half of it away and repeat. Deeper dent means yeah, it's only hardened skin deep.
I'll have to pop over to kalecoauto and get me one of them Round Tuits for this though.

 

Thanks for the insight.

 

Yeah, like MB says, if we create a sharp corner by grinding where we need a slight radius that could cause an issue. Granted it wouldn't be much since we would only be grinding one or two thousandths of an inch but it could be an issue. I will try to remember to check and see what the corner looks like. I also have access to an optical comparator so that would be no problem. But that would not be my first concern. My concern is removing the nitrided surface.

TtR, I suppose you are right in that if we ground the numbered side that sits on the shim bucket we would be safe. I just don't know. For me to feel safe doing it I would want a lot of testing before I risked my bike's engine. But you may well be correct in that we can get away with it. Before we (Bendix brakes) ever release our products we do an enormous amount of labratory testing so I have probably been heavily influenced by that mindset. Our standard before releasing a product to the market is at least the equivalent of one million miles (this is for the heavy vehicle market).

I have engaged the help of our metallurgist so we will do some additional testing as time permits (so we don't steal from our employer). We did some additional chemical analysis and it appears that the shims are D2 or D4 which are tool steels. This analysis was done with an xray machine that operates in a vacuum chamber and enables us to measure certain chemicals but not carbon content so we can only get close with this.

In the next couple of weeks we will have a "spectrometer" up and running so we will be able to get an extremely accurate analysis of chemical content.

In regard to MB's idea of doing his own hardness test, sometimes such "real world" tests are worth gold. In this case however, dropping a weight to make a dent is not the issue. And here I should clarify something; the shims HAVE been thru-hardened but they have also been subjected to a "surface treatment" (ie nitro-carburizing) AFTER heat treating and finish grinding. The nitrocarburzing does not really add to the hardness only their "wear resistance". I thought all this info would only confuse the matter in my early post so I sufficed it to say that they were "case-hardened" because I thought that is what most people are familiar with. But you all are a very technical bunch. It was one of those situations where you wonder how much information to give a person because you can imagine their eyes starting to glaze over because of too many details.

 

Seems like an awful lot of effort to save $7. IMHO

 

Agreed! I surrender!

 

yeah, I know about types of hardness. Just don't have all the sample materials to see which scratches which. The dent test is how they do (or at least did "back in the day") other hardness tests. Think about it though... a chunk of carbide isn't going to get a very deep dent in it, is it?
Also it doesn't matter which side you grind. I would prefer to grind off the numbers so that no-body ever assumes it IS that size in the future.
That is the only reason they say to put the number side down, so the cams don't wear off the (acid? laser?... prolly acid) marking.

Fitz, you've seen through my lies and discovered the real reason I don't bother.

Also, SEVEN BUCKS?!? an outrageous sum. Got a guy that'll swap straight across most sizes and charges me a whole dollar to trade if I take one he's low on. I leave him a six pack and am glad to tip.

 

Ok, here is the cross section of the valve shim so you can see with your own eyes what we have.

The darker material at the top is the "potting" material that we use to hold the thin cross section - it is not a part of the shim. Then you will see a very thin bright line - that is the nitrided area. We put arrows with dimensions on it and if you zoom in on that area you will see that the "nitrided" area is only .00014" thick. That is about 1/20th the thickness of a human hair. This is what gives the shim it's "anti-wear" properties.

Immediately under that bright line is a darker area which is the "carburized" area. That area is about .002" thick and it is also a harder area than the rest of the shim but slightly less "wear-resistant" than the nitrided area.

Then you have the lighter gray area under that and that is the "core" of the shim. Even this core is very hard.

Yamaha used a D2 or D4 tool-steel material which is very high quality steel to begin with and then they gave it a surface treatment to add an anti-wear factor! If they carried this kind of engineering through the rest of the bike it's no wonder these things last forever. They did not skimp! I am very impressed with what they did here.

 

That is so cool thank you.

 

You're very welcome. I thought it was cool too. I forgot to mention something. At the bottom right hand corner of the pic you will see a "bar graph". That bar graph is .003" so it can give you an idea of the overall scale - kinda like the scale on a map.

 

Mirco, this is an interesting and enlighting discussion but I wonder what the cost would be for the average joe, were the shims actually "thru-hardened". Not cheap! You could dream it because for you the wherewithals (man, I hardly have a chance to use this word!), like the proverbial mountain, "were there".
Truth be said, 9 British Pounds for each shim at wemoto.com is not cheap too, but my shims are 25mm across (XJ400, a "white fly" as we say down there in Brazil) so be it - no shim pool for me!). My point being, "no matter the cost, I want my darn XJ running soon!"

 

When I need Shims, ... I go to Dunkin Donuts.
Box of Joe, 10 Cups, Creamers, Sugar and Sweet and Lows.

Now go to the nearest Dealership or nearby Bone Yard.
Memorize this phrase:
"God told me to bring you all fresh coffee, ... He also said to ask you if I can swap these for the ones I need on this list".
Bring your Old Shims and KNOW which ones you need.

Bring a Micrometer or a Vernier Measuring Tool.
You might have to measure Shims that have the size stamp obliterated.

 

Or even better, go to your friendly neighborhood yammie dealer and tell them you have something to trade....

and then pull out your shims

Always free, every time.

I picked up a set of shims from someone parting out an engine, and so now i can measure my clearances, figure out what shims i need, then take my spare shims to the dealer so i only have to make the trip once