.002 is worth 18 PSI

[Ted Schefelbein]

I have a friend who was having trouble starting his XJ600, an old bike, about a 1994. Years ago (1994) my brother, my friend, and I went to the Yamaha dealership, and bought three of them. Friend is the only one who still has his, and it has about 60,000 miles on it.
He ran a compression test, and found cylinders 2 and 3 down 18psi compared to the outer two. Turns out each Intake valve was .002 too tight. His shop is a bit more complete than, say, mine, he owns, in no particular order, a Balding Beaver vertical mill, a smaller Bridgeport version of same, a plasma cutter, a square wave tig, a surface grinder, two South Bend tool room lathes, some other cool stuff, and the tooling and skill set to make them all work. His last restoration project was a 1954 Allis Chalmers bulldozer. Yup, he is "that guy". His shims went into the magnetic chuck on the surface grinder, and were ground to fit. He won't be renting our little FJ shim kit, he has options.
All the cylinders are very close to each other, now, on a cold compression test, (it is winter, here, we are done riding) and I'd be willing to bet on a hot test, in the spring, they will be identical.
Anyway, now you have a grasp of what .002 too tight costs you for compression on an intake valve. Posted only because I could.

Ted

[RPM - Robert]

We have seen a few shim failures resulting in damaged cams after the surface hardening had been ground off. Especially when, what I can only presume, the ground/softer side facing towards the cam getting worn down. Usually it chews up the cam lobe & bends the valves. I have seen a few that ate a piston, bent a rod, and even cracked the cylinder head(one time), I thought I had a photo of this but I guess I didn't save it to the computer from my phone.

[Ted Schefelbein]

I wondered if the shins were, A. Tool steel, and B. Hardened all the way through. If the shims are tool steel, they would be hard as a rock, one side to the other. If not, then, who knows how deep the case of the hardening is?

I won't be able to tell him, since this isn't the first time he has surface ground shims and put them back in. He has done it before.

Ted

[RPM - Robert]

No worries. Just giving a heads up. The shims in question on these motors weren't genuine Yamaha and being as there wasn't anything left of them hard to tell how they were hardened, I do know from seeing shims come out of some motors. There are aftermarket ones or maybe OEM for different motors that are only surface hardened. With as brittle as the Yamaha shim I just broke is and the single color all the way through. I believe the Yamaha shims are hardened all the way through.

[Ted Schefelbein]

I'd bet the genuine Yamaha shims are tool steel. Damn things are tough. All bets are off with the aftermarket versions. Wouldn't use them on a bet.


Ted

[ribbert]

I wondered if the shins were, A. Tool steel, and B. Hardened all the way through. If the shims are tool steel, they would be hard as a rock, one side to the other. If not, then, who knows how deep the case of the hardening is?

I won't be able to tell him, since this isn't the first time he has surface ground shims and put them back in. He has done it before.

Ted

.... what I can only presume, the ground/softer side facing towards the cam getting worn down. Usually it chews up the cam lobe & bends the valves. I have seen a few that ate a piston, bent a rod, and even cracked the cylinder head(one time)

The following is an opinion piece from my mechanic, Arty Bishop.

I'm not going to buy into the case hardened vs through hardened vs tool steel etc argument but when you grind the average amount of a valve adjustment off a shim, you are only reducing it's thickness by less than 0.2 of a percent of it's total thickness, this is not a problem. As for hardness, what sort of wally would put the ground side to the cam anyway?
Shim grinding in itself is not the problem, it's doing it without the proper equipment. 13 of the 16 shims in Noel's bike have been ground and a visual inspection can't pick the machined side from the original side.

By grinding his shims I was able to set the clearances to within 0.001mm of ideal tolerances, something they probably didn't even leave the factory with. That was 100k ago and I know I should check them but hell, the comps still sound even when cranking, what more do you need?   So, if he can get 100k out of an adjustment by reducing the thickness of the shims by less the 0.2 of one percent I figure you're probably looking at a 1,000,000 km's before the you'd be worried about the shims getting too thin (and probably then some!).

This discussion is largely academic anyway because hardly anyone reading this (yeah, yeah, I know there's a few) has access to the machines to do it properly and why would you bother, most of these bikes don't do big miles. Statistically speaking, one or two valve adjustments would cover most owners lifetime ownership.

Just buy, swap or trade the shims you need and be done with it. NEVER attack shims with workshop tools. People who think they can machine shims to the tolerances and uniformity required with hand tools should give up wrenching on their own bikes. Their involvement should be limited to maintaining tyre pressures (under supervision).

Noel

[Ted Schefelbein]

I believe my friend was shooting for exactly mid point clearance on his valves, if the spec was .004-.006, his goal was .005. Not .0055, and not .00575. By grinding them on his surface grinder, he achieved that. You WILL NOT DO THAT by swapping shims, in my experience, you always compromise a bit. Yes, he knows better than to put the ground side toward the cam. I'd guess all of us, here, do. That is basic.

I'm content to rent the kit, and make the compromise. And, as a side note, to leave the shim under bucket stuff to others.

My favorite was the adjusters used in the Suzuki GSXF. Easy to adjust.


Ted

[RPM - Robert]

I wondered if the shins were, A. Tool steel, and B. Hardened all the way through. If the shims are tool steel, they would be hard as a rock, one side to the other. If not, then, who knows how deep the case of the hardening is?

I won't be able to tell him, since this isn't the first time he has surface ground shims and put them back in. He has done it before.

Ted

.... what I can only presume, the ground/softer side facing towards the cam getting worn down. Usually it chews up the cam lobe & bends the valves. I have seen a few that ate a piston, bent a rod, and even cracked the cylinder head(one time)

The following is an opinion piece from my mechanic, Arty Bishop.

I'm not going to buy into the case hardened vs through hardened vs tool steel etc argument but when you grind the average amount of a valve adjustment off a shim, you are only reducing it's thickness by less than 0.2 of a percent of it's total thickness, this is not a problem. As for hardness, what sort of wally would put the ground side to the cam anyway?
Shim grinding in itself is not the problem, it's doing it without the proper equipment. 13 of the 16 shims in Noel's bike have been ground and a visual inspection can't pick the machined side from the original side.

Noel

Noel,

I would only presume the people that would put the ground side up would be the same people who put the number side up so it gets worn off and no one knows what it is unless it has been documented. Which from the customer service side of your career, I am sure you know most people do not do.

But if you are doing your own work and truly machining your own shims (or someone truly machining them) the number no longer matters, unless the bike is sold. If you are doing this then, you would likely have the wherewithal to document what size went where, that way you didn't have to figure out which shim is on what valve.

I don't know that I have seen a truly machined shims in bikes we have worked on. Seems like the time to chuck it up, make sure it is true, and machine it down is surely worth $9 or more to buy a new one. But I don't use a lathe often enough or have one here at the shop so it might be worth the effort to get it set up and grind them if you are proficient enough. However, the ones we have pulled out here looked like someone hit them on a belt sander or grinding wheel. Which would make them likely not true and worthless. I don't try and structurally engineer buildings, some people shouldn't try and work on their own cars/bikes. There is something in this world for all of us. You can only have so many irons in the fire and stay proficient at things. A jack of all trades but a master of none.

Ted,

The off sizes from Yamaha the 2s and 8s (252 258 etc) get you to .001" if you wanted you could buy those. But as the saying goes a tappy valve is a happy valve. On our own and customer cycles we set them to the loose side. It will give you that much longer between changing intervals. On a race motor we would set them to minimum, but these guys are checking their valves every other weekend in most cases.

All that said. Working on your own bike is one thing but when a shim shows up here and you can tell it is ground it goes right in the bin. We give shims back to the customer after adjustments for future adjustments but ground shims have a photo snapped and go right to the steel recycle bin. So they do not end up in back in someone's motor.

For the most part on these motors, once run in these valves seem to find a home and don't need much adjusting.

[Ted Schefelbein]

I always shoot for mid to loose on my own bikes. Mine live relatively easy lives, anyway, I am mostly a fair weather sometimes rider, these days. Having to bu, bu, bu, bu, buy, the shims, to get to the sweet spot, naw,  I've actually got more important things to deal with, like, is the beer cooling area in my shop holding at precisely at 34 degrees F? But, hey, .002 is 18psi.

Carry on.

Ted

[Millietant]

Yes, he knows better than to put the ground side toward the cam. I'd guess all of us, here, do. That is basic.

Methinks thou dost overestimate some of us on here Ted 

[ribbert]

Noel,

But if you are doing your own work and truly machining your own shims (or someone truly machining them) the number no longer matters, unless the bike is sold. If you are doing this then, you would likely have the wherewithal to document what size went where, that way you didn't have to figure out which shim is on what valve.

Seems like the time to chuck it up, make sure it is true, and machine it down is surely worth $9 or more to buy a new one........ I don't try and structurally engineer buildings, some people shouldn't try and work on their own cars/bikes. There is something in this world for all of us. You can only have so many irons in the fire and stay proficient at things. A jack of all trades but a master of none.

Robert, I posted about this in 2014 when I did it. Subsequent adjustments are not a problem (and at 100k between them one more will probably see me out.), because the number no longer applies I only to need to measure the amount by which the shim thickness needs to be reduced then bag and tag them with the location and the finished thickness, same as I did last time.

I did this at the time because it worked better for me, I reported it for novelty value and was not recommending it as a new normal and certainly not something to try with commonly owned tools, including lathes. I didn't have a supply of shims  but I did have access to a shop with the proper equipment and it was a freebie because it was my own bike and because of the work I send them. The job was done on a fancy milling machine for which they had a jig for just this purpose. The nature of this company's business is such that even without checking I'm sure the ground shims were micron perfect in uniformity and thickness. As you rightly point out, under normal circumstances this would not be an economical alternative.

You make a good point about being a jack of all trades..... Other than extensive knowledge of his own trade, a good tradesman knows and will happily admit his limitations and when it's time to pass a job on to some other expert in the relevant field.

A general caution to the readership - Under no circumstances try to grind your own shims!

Noel

[Motofun]

I have several hundred shims due to owning 2 FJ's and previously a CBX (same shim).  I organized them and mic'd them finding that the printed number wasn't always accurate.  As a result I can usually get pretty close to the gap I'm shooting for.  I do go to the loose end of the spec as power isn't the goal, rather reliabilty.

[T Legg]

I have also found many shims that vary significantly from their marked size and many that the numbers are very difficult to read with old eyes so I always have my caliper and check the thickness of every shim I have to replace and the shim I replace it with . It's quicker to check than to have to go back and replace the shim a second time.

[RPM - Robert]

We found when using the K&L shims they varied some. The Yamaha shims seem to be very consistent.

Noel, that comment wasn't aimed at you. I was thinking of the guys like "theleopard" or whatever his username was. I don't know if you recall but he decided it was a good idea to start his bike put it in gear and then use a rag to clean his chain.

My wife working in the emergency room tells me stories like this all the time. This guy had his car jacked up with no jack stand while he was underneath it, lost an arm. No wheel chock car ran him over etc etc etc. Hell, not mechanically related, but a guy decided it would be a good idea to hop a ranchers fence and take a picture with a horse. According to the mans wife, the horse knocked him down and stomped on his chest collapsing his sternum and one of his lungs. He had never been around horses and thought the horse would be tame enough. Unfortunately, for him, the horse was still a colt and had not been broke yet.

Anyways its was more of a generalized statement for everything in this world.

[Bozo]

When fitting new cams I was told to fit new shims (by Randy), I couldn't get the shims I wanted from Yamaha (I did get 8 shims from RPM) but the others I had in my collection from a local supplier. They were slightly used so I decided to use them with the number side to the cams because that face was new. After 500km I re-checked the shims and to my dismay I found the 8 RPM shims in perfect condition but the others were starting to score. I checked the cam surface under a strong magnifier and no visible damage. I have photos of these, it appears they only harden the non number face.
After 20K km the cams are still perfect (I checked yesterday) but I'll think twice about using other manufacturers unless really desperate (and number side to the bucket). Unfortunately here in Oz getting OEM shims is hard and expensive.