Question for our dealer guys and others that are in the know.

[spicholy]

Since my Bird has around 44,000 miles, I thought I would check with my local dealer to see what they charge to check the valce clearance. They quoted me 4.5 hours at $80/hour. $360! He said that if any shims needed adjusting it was all included in that price.

My question is this; does it really take 4.5 hours to check and adjust the valves in this bike?

If that is a reasonable time frame, it sounds like something a bit more involved than I want to do on my own.

[Redbird]

It shouldn't take that long to check them, it'll probably take considerably longer to adjust them. Sounds like they might be splitting the difference and betting they won't need adjusting.

Spend 2-3 hours checking them yourself. If they're in spec, you're golden, if they're out of spec, that $360 ain't a bad deal.

[spicholy]

Thanks. That is what I was thinking. They are hedging their bet.

[02XXCA]

It shouldn't take that long to check them, it'll probably take considerably longer to adjust them. Sounds like they might be splitting the difference and betting they won't need adjusting.

Spend 2-3 hours checking them yourself. If they're in spec, you're golden, if they're out of spec, that $360 ain't a bad deal.

I don't trust dealers. I think they will take your money and lets you go even if a number of them are on the tight side.

I would rather do them myself. Mine at 68K had only one Exhaust that was out of spec, but since i was there I reshimmed them to the loose side, cause I don;t want to go back in for another 68K.

[spicholy]

Let me ask this. If I do it myself. Am I reading the other threads about this correctly? That you actually shim to the loose measurement. The shims get tighter as they wear. This seems illogical. How do they gain mass?

[MontanaXX]

Let me ask this. If I do it myself. Am I reading the other threads about this correctly? That you actually shim to the loose measurement. The shims get tighter as they wear. This seems illogical. How do they gain mass?

The valves don't get longer [more mass], but rather they pound their way into the valve seat thus tightening the clearance over time.

I checked my valves last Fall on my 30k mile 97 model, no shim adjustments were needed.

[spicholy]

Let me ask this. If I do it myself. Am I reading the other threads about this correctly? That you actually shim to the loose measurement. The shims get tighter as they wear. This seems illogical. How do they gain mass?

The valves don't get longer [more mass], but rather they pound their way into the valve seat thus tightening the clearance over time.

I checked my valves last Fall on my 30k mile 97 model, no shim adjustments were needed.

Ahhhh! That makes sense. Thank you. I hadn't thought about the valve wearing into the seat.

[rockmeupto125]

Montana is correct, but just to expand on what he said. As noted elsewhere, the meds are kicking in today.

Its a common and understandable misconception that the reason a valve changes adjustment is because the area of actuation gets worn down. By this, I mean the stem, or round cylindrical end that makes contact with the cam follower..outside the combustion chamber. If this area were to be worn down through repeated usage, it would indeed make the valve clearance looser. However, wear on the cam side of the valve is almost nonexistant unless there is a big problem. There are several reasons for this. One is the extremely tough hardening procedures of the metal of the cam lobe face and the follower bucket...the "can" that sets over the end of the valve/spring assembly. Another is the relatively large contact area these components have that greatly reduce the the load over area squared. Excellent temperature management of newer engines help to preserve the hardening treatment of these components, and better science in lubricating oils have given us greater surface tension and protection even from cold startups. So if your clearances are changing on the top end, you've got a heat problem or an oiling problem that has led to deteriation of the hardening treatment of the valve actuation components, and that ain't good...in fact, you've got a very sick engine.

What really happens in a healthy engine.....that is to say, one living an untarnished life....is considered to be just normal wear. The valve bells out in the combustion chamber to cover the hole that allows air and gas either in or out. The edge of that bell is machined to match the valve seat and creates such a fine match that it seals the combustion chamber nearly perfectly against the flow of gas...keeping compression and combustion contained.

So what cause the wear here? Very simple, in a complicated way. If you take a flat hammer, and hit a flat piece of strong metal in perfect alinement 100 million times, some of the metal is going to wear off (3500rpm=210,000rphx1000hrs to a theoretical 60,000 miles, valves open and close every other revolution). Well that sucks. How about we put some oil on that instead...after all, isn't that what we do to the other end of the valve to prevent wear? Actually we do put oil in there. In the old days, we used tetraethyl lead to lubricate valves. Now its some other additive that we put into gas before its sent to consumers.....and we'd notice it pretty quick if that wasn't in there. Okay, that end is covered. Why don't we soften that hammer blow? Why do we have to have a hammer blow at all? If you set a machined head on a workbench upside down with the valves set in the cylinders, without springs or cams or valve seals or anything, and pour oil in the in the cylinder head over the valves.....you'd expect to see all that oil still in the cylinders when you came out to the garage the next morning....or you'd know the head and valves ain't machined right. So if valves seal so good all by themselves, why do we have that hammer blow thing going on? (I told you it got complicated)

That hammer blow comes from the springs on the valve that make it retract into the cylinder head when the cam stops holding the valve open. As we all know, those springs are pretty stiff...and designed to make that valve close fast----real fast.....because that's how to make more power, right...more rpm? At 11,000 rpm (you know...the rpm where you DON'T want your valves staying open and wacking up against a busy piston), that valve has to accelerate from a dead stop and move roughly 10mm in less than 0.0018 seconds....repeated 91 times a second. It takes a hell of a spring that makes a hell of a hammer blow to that valve/seat combination to do that. BTW, we can make engines that don't have any particular method (springs, air, mechanical actuation) other than cylinder pressure to close the valve...but they're highly inefficient.

So we can't get away from this hammer blow, at least not at the current state of technology. We've lubricated the valve as best we can, and are resigned to the fact that we're going to have valve wear. But we still have choices. If we make the valve and the valve seat that the bell of the valve seals against out of different materials, could we influence the wear patterns? Certainly! So the choice is to make the valve seat out of a soft material, and the valve out of a hard material. Now why is that? Okay......last concept. The valve in design has a sharply defined edge. Its thin and light as we can make it, because its a moving part, takes power from the engine to make it move. If we make it lighter, we can use less powerful and lighter valve springs, have less wear on the cam and followers, and the world will be a better place. The thin edge of the valve is its weakest point, and at least one of the valves in any given cylinder (two in the XX) has fire and brimstone of over 1200 degrees flowing past the edge every time it opens. That valve has some incredible heat treatment on it, and we want to absolutely minimize the amount of wear on that very thin treatment area of that very thin piece of metal....and the way to do that is make sure the metal we slam it into is so much softer than the valve that it won't ever damage it. That material is the valve seat, and that's what gets worn away in the engine to protect the valve from wearing.

There's your overview. As that valve seat gets worn away, Montana said the valve then recede deeper into the head, sticking further out the top towards the camshaft, and DECREASING the valve clearance. When the valve clearance decreases enough so that at some combination of rpm, heat, and stress, the clearance is less than zero and the valve stays open the most minimal amount, superheated combustion gas will blast out around the valve, destroying the heat treatment of the valve, and breaking down the metal quickly. But wait.........doesn't the hot gas go out around the valve anyway when its normally open? Nope......not like that. Normally, the valve opens as most of the combustion has already occured and heat has been transferred to the cylinder wall and piston..diffused throughout the combustion chamber and weakened due to the expanstion of the combustion space. The hot gas that passes by a valve held marginally open on the combustion stroke of the engine is much hotter (2400 degrees F---a thousand degrees hotter than "normal" exhaust valve flow) and experiencing active combustion...not to mention being concentrated on a very small portion of the valve...the area with the easiest flow. Think of a gas stove and a frying pan. Not a problem, right? Well, fire up your gas cutting rig, point it at that pan, and half a second later, there's a hole in it. That's what happens when your valve clearance reaches zero. Exhaust valves are the valves that have the most problems, but you'll still damage an intake valve that gets tight, because the exhaust can blow around any valve in the cylinder. The intake valves are a different material and heat treating because they aren't supposed to be dealing with exhaust gas....so they'll actually fail sooner than an exhaust valve once the clearances are too far out.

I hope I've at least stimulated some thought, understanding, and a desire to make sure your valves are in spec. One last expectoration.....as clearances decrease, valve actuation more closely follows the cam profile. For most performance based engines, that means higher horsepower. If you set the valves toward the loose end of the range, you won't get as much power....that's why performance guys are always checking their valves...they've been set tight and require a greater frequency of inspection. On the other hand, if you set them a bit loose, you'll get more torque, and perhaps won't need to be as diligent with your valve checks.

Thanks for listening!

[spicholy]

Now that's an explanation for ya. Thanks Joe. I do love the edumacation I get at this place. Just proves you should never be afraid to ask a question.

[MontanaXX]

Wow. I copied that explanation and intend to post it when I see this question on other forums, with proper credit given of course.

1,387 words; that's longer than the papers I wrote in school!

[Banshee]

An excellent explanation, thanks. Now if only we could get away from those pesky hammer springs & close the valves quickly, but gently we'd be on a winner! The only thing I can thing of that comes close is the desodromic system or rotary valves. One tried & tested, but mechanically complex, so more parts subject to wear... The other, around in various guises for some time, but has rarely been used in 4 strokes as far as I am aware.

[BackStreet]

Now that's an explanation for ya. Thanks Joe. I do love the edumacation I get at this place. Just proves you should never be afraid to ask a question.

+1 was does not cover it; I am in awe. :icon_clap: