LLoyd,
I'll try and explain this to you as best as I can, altho' you'll probably get a flood of responses.
First, all autos and motorcycles (excluding Ducati) have valve springs. The purpose of these springs is to slam the valve closed during compression and ignition. This essentially seals off the cylinder so compression and ignition can take place without the loss of the expanding gasses that force the piston down, be converted from a linear motion to a rotatry motion by the crank. To open these valves at the proper time, you need a cam. You've had yours open so you know what these look like. The cams in the KLR operate the cams by direct contact of the cam lobe(s) to the top of the valves through the shims and the buckets they rest in. In this type of arrangement there is no latitude of error with the valve clearance. This adjustment is determined by the thickness of the shim.
A things wear over time, this clearance changes. The repeated slamming of the valve against its seat can wear the valve and it's seat allowing it to effectively sink further into the head. When this occurs, the clearance between the end of the valve (throught the bucket that sits on top of the valve & spring, and the shim) close, and the valve clearance between the shim and the cam closes up (gets tighter). To correct this, you will need to replace the shim with a thinner one.
BUT, the cam lobe, the top of the valve, and the shim are also wearing - having the tendancy to open the clearance between the top of the shim and the cam. Which one wins in the wear department? A good question and one that can't always be pre-determined. The manuf., however, has a pretty good idea when they engineered the engines and they came up with a conservative number. This is the mileage number they give you in the manuals as far as valve adjustment interval.
This, however, should be used as a guide only. If you are a red-line kinda rider, its probably best to check them more often. Constant high speed operation and the resultant slamming of the valves has a tendancy to cause them to sink into the head faster, which closes up the clearance as described above.
Suffice to say, the above decribes a purely mechanical valve actuation mechanism. There are variations, of course, where the cam activates a rocker arm, which in turn actuates the valves. In these schemes, the adjustment is made through a shim on top of the bucket the rocker hits, a shim under the bucket, or a screw and nut adjuster typically on on the end of the rocker. All of these mechanical schemes allow for no compensation in wear. If something does wear, the resultant valve clearance is going to change in one direction or the other; either tighten, or loosen up.
Most autos today, and some bikes, have what's called hydraulic lifters (HL). These are basically a cylinder that has one end closed off, and this end rides on the cam and follows the cam lobe. Inside this cylinder is a piston that is captured on the other end by a clip (or swaged end). There is usally a spring inside that will keep this piston pushed up against that clip. Push on the piston, and it will sink into the bore of the cylinder as far as the spring will allow or runs out of travel.
Now, add a fluid, such as motor oil, into the cylinder. Since liquids don't compress, you won't be able to push the piston down; it might as well be a solid piece. Now, add a port in the side that will allow engine oil to enter, or escape, and this changes the ball game.
If this hydraulic was used to ride on a cam, that then pushed on a valve (through a rocker arm) and there was no port, you essentially have a mechanical system as described earlier. The hydraulic lifter might as well be a solid chunk of metal. Nothing gives and any clearance would have to be compensated for by the length o the lifter, an adjuster on the rocker arm, or a shim on the top of the valve the rocker arm was working against.
Add in the port and things change.
At rest on the low side of the lobe (when the valves are closed), oil that had been captured in the lifter is allowed to escape. The spring under the piston allows any mechanical pressure caused by the valve spring allows it to move. The valve spring pressure overcomes the lifter spring pressure and the valve remains closed during the compression and ignition stages of engine operation. When its time for the valve to be opened, the cam lobe will push up on the lifter and its port will close by a machined groove in the bore it is operating in. Once again it becomes a solid object that can open the valve against the valve spring pressure.
As the cam rotates around and the lobe is no longer trying to lift it, the lifter is pushed back down into its bore, the port is uncovered, and the captured oil escapes. Any wear that may occur in the valves, the cam, the rockers, etc., is now compensated for by the lifter's piston and the spring that is keeping it floating in the bore of the lifter.
You've probably heard the expression that an engine had a 'collapsed lifter.' This is usually associated when talking about an engine whose valves are rattling pretty god during initial start up in the morning, or after sitting for an extended period of time. This is when the engine was stopped and one, or more valves were in the open postion. This would be when the port in the lifter was closed off, so the lifter should be a 'solid chunk.' What's happened is that the lifter piston-to-bore clearance has worn, and the catured oil was allowed to escape. The valve that was opened is now closed, or partially closed, and the only thing keeping pressure on the valve stem is the spring under the piston in the lifter. Once the engine is started, excessive clearance will be present until the lifter can fill with oil to, once again, make it 'solid' so it can open the valves like it should.
There are several variations of where the hydraulics come into play in this type of system, but the bottom line is that the hydraulic lifter compensates for valve train wear so adjustments are no longer needed.
A quick and dirty explanation, but hope this helps.
Guy
A16
Richmond, VA
-----Original Message-----
From: "Lloyd F. Rauschkolb"
Sent: Jan 10, 2005 6:48 PM
To:
DSN_KLR650@yahoogroups.com
Subject: [DSN_KLR650] KLR Valves Observation and Question
Adjusting KLR valves is probably easy for those that are mechanically
inclined I guess, but some of us struggle with it and then wonder if
we did it right when we get through. (Don't suggest taking the bike
to a dealer, that is just not an option any more).
Believe me I would rather do that, but I don't believe for a second
that dealers actually adjust the valves, and even if they do, I doubt
they do a half ass job of it. I have done it myself a few times, but
I just don't like to do it and I always end up wondering if I did it
right.
Can anybody explain why it is necessary that valves need to be
checked/adjusted so often on most motorcycles and never have to be
checked/adjusted on most cars?
Seems like this aggravating procedure could easily be eliminated for
motorcycles like it has been for cars.
Lloyd Rauschkolb
Gulfport, Ms.
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. However, the increased
cylinder head height needed to fit hydraulic valve lash adjusters and
associated rocker arms into a dual-overhead-cam cylinder head definitely
was an issue, given how tall the KLR already is. Either Kawasaki would
have needed to move the crackshaft further back and lean the cylinder head
further forward and lengthen the wheelbase, or ... well, anyhow, they did
nothing of the sort, and instead did the shim-in-bucket trick to make the
valve train less lofty.
-E