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Discussion Starter · #1 ·
If one were to never check the valve clearence what performace symptons would eventually begin to appear, and what would the long term damage be to the engine ? Of those that replied how many miles did you ride before you had to change your first valve shim ? Just curious..... :?:
 

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Mike,
If the clearance is too tight, the valve will not close completely and you will have a loss off compression if it is the intake, along with possible backfire through the air intake. If the exhaust is too tight the valve will not close completely causing a decrease in compression and a possible burnt valve. You do not want the latter. If the clearance is too loose the valves will close too early and your performance will suffer along with increased wear to the valve themselves, camshaft, buckets and rockers. I suggest you get the valves checked when called for.
 

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All this valve clearance check stuff is getting to be a drag. When is someone going to come up with a retrofit hydraulic lifter kit?
 

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Blue Winger said:
Mike,
If the clearance is too tight, the valve will not close completely and you will have a loss off compression if it is the intake, along with possible backfire through the air intake. If the exhaust is too tight the valve will not close completely causing a decrease in compression and a possible burnt valve. You do not want the latter. If the clearance is too loose the valves will close too early and your performance will suffer along with increased wear to the valve themselves, camshaft, buckets and rockers. I suggest you get the valves checked when called for.
I don't think that's correct. Assuming proper adjustment, as the shims wear, they get thinner (they can't get any thicker), increasing the valve clearance. That would result in the valves not opening as much as they should. They still will close completely. It is true that valve timing will gradually shorten, i.e., opening later and closing sooner.

If one were to never check the valve clearence what performace symptons would eventually begin to appear, and what would the long term damage be to the engine ?
The shims would have to wear a lot before any performance issues would be felt. As the shims wear, increased clearance would result and more valve clatter would be heard. The ECM regulates air/fuel mixture. As valve opening decreases, the ECM will adjust the A/F ratio to lean it up because it's not getting as much air. The A/F ratio would still be correct for the amount of air entering the combustion chamber so you really wouldn't have a lean condition. Eventually, though, the power would decrease. Theoretic worst case, the valves would fail to open and the engine wouldn't get any gas.

When is someone going to come up with a retrofit hydraulic lifter kit?
True, with haydraulic lifters, you would eliminate the valve clearance check. You would also suffer in the performance department... but not much the way this engine is set up. As cam lift increases (there are no aftermarket cams that I know of for the 1800 so this point is moot for it), solid lifters become more important at high RPM's to ensure the valves don't float.
 

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Let me add to the confusion.

With normal wear; you will not notice symptoms of the wear until its too late. With this engine design, wear makes the clearance we check get tighter. The parts that are actually wearing are the valve faces and seats. The shims wear so little that you can still read the sizes printed onto their surfaces. The bucket tops and cam lobes may wear some, but that is relatively negligible to nill -- your oil is taking the beating there instead of the metal; the same with the valve stem ends and teh inner surfaces of the shims. As the valve faces and seats wear, the valve springs pull the valve stems deeper into the heads and the tops of the stems protrude further out toward the shims and bucket bottoms. Thus the cam lobes depress the buckets, the shims and the stems inward and then these parts return as the cam lobes pass the buckets. The dwell time, that brief period of time in wich the valve faces are in contact with the valve seats per cycle, decreases. The seats are in the heads, the heads are water cooled and thus the only opportunity for the valves to lose heat to the water cooled heads is while they "dwell" upon the seats. AS the dwell time shortens, the valves get hotter, expecially exhaust valves. They get hot enough to errode and distorta nd that allows jetting and things go from bad to worse in a hurry. You will hear no clatter of the valves. you will lose power and get backfires and its too late baby; you need new seats and new valves. $.$$$.00; maybe new heads. Its wasy to check, get the tools and a spare set of valve cover gaskets incase you tear one and fresh tube of safe silicone gasket RTV for the front semi circle. This design is resistant to wear and typically once they are broken in and set, there is very little wear if the oil qulaity is decent and changes occure before oil breaks down. But, its simple check to prevent big consequences.

prs
 

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Wanderer said:
I don't think that's correct. Assuming proper adjustment, as the shims wear, they get thinner (they can't get any thicker), increasing the valve clearance. That would result in the valves not opening as much as they should. They still will close completely. It is true that valve timing will gradually shorten, i.e., opening later and closing sooner.
Shims don't wear in a shim under bucket valve train, not even a little bit. I have checked them with a micrometer and they are exactly what is stamped on them, even after 100k miles. The shim simply sits in the top of the valve and the bucket rides on it. There is nothing to wear.

Blue Winger and Pigeon Roost are correct. What wears are the valve seats, and as they do, the valves recede into the head, making the clearance tighter. You will normally find the valves tighten as the engine gets more miles on it. If a valve gets looser, you have something going wrong with the camshaft, and that is an abnormal situation.

I changed my first shim around 65k miles or so, but it was technically still in spec.

The valve specs are .006 inches (+/- .001) for the intake and .009 (+/- .001) for the exhaust.

I did the valves on a bike with 133k miles on it last week, and it had never been checked. All the intakes were at .005 and the exhausts were at .008. Again, technically they were still in spec, but I went ahead and pulled the cams and dropped each shim one size, bringing all 12 valves back to center spec (.006 and .009). The owner reported to me that their gas mileage increased fairly dramatically afterwards.
 

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Fred H. said:
... I did the valves on a bike with 133k miles on it last week, and it had never been checked. All the intakes were at .005 and the exhausts were at .008. Again, technically they were still in spec, but I went ahead and pulled the cams and dropped each shim one size, bringing all 12 valves back to center spec (.006 and .009). The owner reported to me that their gas mileage increased fairly dramatically afterwards.
I know who that was! :wink:
 
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