Camshaft Gear

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有话就说限制小排量就是不让多数人用车

——摘自搜狐网(http://auto.sohu.com)

　　事件起因：88个城市歧视小排量车油价高涨可望破局

　　据2003年出版的由国家工商行政管理总局消费者权益保护局等部门主编的《中国汽车消费指导手册》介绍，全国有28个城市限制微型轿车使用，有近30个城市禁止微型客车作为出租车使用。而在今年两会期间，全国人大代表、长安汽车（集团）公司董事长尹家绪向新华社记者介绍的最新数字是，全国有22个省区市的84个城市出台了歧视小排量汽车的政策，包括北京、上海等大城市。

　　去年下半年以来，由于燃油价格居高不下，小排量车市场出现热销局面。据中国汽车协会统计，今年1至5月，国内制造的1．0升以下排量乘用车，销售量达到438773辆，占同期乘用车总销量的32．84％，可谓三分天下有其一，同比增长了20．71％。如果再加上1．0升至1．6升排量，则销量达到了936666辆，占总销量的70％，增幅达到33．3％。与之相反的是，同期1．6升以上排量的乘用车却是负增长，小排量车的市场表现可见一斑。

　　然而一方面是小排量车的热销，另一方面却是全国60多个城市相继实行了对小排量车的限行规定，而且限行之风大有愈演愈烈之势。最近在全国政协常委会上委员们再次发出质疑，还有院士出面大讲一些人们已经耳熟能详的道理，呼吁取消对微型车的不合理限制。

　　其实对小型车的限行...

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Camshaft Gear

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If the camshaft and crankshaft drive gears require replacement, this can be done with the engine in the car. Manufacturers of engines with pressed-fit camshaft gears make special tools that can be used to hold the cam forward during gear installation.

NOTE

If the cam sprocket is the nylon type and chunks of gear teeth are missing, the oil pan must be removed in order to extract teeth from the oil pump screen and oil pan.

This oil pump sprocket is filled with the teeth of a nylon timing sprocket that failed.

Replacing A Camshaft Gear

When replacing a pressed-fit camshaft gear, use a puller to remove it from the cam.

Disconnect the negative battery cable.
Remove the covers protecting the camshaft drive gears.
Check for proper alignment of the timing marks on the timing gears.
Remove the timing gears according to the service manual.
Clean the timing gears.
Inspect the gears for wear or cracks, and replace necessary parts.
After replacing any worn or damaged gears and drives, set the timing marks according to the service manual.
Rotate the engine through two complete rotations of the crankshaft. Check to see if the timing marks on the gears are still in proper alignment.
Reinstall all covers removed for access.
Reconnect the negative battery cable and start the engine.
Set the ignition timing to the manufacturer's specifications.

Installing A Camshaft Gear

When reinstalling the gear, take care that the cam does not move to the rear; it could knock loose the core plug in the rear of the block or chip cam lobes on neighboring lifters.

The rear of the cam gear must be supported while the cam is pressed from its center.
After the new cam gear is pressed on, end play is checked with a feeler gauge.

Checking the clearance behind the thrust plate to determine camshaft end play. Courtesy of Federal Motors Corporation, Service Technology Group.
The clearance between a cam thrust plate and the sprocket or gear varies from 0.0015" to 0.005".
If a spacer is used, it must be from 0.0015" to 0.005" thicker than the thrust plate.
The cam will press against the spacer, which fits inside the thrust plate hole, controlling end thrust.
In some cases, adjustment is made by replacing the thrust plate.
Some engines limit the end play of the camshaft through the use of a cam button.
A nylon button or torrington bearing sets on a spring and is installed between the camshaft timing gear and the timing chain cover.
Aluminum gears can be heated for easier installation.

NOTE

Do not forget the spacer on a cam with a bolt-on sprocket. The result could be a cam that will not turn after the bolt is tightened.

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