老福特係列:PCV valve,發動機的減壓保險閥門(多圖)

Do it at your own risk!

PCV valve(Positive Crankcase Ventilation valve)，不是PVC(Polyvinyl chloride - 聚氯乙烯，俗稱塑料)。雖然我的原裝PCV很像PVC做的。頭大了嗎~~

PCV valve，我有一個最簡單粗略形象的解釋：如果你知道早期的高壓鍋，那PCV valve就是高壓鍋上的減壓保險閥，高壓鍋代表發動機。

PCV如果堵塞，導致發動機內壓力升高，engine oil 尋求薄弱部位突破，是引起valve cover gasket leak的原因之一。

這裏有網上抄來的詳細解說:
---維基百科---

As an engine operates, high-pressure gases are contained within the combustion chamber and prevented from passing into the crankcase (containing the crankshaft and other parts) between the side of the piston and the cylinder bore by piston rings which seal against the cylinder. However, some amount of gas always leaks past the piston rings into the crankcase. This amount is very small in a new or properly rebuilt engine, provided that the piston rings and cylinder walls are correctly "broken in", and increases as the engine wears. Scratches on the cylinder walls or piston rings, such as those caused by foreign objects entering the engine, can cause large amounts of leakage. This leaked gas is known as blow-by because the pressure within the cylinders blows it by the piston rings. If this blow-by gas could not escape then pressure would build up within the crankcase.

Before the invention of crankcase ventilation in 1928, the engine oil seals were designed to withstand this pressure, oil leaking to the road surface was accepted, and the dipstick was screwed in. The hydrocarbon rich gas would then diffuse through the oil in the seals into the atmosphere. Subsequently, it became an emissions requirement as well as a functional necessity that the crankcase have a ventilation system. This must maintain the crankcase at slightly less than atmospheric pressure and recycle the blow-by gas back into the engine intake. However, due to the constant circulation of the oil within the engine, along with the high speed movement of the crankshaft, an oil mist is also passed through the PCV system and into the intake. The oil is then either burned during combustion, or settles along the intake tract, causing a gradual build-up of residue inside the inlet path. For this reason many engine tuners choose to replace the PCV system with an oil catch can and breather filter which vents the blow-by gases directly to atmosphere and retains the oil in a small tank (or returns it to the sump), although this technically fails to meet most engine emission legislation.


倒騰我的老福特，保養手冊讀了又讀，猛然發現廠家居然提到定期更換PCV valve。鑒於其可能和發動機抖動存在相關性，零件也極端便宜，所以毫無疑問要下手整這個。

相關安全措施：停車，熄火，拉閘，斷電，眼鏡，手套，口罩。不一定每次全用上，自己看著辦。

我見過朋友烤肉的PCV，就在發動機殼右上角，很容易用Ratchet Wrenche搞下來。老福特就不一樣了，PCV是藏在發動機殼的後上方，雖然沒有螺絲口，但是比較難下手。打開前蓋，燈照的範圍是我搜索方向。哦，你看見右前輪fender上那個癟膛(dent)啦?那不是我幹的，不過是我未來的DIY目標之一。





圖正中間那個白色的冬冬 --- PCV valve



三通結構，下邊PCV，上邊左右分處兩條管道，進入左右intake.



新PCV，換成金屬了。$1還是 $2，忘了。



需要兩隻手操作空間，左手從下邊固定，右手從上邊拔管子。發動機上的塑料蓋子需要拆掉。



移開塑料蓋，兩個intake黑管子之間的空間暴露，足夠右手向後下方伸進去。



正前方看過去。PCV的兩根管子分別連接在左右彎曲段的intake管子上。



Throttle 和intake. PCV就在後邊。



左手從這一側伸過去抓住，右手從上方下來，拽住三通結構，搖晃幾下，順利拔出PCV(圖中間白色的小東西)。



這一側看過去。已經拔出來的PCV從intake 之間暴露出來。沿著兩根管子，很容易找到與intake 的連接。同樣拔出來。



PCV和管子移除後，留下的PCV接口。是下邊那個。上邊的不是接口，隻是一個塑料外殼上的多餘結構。估計是加工用的，網上很多人詢問過這裏是否丟了什麽管子。



PCV三通和管道



新舊PCV



比較。舊的PCV有點髒，但是裏邊的小活塞活動看上去正常。



dust cleaner清理疏通管道。其實打氣筒就夠了。這麽粗的氣管，堵塞的可能性很小。



新PCV安裝。我先連接兩根管子到intake.



最後把PCV坐死。我的車型不需要固定卡子。



液體二氧化碳dust cleaner，也是居家DIY很常用的工具。pop dent也用得著，隻不過我的dent不太好搞。

所有跟帖： 

• 碼這麽詳細的圖,謝謝. 我是把舊的洗一洗又安回去了,沒什麽反應. -我胡說八道- ♂ (0 bytes) () 09/09/2010 postreply 10:50:23

• 頂！ -睿安- ♂ (86 bytes) () 09/10/2010 postreply 12:45:30