Thursday, January 4, 2018
3412 valve adjusting method
I love the Caterpillar 3412 engine. Not the over rated high horse power engine in yachts but the commercial fisherman that turn out 600 hp continuously. Having serviced the sea scallop fleet out of Virginia for some 38 years I've come to know them very well. Let me share some of what I know.
Let's not get technical. I don't design them, I only repair and overhaul them when they break or wear out. All engines have design problems but for this application I believe this is the best there is . I was so sorry to see them replaced with newer C32 engines that are far more complicated with overhead cams and all electronics. I understand this was required to meet new Federal emission standards but they will be sorely missed.
Let's talk about valve adjustment. Cat's method requires that you find TDC #1 or #11, set certain valves, turn one full rotation and set the rest according to a chart found in the testing and adjusting section of the service manual. After all these years I don't need no stinking book to assemble this engine.
On a four stroke engine two cylinders will TDC at once. One is at the top of it's stroke on compression and the other on exhaust. If you understand the four stroke engine you will know this. The firing order of a six cyl, engine is 1-5-3-6-2-4 for most engines. (There are exception to all my rules). Each side of a 3412 engine fires like a six cyl. so cyls. 1 and 6, 2 and 5, 3 and 4 when counted from the front on the left bank will TDC togather and the same is true for the right bank. I call these companion cyls. To determine TDC on any cyl. simply watch the valves as you hand crank the engine. When you see the exhaust valve closing and the intake valve begin to open you know that cyl. is at the top of it stroke on exhaust. It's . companion cyl. is near TDC on compression and you can set both valves on that cyl. because the engine would need to turn 180 deg. in either direction before a valve opening on this cyl. Adjust valves .015 int. .030 exh.
If you just set valves on the fifth cyl watch the valves on the forth cyl to find TDC on the third cyl. Refer back to 1-5-3-6-2-4 and this will be clear. Simply walk thru the six cyl firing order to set each side of 3412.
This works well on a vee 12, 6, 4, 2 cyl engine but not on a vee 8 as companion cyls are on opposite banks. Eight cyl fiing order 1-8-4-3-6-5-7-2 (most, depending on cyl numbering method)
#1 cyl is always the farthest one forward. That makes #1 on the left bank of a 3412. Right and left are determined by standing behind the engine looking forward like seated in your car. Standard rotation is counter clock wise when standing at the flywheel end looking forward. Engines do not have port or stbd sides only left and right. On a 3412 the right bank will be even numbers, left bank will be odd numbered cylinders.
.Two revelutions are required for all cylinders to fire. Six cylinders fire on each rev. Six cyl by 60 degrees =360 degrees. This engine has a 60 degree vee providing smooth firing. This means a piston on TDC on the right bank will be at TDC on the left bank in 60 degrees.
Given what you have learned or know what is the firing order of a 3412 engine? No cheating, right or wrong you will learn something.
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