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I'm not sure how specific to my car this is or not, so I will include my car information just in case: It's a 1991 Honda CRX, base trim(the motor is the d15b2).

On to the question: How do I go about manually rotating the engine to TDC? Are there any considerations that I should take before doing so? I'm attempting to change the head gasket and I need to take it to TDC before I remove the distributor and heads.

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5 Answers 5

up vote 4 down vote accepted

there should be markings on your crank pulley that line up when the motor is in TDC. Make sure the car is in neutral, put a socket over the crank pulley and turn it until it lines up.

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So it won't hurt anything to just manually spin it? I was slightly worried that there was something I'd need to do before trying to rotate it manually. –  Annath Mar 15 '11 at 20:39
    
No, it won't hurt anything. Everything that matters is mechanically connected to the crankshaft, and will turn while you turn the crank manually (assume you don't have a broken timing belt/chain). –  S_Niles Mar 15 '11 at 20:41
    
That makes sense. Thanks! –  Annath Mar 15 '11 at 20:43
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You must have the number one spark plug out and make sure you are on the compression stroke. If it's requiring TDC before disassembly this is where it's talking about. If you only do the steps you have listed above the Cam can be 180 degrees out –  Larry Mar 17 '11 at 17:15
    
@Larry: You don't necessarily need to do it that way. There's a marking on the cam pulley too that should be at the top. –  R.. May 4 '13 at 13:43

If all else fails, removing spark plug nr.1, and rotating the engine until you can either see the piston reach tdc, or feel it reaching tdc position with a screwdriver. But be careful to not drop anything down the hole..like I said, if all else fails.

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Try removing all the sparkplugs before turning the engine. Otherwise you will be pushing against the engine that tries to compress the air in the cylinders and it will be very hard (if not impossible) to turn the pulley.

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First of all, keep in mind that in a a 4-stroke engine (which virtually all cars are) each piston will hit TDC twice in the course of a full combustion cycle, once between the exhaust and intake strokes, and once between compression and combustion. When a procedure calls for putting the engine at TDC they're usually referring to piston #1 being at TDC before the intake stroke.

Rotating the engine to TDC really involves two things, manually rotating the crankshaft, and determining when you've reached TDC.

Rotating the crank is most easily done with a ratchet attached to the crank pulley. Things to consider before doing this:

  • Make sure the transmission is in neutral, or if you're doing major work, completely disconnected from the engine.
  • If the engine is fully assembled (head(s) on and spark plugs in) it can be difficult to turn by hand due to the engine compression. Even with the heads off the friction between the pistons and the cylinder walls will prevent the crank from spinning easily. The amount of force required to turn the crank will depend on how many cylinders you have as well as the compression ratio etc. You shouldn't need a 4 ft. breaker bar, but don't be surprised if you have to put your body into it a little.
  • It's generally a good idea to turn the motor in the same direction as when it runs. If you need to back up a little bit, that's ok, but generally avoid freely rotating an assembled engine backwards.

Determining when the engine is at TDC can be done a couple of ways:

  • Assuming it was assembled properly there is usually a mark on the crank pulley that will match up to another mark on one of the front covers when the engine is at TDC.
  • You can remove the #1 spark plug and put a straw down the hole such that it's resting on the top of the piston. As you turn the crank the straw will move up and down. When it's at its apex just before it begins to fall the engine is at TDC.

Finally, as I mentioned at the beginning you will often need to know if the engine is at the beginning of the intake or combustion stroke in addition to knowing if it's at TDC. Keep in mind, if the head is off or the timing belt/chain is removed there is no difference between TDC before intake and combustion, this is about the valve train's position as opposed to the piston's position.

  • If the valve covers are off you can watch the motion of the valves for the #1 cylinder. At the start of the intake stroke the intake valve(s) will be opening and the exhaust side will be closing. At the start of combustion all valves will be closed and not moving.
  • You can also look at the cam pulley(s). They will have some sort of markings to indicate when the valves are in TDC alignment. This varies greatly by engine so I can't give any more specifics.
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Just remove the cylinder head and rotate the crankshaft. When you put back the head the pulley has two lines make sure their horizantal and just put everything back together

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I would recommend having it lined up before you take it apart and trying not to move anything. It's easy to get the timing off by one tooth when trying to realign it, especially if you have no experience doing this before. –  R.. May 4 '13 at 13:46
    
The OP want's to do this before disassembly, not after –  Larry May 6 '13 at 1:48

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