#1 Piston at TDC...Is it necessary? - Toyota Nation Forum : Toyota Car and Truck Forums

***dz63*** · 01-28-2009, 05:21 PM

When I hear and read about setting the #1 piston to TDC when installing a timing belt on the Camry, I get a little confused. I do not really understand why this is necessary?

Setting aside the camshaft for a moment, as far as the #1 piston is concerned, it is at TDC when the mark on the crankshaft pulley aligns with the "0" mark on the timing cover. If you turn the crankshaft one full revolution, the #1 piston is once again at TDC. The piston itself does not know if it is on a "compression" stroke or an "exhaust" stroke. It makes absolutely no difference to the piston.

Now let's talk about the camshaft. When the hole in the camshaft pulley is aligned with the "V" notch on the bearing race, it is my understanding that valves on the #1 cylinder are correctly postioned for a compression stroke. But, it really doesn't matter! As long as the hole in the camshaft pulley is aligned with the "V" notch on the bearing race, and the notch in the crankshaft pulley aligns with the "0" mark on the timing belt cover, you can install the timing belt and it will work perfectly.

I have read some advice on this forum to people that are having trouble with their timing, to remove the timing belt and rotate the crankshaft one full revolution and replace the belt. To me this does not make sense. Rotating the cranshaft one full revolution simply puts the #1 piston back to TDC again. It is in the exact same position as before it was rotated.

In my opinion, Toyota does a nice job of marking both pulleys on the Camry. As such, I do not think it is even necessary to even know where the #1 pulley is. Just align the marks and you are good to go.

Having said the above, I am not an automobile repair expert, so I could be totally wrong. What do you think?

***toyomoho*** · 01-28-2009, 06:48 PM

You are correct if the timing belt is off.

Guessing this verbiage is from setting the crank before the engine is taken apart. In this case might need to go more then once around at the crank to get it right.

Suggest after releasing the tensioner to turn the crank two times CW and recheck all marks.

This all sounds straight forward but more then one person has gotten the marks off. The job is easy if done before, not so if the first time. The manuals don't explain as you have and in some cases make it even more complicated! Plus not everyone has access to a manual.

nevanerviss · 01-29-2009, 07:13 AM

So, if a person were doing a timing belt job where the belt was OFF THE CAR, and the crank position got all jacked up, in order to get the timing correct, one would have to position the CRANKSHAFT on that little "O", leave it there, put the belt on, and adjust the timing on the CAMSHAFT?? So then, if the timing is off, then release the belt tension, and adjust the CAMSHAFT as opposed to the CRANKSHAFT??

From what I gather, the crank doesn't know anything, nor does it care, it's the cam that determines if the both valves are closed, or if the exhaust valve is opened, correct? So, if that's the case, then how does the CAM know if it's on the compression stroke? My cam had two marks; one that looked like a little "V" and one that looked like someone tapped it with a center punch (just a little circle)...

***dz63*** · 01-30-2009, 11:34 AM

toyomoho - Rephrasing my question...Is there any point to ensure that the #1 piston is at TDC when doing a timing belt job? I can't see why. My theory is that you just make sure the marks are aligned on the crankshaft and camshaft pullies, put the belt on and you are good to go. If the crank pulley is at the "0" mark, the #1 piston is automatically at TDC. Why open the distributor to look at rotor position or remove the #1 spark plug and put a rod in the hole. I read this time and time again. I dont' get it. Am I missing something here?

nevanerviss - IMO, if the timing belt breaks, it is no different than doing a planned timing belt change. Just align the marks on both crankshaft and camshaft pullies, put the belt on and you are good to go.

***toyomoho*** · 01-31-2009, 07:57 AM

It depends on what you want to do and which engine you are working on.

If the engine is still together and one wants to set things up. Set the crank at the 0 degree mark when No 1 piston is at TDC. This allows using the crank to rotate the cams which is a lot easier then using the cam pulley and all parts rotate in correct order.

Not all engines are non-interference, use a timing belt, etc. Some Honda's are interference and use an additional belt to drive the balances shafts. Rotating the cams separately can drive the valves into the pistons, getting every thing else to line up is a little harder.

Much easier to have all this setup correctly before removing the belts.

***new echo owner*** · 01-31-2009, 01:41 PM

What it boils down to is how familiar you are with the engine that you are working on. When you know what you are doing, you can get away with a lot of things.

N.E.O.

***dz63*** · 01-31-2009, 02:07 PM

toyomoho & N.E.O. - Sorry guys. I now see that my previous question was a bit vague. I meant to say...On the GEN3 Camry with a non-interference 4 cylinder 5SFE engine, is there any point to ensure that the #1 piston is at TDC when replacing the timing belt?

***new echo owner*** · 01-31-2009, 02:22 PM

I understand your question, and you seem to know exactly what you are doing, that is probably why you are asking about the necessity of setting #1 on TDC. And you are correct in that you don't really have to; however, the reason you can do that is because you are familiar with the engine. On the other hand, if you are not familiar with the engine or if you are just replacing the timing belt, putting the engine at #1 TDC would make the work easier. It is all a matter of reference. For example, you can time the engine if you connect the timing light to #4 cylinder plug wire and get the same result as if you were timing it off #1 cylinder.

N.E.O.

***dz63*** · 01-31-2009, 02:45 PM

Thanks NEO. Just to clarify, if the hole in the camshaft pulley is aligned with the "V" notch on the bearing race + the notch in the crankshaft pulley aligns with the "0" mark on the timing belt cover, then #1 piston is automatically at TDC and both valves are closed (ie. compression stroke) - yes?

If this is the case, then there is no need to independently verify that the #1 piston is at TDC by removing the spark plug and inserting a rod. Also, there is no need to independently verify that the camshaft is in the right position by removing the distributor to ensure that the rotor is pointing to the #1 spack plug wire - yes?

***toyomoho*** · 01-31-2009, 03:11 PM

If you only work on 5S-FE you can use your approach.

You might some day work on an engine and no info on what marks to use, using an established proceedure allows this.

***new echo owner*** · 01-31-2009, 05:19 PM

Quote:

Originally Posted by dz63

Thanks NEO. Just to clarify, if the hole in the camshaft pulley is aligned with the "V" notch on the bearing race + the notch in the crankshaft pulley aligns with the "0" mark on the timing belt cover, then #1 piston is automatically at TDC and both valves are closed (ie. compression stroke) - yes?

If this is the case, then there is no need to independently verify that the #1 piston is at TDC by removing the spark plug and inserting a rod. Also, there is no need to independently verify that the camshaft is in the right position by removing the distributor to ensure that the rotor is pointing to the #1 spack plug wire - yes?

In this case, you are correct! On the other hand, for someone who is new or not familiar with the set up it can still be confusing.

N.E.O.

***dz63*** · 02-01-2009, 12:55 PM

^ Got it. Thanks!