Align marks at TDC

8 replies to this topic
  • boer

Posted October 16, 2006 - 10:17 AM


I checked my valves today. 1133km and nothing and still within spec. Inlet 0.10mm and exhaust 0.20mm. I have some questions though:

Firstly, I noticed that when aligning TDC the mark/line on the rotor is a little off (1mm or 2) the mark on the crankcase cover when the punch marks on the camshafts are parallel to the head surface. Is this normal and OK?

Secondly, how accurate does one need to be at TDC when checking valves. is 1 or 2mm from the head surface OK for the punch marks form the cams or does the profiles of the cam lobes already start affecting the clearances at the smallest movement away form TDC?

finally, I accidentally turned the crankshaft clockwise for about 30 degrees. It made a clicking sound like a ratchet. Is this normal, have I damaged anything? Once I rotated counter clockwise everything sounded fine again.

Thanks in advance for the responses :devil:

  • jandmsuburban7

Posted October 16, 2006 - 10:54 AM


Hi, I have the same question about TDC. Mine is off the same. I spoke to a mechanic at the local shop and he stated that it is probably fine. It could have one tooth off. His question to me was if it is running fine and mine is. However, my middle intake valve is off a little. Talk at ya later. Thanks, Jason :devil:

  • Indy_WR450

Posted October 16, 2006 - 11:26 AM


You need to be at TDC the cams come away quickly. Put a straw down the spark plug hole and watch it come up and down as you rotate back and forth around the TDC I mark. That way you will know for sure if the mark is off or not. :devil:

  • NuckingFuts

Posted October 16, 2006 - 11:47 AM


Ditto what Indy stated. If your chain is slightly stretched then your marks will be off so its better to use a straw. If you are a tooth off then your marks would be more than a mm or 2 off.

If you're still not sure wait until after the site is upgraded tomorrow and search for posts by me on this subject. I was fixing an auto decomp cam that was installed incorrectly by the dealer. Lots of pics and advise from guys on that thread.

Good luck!

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  • JJHayesIII

Posted October 16, 2006 - 01:20 PM


To be sure the punches on the cams are in the correct spot, I've had to adjust to one tooth off on both sides...once you do that, it's easy to tell which is the correct position.

I've also always made a point to be sure that the "I" mark lines up exactly, even if I have to hold it there somehow....

  • boer

Posted October 16, 2006 - 07:52 PM


The misalignment is less than a tooth. If I move 1 tooth it will be out even more. I guess it was fine before, so should be OK now.

How much tolerance/degrees in the cam rotation is there before the profile of the lobes changes to affect the clearances at TDC??

  • boer

Posted October 16, 2006 - 10:01 PM


You need to be at TDC the cams come away quickly.

Hey Indy, what do you mean by that?

It seems that profile of the cam lobes are all round around TDC and do not have elliptical profiles. Am I right? :devil:

How many degrees approx. before and after TDC will the cam lobes be concentric until the profile starts to take action to close the clearance and move the valves? :thumbsdn: Any one got some ideas?

  • Indy_WR450

Posted October 17, 2006 - 11:42 AM


it is difficult to see a few thousands of an inch with your eye. Just put it as close to TDC as you can and read the clearances. Dont worry about retiming the cam sprockets. leave them in the stock position.:devil:

  • motosv

Posted October 17, 2006 - 03:51 PM


I agree that the cam lobs will allow serveral degrees before they change the clearance but I would suggest that if you are wondering, then move the marks and see how, if any, that changes the tollerance. Also consider that the mfg provides a tolerance so that provides additional evidence that there is room for imperfection. Now when you talk about setting the degree of the cams compared to the crank shaft then you will be looking for exact placement, of course you would need adjustable cams for that procedure. Hope that helps.


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