finding TDC


11 replies to this topic
  • rmcr250r

Posted March 18, 2010 - 06:30 PM

#1

First time checking the valves on my 09 yz450f and I am a bit confused about finding tdc. There are 3 lines and it seems to be in tdc at the last line. Should it be completely centered with the top indicator for it to be in tdc. Also should the punch marks on the cams be facing out not perfectly aligned. The manual imo does not do a good job being specific which makes it hard to learn how to work on the bike. Ive used the search feature and read the sticky but they dont seem to give definate answers to my questions.

  • grayracer513

Posted March 18, 2010 - 07:32 PM

#2

The farthest line to the right, or the third one to appear as you rotate the engine forward, is the TDC mark. It is not uncommon for the marks not to line up perfectly, too. The test is to imagine them being one tooth away from their actual position, and see if that would improve their alignment or worsen it.

  • rmcr250r

Posted March 18, 2010 - 07:35 PM

#3

so you are saying if the punch marks on the cams are one tooth away in TDC that is acceptable?

  • grayracer513

Posted March 18, 2010 - 07:42 PM

#4

Where did I say any such thing?

If they don't line up perfectly, it's acceptable UNLESS they would line up better if they were moved one tooth one way or other.

  • rmcr250r

Posted March 18, 2010 - 07:56 PM

#5

Where did I say any such thing?

If they don't line up perfectly, it's acceptable UNLESS they would line up better if they were moved one tooth one way or other.


Thanks appreciate the help you just need to make what you write alittle more clear. If in fact they line up better if they were moved one tooth one way or other do you just simply rotate to that direction. Ill post a pic in the morning just to double check the the marks cause i am gettin all types of measurements when checking the valves

  • grayracer513

Posted March 18, 2010 - 09:13 PM

#6

... you just need to make what you write alittle more clear.

Whatever you say.

If they need to be moved, the only way to accomplish it is to remove the cams, reposition the chain, and bolt it all back up. There isn't enough slack in the chain, even without the tensioner removed, to allow one to retime it by any other means.

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  • rmcr250r

Posted March 19, 2010 - 06:13 AM

#7

Heres what the punch marks look like and TDC. The exhaust valves measure at .008 and the intakes so far r tighter than .005 ive gotta get a feeler with smaller measurements. But do these marks look right?
Posted Image
Posted Image

  • grayracer513

Posted March 19, 2010 - 07:28 AM

#8

In the first picture, all I can see through the port is a big white glare. But if the TDC mark is lined up, your cam timing is OK where it is.

  • rmcr250r

Posted March 19, 2010 - 08:02 AM

#9

the tdc mark is at the right of the glare. I took about a million pictures and couldnt get it to stop showing a glare. All three intakes are at .004 and the exhaust are at .008 are these typical measurements for 30hrs on a brand new engine that was trail ridden?

  • grayracer513

Posted March 19, 2010 - 08:45 AM

#10

Those are the minimum specified clearances for each set of valves, and yes, it's absolutely typical. Yamaha builds all of their engines to the lower limit of the specified range deliberately, and even uses shims in .01mm increments that aren't available to the public in order to accomplish this. What this means to you is that your valves have not closed up even slightly as of yet, which is what I would expect from a 30 hour engine. Neither of my '06's have receded at all, either, and both of them are over 100 hours. The '03 I had was close to 400 when I sold it, and never had a valve adjustment. Typical? Yup.

  • rmcr250r

Posted March 19, 2010 - 08:54 AM

#11

Thank you very much grayracer for your help and making it possible for me to gain experience and confidence working on my bike:thumbsup:

  • MR2turbo4evr

Posted March 19, 2010 - 09:23 AM

#12

....Neither of my '06's have receded at all, either, and both of them are over 100 hours. The '03 I had was close to 400 when I sold it, and never had a valve adjustment. Typical? Yup.


That's amazing and makes me very happy that I own a Yamaha. Not sure how many hours my 06 has (bought it used) but the valves are also spot on. I recently checked the valves on my friends '07 KX450F, which, judging by the overall condition of the bike, should have a similar amount of hours on it, however the intake and exhaust valve on the right side of the engine were out of spec.....





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