No compression or Very little


4 replies to this topic
  • gio

Posted February 02, 2008 - 10:27 PM

#1

Heys Guys

I just changed the head gasket on my YZ400 and now that its all together i have no compression or very little. I checked the timing numerous times and it matches the specs in the manual. I not sure what i did wrong. Could it be something simple like the decompression shaft. I did not adjust the valve clearances as they were ok. The timing marks on the cam are spot on but once i put the tensioner on it pulls it very slightly off, is this normal.
.
Need help as to possible causes, hoping its something simple that i have forgot.
I have the cam marks lined up as E-I E-I, when the timing mark is on the I on the crankshft. I just read another post i may have put them on the exhaust stroke. I did not change the base gasket and the valve clearances were only just done.

  • grayracer513

Posted February 02, 2008 - 11:14 PM

#2

Could it be something simple like the decompression shaft. ...The timing marks on the cam are spot on but once i put the tensioner on it pulls it very slightly off, is this normal.
I just read another post i may have put them on the exhaust stroke.


Check for free play the compression release. The cams will never line up totally perfectly, but the question is, if you move the cams one way or other, will they be closer to perfect, or farther from it?

Without the cams, there is no difference between one TDC and the other, so it's impossible to have them "on the wrong stroke".

You either have a tight compression release, a worn, bent, sticking or tight valve. or leaking rings, simple as that. Have a shop do a leak down test.

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  • gio

Posted February 03, 2008 - 12:29 AM

#3

I just checked the cams again, the timing is ok. It had plenty of compression before i pulled it apart and the valve clearances were only just done. By me pulling the head off this shouldn't affect the rings if they were fine before, is this correct. Whilst installing the head one or two of the shims fell out i'm now wondering if i put them in the wrong way. Are the shims on the same size for each side (exhaust), or are they different for each valve.

  • William1

Posted February 03, 2008 - 05:56 AM

#4

Shims are different for each valve. You swap them for different thickness ones to change the valve clearances. You need to check the valve clearances, and play "musical shims" to find out where each one belongs.

  • grayracer513

Posted February 03, 2008 - 10:29 AM

#5

The shims are marked, although yo may need to take them into direct sunlight in order to read them, or resort to a micrometer. But, as William says, each one is different, because the shims are the part that is used to adjust the valve. Start by checking the valve clearance.





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