Discussion:
Low compression in one cylinder

So I got my new little jewel home today, and started working on it. Cylinder 1 has 0 compression. All other cylinders have 125 psi. The machine has 10,580 hours on it. It has been worked, but hardly abused. I am going to do a valve adjustment tomorrow, as I bumped the starter with my finger on the exhaust rocker through the oil cap and at no point can I feel any lash. It is my understanding I should have.012" of lash, so hopefully I just have a tight valve. Otherwise a leakdown test will come next and see where the wind is going.

Is there anything common with these motors? It appears to have been maintained, but I doubt a valve adjustment was ever done.

Also, is 10K hours excessive for one of these machines? What else should I look into before I put it in service?

And lastly, it appears to be starving for fuel at times. I get a lean backfire and lack of power, but I am not going to address this until compression is back up. Is there a fuel filter or a jet in the fuel system that could be a problem? The machine has been sitting for two years so I know it will need some love at this point, and no it is not out of propane.

Thanks again for all the help.

Matt
  • Posted 22 Mar 2012 11:05
  • By mitsumatt
  • joined 22 Mar'12 - 3 messages
  • New Hampshire, United States
Showing items 1 - 1 of 1 results.
At 10K hours, pretty good chance your intake valves are carboned up and not seating. Pretty common issue on my high hour trucks. Generally doesn't reveal itself unless the truck has been sitting and the carbon hardens up. A shot of compressed air through the spark plug hole with the cylinder on the compression stroke will confirm this with leakage back through the intake.

The right way to fix it is to pull the head and replace with a reconditioned one.

There are a couple of tricks to try to get it to seat, but I'd have to write a long disclaimer before I'd publish them.
  • Posted 27 Sep 2012 07:00
  • Modified 27 Sep 2012 07:01 by poster
  • By Beeker
  • joined 27 Sep'12 - 32 messages
  • Indiana, United States

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edition #1251 - 9 October 2025
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