Leak down test?


8 replies to this topic
  • honyam83

Posted January 10, 2009 - 11:36 AM

#1

Hello, I'm sure that this has been covered in previous threads, but my search has turned up nothing. When performing a leak down test should the bike be warmed up prior to test. I have a clymer manual that says that is should be. I just want to know if this is correct. The shop that performed a leak down on my YZ426 F (01) said it should be cold and it was I hauled it about 20 miles in 30 degree weather. Would this affect the out come of the test? I was told that the motor was @ 11%. Thank you for your time and Knowledge.

  • APE Jay

Posted January 10, 2009 - 05:05 PM

#2

Probably should be at riding temperature. One issue we saw doing this was the cylinder head cooled off some while the hose was in the plug hole, and it got tight and didn't want to come out.

Be sure the plug hose has a small amount of grease or anti seize on it if installing in a warm head.

Jay

  • heykenny

Posted January 10, 2009 - 05:14 PM

#3

the leakdown test is pretty definitive.. if it's bad ,it's bad... you won't save a marginal motor by warming it up... 11% is not an encouraging number

  • APE Jay

Posted January 10, 2009 - 05:32 PM

#4

11% you should be able to hear.

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  • grayracer513

Posted January 11, 2009 - 09:37 PM

#5

The rings will perform better at operating temperature than at cold.

OTOH, one of the reasons you might test cold would be if you're having more than the usual cold start problems, and/or a lack of cold cranking compression. Valve clearance should be checked prior to doing the test, and corrected if necessary.

  • honyam83

Posted January 12, 2009 - 03:11 PM

#6

The top end is kind of noisy. And I sure that the guys at the shop did not check the valves. i think that the top end was fresh last spring and not ridden much. Is there any way valves and temp could be the reason for an 11% leak down reading I also have what I believe to be is a leaking valve seal. So If I can get away with out a new piston and ring I would like to. should I correct my valve problems and retest the cylinder? I just don't know if the shop is trying to drum up some work. I would do all of this myself but have not the tools. I guess that I should get the tools and cut out any variables. thanks for the replies, I really appreciate the knowledge that this site offers, and the time that people spend helping others like me.

  • grayracer513

Posted January 12, 2009 - 03:23 PM

#7

Check the valve clearance. If it's OK, then your leak down test is what it is, and you should be able to hear where it's leaking (at least, if it's mostly in one place) by opening the throttle and listening under the seat, Listening at the exhaust tip, and listening at the timing plug.

Why do you think you have a leaking valve seal?

  • honyam83

Posted January 13, 2009 - 07:21 PM

#8

When I fire the bike up it blows smoke, It smells like oil has a blue tint and does not dissipate. The smoking does stop after some running, a minute or so. That leads me to believe that it is a leaking valve. The bike runs good except for a "hanging Idle". This bike is newly acquired, so I do not know all of the history. My dad suggested that the smoke may be caused by the motor not being fully broken in, is this possible? Thanks Again.

  • grayracer513

Posted January 13, 2009 - 09:19 PM

#9

When I fire the bike up it blows smoke, It smells like oil has a blue tint and does not dissipate. The smoking does stop after some running, a minute or so. That leads me to believe that it is a leaking valve (seal).

Classic symptoms.





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