compression test?


7 replies to this topic
  • brandonvick83

Posted November 06, 2010 - 11:08 AM

#1

Can I do a compression test on my 99 400? and if so whats the procedure and allowable compression?

  • grayracer513

Posted November 06, 2010 - 02:18 PM

#2

No. A completely healthy YZ4** can't be kicked through a full compression stroke in the first place, and Yamaha never published an specs for them because of it.

A leak down test is far more definitive than a compression test ever was, anyway. See a shop about having one done.

  • brandonvick83

Posted November 07, 2010 - 10:46 AM

#3

the guy I bought the bike from didnt know the "procedure" and would kick through the compression and doing so ruined the kickstarter lever and put a crack in the clutch side cover near the starter lever. If I kick it over till it gets hard "compression" I dont usually use the comp release I just apply constant pressure and it will move past compression to were I need to be. Does this sound incorrect?

  • grayracer513

Posted November 07, 2010 - 02:23 PM

#4

It's the incorrect starting procedure, yes. Apart from that, your rings are probably leaking a bit. A leak down test will answer your questions without speculation.

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  • brandonvick83

Posted November 07, 2010 - 04:14 PM

#5

I just rebuilt the motor havent had it runin long enough to even set the rings will this affect the leak down? Im concerned with leakage at the valves becuz I didnt replace them. I put gas in the ports and had some slight leakage through the valves but not bad.

  • Montana-Snipe

Posted November 07, 2010 - 04:44 PM

#6

The leak down test is the only acurate method. If your valves are not sealing or your rings, you should be able to notice it very quickly. If your valves are leaking from your "gas" method your performance is not going to be good either.

  • grayracer513

Posted November 07, 2010 - 05:04 PM

#7

I just rebuilt the motor havent had it runin long enough to even set the rings will this affect the leak down? Im concerned with leakage at the valves becuz I didnt replace them. I put gas in the ports and had some slight leakage through the valves but not bad.


Then quit worrying about compression and get it running.

  • brandonvick83

Posted November 08, 2010 - 07:57 AM

#8

Im really not worried about compression I just want to eliminate everything else before I go to the newer yzf carb you suggested





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