What should my PSI Be on the topend?


3 replies to this topic
  • TampaBoy813

Posted October 13, 2004 - 08:05 AM

#1

Going to check and see if its time for a rebuild....what should the compression be at? :cry:

  • grayracer513

Posted October 13, 2004 - 10:07 AM

#2

Don't know the spec on the 426, but I would guess somewhere between 180 and 210, or even higher with the compression ratio they have.

An even more valuable thing to test for is to observe how many kicks it takes to arrive at the max. Compression on the guage should more or less peak after 4-5 kicks.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • onekyoung

Posted October 13, 2004 - 12:21 PM

#3

Compression on the guage should more or less peak after 4-5 kicks.



Good to know, I always thought the rule of thumb was to kick it (or turn it over) until the reading stopped increasing.

  • grayracer513

Posted October 13, 2004 - 03:03 PM

#4

Most contemporary ring designs cause them to seal better under pressure than otherwise, so that compression and combustion pressures help force the rings against the cylinder, and allows a little less friction during the exhaust/intake strokes.

If the compression readings take too long to run up to their peak, it can mean that the rings are loosing their tension on the cylinder, and have become more dependent on compression pressures to seal than they should. In a dynamic sense, this can result in low intake vacuum and poor low speed and idle performance. Hard starting, too.





Related Content

Reviews

Yamaha YZ450F 2017 by Chris.GVS


Yamaha YZ450F 2017
  • - - - - -
  • 0 reviews
Forums
Photo

2016 YZ450 by CaptainKnobby


Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies
Forums
Photo

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride


Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies
Forums
Photo

Megabomb Fitment by 288yz450


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply
Forums
Photo

Snake pit oct 30th by The Anvil


Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies
 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.