Posts: 287
Joined: 2/26/2012
Location: Tulsa, OK USA
Searched for several hours and can't find what is an acceptable top end compression on a 18 450 SX-F. I want to test before pulling apart but can't find what it should be anywhere.
Anyone able to help? Also, should I test it with engine hot or cold?
TIA
Rick
Posts: 3455
Joined: 4/3/2013
Location: Benton, LA USA
You will not find much on this as the auto decompression device lowers the compression for starting and can vary a good bit.
Paw Paw
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Joined: 1/31/2018
Location: Mansfield, OH USA
Service manual will tell you. Its going to be a low spec. Like 60psi due to auto decompression.
Posts: 287
Joined: 2/26/2012
Location: Tulsa, OK USA
Thanks guys. I have service manual but that wasn't helpful probably due to auto decompression. Thanks!
Posts: 1675
Joined: 11/30/2009
Location: MS, USA
Edited Date/Time:
Most everyone now uses a leakdown test vs a compression test. It is more difficult to perform but tells you much more. If you call the tech dept of most mfgs they are going to ask if you have done a leakdown test. KTM does have a TDC locking screw to help perform the test.
Posts: 287
Joined: 2/26/2012
Location: Tulsa, OK USA
dcg141 wrote:
Most everyone now uses a leakdown test vs a compression test. It is more difficult to perform but tells you much more. If you call the tech dept of most mfgs they are going to ask if you have done a leakdown test. KTM does have a TDC locking screw to help perform the test.
Thx. I now remember the TDC locking screw from when I did a top end on one of my earlier KTM 450's. Makes it much easier.
Posts: 458
Joined: 11/28/2011
Location: Phoenix, AZ USA
I about fainted when i did a compression test on my 450sxf and got 105 psi. I squirted some oil into the cyl and got 110. Oh shit!.. LOL yeah its the auto decompression mechanism.
Posts: 6977
Joined: 9/18/2007
Location: York, SC USA
Ok was freaking after doing several compression tests and got 70 each time and google found this
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Location: Suffolk, VA USA
Posts: 21
Joined: 1/1/2019
Location: South Bend, IN USA
You might try doing a cylinder leakage test. I usually do it in conjunction with a compression test.
