HELP PLEASE - Compression Test on a 2018 KTM 450 SX-F

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11/4/2018 8:19 AM

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

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11/4/2018 8:21 AM

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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11/4/2018 8:25 AM

Service manual will tell you. Its going to be a low spec. Like 60psi due to auto decompression.

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11/4/2018 8:31 AM

Thanks guys. I have service manual but that wasn't helpful probably due to auto decompression. Thanks!

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11/4/2018 8:38 AM
Edited Date/Time: 11/4/2018 8:40 AM

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.

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11/4/2018 9:47 AM

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.

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11/4/2018 3:02 PM

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.

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3/1/2020 2:32 PM

Ok was freaking after doing several compression tests and got 70 each time and google found this

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3/1/2020 5:05 PM

How many hours you guys putting on a piston?

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3/2/2020 6:08 PM

You might try doing a cylinder leakage test. I usually do it in conjunction with a compression test.

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