The Autonerdz Community Forums

The Autonerdz Community Forums
https://yabb.autonerdz.com/cgi/yabb2//YaBB.pl >> >> Vfr800 relative compression test https://yabb.autonerdz.com/cgi/yabb2//YaBB.pl?num=1532576155 Message started by mark152152 on Jul 25^th, 2018 at 7:35pm

Title: Vfr800 relative compression test
Post by mark152152 on Jul 25^th, 2018 at 7:35pm

Here is a strange one. I was demonstrating the scope to a friend and one of the tests I showed him was a relative compression test using battery voltage with a inverted signal.

This bike has equal compression using a manual tester. Look at the attached file. It turned out the spacings between tdc for each cylinder is not equal. I've added some lines to show the spacing difference.

This is a good waveform for Honda VFR800 5th gen.

sketch-1531906284270.png (876 KB | )

Title: Re: Vfr800 relative compression test
Post by James H on Jul 26^th, 2018 at 6:48am

That is because it fires at 90 degrees and 270 degrees so what you are seeing is correct ( big bang motor). Unfortunately it means a relative compression test is invalid unless you had a good know one to compare.

Title: Re: Vfr800 relative compression test
Post by mark152152 on Jul 26^th, 2018 at 9:26am

I fully agree this tests invalid but this waveform is a good known waveform. All cylinders were manually pressure checked and all with 5psi of each other.