1997 Mercury 135 offshore compression - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  1997 Mercury 135 offshore compression

search | FAQ | profile | register | author help

Author Topic:   1997 Mercury 135 offshore compression

surferkevman posted 06-28-2009 12:22 PM ET (US)
I just had the compression checked and it was 100 per cyl. Is that about right? Thanks.
jimh posted 06-28-2009 02:52 PM ET (US)
What you probably mean is you that you measured the maximum pressure in each cylinder and found it to be about 100-PSI.
Atmospheric pressure, nominally 1-BAR, is about 14.7-PSI. Compression ratio can be estimated from
Pressure at dead top center = 1-ATM X (CR)^1.4 where CR=compression ratio:
Thus
CR^1.4 = 100/14.7
CR^1.4 = 6.8
CR = 3.93
Your compression ratio is 3.93:1
Cf: http://en.wikipedia.org/wiki/Compression_ratio
Measurement of cylinder pressure relies on the accuracy of the gauge being used and on the technique and conditions of the measurement. There are many variables in the technique to measure compression. A general guide to making cylinder pressure measurements is given in
http://continuouswave.com/whaler/reference/outboardCheck.html
See the subheading Compression Check
The usual metric for assessing the condition of the engine is to compare measurements among the cylinders. If the variation is less than 15-PSI your engine is in good shape.
surferkevman posted 07-01-2009 09:26 AM ET (US)
Thanks Jimh,
Have a nice summer whereever you are.

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: 1997 Mercury 135 offshore compression
surferkevman	posted 06-28-2009 12:22 PM ET (US) I just had the compression checked and it was 100 per cyl. Is that about right? Thanks.
jimh	posted 06-28-2009 02:52 PM ET (US) What you probably mean is you that you measured the maximum pressure in each cylinder and found it to be about 100-PSI. Atmospheric pressure, nominally 1-BAR, is about 14.7-PSI. Compression ratio can be estimated from Pressure at dead top center = 1-ATM X (CR)^1.4 where CR=compression ratio: Thus CR^1.4 = 100/14.7 CR^1.4 = 6.8 CR = 3.93 Your compression ratio is 3.93:1 Cf: http://en.wikipedia.org/wiki/Compression_ratio Measurement of cylinder pressure relies on the accuracy of the gauge being used and on the technique and conditions of the measurement. There are many variables in the technique to measure compression. A general guide to making cylinder pressure measurements is given in http://continuouswave.com/whaler/reference/outboardCheck.html See the subheading Compression Check The usual metric for assessing the condition of the engine is to compare measurements among the cylinders. If the variation is less than 15-PSI your engine is in good shape.
surferkevman	posted 07-01-2009 09:26 AM ET (US) Thanks Jimh, Have a nice summer whereever you are.