I was taking a CR reading on my car this weekend using the method described in http://www.c-speedracing.com where they say to count 5 turns of the engine and read the compression gauge. I am just curious, wouldn't it be the same to just crank the engine until the gauge stops climbing ?? I did the test using the 5-crank and the "crank-till-it-stops" method and got different readings. The 5-crank produced about 30psi less on average. Here's what I did:

1) Warm engine (just got home from work)
2) Removed all spark plugs
3) Removed 15amp Fuel injection fuse
4) Crank the engine while holding the throttle to the floor

Can someone elaborate on this ?? Shouldn't I get the same readings either way ??

On a side note, my car needs a valve adjustment badly. Can this alter my compression readings ?? Thanks !!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by iperez &raquo;</TD></TR><TR><TD CLASS="quote">I did the test using the 5-crank and the "crank-till-it-stops" method and got different readings. The 5-crank produced about 30psi less on average. </TD></TR></TABLE>

You're right, usually seems to take 7-8 "cranks" before the readings peak.
A fresh/slightly tight valve adjustment will give somewhat better numbers by a % or two.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by iperez &raquo;</TD></TR><TR><TD CLASS="quote">I was taking a CR reading on my car this weekend using the method described in http://www.c-speedracing.com where they say to count 5 turns of the engine and read the compression gauge. I am just curious, wouldn't it be the same to just crank the engine until the gauge stops climbing ?? I did the test using the 5-crank and the "crank-till-it-stops" method and got different readings. The 5-crank produced about 30psi less on average. Here's what I did:

1) Warm engine (just got home from work)
2) Removed all spark plugs
3) Removed 15amp Fuel injection fuse
4) Crank the engine while holding the throttle to the floor

Can someone elaborate on this ?? Shouldn't I get the same readings either way ??

On a side note, my car needs a valve adjustment badly. Can this alter my compression readings ?? Thanks !!
</TD></TR></TABLE>

did you screw in the compression tester just like you would a spark plug?

 

yeah, you are supposed to wait until it stops climbing, but it usually stops within the 5/7 turns. I've read in other places to turn it over 13 times...

 

so whats the correct way to do it? i did the same thing, cranked it until the pressure didn't go up anymore, then cranked it just 5 times and got different readings.

i would think you would crank it until the pressure stops rising.

what do you guys think?

 

I just did mine and we cranked it untill it stoped climbing... try it again when the car is cold and see if the numbers are different...

 

Wouldn't testing the car while its cold yield different results ??

 

yes it would...
the proper metal expansion hasn't taken place so you'll get false (lower) readings.
Make sure you warm up the car first.

 

i usually crank mine over 9-10 times to get the most accurate readings......

 

The gauge measures the max pressure, so crank until it no longer climbs.