COMP TEST question for JB

[fch2cxr]

JB at one time you stated the following:
* Rope start engines will usually give lower psi readings than your know-it-all neighbor claims are required. Same for big JohnnyRude V6s
I'm especially interested on the bolded part...
Why big johnnyrudes have low readings????
Also why the engine has to be warmed first??? Would that really make a difference on the outcome of the readings

 

[tashasdaddy]

Re: COMP TEST question for JB

V6's are lower compression engines, i just tested one that was 95 across the board. rope start you cannot pull as fast as a starter turns the motor. being warm really does not matter on getting basic readings. you want the readings to be with in 10% of each other.

 

[jonesg]

Re: COMP TEST question for JB

I've never heard the reason the v6 is lower compression, the only thing I can think of is shorter stroke or head design.
But they do run quite well on lower psi's.
My 150 commercial is designed to run lower compression and lower rpm's in order to turn a larger dia prop. lobstah men aren't interested in hole shots.

 

[jtcarter]

Re: COMP TEST question for JB

I've been told they run a softer head gasket, don't know if thats the only reason, but it came from a omc mechanic....take it for what its worth.

Maybe someone should post a sticky... that way when people tell you your motor is junk for having 100 psi across the board your can refer them to it, lol.

 

[tashasdaddy]

Re: COMP TEST question for JB

every compression tester reads differently. each individual does the test a little differently. this is the exact reason, the manufacturers do not publish compression recommendations. the main thing is that the readings are with in 10% or each other. don't expect a sticky.

 

[JB]

Re: COMP TEST question for JB

Yup. What TD said.

 

[rcracerx]

Re: COMP TEST question for JB

My 93 175 has compression right around 95-105 per cyl. I was told that is pretty normal for that motor. Not sure but it runs good.

Rc

 

[tashasdaddy]

Re: COMP TEST question for JB

your fine. i would do a decarb, just for kicks.

 

[fch2cxr]

COMP TEST question for JB

my concern was because my motor, last comp test (3 or months ago) only had like 80 or 85 psi, but evenly all across, the dealer who sold me the motor told me the motor had low compression heads, said that came from OMC like that, but so low compression got me bumed, the motor starts right up just lots of smoke...and another thing I did it cold and w/o opening the throttle and last my teste is a cheap gauge from autozone ($24)