Compression question

[rdharley3]

I am looking for the compression range for a 1996 9.9 h.p. evenrude.

Thanks for any info.

RDH

 

[Solittle]

Re: Compression question

The difference between cylinders is actually more important than the actual compression. A difference of 10% is OK. As for the actual - most OMCs engines like 95 to 110 lbs. My 1975 9.9 tests out around 102-104 lbs.

 

[Texasmark]

Re: Compression question

Mercury won't even publish a number; range between cylinders yes, range no. Too many variables to give you an incorrect reading (for what you are looking for).

Mark

 

[rdharley3]

Re: Compression question

Thanks solittle, and texasmark.

I am having a problem with the OB runing at WOT at cold start it will start and run fine at WOT for about 2 minutes it then drops RPM's about 1/2 still at WOT usually I could run it about 5 minutes in this condition and then it would clear up and run fine the rewst of the day. I pulled the carb and rebuilt it it had some junk in the needle valve put it back together it ran fine for 5 minutes then back to the same symptoms. I then pulled the plugs and checked for spark the lower cylinder was not firing. While I was re-installing the plugs I cross-threaded the plug into the head so now I've got to pull the head to install a helix coil so in the process I am going to check compression and did not know what range if any it should be at I did know that both cylinders should be within 10% of each other but I didn't know if there was a average range the cylinders should fall within.

As soon as I fix the head problem I will be back to running down the no-fire issue. Which with the luck I have had so far may be a simple bad plug wire.n Any tips would be greatly appreciated.

RDH

 

[Texasmark]

Re: Compression question

SWAG (Scientific Wild Arse Guess)....Anything over 100 psig is probably ok considering all the variables.....remember, they need to be close to oneanother. That's what's important.

Markl

 

[Solittle]

Re: Compression question

I don't know the ignition for the 96 but if you have coils swap the coils and plug wires. If the that problem follows you have found it.

 

[rdharley3]

Re: Compression question

thanks for all the advise...8)

 

[rdharley3]

Re: Compression question

a couple more questions if I may. I've been searching in the repair manual for the torque requirements for the head bolts and cannot find it (probably looking in the wrong place) does anyone know the torque requirements for the head bolts? also would you use a gasket sealer (permatex) with the new gasket, and locktite the head bolts?

Thanks,

RDH