Compression Test!

[Thermodude]

My wife came home yesterday with an early fathers day gift....."new compression gauge".......and I didnt hesitate putting it to use. Ive been planing to do a decarb and wanted to get a base number on each cylinder before I did so. I have a 92 Evinrude 150 Spitfire. Ive owned the rig for a couple years and so far its ran great. I do have a question about the #s that I got..........91 on each cylinder. What are the chances of it being that close? I know that the book says that anything below 100 isnt good, but by the same token if they are all the same I feel pretty good about that. Plus each gauge you use tends to read a little different. Im going to run another test after I decarb this weekend...........Im curious to see how much differance that makes.

 

[Dhadley]

Re: Compression Test!

What book did you see that in? As long as the readings are within 15 lbs of each other youre good to go. You might gain some after the decarb but it certianly wont hurt anything as long as you follow the instructions. <br /><br />Great idea on the baseline readings.

 

[KCLOST]

Re: Compression Test!

I've never seen any numbers published regarding compression ranges... Just that they should be consistent... (however, I haven't looked that hard either)...

 

[Thermodude]

Re: Compression Test!

The book I was refering to is the Clymer manual.......quote, "While minimum cylinder compression should not be less than 100psi, the actual radings are not as important as the differences in readings between cylinders when interreting the results." I was just glad to see that they were as close as they are. Im going to do all I can to make sure it stays there. Thanks for the input guys!

 

[jjboor]

Re: Compression Test!

Are you sure the compression gauge is working on the right scale? I mean it being the first test it has done... Maybe that it gives lower readings then other testers do? Might be.<br /><br />Plz. let us know what the readings are after decarb. I'm about to decarb and I'd love to see what it does.

 

[JB]

Re: Compression Test!

I, too have seen the 100psi minimum spec. in Clymer. But I, too feel good about readings in the 90s.<br /><br />There are so many variables in compression testing that the 100psi spec is often hard to achieve in a good engine.<br /><br />Differences in guages have been mentioned. Also likely to affect the readings:<br />Battery condition, starter circuit wiring condition, engine temp, amount of lubrication present on cylinder walls, position of throttle plates, number of cycles used to get each reading, and others I don't think of at the moment.<br /><br />One thing that everyone agrees on is that the span of readings from the highest to the lowest is the important part of a compression test.

 

[sterritt]

Re: Compression Test!

Thermo - I've got a set of the same engine's, just bought them, compression is identical (low 90's) except for an oddball couple up around 100, I attribute the couple higher readings to carbon and/or mabye some extra oil.<br /><br />Wish I could stick a guage in a new one, but my guess is they were 95 new or something. My Johnson 25 HP, much different engine obviously though, had 90 psi new.<br /><br />Alot depends on the ratio's. <br /><br />Is your clymer manual actually for that engine? Out of all the manuals I have, not a single one mentions what good compression is other than that it should be even.<br /><br />Jon

 

[KCLOST]

Re: Compression Test!

What motor do you have, and the year?

 

[sterritt]

Re: Compression Test!

KC - which ones<br /><br />'91 V6 150 looper:<br /><br />Powerheads were replaced w/ new ones somewhere in the mid-90's, but I tend to assume they didn't change anything.<br /><br />Out of 12 cylinders (two engines) most were 92 with a couple at 90/94 and a couple in the high 90's.<br /><br />2001 25 HP Johnson:<br /><br />90 psi, both holes.<br /><br />Jon

 

[Thermodude]

Re: Compression Test!

Hello sterritt,<br /><br /> The clymer manual that I have talks about the intruder series of engines and actually shows one on the cover. I have a 92 Spitfire 150 which is supposed to be one of those....."same but different".....situations that you run accross from time to time! In my manual there is a section that pertains to compression and it does state that the good numbers start at 100psi......they use that as a benchmark. I dont have it in front of me at the moment but I can see if it has a serial number and post that. None the less I feel very good that my numbers are all that close. I plan to decarbon this weekend and Ill see what happens then. To be honest I dont expect much becuase the engine has been taken care of and its clean. My feild of work is Predictive Maintenance....Infrared Analysis, Oil Analysis and so on............I try to apply this to my vehicles as well as my boat. If the numbers change Ill post them.

 

[G DANE]

Re: Compression Test!

I have a 1973 25HP - 2 x 122<br />A 1984 35 HP 2 x 135<br />A 1988 40HP 148 and 150<br /><br />A 1991 V4 3X125 and one at 135 ( will need to look at that.<br /><br />Manny V6's have low compression gaskets, newer seem to be designed with low compression - all show somewhere in 90 ties. Remember compression is an enemy of cranckshaft, rods and bearings. Lowering compression and still having good combustion reduces wear, noise and need for lube.

 

[phatmanmike]

Re: Compression Test!

1972 50hp 155 both holes<br />1988 14 hp 120 both holes<br />1977 merc 1150 160 all 6 holes<br />1972 evinrude 6hp 110 both holes<br />1994 nissan 5hp 130 , single cyl<br />1970 clinton sea king 3.5hp 120 single<br />1970 clinton sea king 3.5hp 110 single<br /><br />thats all i have running right now