What should the compression be

[Aydelott]

What should the compression be on my 1958 Johnson 7.5 everyone keeps telling me to check it so I got a tester but i dont know what it needs to be do I need to warm the engine up first ? Some sites say I do

 

[racerone]

Re: What should the compression be

Just test it cold !---They need to be the same and around 80 PSI

 

[tav]

Re: What should the compression be

question....i never done this before. plug in the gage to the plug hole and turn the fly wheel till you get a reading?

 

[Aydelott]

Re: What should the compression be

There both right on 75 that good right

 

[boobie]

Re: What should the compression be

Take the plugs out and ground the plug wires with jumper wires. Then install the gauge and crank the motor until you get the highest reading.

 

[nwcove]

Re: What should the compression be

tav, what type of tester are you using? if its one of those rubber tipped jobs, its gunna take two people, and you still wont get an accurate reading. if its a screw in type, make sure the fitting on the end is not longer than the threaded part of the plug. either way, pull the cold motor over like ya hate it.....maybe 5 or 6 times on each hole or until the guage stops going up....(both plugs removed)

 

[boobie]

Re: What should the compression be

That's good........

 

[nwcove]

Re: What should the compression be

^^+1, an even 75psi for both cyls is just fine.

 

[Aydelott]

Re: What should the compression be

Thank u guys again and it's the screw in type

 

[tav]

Re: What should the compression be

don't have a gage yet , just want to now the right way to check it. mines a 2004 40 2 stk

 

[nwcove]

Re: What should the compression be

don't have a gage yet , just want to now the right way to check it. mines a 2004 40 2 stk

well, thats ^ a bit different, you should start a new thread and ask the guys that know about your more modern ignition! you may need to be extra carefull not to fry the electronics .