78 Evinrude 175 Compression

[snagroms]

Just picked up a 1978 175 Evinrude. I plan on going thru top to bottom and fuel as suggested by OBJ. <br /><br />Before I get into parts and manuals I want to run compression test. Does anyone have the compression numbers and variance.<br /><br />Also, I see refernces to Looper and Crossflow engines. What is the difference and what might the 78 I have be? Just curious.<br /><br />Thanks,

 

[Joe Reeves]

Re: 78 Evinrude 175 Compression

Compression should be in the 100+ psi range and even on all cylinders. List what you have.<br /><br />Loop charged pertains to the design of the crankcase, the design of the pistons, and the manner in which fuel is delivered to the combustion area (to keep it simple).<br /><br />Your engine is a crossflow model.

 

[snagroms]

Re: 78 Evinrude 175 Compression

Joe,<br /><br />Working on getting the motor on a stand in the next day or so. Will post the compression figures after that.

 

[snagroms]

Re: 78 Evinrude 175 Compression

Joe,<br /><br />Here are the compression figures. 1st # is cold second is after 20 minute idle on the stand with muffs.<br /><br />1) 102/102 2) 102/102<br />3) 114/111 4) 105/102<br />5) 111/115 6) 105/105<br /><br />Only did some slight reving (no tach hooked up yet) and the heads were just warm to the touch after 20 minutes. Sounded great! What do you think.

 

[boltbreaker]

Re: 78 Evinrude 175 Compression

It looks like the compression is good enough to tune the motor.<br />Am I wrong in thinking that compression should be HIGHER on a warm engine?<br /><br /><br />Buy a manual and HAVE AT IT!

 

[boltbreaker]

Re: 78 Evinrude 175 Compression

It looks like the compression is good enough to tune the motor.<br />Am I wrong in thinking that compression should be HIGHER on a warm engine?

 

[snagroms]

Re: 78 Evinrude 175 Compression

My thought also on #3 and #4 being lower when warm. Not a typo there. They went down.

 

[snagroms]

Re: 78 Evinrude 175 Compression

^

 

[snagroms]

Re: 78 Evinrude 175 Compression

^

 

[walleyehed]

Re: 78 Evinrude 175 Compression

warm, cold...doesn't matter as long as it hasn't been setting for a long period of time.<br />As Joe says, if you've got a 100+, and are simular in all, and you are, you're fine.<br />As for being higher when warm, that can vary from engine to engine. There are too many variables to say "that's a problem"...it's not.

 

[snagroms]

Re: 78 Evinrude 175 Compression

Many thanks to all for your help. A service manual should be here this week and work starts shortly after.<br /><br />Thanks