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Compression

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17arrowglassstinger

Contributing Member
hello my question is if a moto

hello my question is if a motor has bad compression if it would still make your boat drive or if it would just die or not go anywhere
 
"I guess it depends on how bad

"I guess it depends on how bad the compression is. Yes, at a certain point, compression can get so low that it won't run - it takes a certain amount to actually compress the gas / air enough for the minimal spark from a plug to ignite - I forget the number though.

Anyway, my motor was 120, 105, 120, 120. The low cylinder eventually got to 95psi (although on a different gauge, so that # may not be accurate). The motor did run though. Like crap at idle, constantly stall, etc, but fine on the top end. That's not to say that it's okay though - you'll definitely be doing some damage."
 
i have a 1974 70 hp johnson an

i have a 1974 70 hp johnson and can i get a compression gauge from a marine store and do you know an estimate of how much it would cost
 
"hello, i try to find out how

"hello, i try to find out how must the compression needs to be, i measure 7 bar .
its a johnson 4,5 hp 1980"
 
"I think 1 bar is equal to 14.

"I think 1 bar is equal to 14.5psi, so that would be 101.5psi. I have no idea what the ideal compression for that motor is, but I would guess that 7 bar is low."
 
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