1978 mercury 175 compression

[fish4970]

my readings are as follows #1-#6 <br />137, 140, 137, 137, 140, 137<br />as i understand, it is good if there is no <br />more than 15% lowest & highest cylinder<br />my question is what is the factory compression.<br />i have an oem manual but it says nothing<br />about compression.<br />ps motor supposedly has 6 hours on overhaul with weisco pistons<br />thanks in advance

 

[G DANE]

Re: 1978 mercury 175 compression

Hi fish4970<br /><br />You will definately be fine. New compression probably between 135 and 140 on most mercs of these vintages.

 

[JB]

Re: 1978 mercury 175 compression

Howdy, Fish.<br /><br />The reason manufacturers usually don't specify compression readings is that you can get different readings if:<br /><br />You use different guages.<br />You use different techniques.<br />The temp of the engine differs.<br />The time since decarbing differs.<br /><br />As long as all of these factors are the same for all cylinders, the differences from one cylinder to another will be consistent, and will indicate any sick cylinders.<br /><br />Most engines are fine as long as all cyl. are over 100 psi and span less than 10-15%.

 

[fish4970]

Re: 1978 mercury 175 compression

thank you very much<br />i just overhauld the carbs <br />set the timing to factory specs<br />just need to rebuild water pump & go fishing

 

[fish4970]

Re: 1978 mercury 175 compression

I HAVE A GOOD QUESTION<br />I CHECKED THE WATER PUMP BECAUSE OF NO TATLE TALE<br />WHEN I TOOK THE WATER PUMP APART, IMPELLER LOOKED OK TO ME (ALL VANES INTACT & SNUG AGAINST SLEEVE)<br />SO JUST FOR GRINS I HELD A GARDEN HOSE TO THE<br />PIPE THAT GOES UP THE SHAFT HOUSING TO THE POWER<br />HEAD, THE RESULTS WER LOTS OF WATER RUNING OUT OF <br />THE DRIVE SHAFT TUBE, SOME WATER OUT OF THE EXHAUST TUBE , AND A LITTLE WATER OUT OF THE <br />TATLE TALE <br />IS THIS NORMAL<br />I WOULDEN'T THINK THERE SHOULD BE WATER IN THE DRIVE SHAFT PASSAGE<br />THANKS IN ADVANCE fishertodd1@msn.com

 

[jim dozier]

Re: 1978 mercury 175 compression

Tilt the engine up and do what you did with a flashlight shinning up the driveshaft housing and verify where the water is coming from. Are you sure it wasn't coming from the exhaust housing?

 

[fish4970]

Re: 1978 mercury 175 compression

i am pretty shure that it was coming from the drive shaft passage there is a partission between it & the exhaust itlooks like it goes all the way up

 

[jim dozier]

Re: 1978 mercury 175 compression

If you're correct, I don't think water should be spraying in the driveshaft housing. I don't know your engine but I would suspect the seal/grommet at the top of the water tube or the powerhead seal is leaking.

 

[fish4970]

Re: 1978 mercury 175 compression

it is a 1978 mercury 175 black max

 

[fish4970]

Re: 1978 mercury 175 compression

would the water pressure relief valve affect the<br />amount of water from the pee hole

 

[fish4970]

Re: 1978 mercury 175 compression

would like to hear what jb thinks

 

[JB]

Re: 1978 mercury 175 compression

Thanks for the confidence, Fish, but this is one I don't know much about.<br /><br />12Footer knows Mercs pretty well. I wonder what he thinks.

 

[fish4970]

Re: 1978 mercury 175 compression

how about it 12footer do you have any insite on this subject