Mariner 15hp 1993 compression

[werdna]

I have come to the realization, that, along with me getting a 'little' heavier that my motor isnt performing quite as well as it has been. I'm thinking about checking the compression, and wondering what should it be ideally and what is absolutely shocking. I realise that the two cyl should be close in compression.<br /><br />I bought the motor second hand a year ago and have done about 300 hours in it since, with regular servicing, but I'm wondering if something else that's wearign out. Would a new set of rings be alright if the cyl is in good condition?

 

[The Marine Doctor]

Re: Mariner 15hp 1993 compression

You of course would be best to check out the compression. You engine might be getting tired. <br /><br />If the compression checks out fine..work from there.<br /><br />TMD

 

[werdna]

Re: Mariner 15hp 1993 compression

Doc,<br />Thanks for that. Any suggestions as to what it should ideally be? It is currently running on a couple of NGK plugs that my mec has put in, so they are to spec, although i am not sure what the plug gap should be. it is a Mariner 15MLH/ALT. Also i have just checked and cleaned the fuel filter, so hopefully that'll make a difference. I had it out again today, and it ran fantastically with just me in the boat, although it struggled get going with three people in there. It was most of the way to planing - you probably know the feeling. Tried moving weight around in the boat, but it just 'couldnt get it up' hehe.<br />Cheers<br />Andrew<br />P.S. any ideas if this is in fact a 1993 model? It was purchased by a friend in South Africa, from whom i have bought the motor off. I assume that the '/ALT' in the model name refers to it having an alternator, but it puzzles me as there isnt an alternator on it

 

[werdna]

Re: Mariner 15hp 1993 compression

OK, out again today, and same problems. I cleaned out the fuel filter last night, but to no avail. After i came back, i checked the plugs (as i didnt have the complete set of feeler guages prior) to find that the plugs (NGK BP8H-N 10) were set at .055 as opposed to .040 which is indicated by the '10' in the plug model number.I am hoping that this will make a difference in the power of the motor. Any ideas? Would that gap have significantly weakened the spark?<br />Cheers<br />Andrew

 

[werdna]

Re: Mariner 15hp 1993 compression

Me again,<br /><br />Below is a pic of the plug

- hopefully that gives you some idea of what condition they are in. they are not oily (ie a greasy film) although seem rather clean and dry.<br /><br />Andrew