still lurking about - ? on 1986 75 Mariner

[udoittwo]

Hello yet again,
Sorry that I only get time to look at my motor when I am not working 2 jobs or the weather is nice and I am not expected to do something else on a nice day. VERY LITTLE TIME! Anyway, the story again - my motor ran great for the past 27 years. Tried to start it last year[did all the right things to store over winter] and it would not start. Poor compression in top cyl. of my 1986 4 cly 75 HP Mariner. I asked at this site about it and was told to remove exhaust cover look at possible stuck rings. I couldn't figure out how to remove the lower cover to get at exhaust cover and not even sure what the lower peice is called? It is not named or is it explained how to remove in my SELOC shop manual. Someone here said I just need to remove the bolts and drop it down. What bolts ? Here is a picture of the [my name] "lower shround". What/where are the bolts I should remove. Even if I remove these bolts, will this peice drop down low enough to expose all the exhaust cover bolts?
Just curious, I've had car motors that have lost compression in a cyl. before. They still would run but they would run with a miss. I understand that this is only a 4 cyl, but will one bad cyl. keep it from not firing at all?
Again, I am really sorry for my ignorance. I look at this as compared to a car motor and there is so much going on here and to me it is a little overwhelming.
Thaks yet again for your patience and any help,
Karl.

 

[carholme]

Re: still lurking about - ? on 1986 75 Mariner

I don't think you can split that lower cowl. You will have to lift the power head from the rest of the engine.

Items 27/28 in this link are the ones you need to remove to inspect the pistons/rings:

Mercury, Mercruiser, Force, etc. - END CAPS, MANIFOLD AND EXHAUST COVER - 75 H.P.

What were the compression values you got?

One would think you would still get the engine to fire if you have spark and fuel. Have you verified spark and fuel?

What is your engine s/n?

Gerry

 

[udoittwo]

Re: still lurking about - ? on 1986 75 Mariner

As I recall, I got 140-145 for the lower 3 cyls. and 60 or 70 for the upper.
Serial #A199493.
Not really sure if its getting spark or not but I think I'll make sure the motor sound and then I'll check on the fuel & spark.
In the diagram you sent, it is showing a split exhaust cover, so you could pull the upper or lower 2 cyls.? Just to be 100% sure, the exhaust cover plate is the single peice verticle plate towards the rear of the motor in my picture with the dozen or so bolts?
The lower cowl in the way is 1 peice. It is loose now to the motor but looks like it can't be lowered out of the way.

 

[carholme]

Re: still lurking about - ? on 1986 75 Mariner

Your s/n comes up as:

MARINER - ( 75 H.P. (1986 ))
Serial No: 0A199493 Model No: 7075726

Parts Listing for model 7075726:

75 H.P. - Mercury, Mercruiser, Force, etc. Parts Lookup

Yes re the bolts, there are 14 total and you can just remove the upper cover as that is where your low compressions are. Once the cover is removed, you can rotate the flywheel (sparkplugs out) and see if there is any scuffing on the pistons, broken or stuck rings, etc. You can use a screwdriver to press against the exposed piston rings. They should have a spring feel to them if they are intact and not seized with carbon.

Gerry

 

[udoittwo]

Re: still lurking about - ? on 1986 75 Mariner

Thanks Gerry.
I was able to get the lower cowl a little out of the way that I should be able to get to all the bolts. At a quick glance, it looked like the shifter bracket[?] is permanently in the way but I just noticed a bolt and I'm hoping it can be moved.
It was mentioned about the probability of having issues with corroded bolts. I've put the wrench to check all of them and they all loosened up fine. Probably because it was never in salt water and the cover was never off before.
There's no way I'll be able to get down there with a torque wrench but being an exhaust cover, I'm hoping this should not be too critical. I'm going to snug them as I would any 5/16 bolt. Will I need any gaskets? Finally, I pulled a couple of the bolts. They look like they MAY have had lock-tite or something on them. Now that I've removed the factory paint and probably exposed them to a little more of the weather, I am wondering about possible future removals. Should I go with stainless bolts? Should I use lock-tite or should I use neverseize?
Thanks again for your help,
Karl.