[nightimefishn]

I am wondering if someone can confirm something for me. I have a 78 or 79 mercury inline 6 115 HP with low compression on 4 (about 40 psi). All others have around 120. I am showing some milky substance around carb and plugs. So I had a mechanic come take a look. He is saying head gasket.
I am a little confused because I thought I have read that these didnt have head gaskets?
So two questions
1. Does the 1978 or 79 inline 6 have a head gasket
2. What causes head gasket to go, age? I do not think there is an overheat issue.

Thanks

[daveswaves]

Originally Posted by nightimefishn

I am wondering if someone can confirm something for me. I have a 78 or 79 mercury inline 6 115 HP with low compression on 4 (about 40 psi). All others have around 120. I am showing some milky substance around carb and plugs. So I had a mechanic come take a look. He is saying head gasket.
I am a little confused because I thought I have read that these didnt have head gaskets?
So two questions
1. Does the 1978 or 79 inline 6 have a head gasket
2. What causes head gasket to go, age? I do not think there is an overheat issue.

Thanks

Find another mechanic, there is no head gasket on the inline 6 merc,. You can inspect the piston for number 4 by removing the intake port cover that is in the center, each cover reveals two cyl. Likely the piston is damaged, you will be able to see how badly by removing the cover. Post a pic for more input.

[nightimefishn]

Thanks Dave!
That's what I was afraid of. I am no mechanic by any means but such low compression on that cylinder is really bad right. Would it be worth a rebuild and if so how much should I expect to pay for such a job?

I will take some pictures as soon as I can.

[Chris1956]

A single oversize piston+ring set is abut $100. Gaskets about $100. Boring a single cylinder about $50.

Labor to completely tear down the motor, and to reassemble is going to be $500-$1000. You also need to fix the cause of the damage, likely clean the carbs and adjust them, likely $250-500.

[nightimefishn]

So bad carbs could be the cause of this?
I am going crazy with this engine. It ran excellent for like 2 weeks then all hell broke loose!
I was originally having issues when I would be WOT for about 15 mins I would shut her down and then try and start her up it would just tick. So I inspected wiring harness, internal wiring harness was shot. So I have since replaced the harness along with several other corroded wires.
Engine starts just fine now but sounds like it is missing. Timing is dead on so then figured let me call someone to take a look. Guy came over did compression test and good compression on all but #3 and #4 like 45 psi. He said looks like a head gasket. After I heard him say that I started looking more on head gaskets. I remember reading that the inline 6 doesnt have a head gasket. Now I am at a total loss and extremely frustrated.

I had originally thought all was due to bad wiring harness, not so lucky I guess.....

Thanks for all your responses I am sure I will have some more questions over the next few days.