Merc inline 1150 Rough idle, low comp and water intrusion?

[kswiatk]

1983 Merc 1150 inline serial number 641xxx.


Bought it last year with 120psi on all cylinders, ran almost 50 mph if you feathered the throttle at start up, but would constantly die at idle and in gear idle.


I figured that it was a link/sync or carb issue. Ignition checks out all good after replacing plugs and a switchbox.


I decided to rerun compression after not being able to make any difference with carbs or sync. #3, #4 and #6 plugs looked concerning, and #4 now showed 90 psi, the rest 120psi.


I purchased a cheap boroscope and the issue is obvious now. #4 looks cleaned, and I believe #6 may be showing issues too? The pics are attached below and label with cylinder number.


Plugs #6 on left, #1 on right

#1

#2

#3

#4

#5

#6


I was able to get the transfer covers off and found scoring on only #4


Now is this indicative of a inner water jacket leak causing scoring on the cylinder? The exhaust manifold has new gaskets from previous owner, is it just possible that they did not check the inner plate for flatness?

What are my best options for this engine? Replace only #4 piston/ring after boring, as well as any others if damage? All of them are .015 over already.

Is there any shop or person that does cylinder boring or have ring compressors for these motors in the Lower Lake Michigan area ( Illinois , Indiana, Wisconsin, MI)?

Thanks for any help

[FMP]

A beautiful last year inline 115 is for-sale by a member.
https://www.screamandfly.com/showthr...58#post3140758

[rock]

There is a shop in central Illinois that bores and has the ring compressors. However since I am as busy as I am it would be better to bring your cheap borescope down here with about $250 and if it looks satisfactory to you take home a rotating assembly with a couple new pistons, new rings, and rod bearings. If I remember correctly it is a standard bore motor hence the need for the borescope. Bring another $250 and you can have the rest of the motor. Integral trim mid section with lower and I am pretty sure the rest is in a tote. This came from a local dealer that had a project in mind but changed his mind. New pistons Mercury as are the rod bearings everything else Pro Marine and total cost for just those parts well over $250.

Rock

[kswiatk]

So my understanding is that this a motor and rotating assembly that you own? So it would likely need machine(hone?) work to go back together? Just a bit confused on the status of it.

Do you have anymore information on that shop? I am currently in Indiana but travel to that area for work every so often.
The only issue i forsee with my motor is finding a shop to bore a one piece head/block design, and the reassembly with special ring compressors. However, I should only need work on the one cylinder since the oversize pistons and new gaskets point to recent work.

[rock]

Which would make me wonder why it needs another piston if there was "recent work". This is a motor that came to me in a trade. Block was surprisingly good considering the piston condition. Installed 2 new and 4 good used pistons, new rings, new rod bearings, and seals. Rotating assembly is ready to dress and everything is there to complete motor. No honing, ring compressors, or machine work necessary. Already done and already assembled. I have way too many motors in my shop so I need to thin the herd so to speak. I believe motor to be an 84 model with integral trim mid and lower unit. Would probably even throw in the stand it's on. As far as information on shop it's mine. I was a self employed cabinet maker with a metal fab and machine shop as a hobby. Retired from cabinet work 3 years ago and now trying to downsize and move to a much, much smaller shop. I am near Peoria so not all that far from you.

Rock

[kswiatk]

Which would make me wonder why it needs another piston if there was "recent work". This is a motor that came to me in a trade. Block was surprisingly good considering the piston condition. Installed 2 new and 4 good used pistons, new rings, new rod bearings, and seals. Rotating assembly is ready to dress and everything is there to complete motor. No honing, ring compressors, or machine work necessary. Already done and already assembled. I have way too many motors in my shop so I need to thin the herd so to speak. I believe motor to be an 84 model with integral trim mid and lower unit. Would probably even throw in the stand it's on. As far as information on shop it's mine. I was a self employed cabinet maker with a metal fab and machine shop as a hobby. Retired from cabinet work 3 years ago and now trying to downsize and move to a much, much smaller shop. I am near Peoria so not all that far from you.
Rock

Just making assumptions, since I don't know its history, nor what really went wrong with it yet.
I tried to PM you earlier but your inbox was full.
So just trying to be sure... $250 for crank/rods/pistons and block assembly? Another $250 for mid and lower?