Merc 1150 bad cyl?

[Trav454]

I picked up a ‘75 merc 1150 for the ignition parts and decided to test the compression out of curiosity.

Cyl #3 is 90 psi…all others are around 140.

Is the block worth messing with? I would assume there is a significant issue with #3.

Thanks

 

[Scott Danforth]

When a TOP is overheated, #3 gets killed.

 

[Chris1956]

90PSi is pretty good for a damaged cylinder, as they are usually zero compression when damaged.

Pull the middle transfer cover and take a look at the piston and cylinder walls.

I would run it until the compression reaches zero, if that ever occurs. First, clean the carbs, rebuild the waterpump and check the link and synch.

 

[racerone]

Well ---#3 is often the first one to suffer.___-find / correct the cause.--Inspect all parts.------Install a new O/S piston now.-----If you keep running it it will suffer major damage.-----These motor need a new impeller every 2 or 3 years.

 

[Chris1956]

Gee, it is a 1975 that he picked up for ignition parts. It is nearly 50 years old. Why should he rebuild it?

I say run it, if you need to.....

 

[racerone]

Every body has different standards and budgets I suppose.------Parts motors like that are plentiful in some areas.----Often free !

 

[Trav454]

Gee, it is a 1975 that he picked up for ignition parts. It is nearly 50 years old. Why should he rebuild it?

I say run it, if you need to.....

Thanks Chris that was the confirmation I needed.

My plan was to run this motor temporarily on my fishing rig while I have my main ‘77 1150 tore down replacing the exhaust gaskets.

Just didn’t want to go through all the trouble of swapping motors if the low cyl pressure was going to cause performance issues.

Do you have a preferred method of cleaning the carbs? Complete disassembly and soak in a can of cleaner?

 

[Chris1956]

I just disassemble the carb and blow out the carbs with some spray carb cleaner. Make sure to get the small holes just inside the throttle plate in the carb throat. Those are the idle circuit.

I would not expect any significant loss of performance. 90 PSI is pretty good.

On your '77 1150. The inner exhaust covers and exhaust baffle are a PIA to get them to seal after all this time. Make sure they are flat, and you may want to use gasket dressing to help with the seal. If you have not disassembled it yet, those 5/16" exhaust cover bolts like to break. Use some heat and impact to try to loosen them. They were epoxied in at the factory.

 

[Faztbullet]

Run it awhile and it will become a parts motor for sure.

 

[Trav454]

I just disassemble the carb and blow out the carbs with some spray carb cleaner. Make sure to get the small holes just inside the throttle plate in the carb throat. Those are the idle circuit.

I would not expect any significant loss of performance. 90 PSI is pretty good.

On your '77 1150. The inner exhaust covers and exhaust baffle are a PIA to get them to seal after all this time. Make sure they are flat, and you may want to use gasket dressing to help with the seal. If you have not disassembled it yet, those 5/16" exhaust cover bolts like to break. Use some heat and impact to try to loosen them. They were epoxied in at the factory.

 

[Trav454]

I did pop the transfer port cover off. Here are some pics of #3…

Piston looked to be chipped in some places and rings definitely have some gouges…aluminum flakes accumulated in one of the pockets of the port cover…

Overheat?

 

[racerone]

Typical damage .----rebuild it now or it will be 10 cent / lb soon.----Are the bleed inserts there or gone like most of them?

 

[Trav454]

Typical damage .----rebuild it now or it will be 10 cent / lb soon.----Are the bleed inserts there or gone like most of them?

I didn’t pay any attention when I had the cover off but it looks to be missing in the attached picture.

Just curious but is that notch on the front facing edge of the piston directly behind the cylinder wall suppose to be there? I just assumed it was a broken piece since the piston in the cyl directly below it didn’t have it.

 

[racerone]

I usually see 3 of the 5 bleed inserts missing.-----Looks like damage to the piston.

 

[Faztbullet]

The aluminum throw off(sandy,crusty metal) is preignition. Usually the trigger is bad when #3 or #5 fail. Usually it will be double firing

 

[Trav454]

I just disassemble the carb and blow out the carbs with some spray carb cleaner. Make sure to get the small holes just inside the throttle plate in the carb throat. Those are the idle circuit.

I would not expect any significant loss of performance. 90 PSI is pretty good.

On your '77 1150. The inner exhaust covers and exhaust baffle are a PIA to get them to seal after all this time. Make sure they are flat, and you may want to use gasket dressing to help with the seal. If you have not disassembled it yet, those 5/16" exhaust cover bolts like to break. Use some heat and impact to try to loosen them. They were epoxied in at the factory.

Chris thanks for the heads up. I have not started disassembly yet as I didn’t know exactly where to start.

Motor had begun acting “strange” all of the sudden the last few trips out. Sometimes it would take off fine…other times it would take several minutes trying to build up rpm and get on plane. The last trip out it started having severe sporadic misfire at WOT.

There is definitely evidence of water on some of the plugs and even rust after setting a few weeks. The block itself appears wet and there is washout looking crud at the bottom of the block below the carburetors.

I was going to start with replacing the exhaust plate and baffle gaskets.

 

[Faztbullet]

Wasting your time and money....either pull it down and fix it or part it out. Trigger most likely bad as cylinder had preignition and now has WOT misfire.

 

[Trav454]

Wasting your time and money....either pull it down and fix it or part it out. Trigger most likely bad as cylinder had preignition and now has WOT misfire.

Fazt,

I got two motors being discussed here. The motor with the questionable cylinder was just a parts motor I picked up and was thinking about using temporarily while I
replaced gaskets on the one with water intrusion. That motor still shows good compression across the board.

 

[Chris1956]

If the cylinders that have water in them are #5 and #6, the lower crankshaft seals are likely bad. That is an easier repair. Simply loosen the crankcase bolts on the very bottom, and remove the end cap bolts and endcap. Replace the seals (3 is better than 2), and inspect the bearing for wear.