Logo

1987 Mariner 25 hp

thfrider

New member
"My 1987 25 hp Mariner will no

"My 1987 25 hp Mariner will not fire on one cylinder. I have a very good mechanic looking at it, and he has tried everything. He thinks it is a bottom seal now. The motor did not run for 5 years. I don't want to spend a lot of money on an old boat. Can an average mechanic do this job?"
 
"Troy, you say it won't fi

"Troy, you say it won't fire on one cylinder. Does that mean you have no spark on that cylinder or it sparks good but produces no power.

The seal won't stop the spark, but without the compression (and the gas/air/oil mix) there would be little/nothing to burn..."
 
Your mechanic is not much good

Your mechanic is not much good if he can not check / diagnose crankcase compression.Have him check the reed valves and have him listen for the " poooofff " on the bottom cylinder.
 
"It sparks good, and at the co

"It sparks good, and at the correct time, but does not ignite. Mechanic came highly recommended by several dealers and customers. Suppose to be one of the best in the area. Is there a good way to check this seal wihtout a complete tear down?"
 
Start with removing the carbur

Start with removing the carburetor to look at / check the reed valves.Simple to do.
 
"Carburetor has been rebuilt,

"Carburetor has been rebuilt, the reed block removed and inspected, like new, and a new seal for the block changed twice."
 
"for the seal, pour oil down t

"for the seal, pour oil down the carb and see if it runs better, or see if it runs down the drive shaft"
 
"Sorry, I did not know " e

"Sorry, I did not know " everything " included checking the reeds. So remove sparkplugs , rotate flywheel till #1 is just past TDC and quickly push the piston to BDC with a screwdriver. You should hear a definite " pooofff " which is crankcase compression. Repeat for #2 and compare."
 
a compression tester would be

a compression tester would be a quick way compare readings 1 and2 you should hope to see no more than 15psi differ or pull exhaust cover andbaffle plate off you can see some of rings and cly. wall will get rid of some guessing right away gaskets are cheap and easy to get
 
"Similar problem I had with 40

"Similar problem I had with 40hp merc 2 cyl. Bottom cylinder would not fire and engine would only run on top cyl. The powerhead sits on the exhaust plate which attaches to the midsection. if the gaskets are perished at the exhaust plate or if the exhaust plate is corroded out like mine was! The bottom cylinder when it is at the bottom of its stroke is exposed into the exhaust chamber, my engine was spitting water from the persihed gaskets in the exhaustplate and the piston was sucking it in therefore wetting the plug causing no fire."
 
Back
Top