MERCURY 115 HP INLINE 6 CYLINDER COMPRESSION test readings, opinions please.

MACH1SCJ

Petty Officer 3rd Class
Joined
Jun 8, 2010
Messages
82
COMPRESSION READINGS

(top to bottom, where is #1 cylinder?)

------------------------------------ 3 complete
1st full compression stroke.----- revolutions ------------------ max build up, 5 to 8 revolutions

25 -------------------------------- 105 ------------------------- 150
40 -------------------------------- 105 ------------------------- 150
50 -------------------------------- 90 to 105 ------------------ 125 to 135**
40 -------------------------------- 105 ------------------------ 135 to 145*
40 -------------------------------- 115 ------------------------- 140 to 147*
30 to 35 ------------------------- 100 ------------------------- 140 to 150*

What do you guys think about these readings?

I checked each cylinder around 8 times & went over them twice, very consistant with these readings. the astrik readings were the most inconsistent & not by much.

Also I can not find the id number plate on the engine I think it is missing, the boat title has an engine number on it & comes back as a 1972.

It needs a wire harness, stator, fuel line from pump(s) and the normal stuff from sitting .
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Re: MERCURY 115 HP INLINE 6 CYLINDER COMPRESSION test readings, opinions please.

Good looking numbers to me. Nice and even. The variance in the last column could be instrumentation error. The lowest has ok readings in the first two colums. 120 min is what my merc manual say is passing.

Mark
 

oldman570

Lieutenant Commander
Joined
Mar 25, 2011
Messages
1,615
Re: MERCURY 115 HP INLINE 6 CYLINDER COMPRESSION test readings, opinions please.

Compression test need to be done with the throtal in the WOT position and the motor should be turned over 3 to 4 times on each cylender. From the readings posted at 3 revs everything looks good as they are all lest that 10 percent overall diffrence. I always have the motor hooked up to muffs while running compression test as not to do harm to the waterpump. Alot of the parts can still be had at oldmercs.com if not here on Iboats. Otherwis Ebay or one of the salvage yard listed in the Johnson motor sticky 'top sacret'. might have what you need.
The serial# for the motor should be stamped on a welch plug, siliver and about the size of a quater, on the side of the block if no plate on the transom bracket. A call to Mercury Marine or a post here will help be sure of the year and modul of the motor.
Oldman570
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: MERCURY 115 HP INLINE 6 CYLINDER COMPRESSION test readings, opinions please.

Your compression is fine. Anything else you need to know?

A 1972 inline 6 will have battery powered CDI ign with a distributor. The rotor is not replaceable and pretty fragile. Usually the motor wiring is all bad....
 

MACH1SCJ

Petty Officer 3rd Class
Joined
Jun 8, 2010
Messages
82
Re: MERCURY 115 HP INLINE 6 CYLINDER COMPRESSION test readings, opinions please.

Much thanks for confirmation on compression. I will try to repair the engine harness- I'll have to see how it looks when I get into it though.

I fixed the stator wires today by cutting into the epoxy encapsulation & soldering, liquid elec tape, heat shrink & heat shrink w/ glue inside. Turned out nice I think, and it produces .06vac per coil with a little magnet & my AC volt meter,so hopefully it functions on the engine.
 

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