Old 15 hp Mariner compression

Tarosaki

Cadet
Joined
Nov 12, 2018
Messages
7
I have an old Mariner 15 hp with fireing problems on the bottom cylinder. We swopped the coils. Swopped the points, condenser, coil in the flywheel area . Also the wireing from the points to coils(harness) Plugs ect.
The pressure test shows a reading of 750 on the top and Almost 1000 on the bottom non fireing cylinder. Sometimes when cranking the flywheel by hand past the point marks on cylinder one there is a good spark on one and no 2 is also giving a spark on the plug when both are earthed to the block .
While running I pulled the bottom HT lead and there is no change in the running of the engine. If i pull the bottom lead it stalls.
Why is the compression so High in the bottom cylinder. Why are both plugs fireing at once
The Engine was resprayed by previous owner.I dont know where the points marks are and where the TDC should be. Where must the points marks be? Before tdc or after and how many degree?
Could it be timing settings?
The engine was running good. We parked the boat and it Broke down while it was resting.

The model is unknown as the Plates was removed by previous owner.
 

Tassie 1

Chief Petty Officer
Joined
Apr 13, 2018
Messages
581
Dunno whether this info nicked from clymer manual B712 ( mariner '76 -'84 2hp -48 hp ) will help or is what you need,

FO alternate
plug NGK B7HS
Spark plug gap 0.019 -0.024 1n
static WOT timing 0.098 + -0.016
breaker point gap 0.012 -0.012 in
WOT range 4500 - 5500 rpm
idle rpm 1100- 1200 in fwd gear

probably need more info re timing degs but it's a start,

no experience with your model, take the above with a grain of salt
had a 28hp years ago, it would come in handy atm
 

Tarosaki

Cadet
Joined
Nov 12, 2018
Messages
7
Now that you say Water in Bottom cylinder. We did remove the cover on the exhaust side. It looked a bit juicy there. Thought it was fuel not burnt up due to the not firing.. Even tasted like fuel. I will investigate that. ..Will it be a headgasket maybe?
 

Tarosaki

Cadet
Joined
Nov 12, 2018
Messages
7
Took off the head. There were water droplets in the bottom cylinder. The thermostat were rusted shut or maybe partly. One side of the chanal around the barrels were gunked up with calcium deposits with no flow. No real tell tale marks that water seaped into the cylinder. , but I can be mistaken. Where else could the water come from. Or should it only be from the head gasket?
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
What is the unit of measurement on your compression test ? If you meant 75 and 100 psi, that wouldn’t be ideal to start with. The variance between them and the figure of 75 is lower than tolerance I’d imagine. Perhaps a separate issue, but of concern anyway.
 

Tarosaki

Cadet
Joined
Nov 12, 2018
Messages
7
QBhoy . I can not tell you. borrowed from a friend. Did not look at the scale. but the needle pointed to that. Would like to know where else to look for the cause for the water drops on the cylinder that we found. One issue to me was slight rust spots arround the seal ring on the old head gasket. Got a new one and it looks very nice compared to the old one 😁 we cleaned the area inside the head with a dremmel and also all the calcium arround the barrels where we could reach. It looks as if there was only partial wayer flow if any to the head.luckely we never drove more tha say 500 metres with the boat at a time. never had steaming issues also. The tell tail was also not so great but there was medium flow.
 

Tarosaki

Cadet
Joined
Nov 12, 2018
Messages
7
Think we fixed it. Replaced the head gasket and it fired up on both cylinders. Half pull. Thank you for the advice and pointing me to water in the bottom cylinder.
 

raczekp1

Lieutenant
Joined
Mar 30, 2010
Messages
1,327
did you flatten the head surface in machine schop before instaling ne head gasket?
 

Tarosaki

Cadet
Joined
Nov 12, 2018
Messages
7
I have done a backyard job on it:D. Glass and sanding paper and straight edge test. Little bit of gasket sealer. Only tested it in a drum so far and let it idle for 20 min at a time 3x over 3 days. So far so good. The telltale stream is also nice and strong compared to what it was before.
 
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