79, 3cyl 70 hp Mariner Issues

Hi everyone, I'm new and I don't know what to do! I have small engine knowledge Briggs and stratton, Kohler, Kawasaki to name a few. I was hoping that outboards won't be to far of a jump.
I just recently purchaced a small boat and it has a 1979 Mariner 70 hp 3cyl, when I finally got her running there was a rattle and I could tell it had a mis replaced all three plugs and checked for spark, still a mis so I rotated each piston to the top end and cyl #1 moves side to side if you push on the dome with a screwdriver(found that rattle). The other two cyl are good and stiff, any hints before I tear into this thing other than get a manual?
Speaking of manual can anyone help me with which one to get or could send me link or file with diagrams? I have been told that Seloc leaves a lot out in there's? I would love to fix this motor it is in decent shape as well as the boat. I bought it off of a young guy who didn't have a clue, my guess is that he didn't realize that you have to add oil to the gas 2 cycle!!

 

Not my favorite engine ( nor Mercury's )but i'd first do a compression test
How much side to side are we talking, rocking the piston over sometimes makes it look worse than it is.
Was it a freshwater engine?
Second check the oil in the gearbox, could be plenty of money to spend there as well if you find water.
Third I'd try to get the gearbox off to ensure drive shaft not stuck in the crankshaft

I'd say a 2 stroke with blind cylinders is quiet a jump from a conventional 4 stroke when it comes to rebuilding

 

I am not sure what year it started but many mariners were Yamaha re badged ....worth checking if there is any sign of japan manufacture ...manuals are all over e bay on disc as are spare piston sets from japan..Dont over capitalise on it ..may be better to buy another non runner and make one out of two..or check out an outboard wrecker

 

Had a similar case about 2 months ago with a 3 cyl 30hp Suzuki with a rattling noise when revving motor. Took the top off and also found excessive movement of the top piston in the sleeve and assumed rings were shot since the motor did overheated previously.
Bought new rings and when the motor was stripped the problem was not the rings, but found the gudgeon pin hole on the connecting rod to be worn oval on the sides, resulting in sideways play of piston. Since this engine runs on roller bearings and the crank press fitted together, I just silver soldered the worn sides up and pushed a reamer through and the problem fixed and cylinder play eliminated. Engine runs like new again.

However, your engine is a Yamaha unit used by Mercury at the time for their Mariner brand and the engine have split roller bearings, thus easy to disassemble the connecting rod from the crank for replacement if the problem turns out to be a worn gudgeon pin hole in the connecting rod...

Hope this help.

 

79 the biggest jap engine in the Mariner range was that horrible 2 cylinder 55 ( which was where they started, Australia was the test launch market for the grey engines)
everthing above that was a Merc

 

I really must thank everyone for the info, I'm currently awating the delivery of my manual and I have not dug into the motor yet.

 

Everything above that 2 cylinder motor? My motor is grey but I noticed taking a close look to all the mold numbers and words on the engine are in english?

 

the best way to thank us is to let us know what happens when you strip it ..so often we hear nothing ...

 

My wrong, the three cylinder is indeed a Mercury unit as powerabout pointed out.
However, some Mariner motors in SA of that vintage was 60hp with the two cylinder Yammie powerheads

 

OUTCH any idea what may have caused this?? I torn right in to the motor and I have it all laid out. When I pulled out the crankshaft to reveal an ugly discovery. I am puzzled at what could've caused this..... Bet they used straight gas

 

no water flow ..top piston is the worse as it did not get any water to the top of the block.. new pistons and hone the bores ( you can do that yourself ) if its not too bad.

 

Any ideas on where about to get some parts for this motor. What I have priced for .030 pistons, rings, a gasket set and head gasket would be over $400 I'm trying to get this thing done and in the water this season but with these prices I wouldn't even make it out of the driveway!?

 

you gona have to buy at least one piston possibly 2 ..but if you go oversize then you got to get it re bored ...what are the bores like ??? if you can rotary hone them yourself then put std pistons in and maybe oversize rings trimmed to match the bores ...of course if you dont know what I am talking about just bin the lot and go buy another one

 

As much money as that would save me to buy just one or two pistons, I have always been told what a bad idea that is. The bore is rough, I don't think I can do the work I have a friend who can fix it if possible I'm waiting on a phone call____?