djtalon

New boat to me; ran for a few minutes on the trailer and one rod snapped and the one next to it went through the oil pan. (on a trailer no mre the 2000 rpms) Piston 1 and 2
When i tore the engine apart i found that rod bolts on piston 4 were loose and Rod 7 one bolt fell out and the other bolt was loose.
Gas tank for that motor has alot of water in it, carb was pretty much shot for that motor (1/2 filled with corrosion) Fuel pump was also bad on that motor.

Boat has twins with one tank for each motor.
WHAT WOULD MAKE THE ROD BOLTS COME LOOSE??

lean engine condition??

Vinny P

Was the engine original from the Merc Factory? If not, what rods and bolts were in there? How many hours on the engine since it was put together?
It is very unlikely that the nuts just came loose. It is more likely that the nuts were never torqued correctly. Maybe the rod bolts were replaced and not seated correctly ? That would cause the bolts to move forward amking the nuts loosen.

eyezlee

Sounds like it was improperly repaired. Sounds like you need to be calling the seller.

mike11

If the rod bolts replaced they must be streatched before final assembly, if not they will after assembly leaving you with what you have there.


Mike


Roccard Marine Engines
www.roccardmarineengines.com
[email protected]
570-956-2840

JCPERF

No one torqued them

US1 Fountain

iTrader: (1)

Or over torqued them. Got their rod and main torques confused. Seen that before.

djtalon

89 merc 420, no idea if the engine was ever apart. How would i tell? None of the pistons are stamped .30 or 60 over. Has all the stock merc 420 guts

Ted G

iTrader: (1)

Okay, here we go. Did you find pieces of the rod brgs in there when you got it apart? I suspect they are spun or severely worn. When a bearing spins it causes clearance between the rod and crank and hammering begins (rod knock). This hammering also starts to stretch the rod bolts (weakest link). As the bolts stretch the nuts begin to loosen. In some cases the nuts falling off and the caps coming loose is what causes the engine to stop, since most will run with spun bearings just fine (but noisy). Don't read too much into the loose nuts, it was most likely just bad brgs from water contaminated oil (condensation from sitting).

djtalon

just worried about the other engine that is all. I did notice that when i was cranking the engine is was on teh noisy side. SO i am thinking this did not happen from a few minutes or running. But then again maybe it only takes a second for things to go to hell.

offthefront

iTrader: (1)

can the previous owner give any input ? if both motors have not been gone thru I would go ahead and pull the other motor and go thru it ....