Bad crank bearings

[jhopkins]

I have a 88 Mercury 35hp motor on a Bass Tracker Pro 17 that runs great but RPM's are only 4400 @ WOT. My father-in-law bought this boat new and we just picked it up from this past fall. I have only put abot 10 hours on the boat since I have had it (probably less than 35-40 hours total on the motor) and decided to change the prop to get the RPM's up where they should be running. The motor originally came with a 3 blade 13p and after talking to Mercury I picked up a used 4 blade 9p that has no visual damage from a local shop.

I put the prop on Friday and headed out to the lake for a test run that didn't end well. My wife backed me down the ramp and I had the boat idling probably 10 minutes waiting for her to get back to the boat, we idle out past the no wake zone and and as soon as the rpm's get up to around 4300 the motor starts clanking really loud so I shut the motor off. Thinking the used prop I had bought was spun I put the motor in neutral and started the motor, but the clanking was still there so I shut it down and used the trolling motor to get the boat back to the trailer.

I can grab the flywheel and rock it side to side quite a bit and there is also a slight up down play also. Is it normal for crank bearing to go bad without any warning or could there have been a issue with the prop that caused the problem?

 

[racerone]

If the flywheel has a steel flexplate then check it for cracks.----Or perhaps the crankshaft is broken.

 

[jhopkins]

If the flywheel has a steel flexplate then check it for cracks.----Or perhaps the crankshaft is broken.

No flexplate. With the spark plugs out the crank turns both pistons but the bottom piston does not immediately move like the top piston does.

 

[racerone]

Motor likely has to come apart for inspection.----------Sounds like $$$$$ needed.

 

[jhopkins]

I will probably start disassembly next week.

 

[jhopkins]

Due to having wrist surgery I have been unable to tear down the motor until tonight and I have found the problem.

The crankshaft is broken above the top cylinder rod and the main bearing / reed block has some wear on the inside. I am assuming the wear is from when the crankshaft let go?

Shortly after my father-in-law bought the boat new the top cylinder rod bolt loosened and ruined the bearing and journal. The crank journal was repaired by welding and re-grinding. Could this repair possibly have stressed the crank and caused my current issue?

 

[racerone]

Just like I thought---Broken crankshaft.----A good welder would know that these precision parts can not be welded.------You can stick them back together with welding , yes.----But they are never the same as factory new as far as tolerance / fitment goes !!!!