Crankshaft bearing

[rcjr1941]

How can you tell when a crankshaft bearing is going bad. Motor cranks and runs good at slow speed. When put on plane alarm goes off and motor stalls. Motor 1990 50proDL.

[boscoe99]

I presume that you mean a PRO50LD.

http://www.boats.net/parts/search/Ya...0LD/parts.html

Two things generally set a Yamaha alarm. One is low oil tank quantity and the other is an over temperature event. I have never heard of an alarm being set for a bad crankshaft.

With an alarm being set, the motor will normally go into RPM reduction mode but won't stall. By stall I presume that you mean the motor quits running. Correct?

The fact that the alarm is being set when on plane would lead me to investigate it for an over temperature event.

When was the water pump last replaced? When was the thermostat last replaced? Is this a saltwater or freshwater motor?

[rcjr1941]

crankshaft bearing

The motor does not quit. I can turn it off and restart and run at slow speed. The water pump was just replaced by boat dealer. I put in in the shop when I took it out and it was not pumping, they replaced all parts and the stall occurred when it was returned and put in the water. It was returned to the shop and they said it needed all carburators replaced. They found carburators and reolaced to the tune of $800. Picked up put in water and travelled at slow speed about 11/2 mile and drift fished for several hours. Cranked up and started to run back to launch and stall and alarm went off in about 30 seconds cranked back up and ran at slow speed back to launch. Took to another shop in Gulf Shores and they put boat in water and called and said the crankshaft bearing was bad. salt water

[99yam40]

still no definition of what you call stall.

Is the alarm buzzer coming on and RPM reduction happening?

Where are you located?

Have you looked at the oil level or felt the motors temp when alarm is going off?

[rcjr1941]

crank shaft

The oil level is always checked before the boat is put in the water- habit
Stall- motor goes from 4500 rpm t0 1500 rpm but does not stop running
The alarm goes off about 1 minute after running motor at 4500 rpm
When the alarm goes off the reduction of rpm occurs
I ran the motor at 1500 rpm for 30-45 min. when I left the launch with no problem. When I was returning to the launch I ran about 5 min. at 1500 rpm
I then increased the rpm to 4500 and within 1 min. the alarm went off and the rpm of the motor fell down to about 1500 rpm. I turned the motor off and checked for over heating I cranked the motor in about 3 min. and ran it about 15- 20 min at 1500 rpm back to the dock with no problems.

[99yam40]

RPM is restricted to about 2K when alarm comes in.

If it is not an oil level problem then you need to be checking on what is causing the over temperature to occur.

You can pull and test temp switch and thermostat to make sure they operate within spec. If they are working as they should then you need to make sure the water pump is pumping as it should.

Did they replace the plastic water pump housing along with the kit ?

May need to pull head and clean passages if all else is working properly

Only thing I can think of with the crank would be seals leaking and leaning out the top or bottom cylinder causing higher temperature in that cylinder