1200 Engine Diagnosis

[Adam5oh]

Hi All,

Had some bad luck in the Keys last week and managed to drop both rear cylinders in my 99 LS2000. On the way out to the reef the starboard motor shut down at around 5200 RPM. Was able to restart and found that it wasn't cutting out immediately, it was losing RPM and would actually stay running if I throttled down. Did this 2 more times and then everything seemed normal. At the end of the day we were coming back and then the same thing happened on the port motor! Exact same situation, different motor. I was hoping it was just a fuel issue or something but when I got home and checked the compression both rears had around 30 PSI. The port engine is an SBT with around 40 hours on it, bought it last September but got it installed back in March. It is now back with them awaiting teardown. I tore the starboard engine down today and here are the pics. I would appreciate any armchair diagnosis that can be offered, need to know the best option to get this motor running while I wait for the other warranty replacement.

[Technical Support]

Re: 1200 Engine Diagnosis

Check to see if the rear crank seals are coming out of the case. Also see if the oil lines are still attached to the block.

[JRock]

Re: 1200 Engine Diagnosis

Adam, I purchased a 2001 LS2000 this past spring and soon after discovered that the rear piston in the starboard motor was melted even far worse than yours. After tearing down the motor, I had a local motorsports shop bore the rear cylinder 1.5 mm over for a new SBT piston. They bored and honed the cylinder for $65. After getting the cylinders back I noticed that the intake side of the cylinders (internal water chambers) were packed almost half way full with hard corrosion. I removed all the corrosion and cleaned out the chambers as best as possible and concluded that the loss of cooling effectiveness combined with the extra strain that the rear cylinder receives had over-heated that piston and caused it to melt.
I ended up pulling the lower crankcase out of the boat to clean out all the metal debris from the broken piston and reassembled the engine on the work bench. I also replaced the wrist pin bearing and head gasket for the repair. I re-installed the cylinders alone (which was really tricky) and would reccomend having a helper assist for that step. For the single piston repair, it only cost me about $200, excluding the cost of the head gasket. If you do the work yourself, make sure to follow all the torque specs and use thread locker everywhere necessary.