Not A Pretty Picture

[Outrage 19]

Recently I inherited a 19’ Boston Whaler with a 1986 Merc V150 SN#0B156087. The engine ran great at WOT but wouldn’t idle. I pulled the crabs (of course they were all gummed up) cleaned them and the engine ran at idle but at WOT seized up. I let it cool down and was able to start it and head back to the dock but again this time at about 2/3 throttle the engine seized. This time when I got it started I heard what I thought was a rod knocking. A compression test showed the following results.<br /><br />2 – 100 1 – 105<br />4 – 120 3 – 105<br />6 – 0 5 – 100<br /><br />I pulled the head and found #6 piston chewed up, and #4 stem cleaned. I took a good look at all of the cylinder walls and with the exception of some aluminum caked on the side of #6 there was no scoring.<br /><br />The questions I have are, how can I tell if this was a cooling system failure or a fuel/lubrication delivery system failure, and why did #4 get stem cleaned?<br /><br />I have been reading this forum for a couple of months now and think as stated by many others this has got to be the best collection of outboard mechanics both pro and shade tree. I appreciate any and all input and thank everyone in advance for your advice.

 

[Outrage 19]

Re: Not A Pretty Picture

Bump

 

[ob]

Re: Not A Pretty Picture

sounds like a fuel/oil lubrication problem assuming it ran for some time at wot before carbs were serviced.probably too lean.cooling system problem at this stage is mute since it is recommended to replace all cooling system components if you choose to overhaul engine.Is this motor oil injected or do you pre-mix?

 

[Outrage 19]

Re: Not A Pretty Picture

Oil injected

 

[ob]

Re: Not A Pretty Picture

probably lost oil after carb job.lost prime.alarms don't always work assuming they're hooked up.should have mixed oil in gas till oil injection working could be established.Dis connected mine three weeks ago and mix own.gained peace of mind.Don't get second chances with oil flow failure when engine running even if alarm bites you on ***

 

[Outrage 19]

Re: Not A Pretty Picture

If the oil injection had failed wouldn't that have left some scoring in the cylinder walls?

 

[ob]

Re: Not A Pretty Picture

depends whether failure was complete or not .possibly just oil lean. pistons are of more sacrificial material than cylinders.

 

[Outrage 19]

Re: Not A Pretty Picture

Good point, with a full 50 gal. Inboard tank it’s not practical to premix so once the overhaul is completed how can I determine if the oil injection is working?

 

[ob]

Re: Not A Pretty Picture

run with pre-mix and oil injection until you can possitively verify oil consumtion from reservoir.calculate the volume of consumption with volume of fuel used if able to do it accurately.This is a topic of diverse opinions but regardless of hastle involved I would defeat oil injection system and go to pre-mix. A drop of oil in the right place is better than two along side.

 

[Outrage 19]

Re: Not A Pretty Picture

Thanks for the advise ob