99 2.5 200 crank

[oldblue82vector]

Crank came out of virgin 200 that had melted #6 piston. Top bearing journal and #1 cylinder journal have issues. Both bearings were in perfect shape when removed. Issue with the crank had to have been there for many years without causing problems. Not sure what it would be worth in this condition so make me an offer. Rest of the crank is in perfect condition.
420040420041420042420043

[Merc 2.5]

I'm pretty sure it's a lamp post now, least thts what I was told about mine ,and it wasnt as bad as urs

[nitro_rat]

Yeah, that crank is roached. Repaired cranks don’t live long. There used to be a couple places fixing them but I don’t think it’s even an option anymore. #6 is probably indexed several degrees advanced from #1 on that crank anyway. That’s why it melted #6 piston (common problem). 23* timing on #1 = 28* timing on #6! There’s a thread going on now about indexing your flywheel to prevent this...

[oldblue82vector]

Can anyone explain how this could have happened and not had problems with it? I’m pretty sure that if piston would not have melted that this motor would still be running today. Just curious.

[nitro_rat]

Can anyone explain how this could have happened and not had problems with it? I’m pretty sure that if piston would not have melted that this motor would still be running today. Just curious.

Was the engine still running oil injection at the time of the failure? If so when was the last time the oil pump’s performance was checked? What I can see in your pic of the pump drive gear looks okay but that’s no guarantee the system was working properly.

Was the cause of the failure of #6 determined? Was it oil related, timing related, bad switchbox?

Another likely contributor to that the damage to the top bearing could have been a problem with the bleed circuit that feeds oil up to that bearing. A leaking bottom seal can starve oil to the top bearing as the bleed system takes excess oil from the bottom bearing and feeds it to the top.


Both bearings were in perfect shape when removed.

What is your basis for that conclusion? Judging by the condition of the inner race of those bearings (the crank journals) there are major problems with those bearings. Just because the rollers look “okay” by eye doesn’t mean they’re “good.”


Issue with the crank had to have been there for many years without causing problems.

It just looks to me like the #6 piston beat your bearing problem to the finish line! It doesn’t mean that that crank would have run infinitely with the journals in that condition had the #6 piston not failed!

[gotboostedvr6]

I have one that looks like that but with less pitting. It's free if you come get it.

[TEXAS20225]

number 6 is a victim of bearing skid thats caused by the cap not lining up properly and the bearing stops rotating inside the rod and crank it stays in one place and wears the plating off the journal just like you seeing. top journal is common plating loss i had a perfect Bridgeport 9 ring crank once that half the plating came off i guess from twisting it up too often or maybe manufacture QC it was a friday nite crank, not too easy some times to pinpoint what happens on every hiccup

[Dave S]

lugging.....

[Merc 2.5]

Was the engine still running oil injection at the time of the failure? If so when was the last time the oil pump’s performance was checked? What I can see in your pic of the pump drive gear looks okay but that’s no guarantee the system was working properly.

Was the cause of the failure of #6 determined? Was it oil related, timing related, bad switchbox?

Another likely contributor to that the damage to the top bearing could have been a problem with the bleed circuit that feeds oil up to that bearing. A leaking bottom seal can starve oil to the top bearing as the bleed system takes excess oil from the bottom bearing and feeds it to the top.



What is your basis for that conclusion? Judging by the condition of the inner race of those bearings (the crank journals) there are major problems with those bearings. Just because the rollers look “okay” by eye doesn’t mean they’re “good.”



It just looks to me like the #6 piston beat your bearing problem to the finish line! It doesn’t mean that that crank would have run infinitely with the journals in that condition had the #6 piston not failed!

So so so very well explained. Thanks nitro

[nitro_rat]

lugging.....

Yes, that could have been the cause of the melted piston also. Outboards don't have a method to decrease timing as RPM's drop under load. Devices that accomplish this are mechanical (centrifugal) advance mechanisms, vacuum advance mechanisms, or computer controlled electronic systems. The distributor and/or electronic ignition do this on your car for example.

The outboard motor has a lever that is directly connected to the throttle position, totally independent of load. If the engine is operating below rated RPM at WOT bad things happen! Pre ignition and then detonation will kill pistons and put a tremendous load on the connecting rods and bearings.

Once you slow the engine down enough the spark plug is igniting the fuel/air charge BEFORE the piston reaches TDC so the incoming fuel air charge is effectively trying to stop the piston's upward travel rather than pushing it back down the hole...

This is just internal combustion 101!