250 inline 6 toasted

Had to run in on my kicker last fishing trip to Nootka sound. Engine (MC165 I6)seemed down on power at start of trip, went thru a bunch of oil, topped up on oil, and on the run home ....... wack wack wack - shut er down. Start up, same nasty noise at idle, start kicker and putt home. No water in oil, pulled plugs to have a peek and #3 and #6 soaked with oil, really wet with oil. I'm not even going to pull the cylinder head, it is headed to a re-builder tomorrow. Interested to hear what the post mortem report on the engine. Hope the core is rebuildable. I don't know how much run time was on the engine, boat was a 1976 and I believe the engine is original. Any one care to make a prediction as to what took a dump inside?
Alan

Re: 250 inline 6 toasted

If it's toasted, you just need to add butter..

Spun a bearing most likely

Re: 250 inline 6 toasted

OK, one for spun bearing (main?) who else has a guess?

Re: 250 inline 6 toasted

Spun bearing wouldn't dump oil inside a cylinder.

Oil in cylinders says rings or valves. On 2 cylinders is very odd. Cylinders 3 and 6 are sequential in the firing order. Here's a possibility (and you're not going to like it).... If the points hold-down screw worked loose, and you have a little wear in the shaft (and at that age, wouldn't surprise me), then the timing will start to retard as the gap closes up, producing the loss of power you experienced. As the gap gets closer and closer the amount of time the points are open will decrease until the gap it too small and producing a very weak spark, not enough to fire the mixture. If the shaft is worn, that would happen on a couple of cylinders first... Those cylinders not firing would start pulling oil up passed the the rings (normally the expanding fired mixture would stop this)....

So, if you had checked the points gap, you might have fixed the problem.... This is my 'guess'....

Chris.....

Re: 250 inline 6 toasted

matt167 said:

If it's toasted, you just need to add butter..

Spun a bearing most likely

Click to expand...

Spun bearings do not put oil in the combustion chamber. A hole in a piston or broken piston (wrist pin area or skirt) would. If it was consuming large amounts of oil on the outbound leg of the trip then it would point to a cylinder issue.

Re: 250 inline 6 toasted

I had replaced the points with a Petronix kit, so I don't think that was the issue. It "seemed" to be running pretty smooth and I don't think it was missing on any cylinders until it went bad. I was wondering about timing myself, and am going to have my distributor checked out to make sure it is advancing as it should. It goes to the rebuilder today so I should be able to report next week what went bad!
Alan

Re: 250 inline 6 toasted

No water in oil, pulled plugs to have a peek and #3 and #6 soaked with oil, really wet with oil.

Click to expand...

achris said:

Spun bearing wouldn't dump oil inside a cylinder.

Oil in cylinders says rings or valves. On 2 cylinders is very odd. Cylinders 3 and 6 are sequential in the firing order. Here's a possibility (and you're not going to like it).... If the points hold-down screw worked loose, and you have a little wear in the shaft (and at that age, wouldn't surprise me), then the timing will start to retard as the gap closes up, producing the loss of power you experienced. As the gap gets closer and closer the amount of time the points are open will decrease until the gap it too small and producing a very weak spark, not enough to fire the mixture. If the shaft is worn, that would happen on a couple of cylinders first... Those cylinders not firing would start pulling oil up passed the the rings (normally the expanding fired mixture would stop this)....

So, if you had checked the points gap, you might have fixed the problem.... This is my 'guess'....

Chris.....

Click to expand...

A compression check might verify that too!


Yeah. Spun bearings will cause noise and in the extreme a busted rod or other catastrophic mayhem.... etc......

I would also think some broken rings and/or maybe a detonation event breaking/burning a hole in a couple of pistons...

No matter at this point.

The drive comes off, the engine comes out.


Good thing is there's a LOT of those engines sitting in wrecking yards around the country!

If you cannot find one up there in Comox, take a ride down here to "South America" and find one. There's wrecking yards all over the place around here with a lot of those old engines sitting on the shelves. When I went looking for one in 2005, the local one here in western, Wa had 13 of them.

Re: 250 inline 6 toasted

Silvertip said:

Spun bearings do not put oil in the combustion chamber. A hole in a piston or broken piston (wrist pin area or skirt) would. If it was consuming large amounts of oil on the outbound leg of the trip then it would point to a cylinder issue.

Click to expand...

Yea, it was late when I posted that, don't know what I was thinking

Re: 250 inline 6 toasted

matt167 said:

Yea, it was late when I posted that, don't know what I was thinking

Click to expand...

Join the club!!!:joyous:

Re: 250 inline 6 toasted

Just got off the phone with the engine re-builder, he said the engine had been re-ringed some time ago. Who ever did it just honed the cylinders, and left the ridge. Apparently there was nothing catastrophic that occurred, just worn rings in a sloppy bore that resulted in the noise which was piston slap. Head is getting new guides and seals, valves etc. The crank cleaned up just fine and will get a 0.030 bore and new pistons. I am happy the core is salvageable and will be ready for re installation shortly.
Alan

Re: 250 inline 6 toasted

Sangster21 said:

Just got off the phone with the engine re-builder, he said the engine had been re-ringed some time ago. Who ever did it just honed the cylinders, and left the ridge. Apparently there was nothing catastrophic that occurred, just worn rings in a sloppy bore that resulted in the noise which was piston slap. Head is getting new guides and seals, valves etc. The crank cleaned up just fine and will get a 0.030 bore and new pistons. I am happy the core is salvageable and will be ready for re installation shortly.
Alan

Click to expand...

I think that's good news.... :noidea:

Re: 250 inline 6 toasted

Good news to me.... glad I don't have to search around for a re-build able core. I knew the engine was tired and I will now have a freshly rebuilt engine, I certainly won't be putting the hours on it to wear it out again. I will feel greater confidence in the boat knowing that it has been freshly re built.