After spending 4 or 5 days prepping my '67 E for a local, very tony, car show I set out. A block from my house my passenger, who like everybody, has better hearing than me, said: “The engine sounds strange”. I said it’s cold the valves are a bit noisy it’ll warm up. She kept repeating the mantra for about a mile then said: “I don’t hear it any more.” I looked at the OP gauge - zero. Three months before I’d installed a mechanical gauge. I shut off and pulled over. Oil and lots of it was dripping off the bottom of the car. Seems the connection of the OP line to the filter block had come apart. No oil on the stick, a flat bed ride home. It had come apart a block from my home - I know because that’s where the massive oil trial started - it was really heavy over a block and a half and slowly petered out by the place I’d parked it. I’m proud of myself that unlike the old, poorer days, I didn’t just drive it home, and I didn’t, once home, immediately refill it with oil and see what happened. I pulled the pan and the bearings. Long story short - all bearings, including big ends, except the center bearing were fine, or at least not damaged by the lack of oil for a mile. In fact they all had large amounts of oil on them. The center main had started to melt (bottom picture) but the journal was fine, or at least no worse for wear. Noted the sizes, got new sets (including a box of NOS Vandervell for the rods) and installed them. It seems that all the big and small journals, except for the center main are drilled with an oil galley and that retained more than enough oil to keep it moist. The center main has no galley so no tiny reservoir, and it was dry.
My question - all of the top main bearings had material missing from the babbitt. This is shown in the top photo - these are the two worst. The missing material is the dark area. It appears to be a long standing issue - that is it didn’t happen on the fateful morning. (Looked at the bottom of the oil pan, took the filter apart, no metal) Bottom mains were ok nothing missing. I’ve shown these to some engine guys, and looked for reference material on the internet, but can’t find an explanation for what happened. The engine was rebuilt 20 - 25 years ago but probably has less that 15K on it since then.
Anybody have any ideas about this?
Incidentally the car used to run normal oil pressure, 40 / 20 hot running/idle, now with 10 -40 dino oil it’s 60/35 psi hot running/idle. (I use an XJ6 filter block with it’s 60 psi spring on the bypass)
Robin I saw something like this 40 + years ago living in Winnipeg when a professional mechanic showed me bearings that he said had acid damage. They were much more pitted than these. Maybe, but wouldn’t you also expect it on the bottom bearings as well?
Possibly, but if the engine sits for a long time (hypothesising here) the crank drops down allowing the oil to drain from the top of the bearing but leaving a film of oil with acid contamination to eat into the bearing surface?
Cool topic… ------>“IF” these are like aircraft air cooled engines<------.
Plain bearings:
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Plain bearings rely on the “hydroplaning” effect to create thousands(?) of pounds of oil pressure between themselves and the rotating part. The metal surfaces never touch. No wear unless there’s a problem or during starting. The hydroplaning pressure rotates round and round inside between the bearing surfaces following the pressure inside the bearing system. The bearing clearance allows the oil pump to fill the cavity when the clearance opens up by the oil intake to the bearing clearance. The 40-50 pounds from the pump does not keep the metal surfaces apart.
Plain bearing shells are several different layers of different metal. They can absorb and hold tiny particles to a point on the soft surface layer.
Since there is no high oil pressure layer when starting, most wear is during the starting sequence. I no longer turn propellers before starting to “limber the oil” (whatever that meant?) like in my early days. Apparently engines can run for years if run continuously.
Snake oil. The only proven additive (I know of) that works is an expensive product called “Camguard”. I don’t know how it would work for water cooled engines. Seems to protect engines that sit for longer periods.
Glad you dodged a bullet here. I had similar thing happen last year on one of my '70’s Chevrolets. Turned out something failed inside the oil pressure switch for the idiot light and would push oil out around the prongs on the switch. I checked oil after driving a few hours over the previous couple of days and was just barely any on the end of the dip stick. I had parked over gravel so did not see any puddles. My after-market gauge never showed low pressure though and not a lot of oil on underside of the engine or car so I lucked out that I caught it at home before I had run out of oil. I have now added that switch as a location to regularly check for leaks.
I just had another thought on this. Aircraft engines have very small orifice at the engine block before the gauge line fitting and that slows the loss of oil for quite a while. This does delay the oil pressure indication for 15-20 seconds or so at start up.
In the case of this thread you would have gone a few miles further from home before noticing the problem. Might have caused a more gradual loss of pressure and if noticed saved the bearings.
I took an MGTD engine apart that I had been running for 3 years. Rings and valves were planned but a total rebuild came my way once I had a look at the shells. Only ONE large end experienced pitting and loss of material - and it was extreme. I’ll never take for granted that looking at one is “good enough”.
