I just read another post where the guy was talking about how he spun a bearing in his motor. he was talking about how the motor was running and started to knock as it warmed up. he shut it down and had metalflakes in the oil. I consider a spun bearing to be when the bearing spins on the crank and ends up with all or part of the two halves on the same side. I did this on my old 70 Z/28 and that motor was stuck and would no longer turn over. that's how I got it figured anyways... what do you think?
when the insert spins in the rod or the main bearing spins in the block this is not my definition it is the definition. unless it is a floating bearing engine
As long as the tangs are no longer holding the bearing in the bore, and it can turn around as it pleases, it is spun.
A spun bearing is when the bearing is no longer being retained by the rod or block in a stationary position and has rotated with the journal of crank shaft. Not good
Doesn't a spun bearing usually trash a journal? I bought a flatmotor off a guy,heard it run and it had a bad knock. Pulled the pistons and main caps and some of the rod cap bearings fell out in my hand. Not chewed up or scored. Looks like the crank just needs a polish. The cap bearings came out in one piece. Wrist pins feel good and tight too. Any ideas on where the knock came from......sounded bad at the time. Hell, the cyls. are good and smooth too.
My 383 Chrysler "spun a bearing" at the track one night. At least that is what my older and more experienced buddies called it when we pulled the pan and found both halves on one side of the throw. It could be a local thing semantics? My engine locked up as soon as I put it in neutral after going through the traps. I was young and dumb....er. This was 1967ish. A lot of terms have morphed since then but that is what we called it.
The "tangs" do not hold the bearing in the bore they only locate it in the bore . It is the bearing "crush" that holds it in the bore.
I think when there is a breakdown of the oil film between the bearing and crank journal(for whatever reason) that friction and heat cause metal to transfer(gall). At some point(very quickly,I'd guess) the galling/heat are sufficient to "weld" the bearing to the journal and the bearing spins, wiping out the tangs and probably the rod or main cap as well. Don't think there would be enough clearance to "stack" the bearing halves until they had spun enough to open up the rod end or main cap?? My .02
so I guess they could spin and not overlap each other. mine spun when I tried to start it one day. spent the rest of the day putting in a new starter. finally decided to see if the motor would turn with a socket and breaker bar. no dice. genuine LT-1 Z/28. sold it cheap after that. wish I had a barn to put it in, it would be worth some bucks these days.
Anytime the rod or main bearing has moved ANY from the position it was installed in, I consider it spun. It's usually in conjunction with a real nasty looking crank or rod journal and burnt bearing surface. I'll agree that a stacked bearing is one bearing half on top of the other. Larry T
Exactly. Generally, you don't spin a bearing in a vacuum, something else happens which relieves the crush on the bearing, allowing it to spin. I've never had one spin that wasn't caused by something else. Might take some time to find it, but it's always there. I once had a race engine that first spun a cam bearing. We could find nothing else wrong, so it was fixed and put back into service. It went two more races (dirt oval track racing), then spun two cam bearings, a main bearing, and two rod bearings. That time, we found the problem. The center three main webs had pulled out of the block, all the way from the pan rail up to the cam bore. That breakage allowed the bearing crush to relax, and the cracks depressurized the oil p***ages that serviced the spun bearings. That all ended up with two rods, one main cap, and a block web welded to the crank, another smoked cam, several bent valves, and an entirely ruined set of H-beam rods and 19:1 pistons. The block broke first, then the bearings spun. Note also, that you can't really spin a bearing without something either galling or welding itself to something else. When the shell moves, it cuts off the oil, and that's all she wrote. BTW, a lot of times, parts can be saved from a motor that locked up from a spun bearing. The above motor had a Callies crank in it, and after we beat the bearings and rods off the journals with a br*** punch, we were able to have it welded, heat treated, straightened, and reground, after which we were able to put it back into service. Now, that was a $1,400+ crank (IIRC, this was several years ago), so it was worth the trouble and cost. A stock cast Chevy crank probably won't be. That crank was the only part besides the bare heads, intake, and valve covers that could be salvaged.
a spun bearing happens right before somehting else gets the **** beat out of it if your really lucky you can catch it beafore the beating starts the faster the motor is turning the faster its gets beat up i have a VW rabbit that spun a bearing on a road trip i could hear it knock at over 2500 rpm i was running 20/50 oil in it i was lucky i nursed it home keeping the revs below 2000 and was able to replace the bearing shells in the rods. rabbits are notorious for spinning #1 rod bearing if the oil isn't changed regularly i am blaming that on the PO but for a car that i paid $150. for i'm not complaining funny thing is it was #3 that spun oh well was a lucky motor it lived to see another day
i was the one with the proublem . i said " spun " as slang it more the likely just wiped the the babbet off the bearing causing too much clearance . i think its a rod it dont act like a main the motor also has a bad vibration now and the oil pressure is the same . sorry my east tennessee slang comes out sometimes
anytime it's moved i'd say spun, stacked is pretty extreme considering how much it would have to be worn down to do that. but still you had to spin it to stack it
I agree - this is what we used to call the result of a spun bearing. It came from friend's flat motor with low oil pressure (full of sludge). It knocked for about an hour, than failed quickly. It looks like the cap finally welded itself to the crank, and the twisting force broke the rod bolts. He said it was almost instant, just a few seconds of increased knocking and POW. I don't know if the bearing actually spun' or just disintegrated.
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