What causes a spun bearing?

[Clark6]

i finally got my engine out & turned over & pulled the oil pan off. all of the rod bearings looked ok which is where i thought the slight knocking or tapping sound was but all of those look ok. took the 2 steel main caps off the number 3 had no more bearing material left & the little bearing tab was no where to be found.. but rotated easily under that crank. the #2 steel cap was on tight but half of the bearing had copper showing on it. & copper material was on the oil pick up screen , i guess that explain my slight oil psi decrease but thats been months ago, ive been to the track twice under 7 passes ea. but what causes this HI BOOST? over revving or what?
im only a low 12 car i figured the steel caps would hold all of that?
Im going aluminum heads this time & roller cam. My flat tappet was ok 12,000 miles. but what could prevent this, this is my 2nd time. Am i doing something wrong please someone tell me what NOT to do? i shouldnt need a girdle should i ?

 

[corymc]

i think the reason that my engine spun a bearing is that the pins where not free floating the were too tight to even move by hand.

 

[Clark6]

thanks cory but which pins?

 

[GNTIM]

Could be detonation, a botched line hone job, oil starvation or ..... If the main caps were torqued at a different spec during the hone processs than the assembly, that could be a problem. Also it could have been too tight upon assemby for whatever reason. I have had similar problems, I had the wrong people line hone my block.

 

[87TIGN]

Correct me if Im wrong but if your main caps werent torqued down to the correct specs, i.e. too low, that could have caused a spun bearing under high rpms or if the motor had been rebuilt by someone before and the crank and rods had been spec'd to chevy specs (.0005-.003.5) too sloppy for our cars, instead of the tight .0015-.0018 that could have also caused the bearings to spin under load due to the extra slop. I know a thousandth dosent seem like much but it is big for boosted cars.
-Andrew

 

[Clark6]

thanks fellas again for the replys i didnt measure clearances which i think he got pretty tight im gonna ask the builder what he'd do the clearances at i know when i got the spark plugs out it was pretty tight to turn but it turned with a little grunt to it (unless you cant measure by that)

but any way like i said i have gotten some detonation but it went away quickly as i was tuning many times i just figured the head gasket would have blew first but if things were wrong i figured it would have went wrong earlier on like i said i didnt see flake in the pan till very recently & i do have 12,000 miles on this build with 30 passes down the track in all maybe 5 in all down the 1/4 the rest 1/8th mile but plenty rompin & stompin on back roads & probably 20 of those passes on the back road lettin people ride in it to feel it & one 1/4 mile back road race where i raced a 71 nova not sprayin with a 454 bored to a 502ci should have seen the look on their faces. after he'd said aint no v6 gonna whip this... any way my brother say ea. time i get on it im taking something out of it. maybe it was just time im just tryin to figure out how to stop the bearing spins i want my bottom end strong enuff after this build i dont want to keep goin in it every 12,000.

 

[bison]

If here is any clearance issues then the bearings can begin to contact the journals and get hot. Then they deflect and start to curl and scrape the oil off the crank and eventually the friction is to great and the tang will break off the insert and it spins. Detonation will curl the rod bearings fairly easily under high hp situations causing spun rod bearings. If the mains are going like in the 1st post then i would suspect a bad line bore and hone especially if the other mains werent too bad. If there was detonation you would see metal transfer between the cap and the block on the mating surfaces. Not all SBC's are set up to have .003in clearance either. This is especially true if they have a high cylinder pressure application like a turbo or nitrous and are running a nodular cast crank like most of the Buicks with stock cranks. They run them tighter in these instances. Just think if we have a Buick V-6 engine making 700 ft lbs of torque vs a SBC with 700 ft lbs the Buick's bearing jourinals and inserts are seeing a much higher pressure because the of the 2 less rod journals and one less main to spread the high load over. It must also be noted that if there are any issues directly affecting the oiling of any of the mains then all the bearings will see less than ideal pressures. This could be incorrectly set up pumps to bad machining or excessive clearances or even plugged or partially plugged oil passages.

 

[corymc]

the piston pins

 

[Chuck Leeper]

Had my first engine done at Ruggles. He mentioned that SUNNEN had a specific proceedure to follow to align hone the v-6 block. The process addressed the fact that the block is much shorter than a v-8. This causes the hone bar to deflect, causing the end bores to be larger than the center 2. If that was the case here, the shop may have checked an end bore, concluded it was "right", and ended up with the ctr bores too tite. Excessive crush will cause the parting line areas of the bearings to cave in, scrape the crank of oil, and you know the rest of the story....

May/may not be the case here. However, if only the ctr brgs are FUBAR, then detonation may not be the cause. [rods get hammered too, when that occurs.]
Bent, out of round journals on the crank??

 

[BadAssGN]

I'd also Suspect the line hone / bore, sounds like things went bad.

What is the cause of the piston pins seizing up?

what pistons?

 

[Chuck Leeper]

The..

I'd also Suspect the line hone / bore, sounds like things went bad.

What is the cause of the piston pins seizing up?

what pistons?

Pins can seize when there's insufficient pin/pin bore clearance, rod is bent, rods on the pistons backwards, insufficient oiling, etc. Also, at assembly, the pins were not oiled well, prior to the engine being assembled.

 

[Clark6]

Thanks again chuck & bison , cory i should have known you were talkin about the piston pins duh. im no mechanic but i have mechaniced alot on my buick always fixin something on these old cars but i love it except when it comes to the engine:frown: by looks now dont hold me to this
1) the rods looked good the rod bearings also --checked those first.
2) i did have bigggg flakes on the pick up screen specially on that bottom intake hole. several months ago i did notice a slight oil psi drop yet i was still pushin it at the track thinkin o well maybe its gettin broke in good.(told you im not a mechanic) but i will work on my own car like simple things.
3) #3 main bearing had no brass left was distorted terribly no tang.
4) #2 main had half silver half copper showin on the very bottom bearing but it was still in place.
5) mechanic did use a SUNNEN machine i think he knew about the tight clearances he'd done a couple before now he works with a buick performace shop on this side of Valdosta ga. i figure he does pretty good work but im gonna have him right down some clearance #s this time so it wont be any misunderstanding i will tell him to have my clearance on the mains right? at .0013-.0015. what about the rod bearing clearances or since they're ok let him do his thing, i dont know what to tell the guy except these 2 things.last time all he asked me was did i want a street car or track car i told him street to drive to work but every blue moon i'd hit the track no doubt.... i guess i turned the blue moon into an off white one more than i thought:redface: .. the crank i have in the car now has been turned .10/.10 i may see if it'd go .20 if not i have a spare. also i have a stand. bore block as back up but im not touchin that one yet, i think i saved this one thats in the car now but i might better go with my other crank. & the block that i bought from him (which is the block thats in the car now that i just took out) thats been .30 over which is this one that self destructed but ive gotten plenty of passes out of it. i think i just need a bottom end job. but i am going with a diff. cam and alum. heads. just dont want to spin any more bearings or money.:tongue: excuse my bunched up typing hopefully it makes some since i'll try to slow down next time.

 

[Chuck Leeper]

One other item, concerning brgs...
When a crank is polished, if the belt used is run the wrong direction compared to crank rotation, the "fuzz" left by the belt, can make fast work of a brg, especially, if it's too tite...

 

[gnxtc2]

The heads have to be on the block when it is line bored. Which bearing were used on the mains?

Billy T.
gnxtc2@aol.com

 

[Clark6]

The heads have to be on the block when it is line bored. Which bearing were used on the mains?

Billy T.
gnxtc2@aol.com

if your asking which brand it was clevite 77. i also dont know if he had the heads were on either but if i take it back to him i'll be sure to ask him about doing that. wonder if i take it to a nearby machine shop (chevy) & make sure that i give him all my specs would he stick to it & do it like i want,? he should since im paying him right or should i stick with those that are familiar with whats going on hoping that he'd be more cautious this time?

 

[corymc]

i dunno there are alot of chevy places around me but i took a drive to take it to a shop that has a good rep with turbo buicks where do you live?

 

[Clark6]

i dunno there are alot of chevy places around me but i took a drive to take it to a shop that has a good rep with turbo buicks where do you live?

DOUGLAS , GA. south georgia 45min. from valdosta,
it is a buick shop in Adel. GA. called wildcat performance which is where the guy works at now

also Green Flag in Valdosta Ga. the only 2 i know of in the south i think they have a couple up around atlanta. next location i guess would be north Fla. but dont know of any i think i may give the wildcat guys another chance they're listed in the poston catalog.....

 

[HP Man]

I agree with most of the above. Bearing crush is very important, bearing cap proper hone, all mean longevity to any bottom end. Chevy shops have ruined many Buick Engines. (just a comment and not pointed to your shop) Extra time spend checking all the short block machining is required. GB

 

[GNDriven]

Not trying to highjack your thread, I cannot offer any information on "what causes a bearing to spin", I was compelled to say the following...

I am in a very similar boat as Clark6. I am able to work on everything from the short block up. Therefore, I had an engine built by a local guy who has very good reputation for building 25,000 dollar all aluminum big block chevs and mopar engines.

My 3.8L engine was the basic $4500 build with two steel center mains, forged TRWs, standard turbo crankshaft, hydraulic flat tappet, heads are Champion irons. I gathered all the information that I could and took to him, but it is a sticky situation when the amateur tries to the professional how to build the engine, bearing clearances and so such.

After I got the engine back 6 months later, I broke it in according to instruction. A short time after that..say a thousand miles, and a few track passes it incurred a subtle knock around 2000rpm, but would clear up after 3000rpm. I was told it sounded like a rod knocking by more than one observer.

After I finished crying in my beer, I took out the engine and took it back to the same shop. He claimed that he took the oil pan off and checked everything over and found nothing. After reading this thread I am not sure if he actually took off the center main caps to check the crank bearings. He did point out that the flexplate bolt holes were the converter bolts to were elongated and that the motor had visible signs of detonation, and this could be the source of the knocking. How does one dispute such a claim. Detonation is a gray area, it lies in between a good tune and a bad one, or between a good engine and a spun bearing, or between a busted engine being the customers fault vs the ability and knowhow of the engine builder. I am not a tunning master, but I can read a scanmaster and an EGT probe. I chase fuel with boost, not the other way around.

Let me get to the point... THANKS to all the professional and semiprofessionals that respond to these threads. You are our sometimes our only source of information that levels the playing field about these engines. You shed light into the dark abyss of the short block. I would love to have a great Buick shop near me, and you guys that do consider yourself lucky. If I want a Buick guru to work on an engine, it means shipping cost out the wazoo. I think in an idea world we would all have the knowledge and the tools to work on our on stuff, and share opinions. But the reality is that there are to many who know too little, and like a moth to a flame we are drawn to the turbobuicks, only to find out that the flame is a spun bearing.

I love these cars...

 

[HP Man]

My last Buick GN Engine was hauled about 450 miles to a great shop that builds a good Buick Engine. Why did I chose this route or place? This shop had a reputation of building a great engine. My only complaint was the time table to get the completed block back. It ran strong, good oil pressure and other than a few minor details no problems over 3 years of hard use. Counting the cost of removing an engine and doing it over several times way out prices sending to a good known shop and doing the work once. Several people have gone through this same experience in the past only to save a buck, myself included. A sore subject to talk about and for sure we all feel your pain. I don't know the reason why your bottom end failed and just gave some possible causes as did others. Take Care. GB