What causes bearings to spin?

[captndave737]

Title say's it all. It seems like if the clearances are on the tight side of spec, good oil pressure, balanced engine this shouldn't happen.

I spun a rod bearing after 210k of hammering the car on the street. Now I'm a little gun shy as I rebuild especially where I'll be putting out quite a bit more power than stock.

 

[ttypewhite]

A heavy foot and a bad tune.... A rebuild doesn't guarantee anything. Tune it on a dyno, check your air fuel. When it is locked in, then beat the brakes off of it.

 

[captndave737]

Well I have a heavy foot up to 60 or 70 mph. otherwise have a GN? I never had more than 2-3 deg. of KR on the upshifts though!

 

[Jerryl]

There are always mutiple contributing factors to failure.

http://www.enginebuildermag.com/2017/03/engine-bearing-technology-spin-spun-bearings/

 

[captndave737]

There are always mutiple contributing factors to failure.

http://www.enginebuildermag.com/2017/03/engine-bearing-technology-spin-spun-bearings/

Thanks. Good info

 

[ttypewhite]

Don't hot dog the car until it is tuned or you will be in the same position again. If you are not comfortable tuning it, or unsure of yourself doing it. Take it to someone that can help you out. It will save you tons of aggravation and grief. If you have done work to the car, get Eric at TurboTweak to make you a chip that you can fine tune through your scanmaster on the dyno.

 

[captndave737]

I'm going to the FAST Sportsman and eDash with the new build and will be quite careful until the tune is right. I'm building a roller engine with billet mains, forged crank etc. I already have 8k just in parts and haven't started the machining yet. I want this thing to last.

Having that done at RC's garage so I think i'll be in good hands.

 

[Nick Micale]

Title say's it all. It seems like if the clearances are on the tight side of spec, good oil pressure, balanced engine this shouldn't happen.

I spun a rod bearing after 210k of hammering the car on the street. Now I'm a little gun shy as I rebuild especially where I'll be putting out quite a bit more power than stock.

Your comment has me really puzzled, after 210K miles of "hammering" on this engine and you wonder why it spun a rod bearing? You are fortunate your crank or a rod did not gave up and do serious damage?

Bearings and other parts do not last forever, wear and fatigue does take a toll at some time as bearings just wear out and give up.

Just this week I had a 60K stock engine on a stand to check it out. All seemed good, oil pressure, compression and ran really good.

Main bearings looked fine, but some wear on the rod bearing was obvious, so all were replaced. Crank journals were all fine with no wear or grooves, so standard size new bearings were installed.

There will be some minor up-grade performance mods, so the owner should have a lots of confidence that this will be a reliable engine for many more years.

 

[750H.P.V6]

Title say's it all. It seems like if the clearances are on the tight side of spec, good oil pressure, balanced engine this shouldn't happen.

I spun a rod bearing after 210k of hammering the car on the street. Now I'm a little gun shy as I rebuild especially where I'll be putting out quite a bit more power than stock.

If you got 210k miles on your first motor I think you did better than 99.9% of all Turbo Buick owners. I'd follow the advice given and have fun with the new motor!

Neal

 

[robertf]

210k of hammering and you should consider yourself a lucky man. Many would be grateful for that.

 

[captndave737]

I wouldn't say I hammered it but I wasn't exactly gentle either. I'm certainly not complaining about the mileage I got and half of that was pulling my sailboat around the country to regattas. It was really fun blowing away some Hemi wen they impatiently went around me at the light because I as pulling a trailer! Who could resist?

I really was just trying to understand the causes since my new build will be double the power and I want to keep it together. Her towing days are over though.

 

[Buick Mark]

Theres a difference between spinning a bearing and a bearing just being worn.
A spun bearing has actually grabbed hold of the rod journal from prolonged lack of oil and breaks the tangs off the bearing shell, then the shell rotates, and REALLY grinds the journal to hell.
Heres a pic of my spun #3 rod bearing journal on my 350 GS.

 

[SCOOBY DOO]

Back when I was apprenticing as an automotive machinist we'd get the 2.8 V6's come in with 1 or more spun rod bearings. It had an aluminum intake on it with no gasket right from the factory. It would start leaking coolant into the oil and it would get behind the bearings taking up the clearance and having the rod bearing(s) spin. I often wonder if that's the case with some of our engines.

 

[bison]

For a bearing to spin it needs to first have lubrication failure. Thai often happens when the parts are hammered and run out of spec. The oil film that separated the parts and transferred the load is gone. So it's metal to metal. once it's metal to metal the bearing clearances will go away very fast like a few seconds and it just becomes a positive feedback loop to failure. Another possibility is that all parts were in spec but the oil experienced thermal breakdown and can no longer protect the surfaces. This isn't typical under normal operating conditions. I've used the cheapest of the cheap bearings in these engines and they are plenty to support the loads at even 800+hp. Plenty of close to stock engines have had smashed bottom ends yet some with 3-4x factory power are fine. Detonation or abnormal combustion will destroy an engine in short order


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[captndave737]

Those spun bearings look pristine next to mine.

I had heard of spun bearings but never really understood it until I tore down my engine and saw what had happened. Thanks all for you educating me.