What is with Rod Bearings dying?

[havok91]

My '91 RT/TT spun a rod bearing while at high speed for awhile (5000-7000 rpm). The stealth was basically stock with a 3 inch full exhaust done to it. It is currently being rebuilt at my shop, just slowly as I'm starting my last semester. A lot of ideas have been thrown around about damaged parts, improper assembly/machining (out of roundness, improper clearances) etc... Lets assume that those variables are accounted for, the motor is assembled/built impeccably. Oil starvation, then, is the prime killer. I don't know what the stock oil pump flows, but, at 7000 sustained RPM, the sump could be pumped dry. A deeper/wider sump and better oil drainage to the sump can allieviate the problem. As soon as the bearing loses its oil film, it's gone to shit.
Now, I don't want to loose another motor this way so I'm looking at a deeper sump (we all know of Supercar Engineering) and coated bearings. No one has mentioned this yet so I thought I would throw it out there. Calico coatings has bearings for our cars from Clevite and ACT. The coating is only about .0002 to .0004 thousandths of an inch thick and it retains oil due to the structure of its substrate. Many people swear by coated parts, bearings in particular. Check out the website at: /www.calicocoatings.com/index.html
Techline coatings (www.techlinecoatings.com/index.htm) also offer the stuff for DIY'ers. It may not be a cure-all, but, it should add some added insurance.

[silky]

I have heard something about oil starvation on #6 cylinder....is it something to do with poor oil flow or bad squirters or something?

[TurboBob]

the squirters must be replaced during a rebuild. They have a poppet valve in them and they stick open when they get old.

When Grooms did my engine they reduced the squirter size to reduce the oil diversion. I had my 91 TT engine rebuilt by them using a (used) 2G forged crank. They had the Clevite engineers look at the oil paths in the engine and made some modifications based on their feedback. Its run flawlessly for 10K miles.

Bob

[scrapiron7]

Subscribing as I am having my 120k done this weekend with all ACL bearings.

[ruben2566]

Coating the bearings is a waste of money. If they needed to be coated the manufacturer would have done it. The engine bottom end starves for oil because the oil is being pumped up to the heads, and if it doesn't return quick enough the rod bearings are first to go when the sump runs out of oil. I have modified the pan and recomended tighter bottom end clearances along with thinner oil. It sounds like the opposite that is recommended, but it works. The thinner oil also uses less friction horsepower, so more power for the flywheel. Better fuel economy is an added benefit.

[cbehnken]

A lot of the problem seems to be that people only replace the rod on the bearing that spun.

If the bearings were in bad enough shape that one of them actually spun in the bore I would worry that other rods were out of round as well. All six rods should be checked for roundness if you ever have to replace the crank.

Just anecdotally, how many people spun bearings and are not on stock rods anymore?

[MustGoFaster]

Originally Posted by cbehnken

A lot of the problem seems to be that people only replace the rod on the bearing that spun.

If the bearings were in bad enough shape that one of them actually spun in the bore I would worry that other rods were out of round as well. All six rods should be checked for roundness if you ever have to replace the crank.

Just anecdotally, how many people spun bearings and are not on stock rods anymore?

And too add, how many have spun bearings after upgrading the rod bolts?

[Patryn]

Well we did replace, the rod that spun the bearing, the others were shotpeened and I assume the builder made sure they were no out of round. The other bearings looked good, not even close to the one that spun. Anyways, at $8000 to rebuild and replace the short block, I might have to find another option than 3SX. Good shop, but prices way to high.

We should probably come up with a list of bearing failures and start to see what we can do to strengthen this area. Like I say I always see the bearings go way before a rod or piston, seems to be the weak link.

[twospoons]

Originally Posted by Patryn

Well we did replace, the rod that spun the bearing, the others were shotpeened and I assume the builder made sure they were no out of round.

what were the clearances between the crank and bearings?

[chargerx3]

Originally Posted by Patryn

Well we did replace, the rod that spun the bearing, the others were shotpeened and I assume the builder made sure they were no out of round.
Like I say I always see the bearings go way before a rod or piston, seems to be the weak link.

You assume! Not to jump on you but ive had machinests "assume" many things. The most of which led to my displeasement and misfortune. Sadly enough you have to detail out everyting ahead of time in order to insure a proper build. Machinests arent psychics.

Yes the bearings are the weakest link...and for good reason. they are easy to replace and keep 20+ other things from going bad in the process. The key here is that bearings dont just fold under preasure especially under 10k miles. something causes them to do so (oil starvation, out of round surfaces, contaminates, fatigue, retardedness etc.

My bet is on the rods. Even simple installation will cause them to fail. All you need to do is pound it with a mallet, over/under torque the nutts, not check for fatigue and so on. I mean have you seen how small our rods are?

oil starvation...ive got 2 tt's with 180k and the other with 270k and no starvation problems. Ive got that little needle in my cluster that likes to hang out at the bottom as well . Your new rebuild should not starve. Not unless you are doing something horribly wrong.