engine bearings: al_si vs tri metal vs coated

[turtlevette]

I had the T/A out and over revved it. It was knocking at idle after.

I'm going to drop the pan and replace the rod and main bearings.

I'm convinced the new aluminum silicon is the way to go. They say it actually polishes the crank during operation.

I've also seen coated bearings for the 4.9 but the coating is applied over a tri metal bearing which doesn't impress me as being more wear resistant than aluminum.

 

[Kawiguy454]

Ive been out of car engines for awhile but aren't the bearings made soft and malleable for a reason. Like sacrificing themselves instead of wasting the crank journals? Aluminum and/or silicon don't exactly strike me as soft and what happens if you over rev with them in?

If you over revved it enough to waste a bearing I would do a tear-down and check for other problems while you're in there.

 

[ARCOgraphite]

How are you going to replace the mains by dropping the pan? I don't think You really want "wear resistant" in rod bigs. I would Stick with factory or simila matl.
How many hours on this engine?

 

[bullwinkle]

Might want to take some polishing cloth to the crank journals, at least the rod ones, & use a micrometer & Plastiguage to verify oil clearances. You may be able to get away with .001" undersize, or you may have to pull the engine & have the crank ground.

 

[A_Harman]

Factory bearings were aluminum lined.
Common terminology is aluminum lined bearings are bi-metal.
Leaded bronze bearings are tri-metal. Tri-metal bearing material is harder than aluminum bearing material and requires an overlay coating for embedding of foreign particles when the engine is new (or just rebuilt).

I agree with bullwinkle about polishing the crank journals, at the very least. If the journal is rough, the new bearings won't last long. I don't think you can do a good job unless the engine is pulled so that accurate measurements can be taken on the bearings and journals. The crank really should be ground so that the journals are smoothed back to factory specs.

 

[440Magnum]

I wouldn't try changing bearing metallurgy unless I knew exactly how the crank was prepped. Was it nitride-hardened? What kind of condition is it in?

My hunch is that if you have an audible knock from a single over-revving incident, you've got more gone wrong than bearing shells will fix. If you rotated a shell and closed off an oil passage, you're done. Even if that hasn't happened and the crank bearing surfaces look OK, you're going to need to know if the conrod bolts stretched, the big-end cap distorted or "walked", if a piston pin boss cracked, and if the rods themselves are 100% still straight. And that's just off the top of my head.

 

[turtlevette]

What convinced me is that I can scratch a tri metal bearing with my finger nail without even applying pressure. Aluminum is the latest and greatest thing other than maybe coated. AZ lists the clevite tri metal rod bearing as obsolete.

This engine only has 72k miles but has been run without oil pressure. I have a soupy mix of Lucas and restore that has allowed me to run around for a while. The high rpm shift was the last straw.

It should be easy to replace the top half of the main. You insert a clip in the crank oil hole and rotate the crank in the opposite direction. I've seen the procedure in rebuild manuals

I don't expect this repair to last 100k miles. If it gets me 10k I'll be happy. This car is a toy.

 

[JR]

Right on, 440magnium. Complete ddisassemble and inspection is needed to know what for sure is broke/worn.



-harvey

 

[440Magnum]

Originally Posted By: turtlevette
What convinced me is that I can scratch a tri metal bearing with my finger nail without even applying pressure. Aluminum is the latest and greatest thing other than maybe coated.




It wasn't designed to be scratched with a fingernail! That soft layer exists to allow harder particles that might get through the filter to "embed" and not damage the crank. Despite its relative softness, it is plenty strong in compression against the bearing journal and it can last 200,000+ miles if you don't go scratching it with your fingernails.

Harder bearing materials are fine if used with crankshaft materials that are compatible, and set up with clearances that are compatible, and oiling systems that reduce the probability of a particle bigger than the clearance ever finding its way in there. In other words if you're building from scratch...

 

[4wheeldog]

Unless there was an oiling issue, I doubt the knock is from the bottom end. And......A knock at idle could be several other things. Bearing knocks tend to come and go more with load than engine speed.

You might want to get someone familiar with your particulare engine to listen to it run, before you tear into it.

 

[Rhymingmechanic]

Is this a 301 turbo that you want to preserve in stock form? If not, I'd be tempted to go shopping for a 400 or 455.

If you do drop the pan and replace bearings, change the oil pump while it's apart. A guy replaced bearings on my Grand Prix years ago using a "special tool" made by bending a butter knife. I think tri-metal bearings were the only choice then.

 

[turtlevette]

Originally Posted By: Rhymingmechanic
Is this a 301 turbo that you want to preserve in stock form? If not, I'd be tempted to go shopping for a 400 or 455.

If you do drop the pan and replace bearings, change the oil pump while it's apart. A guy replaced bearings on my Grand Prix years ago using a "special tool" made by bending a butter knife. I think tri-metal bearings were the only choice then.



Its all numbers matching and is rarer as a 301. The 400/461 swap needs a new flywheel and 400 air cleaner and shaker.

When I'm ready to pull it, I'll stroke the 301 to 400 and that'll have to be good enough. Maybe a nitrous kit. There's no where to play around here without getting in trouble.

I have a rodeck racing block to go in my vette. I'll hot rod the vette and keep the t/a mostly stock.

To the other guys above. I know a rod knock when I hear it. I've been playing with motors a while.

 

[DoubleWasp]

How does the stroker wok out with the turbo system? Does the turbo become grossly undersized at that point, or does it continue to work well?

Do you have the "turbo charge" indicator lights in your cowl, by any chance?

 

[Shannow]

If the bearing can "polish" the crank, then whatever you've done you aren't in the realms of lubrication.

As mentioned, the idea of a babbit layer is embedability of small hard particles and keeping them from "polishing" the crank.

If you are going to do it the way described in the 1955 chevy manuals, you probably should choose the embedable bearings, there will be some junk in there when you've finished.

 

[turtlevette]

Originally Posted By: DoubleWasp
How does the stroker wok out with the turbo system? Does the turbo become grossly undersized at that point, or does it continue to work well?

Do you have the "turbo charge" indicator lights in your cowl, by any chance?


No, its the non turbo version. The turbo doesn't have the shaker. The deck height of the 301 is taller than the SBC and has the same 4" bore. You can use BBC rods, SBC pistons, and stroker crank to get 383 ci or better. There are so many aftermarket parts these days, you can do some neat stuff.


I'm not sure I buy the embedability thing. I could envision many metal particles stuck in the surface acting like sand paper on the crank. I'd rather the particles flush past the bearing face.

 

[Jetronic]

the particles would score the bearing face, esp on the bottom. Possibly the crank journal aswell. Embedding them pushes them deeper every time they hit the crank journal.

 

[440Magnum]

"Embedability" is a well-known and long-used parameter for journal bearing materials across all applications. The need for it in internal combustion engines has dramatically decreased, especially from circa 1930s (when most engine bearings were thick poured-babbitt structures and oiling was splash, partial-splash, and partial-flow filtered at best) to the 1960s (by which point oiling systems had reached pretty much what we have today, but oil quality and manufacturing cleanliness still had a way to go.) Engines with non-embeddable bearing materials really require different design and assembly processes to make sure NOTHING needs to be embedded.

 

[RoadRaceJosh]

The polishing ability of the aluminum bearings was touted as being good for the relatively rough surface found on older OE cast cranks. Tri-metal bearings were being wiped out when the change was made from forged to cast cranks. Crankshaft finishing has come a long way since.

I understand that this car is a toy, but since you want to keep it numbers-matching I would find the knocking rod and pull it to see if the big end is out of round and correct it in case said rod wants to go out the side of the block.

 

[Lapham3]

So, the engine has been run without oil pressure and a 'fix' to get another 10k miles would be the goal=interesting! Yes, you can usually do some crank/bearing work in the car, but difficult and with an F-body probably worse. I've done it in my old Buick Riviera nailhead and my wife's old MG, but wouldn't make that approach anymore. With what is descibed, I'd pull your engine and fully evaluate on an engine stand-good luck

 

[turtlevette]

Originally Posted By: Lapham3
Yes, you can usually do some crank/bearing work in the car, but difficult and with an F-body probably worse. I've done it in my old Buick Riviera nailhead


Its going to be a bit of a pain. I have to lift the front of the engine for the pan to clear the cross member. I have to remove the fan, motor mount bolts, loosen trans mount then probably jack on the balancer.

I figure I put around 2000 miles a year so id be able to postpone the rebuild for several years. What prompted you to replace the Buicks bearings and how long did the new ones last. Did you replace both main and rod bearings?