Mains & Rod Bearings

[NewbVetteGuy]

I'm trying to narrow down my search for replacement Mains and Rod bearings for my SBC; I've read a few articles and I've read King and Clevite's descriptions of their different bearings series, but their descriptions aren't super clear and neither company seems setup to take calls from consumers, rather than distributors.


My application: 1979 L82 SBC 350 "light rebuild" on the bottom-end (stock forged crank). 400ish HP, 6,000 RPM max, roller cam; blocks been hot tanked and I'll run really good air and oil filters.

Goals: Best possible durability, ability to run 1 or 2 grades lighter oil than stock, if possible. (Bi-metal bearings with a moly / graphite coating seem at first glance like they'd be about right...) - Pure street usage.

Machine shop will get back to me with the exact OD on my crank after polishing it, and the ID of my rods on Wednesday; I know I can't order bearings until after that; I'm just trying to narrow down my options.





King Bearings Series (applicable to SBC):

• SI -Appear to be OEM-replacement-style bearings; bi-metal, the description says recommended for performance engines with factory crankshafts (I don't understand that statement at all...)
• HP- "Performance" bearing; description talks about blowers, turbo chargers, NOS, and high RPM usage; increased eccentricity, sounds like its' designed for high loading and probably larger clearances than would allow for a slightly lighter weight oil
• XP -"Extreme Performance" sounds like a pure racing / high RPM bearing series

-Seems to not be a coated bi-metal option at all... ;-(


Clevite (applicable to SBC):

• P Series- Seem to be Clevite's entry level bearings but only available as Tri-metal and description talks about higher eccentricity and crush factor; marketing makes it sound like this is the medium RPM to high RPM option
• H Series- Marketing all talks about being developed for Nascar engines and says appropriate for medium to high RPM; Tri-metal only
• H Series Coated- P series seem unavailable coated; otherwise same as H series
• M series- weird special-purpose bearings for severe crank deflections....??!?

Please tell me the learning curve on this hobby tapers off eventually.....

Thanks!
Adam

[Mark O'Neal]

SI With cast (factory) cranks.

I use the HP and XP pretty much interchangeably. The HP has the highest load capacity and that is what I use for your motor.

[Mark O'Neal]

Oh yeah, Clevitte. I haven't used them since Mahle bought them.

P is for stock cast cranks. H is for forged cranks. Coatings are a preference. I prefer oil.

Never used the M. I'd guess it's a babbit bearing.

[In-Tech]

Hi Mark,
I'm curious of your thoughts on the King AM bearing let's say for a SBC. At what hp would you not use it? Rods, lets say .0025 clearance with 20w50 in a street play app.

Actually, anyone chime in with there experiences with the AM series.

[BillK]

Adam,
First of all there is 2 different "P" bearings. The stock replacement ones and the "P" performance bearings which are different numbers.

Personally for what you are doing I would just use stock bearings. CB663P and MS909P I have never had a problem with them at the performance level you are describing. I am building a 355 right now that should be right about 400-450 hp and that is all I am using. GM steel crank.

If you want to step it up a little the H bearings will be ok too. I have used both on cast and steel cranks and just not had any issues.

I am going to also say that I bet that 95% of bearing failures have absolutely nothing to do with the bearing itself.

The only thing I have seen with the King bearings is a lot of inconsistency in their sizes. They will vary quite a bit from set to set. Clevite is tried and true and I dont see any reason to change just for the sake of change.

Just my opinion,
Bill

[Jeff]

I use mostly king hp bearings, and they do sell them coated.Have used these for years with no problems, but as mentioned most problems are not from bearing failure.

[Jeff]

Talked to king on the AM bearings for a small journal sbc that would be around 400hp and run hard sometimes. Run the am bearings on the rods, the tech at king said they would be fine for the application.

[engineguyBill]

Adam,
The Clevite 'P' series bearings will work very well for your application (stock forged crank) and they are reasonably priced. Clevite bearings are still manufactured in Atlantic, Iowa just as they have been for the past several decades, even though the brand is now owned by MAHLE. 'P' series bearings will hold up fine when using lower viscosity oil as well, as long as there is sufficient oil pressure and volume to create the hydrodynamic wedge of oil between the crank pins and the bearing surface.

Doesn't really matter whether the crankshaft is cast or forged, the bearings do not know, or care, what the material is . . . . . . 'H' series style bearings have a very thin overlay which helps the surface strength and they are narrowed for use in high performance aftermarket cranks which have larger radius fillets.

BillK is correct, the majority of problems encountered by engine bearings are the result of factors other than the bearings themselves. i.e. improper installation, dirt, housing bore alignment (main bearings), etc., etc.

[NewbVetteGuy]

SI With cast (factory) cranks.

I use the HP and XP pretty much interchangeably. The HP has the highest load capacity and that is what I use for your motor.

Thanks Mark. What about for forged factory cranks?


Adam

[NewbVetteGuy]

Thanks all for all the feedback.

I'm thinking P series Clevite; the part #'s that Billk mentioned, unless I need to go slightly oversized on the crank bearing after polishing.

-If anyone thinks this is a mistake, please speak up; sometimes I need smacked in the head with a "Clue-by-4".


Adam

[Newold1]

Most all of the early GM factory forged crankshafts have what are called a pressure rolled (small) fillet at the outside edges of the bearing journals. These crankshafts should use the stock SHAPE bearing in either stock P type or coated P and some H type stock bearing types. Most aftermarket crankshafts especially performance crankshafts have wider ground fillets and require the use of chamfered edge bearings to give the proper clearance on the fillets on both rods and mains. Do not use stock type shape fillet bearings on aftermarket crankshafts with the bigger fillets. Like wise its not a good idea to use the narrower chamfered edge bearings on stock factory SBC crankshafts forged or cast.

I have always found that with a decent oil pump and proper oil system that clearances for rods up of about .0015"to .0025" and mains with 002" to .0025"can use good lighter weight oils with viscosities of 5-20W and 10-30W quality oils with no bearing or lubrication issues as long as the rpms are not in excessive ranges of lets say 7500-8000+ rpms and oil pressures at let's say minimum 15-30 psi at idle and at 6500 rpms are in the 50-65psi with engine at full operating temperatures.

As for brands, especially in the stock type bearings in limited performance usage then Clevite(Mahle), King and GM bearings are all good pieces. Coated bearings can add a little better lubricity and wear on really well machined, straight, round and polished journals. The tri-metals will deform some on not so perfect journals or more extreme loading while the bi-metal alumina bearings can work well in high loads and polished nitrided surface journals with clean oil and smaller size particles 5-20 micron.

The best advise for bearing longevity and wear is really well prepped bearing journals, round even rod journals, adequate clearances, good engine balancing, quality clean oil of proper viscosity and good oil filtering and temperature control.

Select the proper bearing and fitment for your application and put some extra effort and work into setting up great surfaces, clearances and oil to allow the bearings to do their work long term. Good bearings in bad places will give bad results! JMHO

[engineguyBill]

unless I need to go slightly oversized on the crank bearing after polishing.

Adam

Adam,
If done properly, polishing the crankshaft journals will not affect the dimensions of these journals. If sufficient material is removed from the crank pins during the polishing process, to cause changes in the pin diameter, it is very likely that the pins are no longer perfectly round. Crankshaft polishing is a very critical operation and mush be done with upmost care . . . . . .

In other words, if your crank grinder has supplied you with a crankshaft with -0.010" journals you should be able to run -10 bearings after the polishing operation has been completed.