26 OCT-DEC 2009 engine professional

Race engine bearings are called upon tohandle stresses almost un-imaginable tothe average person. Extreme high RPM,extreme operating conditions includinghigh heat, cylinder pressures of 10,000 psiand higher and extremely thin oil viscosi-ty are common. Add to this the fact youhave a bearing size limited either by rac-ing rules or a team’s desire to reduce fric-tion and you have what one might call:“A Perfect Storm”. How to survive the“storm” is obviously critical to the suc-cess of a race engine builder. In this arti-cle, I’ll cover thoughts, observations andtips gleaned from my time working withboth race engine builders and professionalrace teams. Most of these apply at theextremes of our sport/industry but alsohave practical application for a broaderrange of performance engines! Also, Ispeak often of “race engine” and reallymean “high performing engine” regard-less of how it is used!

Leaving horsepower on the tableIf engine bearings in a race engine lookreally good when you tear an enginedown to freshen it, you’re leaving horse-power on the table. You’re almost alwaysgoing to replace the bearings anyway,might as well use them up! Food forthought — if racing rules and budgetsallow it, reduce the size of the enginebearings. Smaller bearings have less fric-tion and reduced drag, equating to morehorsepower. NASCAR finally put a limit

on bearing minimum size last season,standardizing on a 2” main journal mini-mum and a 1.771” rod journal.(Remember where they started: 2.448”main and 2.100” rods). Also, think aboutthe reduced mass of the crankshafts!Bearing width can be and is often reducedas well, especially on the rod bearings.

Reduce friction and drag Many race teams invest in coating theirengine bearings. Anti-friction coatings canreduce drag and resist damage when oilfilms get so thin that bearings and crank-shafts contact each other. We are experi-encing very promising results with specialcoatings and continue to experiment withprofessional teams. For example, we’retesting a coating right now that will allowan alcohol funny car team to get extendedlife on their rear main bearing. We’vegone in initial testing from one pass perbearing shell to 3 to 4 passes, perhapsmore. This can make a coating very costeffective and very attractive. Keep anopen mind and remember technology isconstantly changing!

All oil is not the sameRacing engines need racing oil! There is anumber of racing oil suppliers/manufac-turers and they exist for a very good rea-son: the demands of racing engines over-whelm the average motor oil! Also, it’d besilly to think the oil requirement of aNASCAR restrictor plate engine is the

same as an alcohol pulling tractor or anoff-shore power boat. Your goal with spe-cialty lubricants should be the same asyour goal with engine bearings, pistons,piston rings, crankshafts, connecting rodsand all the other highly complex parts toa racing engine: find a supplier who youlike, who knows what he/she is talkingabout and most importantly, will taketime to help and guide you. Knowledge ispower, so ask questions, take notes, suckup all you can get and store it away.

Recognize the obvious Upper rod bearings and lower main shellsget most of the load so your inspectionalways focuses on them first! A simplethought, not always possible especially onolder performance engines, is: no grooveon the lower main shell. All that groovedoes is effectively reduce the load bearingcapability of an already heavily loadedpart. Most of our NASCAR customersmake their own upper main shells fromun-grooved lower shells. Without givingaway any secrets, they look carefully atboth the width of the groove as well as itsoverall length.

Always remember, regardless of thetype of performance engines you build orthe type of service the engine sees, as youincrease the demand for making power,you will exceed the capabilities of thestandard bearing and eventually, even thecapabilities of the standard racing bear-ing. A recent example is a well-known

Notice the relative size from the 2” NASCARmain bearing to the 2.448” Chevy shaft size

from the older days.

Shown is the the 1.850” NASCAR rod bearing, narrowed to less than .755” compared to the

2.100” SBC Chevy at .792” wides.

Race Engine Bearings

BY BILL MCKNIGHT

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engine professional OCT-DEC 2009 27

west coast builder of performance diesels.They’ve done much work with the GMDuramax® diesel and have documentedexamples producing in excess of 1300 HPon the dyno. This was a gradual processfor them as are many performance engineprojects…someone wondering what’d bepossible. (Just a side note: NASCAR hasfound another 100 HP in the past 10years, while still being limited to 355CID) The stock parts worked pretty wellat first, but they kept pushing the limits.First it was the limit of the stock piston,then it was the stock rod and next thestock engine bearings. We produced a rac-ing rod and main set for them and itworks very well, but I know if they keepincreasing the power, we’ll reach the lim-its of that set, too.

Understand the basicsIf these terms aren’t failure to you, youhave problems: Minimum oil film thick-ness, eccentricity of a bearing shell, part-ing line relief, B wall thickness, crush,cavitation, fatigue, overlay thickness,locating lug location, just to name a few.MAHLE Clevite has an excellenteLearning class on engine bearings andthe best part is, it’s free!

Utilize all the tools you canAERA has failure guides and of course,tech help. MAHLE Clevite elected earlierthis year to put our bearing guide online.It consists of 25 different bearing distressmodes. I don’t like to call them failuressince in many cases they didn’t fail, justlook distressed when you tear the enginedown, plus, bearing manufacturers don’tlike to talk about failed bearings — bad for business! Anyhow, you get 25currently listed (I keep adding them as Iget good examples), complete with multi-ple examples illustrated by digital photos(I keep adding photos and better photosas I get them, too). The modes each have:appearance, damaging action, possiblecauses and correction action outlined.Finally, askmahleclevite.com is availableto all too. It’s our online tech help, avail-able 24/7.

Where do we go from hereThe more I learn about our business ofrace engines, the more humble I am. I getto call on and visit with the absolute “topof the heap”, “pick of the crop” of raceengine builders in the USA. They’re youngand they’re old. They’re polished andthey’re plain. Some are shy, others outgo-

ing. What I realize is they have one thingin common: They’re never satisfied withjust “good enough”. They keep asking,looking, questioning, and challenging meand the other suppliers with: “what if wedid this, what if we changed that?” Itnever ends and hopefully never will!�

Bill McKnight has worked for MAHLE Clevite Inc for 28 years. He ran the engine rebuilding trainingprovided by Dana for 22 years, then moved to Cleviteas director of training. Over the years at Clevite heserved as director of marketing, motorsports salesmanagement, and in his current position as teamleader of training. He has a master’s degree ineducation and has served on the board of directors ofAERA, program committee of PERA and as a technicalpresenter at both AERA and PERA. He’s often found atthe race track, especially NHRA and NASCAR eventsand loves engines that make lots of power!

A screen shot of the MAHLEClevite bearing eLearningcourse (left) and online bearingdistress guide (above).

An example of theindentless lug design

rod bearing used bysome teams.

Here is a used setof rods after a race — when they look this good, there’s power to be gained! Note: teams will use masking tape to keep the samples together makingthem easy to inspect and to show a customer.

MAHLE Clevitecoated bearings.

Pictured above is anexample of smallerbearings, 900 HP or so,things are pretty wellused up – OK for cup,not so good forNationwide and Truckwhere engines need torun 2 or 3 races!

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