Mixing bearings for clearance

[Chris "drooze" Wertman]

Ok, I can say have never personally done this (yeah I havent)

It has always and I mean always sounded just "wrong" but I also havent built a stock eliminator motor from "scratch" so....instead of things I havent done, onto things I may have to do. And I actually cant be playing with the crank a whole lot on this motor to get the clearances Id like....I a)dont have time b)bought the last crank in stock from Ma Mopar in the country

I know were talking hundredths of thousanths, any issues on this ? I dont see any other than my "im used to roller bearings" aversion.

Also, and I know this is a "preference" but since its my first Stock elim motor. On a say rod, where am I looking to be for a motor that is going to be beat to death with minimal breakin of course. I was thinking .0026-0028 ? Is this sounding inline with what others are doing on say a SBC "stocker" ? Same journal size and bearings....

Im using coatings on the crank so Ive got to take that into account, but well.....Gotta do the motor asap......

Cheers

Chris

[Tom Goldman]

Common practice . ...Used to be common among manufacturers before machining tolerences became critical to emissions performance. ......AMC used to color code it's cranks ,different colors for different sizes..0005"plus or minus was common. ........Just be sure to use the smaller size brg on the top on the rods and the bottom on the mains. .....Tom
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[Dragsinger]

It is perfectly normal and acceptable to mix bearing halves. It done regularly to attain the clearance wanted. The clearance numbers you mentioned are fine, personally I would trend toward .003 - .0032

[Chris "drooze" Wertman]

Originally Posted by Dragsinger

It is perfectly normal and acceptable to mix bearing halves. It done regularly to attain the clearance wanted. The clearance numbers you mentioned are fine, personally I would trend toward .003 - .0032

Even on a coated crank and bearings ? Im curious as to the reasoning, I think I know but , thinking and knowing are 2 different things.

Cheers

Chris

[Rich Biebel]

Chris...there is a lot of good info here......I have used this procedure for mixing bearings and it never failed me.....


http://www.enginebearings.com/it_bearinginstall.asp

If you will accept a little advice........Bearing clearance is usually safer on the looser end of a set of specs.......0027" to .0032' is a good range for most engines........

You can buy coated bearings in all the sizes they offer or have them coated. The coating reduces your clearance from uncoated and the companies that do the coating can tell you how much per set.....

I have used coated Tri- Armor Clevittes and also had some done by Swain. Calico is another very good company for coating bearings........

[Chris "drooze" Wertman]

Originally Posted by Rich Biebel

Chris...there is a lot of good info here......I have used this procedure for mixing bearings and it never failed me.....


http://www.enginebearings.com/it_bearinginstall.asp

If you will accept a little advice........Bearing clearance is usually safer on the looser end of a set of specs.......0027" to .0032' is a good range for most engines........

Thanks, I read that earlier and am going to print it out till I have "reflex", Im open, whats the worst that can happen ? At this point weve contributed over 900lbs to the Chineese scrap metal market

Im open to advice, always in the end I weigh it all and the pros and cons, sometimes I make the right decision sometimes not (when not I always say shiiiitttteee, shoulda done X)

Im hearing looser is good and on a motor with 0 run in before it gets flogged, I was just talking with the old man and we decided to target .003 +/- .0002 I think with the coatings that should be "safe" Are you running that across the board (mains and rods ?) Or just rod side ? My gut says a hair tighter on the mains, but well......I think that would be ok across the board.

Im doing my own coatings as usual, so Ive got 2 different coatings that I know and how much 1 is a pretty high build but sick tough, the other a little less durable over the long haul but pretty slick stuff, very very thin, Ive got to mic the cranks a bit better and see which will work better where, Id LIKE to use the Ceramic based but its a pretty high build. Im thinking on the Crank Ill use a moly di, and the bearings a ceramic IF I can clearance wise, already got the "test bearings an parts" set aside......time for the Apron and Cookie sheets ....

Can I have my roller bearings back ?!?

[Rich Biebel]

General rule of thumb has always been stay above .0025" on clearance especially on the mains. What has a lot to do with it is the quality of the parts and how much do they tend to deform also how big they are and how much "grunt" does this engine make. Rods that easily go out of round...blocks, cranks and caps that are less likely to stay round....harmonics that might play into it....and balancing....all add into it....

I built a 555 for a racer and it had the absolute best of parts. It was alcohol injected and was abused pretty good with all kinds of poor tune up issues and some pretty stout rpm.....after 3 season I took it apart for freshening and the bearings were like new.....uncoated Clevitte H's.... clearances all around .003 or a little under....Titan oil pump......So good parts can take it.......and this is an engine making 900hp....

Basically you have to learn about your stuff and what it can take and what it needs....your working on something fairly new.....I have no idea why you hurt some engines but you need to figure it out...

My first question is when the rod broke in your last engine, did it spin a bearing first? If it did that is what hapened first, so your failure was from a spun bearing. If it did what was the clearances when you put that one together...what were you using for oil, and oil pressure and engine rpm....

You need to look at the failures and make changes.....

Loose is good tight is not....coatings won't stop a failure if your parts are scuffing or you lose pressure....