Mixing bearings for clearance
 

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

Re: Mixing bearings for clearance
 

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
=

Re: Mixing bearings for clearance
 

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

Re: Mixing bearings for clearance
 

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

Re: Mixing bearings for clearance
 

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........

Re: Mixing bearings for clearance
 

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 :D

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 ?!? :eek:

Re: Mixing bearings for clearance
 

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....

Re: Mixing bearings for clearance
 

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...

First engine, I do know, not our issue, well not 100% :D
Second engine, well that was a judgment call to run, not mine, I didnt like the pressure drop I had seen in the engine from Dyno , to my day of testing to the next day, old man said, Im running it anyway, and he came out of the water a bit "hot" like , spinning really fast.....so that one ? Who knows....

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....

Clearances were .0026 to .0028 We did not build the bottom end, the ONLY Rods that are "accepted" are SCAT Like the $300 Scat I beams, they do have ARP bolts. But well.....

Nope, On 1 (#3) it appears the bolts broke which would also bear with it coming out freespun at over 8k.....ehhemmm....with "questionable" pressure ? , bearing shells are laying in pan. The other one , well the holes in the block arent big enough to see it :eek: And the motor is still in the car.

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....

Oh I agree there, the only thing Im looking at those coatings to do is lenthen life a hair or against a temporary loss, like running from the pickup, but the accumulator should also take care of that, wear pattern on them by 1 - 2 percent would even be good.

I saw this engine apart after both breakin and after several dyno pulls, it couldnt have looked better, no unusual wear, all bearings looked actually better than I expected, very consistent.

That was done when I "signed off" on the bottom end.

BUT It looks as though there may have been other causes outside of that 1)Filtration flow issues 2)Acculator not , well accumulating, I have to look into the soelenoid, its POSSIBLE I was over , by a lot on oil and foaming it. Or.......Oiling is a known issue on this engine, the 5.7 Im going to run just like Doug Duell is, he well hasnt had these issues cant argue with Success :)

The "old man" said "When we tear this down were gonna see starvation:" I said, "Ok, but what if we dont ?" , His reply .... "Ill find something else to blame it on" .... as he smiled....

Re: Mixing bearings for clearance
 

Scat parts are somewhat questionable.....probably made in China...
Rods maybe can take it...bolts sound like they failed.
Possibly you can find a better rod that you can send to NHRA for aprroval...and make sure to use good bolts no matter what rods you use.

You can't make an engine go to an rpm that it is not going to survive at and if your driver insists on trying to go to a higher rpm than is safe......there must be a rev limiter capability in your ignition......I would suggest that you use it and especially on a burnout.....It is very easy to let the rpm get away from you. I use one in my dragster......I did not use one in any of my doorcars but I have made a lot of runs and always control that rpm during a burnout......There is really no need to do a burnout more than about 500 rpm above your converters flash rpm......so 6000 or maybe a bit more is gonna be plenty........8000 is reserved for Competition Eliminator entrants......LOL

Re: Mixing bearings for clearance
 

Getting another rod of better quality should not take long with NHRA. I've done it in less than two weeks. Eagle and Scat are not high on my list for quality parts. Try getting a Manley, Crower or Oliver. You don't have to run a specific bolt either. There are much better bolts out there than ARP 2000's which is what I assume you have. Go for a bolt with a much higher tinsel strength which requires greater torque to stretch the same amount.
I feel this is so important that missing some races is worth it. Blow up another engine and you'll want to have a bon-fire! Just get on the phone Monday morning and get it done.