Thread: bearing life

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I just resently spun two rod bearings in my 355 and was wondering if there is a set time periode that anyone uses to rebuild the bottom end on a high performance engine. Something that gets run hard for a long time like a circle track motor or maybe a drag racer. Now i didnt put special race bearings in this motor. They were just auto parts special federal mogule's. And would a race bearing last longer. Youd think so ,they are made for that.

Bearing wear should not be an issue. The cylinders should wear out before the bearings do. There aren't many differences between a performance and stock bearing that I know of. Nothing other thans special coatings or narrowed bearings that reduce friction but don't increase the load carrying capability of the bearing. I have not seen it done on gas engines, but I know General Electric had a problem with one of their new series of journal bearing steam turbines in the early 70's. Basically, the bearing was getting pounded to death by the rotor of the turbine. The fix was to add an oil dam in the surface of the bearing, or a relieved area with a sharp edge. Something to do with the hydrodynamics of the oil on the bearing, but I'm no expert so I can't explain why it fixed the problem. Maybe there is something similar for cars, but I doubt it. These bearings aren't going to be exactly the same as on a car because the load does not reciprocate, only the weight of the turbine is supported by the bearing. Also, the speeds over the bearing surface are much higher, the turbine has a 6 inch diameter shaft spinning at 6200 rpm.

I would think balance would affect bearing life quite a bit, especially at high rpms.

Originally posted by joe bogger
I just resently spun two rod bearings in my 355 and was wondering if there is a set time periode that anyone uses to rebuild the bottom end on a high performance engine. Something that gets run hard for a long time like a circle track motor or maybe a drag racer. Now i didnt put special race bearings in this motor. They were just auto parts special federal mogule's. And would a race bearing last longer. Youd think so ,they are made for that.

if stock type federal i do not use them in mild or race engines they have a flash plate on them and this move up on the bearings and build up .not good .i use mich77. or mich H bearings or federal race bearings for big radii cranks . and hi HP

Clevite makes a good bearing...in all my nitrous motors i would scotchbrite the surface before installing...if i had to go into the engine i usually changed em but they always looked good..i gave em to my friends so they werent wasted...aluminum rods will cushion the blow...i've had em make over 200 passes with 1900 or so hp...just fine...are your rod ends egg shaped

I have never heard of a mich77 or mich H, Pat Where could i get these and do you have a time period to change the bearings before the bearings fail. The pro-racers must change them before they fail so they don't have to redo the crank and rods. they have alot of money in them to just change them every time they blow.

Wow that is pritty good Bryan, atleast I would say so. What type of clevite bearings do you use. i dont know i havent had time to check.

Originally posted by joe bogger
I have never heard of a mich77 or mich H, Pat Where could i get these and do you have a time period to change the bearings before the bearings fail. The pro-racers must change them before they fail so they don't have to redo the crank and rods. they have alot of money in them to just change them every time they blow.

mich 77 or clevite 77 . clevite H typ and would not use them on a mild street engine .the mich p type are the 77 i have seen them go for two years + in a engine that gets the hell beat out of it . they look like new 6500 rpm. in big block 540 and up i used the H type with steel rods that go to8000 rpm. what needs to be talk about is adding running clearance and this has a lot to do with the rod not staying round at hi rpm and cap walk.

i've personally never spun a bearing...i'm not sure i even understand how they spin...they snap in one way only...if you dont mix the caps on the mains or rods...and torque properly...how does a bearing spin unless the rod or crank journal is egged...never understood that

Originally posted by Bryan TTM
i've personally never spun a bearing...i'm not sure i even understand how they spin...they snap in one way only...if you dont mix the caps on the mains or rods...and torque properly...how does a bearing spin unless the rod or crank journal is egged...never understood that

They spin from lack of oil wich galls the cranks main or rod journal and causes the crank to grab the bearing and turn it in its seat.....
personally I've never used anything but Clevitte 77 bearings,raced a Fontana powerd midget for a number of years turning it an average of 8500 rpm and never had a bearing failure, bearings always looked like new at the end of season rebuilds.......

Originally posted by HWORRELL
They spin from lack of oil wich galls the cranks main or rod journal and causes the crank to grab the bearing and turn it in its seat.....
personally I've never used anything but Clevitte 77 bearings,raced a Fontana powerd midget for a number of years turning it an average of 8500 rpm and never had a bearing failure, bearings always looked like new at the end of season rebuilds.......

yes clevitte77 is a dam fine bearing .but i think what maybe happing is the rod will not stay round and if it a stock type rod i know it will not at hi rpm. and this will make rod grab the crank. NOT IN A GOOD WAY so running added oil clearance help keeps it alive this is where a bit more clearance help s with stuff that is moving at hi rpm and not staying round

Originally posted by Bryan TTM
i've personally never spun a bearing...i'm not sure i even understand how they spin...they snap in one way only...if you dont mix the caps on the mains or rods...and torque properly...how does a bearing spin unless the rod or crank journal is egged...never understood that

The tabs on the bearing only center it in the rod, they do nothing to hold it in place. Bearing shells are sized slightly larger than the hole they fit in, so when you tighten down on it, everything gets squished. This creates a great deal of friction between the bearing backing and the connecting rod, which holds the bearing in place. When the piston changes direction at the top of the cylinder between the intake and exhaust stroke, the connecting rod goes into tension. The amount of tension at high rpms is so great, the connecting rod bolts stretch like springs. This reduces the amount of squish on the bearing cap, reducing the amount of friction holding it in place and the bearing spins. The amount of crush can be measured, the term used will be crush gap or k-gap. The typical method to measure k-gap is to tighten one connecting rod bolt to full torque while the other is left loose. A gap will open up on the other side and it can be measured with a feeler guage. I have never seen data published on recommended k-gaps for a small block Chevy. The only engines I have done this measurement on were slightly larger than a small block Chevy.

the cush will be more or less is the size of the bore of the rod or main bore the smaller the bore on the the rods or on the mains the more crush the bearing companies know the size of the bore this is some times 0 to 0.0005 or 0 to 0.0007 from small to big on the bores .so the crush will change i do the rod to the small side more crush this set the bearing in good and run more oil clearance with good rod they stay round. but if you think the stay nice and round at 8000 rpm good luck run 0.001 oil running clearance and see what happens. now this is what i do and i have seen my stuff go 8000 rpm with cranks that are 95 pounds and steel rods with4.500 to4.600 big piston on them and have seen my stock stuff 3/8 rods big block chevy go past 7000 rpm and it works and have built them that way for 25 over years and never lost a bearing

Originally posted by joe bogger
I just resently spun two rod bearings in my 355 and was wondering if there is a set time periode that anyone uses to rebuild the bottom end on a high performance engine. Something that gets run hard for a long time like a circle track motor or maybe a drag racer. Now i didnt put special race bearings in this motor. They were just auto parts special federal mogule's. And would a race bearing last longer. Youd think so ,they are made for that.

WHAT WAS YOUR ROD BEARING CLEARENCE?WHAT WAS YOUR ROD SIDE TO SIDE CLEARENCE?

Originally posted by erik erikson
WHAT WAS YOUR ROD BEARING CLEARENCE?WHAT WAS YOUR ROD SIDE TO SIDE CLEARENCE?

yes and what was the crush ???? some machine shops do crapy re con on rods have seen them to big that will make them spin