Visit The Dirt Forum for More Information

Author Topic:   Premature bearing wear
OKC9
Dirt Roller

Total posts: 16
posted February 08, 2003 02:15 PM
383 - Roller, Ran 15 nights, Oil pressure dropped to 40 lbs., dropped pan and caps, bearings completely worn out. Engine built by reputable race engine shop. Does this sound like an oiling/clearance problem? Any thoughts appreciated.

Racer14K
Dirt Freak

Total posts: 247
posted February 08, 2003 03:19 PM
Rods or Mains?

OKC9
Dirt Roller

Total posts: 16
posted February 08, 2003 04:20 PM
Racer 14k, it's both. The rod bearings are almost paper thin and the mains fell apart.

awkwardjeff
Dirt Freak

Total posts: 458
posted February 08, 2003 10:26 PM
Man, this could be a hundred different things........could be bearing fit, could be cheap bearings, could be slag off the welds of heavy metal used to halance the crank, ect.

I would start with taking everything apart and measuring everything.......you need to put the new bearing into the rods and torque, then use a inside mic and measure the inside in 3 different ways.......I like useing 4 different ways.......this is to insure EVERY single rod is round in the big end of the rod. I have seen too many rods that were re-conditioned only to left egg shaped.........that will do what you are talking about.

Next I would line hone the block, and again install each bearing and torque the caps. and again measure in 3 different locations to insure those are round. If you subtract this measurement from the crank you will get you bearing clearances.......If you use plasti-gauge you are only measuring in 1 place and that might be accurate for that location on the bearing......but what about the rest, if it's egg shaped you are wasting time.

Also, Under the rear main cap there is a oil passage that should have a plug installed. Without that plug it allows oil to be re-circulated without being filtered. If that is not installed and you have trash in the oil........again, you have this mess you are talking about.......

I would just start over completely and make sure EVERYTHING is right this time around. I'm sure you want to know what exactly happend this time so it does NOT repeat itself......... Did any of the rods turn blue from heat??? start there.....if there is a problem look for signs of heat....

I don't recall the brand now, But about 5 years ago I had 2 sets of rods......from a top name supplier.........built 1 motor for a friend and didn't check big end of rods for round........guess what.........3 nights and bearings were gone.........saved the motor with turning the crank and starting over.........When I go ready to use the other set of rods I measured those ones....they were out .007 I'M NOT KIDDING can you see what 7 thousands does....when you only have .0025 clearance........

BRAND NEW OUT OF THE BOX.........THOSE WERE THE FIRST AND LAST RODS I USED FROM THAT SUPPLIER.........In fact I sold the 2nd set and didn't use them myself.......I sold them and told the buyer to re-condition them and fix them before trying to use them....

what i'm getting at is the builder may have taken a set of rods out of the box and NOT checked them............We all become lazy and take short cuts.......never had THAT problem before........then it happends.....

OKC9
Dirt Roller

Total posts: 16
posted February 09, 2003 08:03 AM
Thanks Jeff. We're going to take your advise and start over. This was an all new 4340 assembly with Eagle H Beams, Clevites and Lunati Crank.

awkwardjeff
Dirt Freak

Total posts: 458
posted February 09, 2003 10:27 AM
I also had a friend down the alley from me build a motor for his street car. He is a smart guy and mechanic by trade. NOT A ENGINE BUILDER...... He got a block bored, decked, cleaned and ready to build. He had the machine shop install the cam bearings and soft plugs. After about 500 miles the bearings were wiped out......so he started over...........he boiled the block without knocking the cam bearings out......then 500 miles later the bearings were out again.....so he thought he found the problem, and started over again.......500 miles later.......STOP LAUGHING.......yep, bearings were gone..........


He was over one day talking about this, I told him one of the cam bearings were installed too deep, or not deep enough....he did NOT understand........so I walked over and showed him........there it was.....center cam bearing was 1/8 too deep allowing the oil to just flush out......not holding pressure........this was his problem.

I doubt this was YOUR problem, because it came from good machine shop.......but then again so did this guy's ..........he thought installing cam bearings was a big secrete.. adn he didn't have the tool......

Just another thing to look at........

rico 08
Dirt Freak

Total posts: 372
posted February 09, 2003 01:55 PM
was front bearings worse or vice versa?this will tell u alot.

Back to the Archives