spun bearing in the main cap

[djais1801]

the engine in my car lasted about 4 mos, then I was leaking oil like a siv, thought it was the rear main seal, as it was not running poorly at all.
turned out I spun a bearing in the main cap...fast forward: got a 400 block, re-installed the internals from the 383 to the 400, except replaced the .509 cam w/ more street friendly, and put on performer 383 eddy intake instead of the torker II, and changed the stall convertor from 3500 to 2400, and went to a holley 770 street avenger elec choke instead of the 750 double pumper no choke.

My long-winded question is: What can cause a spun bearing in the main cap. My original set up was real tough getting vacuum/timing correct, and most on here stated the cam was too much for a 383.

The cam that I replaced it with isn't lopey enough for me...so I am thinking of changing cam and swapping back in the 3500 stall..

Could the .509 cam have caused the spun bearing?

Forgive my ignorance if the two are mutually exclusive, my tech knowledge is somewhat below novice.

 

[Tempest 455]

Wrong bearing clearance or debris. My bet would be clearance. Was the journal discolored?

 

[Garys1969RR]

A camshaft isn't going to cause a main bearing to go bad. I am running the 509 cam in my 451 and it works fine. I run about 20 degrees initial advance, and it has plenty of low end part throttle torque. Its very unusual to spin a main bearing in these motors. Could be caused by any number of things, including improper installation. Who put it together?

 

[djais1801]

it was put together by previous owner... when I bought the car last January, it was set up as a 1/4 mile car...drag radials, 391's, 906 heads ported, torker 2 intake, holley 750dp, and the 509 cam...I am using the car for local car shows/cruise nights and 90% city driving...a few trips up the parkway...what is optimal compression for the 509, I believe my motor has 9 or 9.5:1

A camshaft isn't going to cause a main bearing to go bad. I am running the 509 cam in my 451 and it works fine. I run about 20 degrees initial advance, and it has plenty of low end part throttle torque. Its very unusual to spin a main bearing in these motors. Could be caused by any number of things, including improper installation. Who put it together?

 

[99ss]

Was he a qualified engine builder? Many many amateurs build engines and they last about that long some not even that long. Improper tolerance is my guess or wrong bearing in the first place

 

[80fbody]

Which cap? Makes a difference on a Big Block. I think one cap is more prone than the rest to failure due to the oil route.

 

[Budnicks]

Lack of adequate oil supply & heat/friction is what causes a spun bearing 99% of the time, it causes the bearing to grab the crank & spin inside the cap... it could have been multiple factors of, rough surface on the crankshaft journal, too much radius ground in the crank with out having the bearing tapered/beveled to match, bearing installed incorrectly or bearing cap over torqued or torqued in the wrong sequence or tightening one side too much before the other, bearing cap out of round, engine needed to be line bored before the assembly started etc., not enough oil supply, wrong kind of oil, debris in the oil, not enough bearing clearances or wrong size/style bearings {possibly a cam bearing, installed incorrectly or blocking off an oil supply passage ??}, oil pump pick up starving/sucking air or partially clogged/blocks, maybe a dent in the oil pan under the oil pump pick up, oil pump bad bad.... allot of way it could have happened, but it comes down to not enough oil supply or inadequate clearances 99% of the time.... I was looking for a photo that shows the path the oil travels thru a BB Mopar I couldn't find it, maybe a Google search you can find it or our resident Professional Engine Builder Mopar Expert Jim IQ52 had posted one on Mopar Muscle a long time ago now... sorry I couldn't help more...

 

[djais1801]

I understand...and I wish I had more information...unfortunately I do not. My motor was rebuilt by a reputable guy locally...Installed by a mopar fanatic buddy of mine who has built his own 73 duster race car, 70 charger, and recently he picked up his 70 RR 440 4spd which he partially traded for his RT10 Rumble Bee...Just wanted to make sure that if I change the cam, I don't repeat what happened.

 

[Garys1969RR]

If it was a 1/4 mile car, then the previous owner could have wound it pretty tight, which doesn't help, if there was a problem to begin with. Here are a few things could cause a problem: 1-Lack of adequate oil supply as Budnicks stated. This would be the most likely cause, assuming it was assembled correctly. Either low or no pressure, or air bubbles getting into the system. When a car leaves the starting line hard at high RPM, a lot of oil is pumped out of the pan, and the acceleration can move what is left in the pan to the rear, and uncover the oil pick up tube. Then air is pumped in, which starves the bearings of oil. This can and does lead to bearing failure. The oil is pumped first to the front of the motor thru the main oil galleys, into the lifter bores, and the upper main bearing halfs. So the rear main would be the last one to receive oil supply. Always prime your oil system with a drill before first firing up a new or re built engine. Install a pressure gauge. Keep the oil to the full mark on the dipstick. I always add an extra quart when drag racing. I like to use a new Melling Hi Volume oil pump when I build an engine. Haven't had any problems, and my gauge always reads 60 to 80 PSI, depending on temperature.

- - - Updated - - -

it was put together by previous owner... when I bought the car last January, it was set up as a 1/4 mile car...drag radials, 391's, 906 heads ported, torker 2 intake, holley 750dp, and the 509 cam...I am using the car for local car shows/cruise nights and 90% city driving...a few trips up the parkway...what is optimal compression for the 509, I believe my motor has 9 or 9.5:1

I am running 13 to 1 C/R with my 509 cam, and it loves it! That cam works well with a lot of C/R, steep gears (3.91 or better), and hi stall T Converter. I had this 509 cam in a low compression 440, ( 8 to 1 at best), 906 ported heads, and it wouldn't get out of its own way. Built a 451 with 12 to 1 C/R, same heads and new Ross dome pistons, went from high 14s to mid thirteens in 1/4 mile. Now I have same 451, with 13 to 1 C/R, 915 ported heads, headers, it runs mid 12s. 3600 lb car. At your elevation you may want to stay around 11.5 to 1. I have found these motors respond well to C/R increases, if you have the hi octane fuel to keep them from pinging.

 

[djais1801]

thanks for the comments...not looking to race her..just want a lil more thump..but w/ 9.1 compression...i think the 509 is not the right cam... can i still swap the 3500 stall convertor in leaving what i have, or would that not make a difference?

 

[Garys1969RR]

My 8 to 1 C/R 440 ran better with the stock .484 lift, 284 duration Magnum cam, than the 509. Comp Cams makes a thumper cam may work for you. Don't think your gonna gain anything by using a 3000 RPM stall T/C in that set up. An 11" stock converter should work well.

 

[67 B-body]

My 8 to 1 C/R 440 ran better with the stock .484 lift, 284 duration Magnum cam, than the 509. Comp Cams makes a thumper cam may work for you. Don't think your gonna gain anything by using a 3000 RPM stall T/C in that set up. An 11" stock converter should work well.

I dont think the 284 / 484 camshaft was ever stock........
However, I did build a 383 years ago using this camshaft from M-P....... It was placed in a 67 Cuda with 727 trans and sure grip 3.90:1 ratio 8.75 diff. That car would run low 14's all day, and could be driven on any summer day without issues! It was a very fun car and very dependable.

 

[djais1801]

i have a B&M Holeshot T/C in there now 2400

My 8 to 1 C/R 440 ran better with the stock .484 lift, 284 duration Magnum cam, than the 509. Comp Cams makes a thumper cam may work for you. Don't think your gonna gain anything by using a 3000 RPM stall T/C in that set up. An 11" stock converter should work well.

 

[ga66mopar]

The one time I spun a bearing was in a 1970 LT-1 350 camaro. I hit 7800 rpm's one to many times.

 

[Garys1969RR]

That hole shot sounds about right for your cam/ engine combo. A longer duration cam normally moves the power band to a higher RPM. That's when you need to go to a higher stall T/C. This allows the engine to get into its power range right off the starting line, Whether that's a stop light or the drag strip. My 509 would start to work about 50 feet out at the drag strip, with the 11" converter. Went to a Street Fighter 3000 stall, and the power is there soon as I start out. Lowered my ET a significant amount.

 

[IQ52]

DIRT! Most of the destroyed bearings I've encountered in rebuilt engines has come from dirt. Plain and simple, the engine and parts weren't cleaned properly prior to assembly.