Why did I spin a main bearing?

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zinser72

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I had .002 clearance plastigauged on all mains and crank was polished. Engine ran great for 3500 miles and with no warning at all I lost oil pressure and it died immediately. Nothing wrong with oil pump, drive shaft, cam gear or timing chain. running amsoil z-rod 10w 30 @ 60psi when its warmed up at idle. What did I do wrong?
 
when you put it back together did you make sure you put all the main caps in the same position that you took them from??
 
Yes, i marked them and torqued them in three steps like i was told. I built this engine with a neighbor that raced stock cars and built a few mopar small blocks in his day
 
recommended clearance for rods and crank:

0025 - .0035 on both

Stock Specs.
torque mains with oil to 85
torque rods with oil to 45

and you had crank polished and not turned?? so you were using stock sized bearings?? what where you doing (rpm wise) when you spun the bearing??
and what do you have for a crank dampner?? is it internally balanced or externally, it is very werid that you had 3500 miles on it before it spun though that is werid. IMO
 
The crank measured out good so i polished the journals with 1000 grit and a shoestring if i remember right. The engine never went to the machine shop. internally balanced. I did not check the balance. I just did a quick, cheap rebuild because the oil rings were collapsed and it smoked bad. after 40 years that's understandable and it sat for about 20 years before i started it back up. also wanted a little more cam so that was the last straw. I made sure everything went back where it came from though. was running about 3000 rpm and just went to grab 3rd. thanks for the quick responses
 
Best bet,do a slow teardown.Inspect any and all parts for odd wear.Post pics if you can.Might also consider listing how you cleaned and prepped the block.The more info you give us,the quicker we can help you.I am sorry,have lost engines the same way.
 
zinser72 said:
I had .002 clearance plastigauged on all mains and crank was polished. Engine ran great for 3500 miles and with no warning at all I lost oil pressure and it died immediately. Nothing wrong with oil pump, drive shaft, cam gear or timing chain. running amsoil z-rod 10w 30 @ 60psi when its warmed up at idle. What did I do wrong?
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I was on your other thread before. Sorry to here it turned out to be a worst case senario. Was just one bearing journal involved or did some of the others look like they were abnormal as well, just curious?
 
not sure. i havent taken it apart yet. i just cut apart the filter and some bearing chunks found their way in their in there. I guess im not sure its a main bearing but its definately in the bottom end. also last year i ran valvoline race oil 20w 50 (high zinc) and made the switch to amsoil this year. could i have a compatability issue? it ran 500 miles this year
 
As far as I know,all Amsoil is good in that dept.You might check the website,you are looking for 800 -1000 ppm on zinc,minimum.
 
zinser72 said:
not sure. i havent taken it apart yet. i just cut apart the filter and some bearing chunks found their way in their in there. I guess im not sure its a main bearing but its definately in the bottom end. also last year i ran valvoline race oil 20w 50 (high zinc) and made the switch to amsoil this year. could i have a compatability issue? it ran 500 miles this year
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Your oil didn't cause this....i agree with bomber, a good slow inspection at disassembly should reveal the root cause. I used to do all the warranty work on commercial lawn equipment engines and we had to document everything to submit a claim. What i'm saying is take your time to find the cause so history doesn't repeat itself. Let us know how it goes and some picks can help everyone learn something in the process. Good luck, Rick
 
.0025" is the minimum spec. Of yours was .002" that IS .0005" under spec. Whether that is enough to cause trouble, I sorta doubt.....but you never know.
 
What I was tought,steel cranks flex torsionally.In the day,you ran a steel crank,you ran a two element bearing.Clraranced it accordingly.Now thatcast cranks are the norm,everyone is thrown Clevite/Michigan 77s.I have become a big fan of King Bearings lately.
 
zinser72 said:
The crank measured out good so i polished the journals with 1000 grit and a shoestring if i remember right. The engine never went to the machine shop. internally balanced. I did not check the balance. I just did a quick, cheap rebuild because the oil rings were collapsed and it smoked bad. after 40 years that's understandable and it sat for about 20 years before i started it back up. also wanted a little more cam so that was the last straw. I made sure everything went back where it came from though. was running about 3000 rpm and just went to grab 3rd. thanks for the quick responses
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if this motor sat for 20 yrs. was it primed before it was started ??? and did the new cam go in easily......Artie
 
Im thinking its not a main bearing. So it died when you went to "grab 3rd", right? Is it a manual? Is it locked up or was it hard to turn over?

Did you install new cam bearings?
 
it didnt lock up, just tight. I did not check the main caps, i thought since it was a good running engine a quick re-ring and bearing change would be all it needed. i was on a really tight budget but looks like i didnt save myself any money now that this happened. I primed it before it was started band i did change all engine bearings when i did the quick rebuild and cam change. cam bearings were a little tight when they were installed but my "mentor" assured me they would wear in fine. since i have the timing chain off i pulled the rocker shafts and spun the cam and it spins nice and freely. Ill tear it down tomorrow and post some pics of what i find. Thanks for all your input. If nothing else, hopefully someone can learn from whatever it is i did wrong
 
MRL Performance said:
Im thinking its not a main bearing. So it died when you went to "grab 3rd", right? Is it a manual? Is it locked up or was it hard to turn over?

Did you install new cam bearings?
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yeah its a 4 speed, when i got it home i checked everything with the cam, valve springs, lifters and oil pump i primed it and everything looked good. so i made the mistake of trying to start it again. oddly enough the starter cranked it fine but its a high torque mini starter, only thing that clears my headers. when it fired it took about half throttle to hold it at 400-500 rpm so i shut her down right away.
 
A hint - Cam bearings will not "wear in". They should be clearanced so the cam installs and turns freely by hand.
 
RAMM said:
Wrong--There is always a reason.

I will post photos of what has happened to me---twice!! It has NOTHING to do with the clearances or crank material. J.Rob
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Well no kiddin. I just meant that no matter how careful you are, SOMETHIN can always SNAFU.
 
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