So I built this engine, and 3 weeks later it is junk. I am a college student and I don't have a lot of money to get another engine. Me and my friend built this engine this summer and 3 weeks later I pull it and the backmost bearing is completely spun (one closest to the crankshaft). So now, the whole lower end is junk. My uncle said he can get me a completely forged bottom end for $800, and I know that's a sweet deal, but I really can't afford it right now.

My main question is, how is it that everyone else can build engines and they are fine, but everytime I touch a car, it goes to ****? Actually, what would cause only 1 bearing to spin??? We can't figure it out.

-Steve

 

did you use plastigage and check the clearances for the main bearings to make sure they were in spec??

 

My rotating assembly wasn't balanced. It was wearing through the front main bearing quickly. Maybe that was your problem. I don't listen to the person who told me that 350's didn't need to be balanced anymore.
If a reputable machine shop is used, plastigage isn't needed except unless you want to see for yourself. I always do. Been screwed too many times.

 

what do you mean closest to the crank shaft. all the bearings are as close to the crank as any other, excluding cam bearings. which bearing failed # 5 main? if you spun a bearing a new rotating assembly isn't going to do you much good since the block would be trashed if you spun a main. did you measure any of the clearances? i wouldn't bother with plasti gage, it's pretty worthless.

not everyone else can assemble and engine and have it last. a lot don't and a lot of them don't post on here and admit to their mistakes.

 

I'm sure you realize he probably means the rear main.

What more lasting way to learn than to screw it up? You'd definitely be making sure not to do it again.

Engine rebuild number 4 for me. First 350 though. All have worked fine except this one. Never will I build another engine without balancing first.

 

Not likely a out of balance problem.

The bearings are retained by the fact that the hole (bearing saddle) is round and of the exact size to put a crush on the bearing when the cap is torqued down.
If the hole or main bearing saddle is out of round or not the right exact size the bearing will slip.
The machining operation to ensure trueness the bearing saddle is correct is called "align boring" and or "align honing".
The main caps is shaved a little and the saddle is remachined to the correct size.

Simular to "resizing the rods' big end.
The two bearing shell halfs are a little bigger than a complete circle and are "crushed" when the cap is tightened.

There could have been insufficiant bearing clearence too. (wrong or mis-labled bearing)

Or an oiling problem.

 

So I found out the problem. There were many mistakes made when putting the engine together. The first one is with the heads. The pushrods were sitting up against the head and causing wear which we think caused the bearing problem. One of the pushrods (the #3 cylinder exhaust pushrod) was bent and broke, which subsequently caused the lifter and cam to get wiped out in the process. So after a new crank, bearings, rod, cam and lifters, we might have solved the problem. We haven't fired the engine yet, but we improved on all the things that we did wrong.

Steve

 

Good luck brotha

Hopefully you won't have the same problems.

 

Mad skill


Seriously a good machine shop that does good work and orders parts that fit takes all the guess work out of a build. Ive never use a plastiguage in my life, never had to, never had any problems either. I still hate fitting rings for custom builds but............................................

 

If you spun the rear main bearing, and didn't replace the block, be prepared to trash some more parts. The first bearing spun because of lack of oil, lack of clearance, or lack of crush. I doubt if the pushrod had anything to do with the bearing problem, IMO.
Good luck.

 

Well we cleaned the block out pretty thoroughly, so I don't think there will be a problem there. But my uncle seems to think that the metal shavings from the broke pushrod caused the rear bearing to spin. I dunno, I'm just crossin' my fingers.

Steve

 

if you spun a main you trashed the block. cleaning it won't help anything other than you'll have a clean trashed block.

 

Metal shavings don't cause bearings to spin. Are you sure it spun? Or was it scored and scratched? Can you post some pics?

Did you measure the crank journals to see if they are too big or out of round? I am a college student too and I know what a pain in the *** it is to be without a car. When it comes to the engine, do it once, DO IT RIGHT...

 

Metal shavings from something won't cause one bearing, and one only, to fail. Those will waste all the bearings equally. One failed bearing is an assembly problem.

Are you sure the bearing spun, which is where the shell attached itself to the crank and rotated in the block? Or is it merely severely worn?

The first thing that comes to mind when the rear main bearing gets trashed, is the oil pump bolt. That bolt goes through the main cap right behind the bearing shell. If you use the wrong bolt, it will go through too far, and press against the back side of the bearing; this can cause rapid destruction of that crank journal and of course the bearing follows soon after.

Make sure you're using a real oil pump bolt, not just some generic bolt, or a short head bolt; the oil pump bolt is a special bolt, 1-15/16" long, whereas the short head bolts are 2". That extra 1/16" is all it takes to create a meltdown. If you don't know what the bolt is that you're using, go to the dealer and buy one.

When you rebuild the engine, be certain you get all the metal shavings out of it. I'd recommend that you take take the block to the shop after you tear it down; have them remove the cam bearings and all the oil passage plugs, and then vat it; and have them return it to you in that condition, with no cam bearings or any of the plugs. Then take it to the quarter car wash and use rifle brushes in all the oil passages and a small wire brush in the grooves behind the cam bearings, with Gunk Engine Bright or similar cleaner (diesel fuel in a spray can), then wash the hell out of every little hole you can stick the wand into. Then paint it, and take it back to the shop and have them put the bearings and plugs in it.

 

Everyone keeps saying that he trashed the block when he spun the bearing but I think he is fine. Aren't most bearings made from a soft material that is designed to wear before the iron from the block does? Wouldn't this problem be similar to a con. rod bearing getting spun? So you guys are saying that that I would need a new con. rod? Well this happened to me on my truck engine cause I used to thin of a head gasket causing the piston to crash into the head seizing the rod bearing and causing it to spin. I just reground the crank and put in new bearings (along with a thicker head gasket this time) and the engine runs like a beast. That was over ten thousand miles ago too!

 

i've never seen a spun bearing not trash the block or rod it was attached to as well as the crank. i'd like to know more about what you were running that caused a piston to crash into the head since most pistons tend to be in the hole .030 or better. and even with all the dome you could find and the smallest chambers you could find it'd still be hard if not impossiable to crash the piston into the head. 10,000 miles isn't proof of anythnig other than it didn't self destruct in the first few miles. if it's still together at 100,000 you got it right the second time around.

 

OKyou know the shape of the combustion chambers on Vortec heads? well the part that is flat, but still over the piston, that's the part that hit the piston. The top of my #1 piston has the vortec "kidney" shape stamped into it.

 

Well that means your pistons stuck out the top of the block. Doesn't matter what heads they are, or what the chamber shape is, or whatever. The flat part of the piston stuck far enough out the top of the block that it made it all the way through the head gasket and hit the head. Just like I put in that other post where you mentioned this.

Poor short block blueprinting, pure and simple.

Who built that motor? I'd like to make sure I avoid ever using them for anything.

 

My Buddy put the short block together and he said that it was just a stock rebuild. I just assumed since stock dish pistons are down in hole around .025-.030 I would be fine so no I didn't measure compression height when I installed the heads. They also didn't seem to come out of the block at all at TDC but I know that my eyes are no match for a dial gauge. Your right the pistons must have been like .020 out of the hole. It was hard tell cause they were those awful stock dishes. The only part to come out of the hole was the ring around the edge of the piston top. Lesson learned.

 

Yup, live and learn...

"You live and learn, or you don't live very long".

Better luck (and improved skills!) next time.

Next time, use a dial indicator to set the short block at TDC, and use a straightedge and feeler gauges to measure the deck clearance.

 

Yeah I already do especially after the "piston" incident. Thanks. Funny how the board feels like Instant messenger somtimes huh.

 

The bearing was completely trashed and spun ONTO the other bearing. It was also scored and scratched severely. I am pretty confident that I used the correct oil pump bolt, I never seperated it from the engine or mixed it with other bolts that it could get confused with. I'm just hoping I have all the bugs worked out and that the engine will run for a while and hopefully make some decent horsepower.

Steve

 

I'm with ede here, if the main bearing spun the block is bascily trashed for a DIY builder. A machine shop can repair it but slapping another bearing kit in it is calling for trouble. I wouldent reccomend doing it again unless it is done right, if you really need the car and are low on cash theres no point in wasting money, If it were me I'd find a junker oil burning peice of crap to slap in for the time being and build your other engine correctly.

Either way Good Luck!

 

You should really try to take your time and go slowly to eliminate minor oversites that can cause major headaches down the road. Remember, it is much easier to do engine work while the engine is out of the car. I know its hard with school and no money, but that's the best way to go. You learn a lot about engines too if you go over every inch with a magnifing glass and fine tooth comb...

Good luck.

Where do you live. I have a 305 I'll give you if you come pick it up to drive in the mean time!!

 

^ I'm with them. You can usually find a good running 305 for free pretty easily. Then you'll have a reliable engine to use for now.

 

So we buttoned up everything this weekend and actually fired the motor. After about 2 minutes of playin with it, the damn thing fired right up and held idle like it was a brand new factory car. It was amazing. I switched to an Edelbrock carburetor from the out of tune Holley that I had and the difference is like night and day. With the Holley, I used to have to pump the gas and crank and then rev until it BARELY held idle, with the new Edelbrock, it cranked for about half and second and fired right up WITHOUT even touching the gas. My uncle suggested the Edelbrock carb and at first I was a little weary cuz all I hear is Holley gospel, but now I've learned to never go against my uncle's judgement because he's NEVER been wrong with anything yet.

So anyway, the motor sounded great. I still have to get the exhaust welded back on and I should be havin it on the road next week. I'm really excited.

Steve

 

I'm not trying to discourage you bud, but SSC and ede have a damn good point! A spun main will damage the block almost every time. If you get a chance, take the block to get it aline-hone with bearing to match and have them check the crank. I know money don't grow on trees but it might cost you more down the road. Good luck, hope it all works out for you.

 

Ok, I don't know if you read the other posts, but here is what we did. We replaced the crank and the faulty rod. We replaced the cam and lifters and also ground out the pushrod holes in the heads to allow for more clearance. We cleaned everything that we could. We have already finished the engine and have started it. It runs better than ever.

My only question is, what exactly doest the spun bearing do to the block to damage it so bad?

Steve

 

if your push rod locating method is the guides built into the head opening up the holes for more clearance might not of been a good idea. a spun bearing ruins the block because it removes metal from the web and cap where the bearing sits. never seen a main spin that didn't trash the block.

 

Same here...

 

Ok, I think I know where the confusion is coming from. The MAIN bearings are fine. The bearing that spun was a ROD bearing. I might've spoken wrong in the past. The last ROD bearing on the crank spun. The MAIN bearings are all perfect. But just to be sure, we replaced them as well. We opened up the holes for the pushrods because the pushrods were wearing up against it and shaving metal off. One of them was burned from where it made contact with the head, and one of them actually BROKE! It was something that had to be done.

Steve

 

So if it was just a rod bearing that spun, did you only replace that rod, or all 8?

Did you have the rotating assembly balanced?