scrappie

I have acquired a couple 455 motors that have spun bearings. I would like to rebuild one or both of these but I am not sure what exactly has to be done or can be done.
When a bearing spins, what exactly happens? is it the main bearing or rod bearings or either? I have rebuilt a couple motors in the past and replaced bearings so I understand how they are replaced but not quite sure how they end up "spinning"
How does a machine shop fix either situation?
Is there multiple options to fix?
What is the best way to fix?
Do I need a new crank or block?
Does it become more fragile after a repair?

Thanks, always learning

Oldsmaniac

Most commonly it is a rod bearing that spins. The bearing is 2 halves. When clearances get too big they become loose and one shell will start to go on top of the other eventually locking up the crank or some other catastropic damage. The crank needs to be checked out good and most likely resized. The piston rod (s) big end also need to be checked and trued. This is the common fix.

pogo69

#7 usually goes, normally a main, OR rod. heat is the culprit to the soft metal bearing melting it and the crank journal gets damaged... either lack of oil(olds have oiling issues) a rebuild is required grinding crank reboring etc

cutlassefi

Not normally. Each bearing half is about .065 thick, if you have that much rod clearance you'll hear it before they overlap I promise. Now if you continue to run it that way then yes it could do that.

Main reasons are, lack of adequate oiling, improper clearances. Too loose and you'll beat it to death, too tight and if it gets a little hotter than designed to, the bearing will grow more that it's designed to and grab the crank, then it spins with it.
Detonation will also beat it to death, then it looses it's integrity, and just continues to beat itself to death more and more.
Improper balance will also make the rod bearing look as if you detonated it, hammering the top shell then eventually the bottom one as well.

Hope this helps.

Octania

The easy cheap fix usually starts with a "crank kit" which is a reground crank with new bearings to match.

Really cheap people might put that in and be done. Provided the rods are not blue and obviously beat to death.

Really picky people will take everything apart and do the $3000-5000 rebuild. Seriously it does add up to that.

In between those two options lie a lot of shades of gray. And various cost levels.

scrappie

Thanks, its getting a little clearer now. So if you did not do the crank kit how do you fix the crank or the journals?

64Rocket

you take it all apart,
crank goes to the crank grinder
purchase beaingr according to the machine work,
have machine shop recondition the rods,
decide what pistons to use,
do it right once, one time only.

Gene

Octania

if you did not do the crank kit how do you fix the crank or the journals?

That's the $ route.
It is possible, and probably faster and cheaper, to just buy a crank kit with bearings. It comes to you already done. Put it in and be done.

http://www.rockauto.com/
shows $390 for the crank or $480 with bearings, presumably plus shipping.
Crikey my local store quoted me $200 delivered for a 403 crank and bearings- I went with the 330 forged crank instead at a cost of about $400-500 all told, rebalance and whatnot.

Yes, the professional correct way is to dismantle EVERYTHING and mightaswell your way into a $5000 rebuild. Many folks prefer that, especially if they are working on someone ELSE's car, because it can become a bigger nightmare if you semi-rectal it and it goes bad again.

Then again, if NOTHING else was damaged- which can happen- you CAN replace the crank and bearings and be done. Well, you know, might as well [here we go] replace all the seals... and the freeze plugs... and tidy up the engine compartment.... say, the body really has only 6 or 8 bolts holding it to the frame....

BTDT

OTOH, I heard of a guy once selling a car, took her for a spin, running rough, so keep her in 2nd on the hiway to clean her out... pcs of valve seal and whatnot clogging the oil pump inlet = starved for oil, seized a rod bearing and stopped the engine.

Dropped the pan with motor in the car. Found tight bearing. Removed bearing, crank ~OK, rod ~ok... polished journal with a strip of crocus cloth. removed pcs from oil pump inlet. Installed new bearing and she ran just fine for YEARS afterward.

it can be done
it's your call, depending on your skills and budget.
If you open it up and find the bearing GONE and blue [from heat] rods, then your choices are $$$$$ full rebuild, or $$ some other engine already in good shape.

64Rocket

There is no way you can install a crank kit and put it all back together.
You spin the bearing and the rod starts knocking you will spin the bearing again.
You will have to recon the rod, no way around it. spinning and knocking distorts the big end and it will not hold the bearing anymore.
If you don't recon the rod, you are asking for trouble.
If you wanted to cheat, you could recon only that rod, just a lot of work to do it half ***.

Gene

Octania

Depends on the severity

remember this is a 3rd hand diagnosis of "spun bearing" so it could be ANYTHING.

I once had a car give to me for fixing another.
"oh yeah it "overheated" "
Start her up, runs but rough
The "overheating" was a leak at the end of the radiator hose. Cut off 2", drove it 300 miles home.

I have seen bad bearings caught before anything past the bearing was toast, per above... and I have seen 'en driven LONG after the banging began, so the rod is beyond salvation, the piston has been hitting the head, the crank is 0.050" smaller than std, and the bearing halves [what's left of them] are scissored together on one side of the journal.

Only a close inspection will tell how bad the OP's engines are and what MUST be done to get running again. Not "should", but "must".

scrappie

Thanks for the discussion guys. This is what I have been told about said motor: It is a 40k mile motor that was sitting in a car that was moved in and out of the body shop when it could be worked on. I was told the motor ran beautiful but all of a sudden one day when it was being moved around the shop it started a little knock. It was shut down right away and removed from the car. So the damage may be minimal?
I heard that starting and stopping the engine and not letting it run or not "blowing it out" could lead to excess fuel in the cylinders that may get into the oil and thin it out causing problems? what are your thoughts?
Still need a crank kit at the minimum?

MDchanic

That's what you were told, but it may have nothing to do with reality.

- Eric

scrappie

I hear ya

VinMichael

Re-grind crank $125
Oversized bearings $140
Big-end on the rods resized $80

aliensatemybuick

PM me and I'll tell you how to keep it from knocking just long enough to sell it.

1976Oldswagon

if you put sawdust in an automatic transmission, it will stop slipping for about 50 miles.

OP, it completely depends on how bad the damage is. I had a moped that spun a bearing while going down a hill at 55 (governer on it was set at 45) and I held it wide open until it stopped on its own. I could fit a dime between the crank and the rod on that one.

another time I was working on a Ford 4.6 that overheated and had a ton of problems, and we just put in .030 oversize bearings and it ran fine.

oldcutlass

Since it is not in a car, why not just pop it apart and see what is wrong with it. No speculation just fact.

scrappie

I could do that but does it take a trained eye to see the not so obvious? Am I looking for a blue rod or a loose rod? Should I take off the mains and everything? Am I looking for one of the bearings to be loose?