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Topic: spun rod bearing , second time (Read 2173 times) previous topic - next topic

spun rod bearing , second time

I did up a purdy pic below but this is what i have here.
A friend of mine showed up today , with 7week old girl in tow i might add, to show me three connecting rod caps and a single bearing he pulled off his 400m.  This engine is sort of fresh on a rebuild but the source of the rebuild i am not sure of.  anyways, a couple rod bearings spun initially and again here yesterday.

I noticed something about the keyway that the bearing locks into so i had to sort of draw a picture.  the rod cap has a blow up of the keyway right next to it.  I noticed that there was an oil stain right in and around the keyway.  that tells me that the bearing was not seating properly in the lock keyway.  next , i noticed that the keyway was sort of ramped instead of being deeply cut on the lower edge.  this ramp made me think that the keyway was full of debris from the past two spun bearings.  If he installs bearings again, id think they would spin again because they are not seating properly with reguard to the keyway being full of .  The oil stain right around the key way area also tells me that there must have been an air gap between the bearing and the cap thus it was not seated well due to this build up.

I suggested he remove all the rod caps and clean out that debris to form some sort of sharp edge like i depict in the second blow up shot of the key way area in the pick below.

am i on to something here based on what ive said?

again,, the below pic shows the cap then the blow up of the keyway with the "ramp" effect i found.  the second blow up is what i "think" it should look like or there abouts.

I also suggested he may want to consider my rebuilding it so that i could go and have the rods broached as well since they might be out of round with all the off roading hammering away and the lack of a double sump oil pan.  Usually with a single sump setup you burn out the rear couple or three if you dont watch out. 

did i notice something here or not?  seems to me that keyway should not be so milled out like its a smooth ramp but have a sharp edge to it so the bearing is retained like in the second blow up of the keyway.

Re: spun rod bearing , second time

Reply #1 –
Been a while since I had an engine apart but I'm pretty sure it is suppopsed to be wedge shaped like that, the rotation of the engine forces the notch in the bearing into the opposite sufrace. Did all the bearing clearances check out okay? were all metal filings cleaned out good after any machining?
1980 birds X 3, 1982 bird, 1984 XR7, 1988 TC

Re: spun rod bearing , second time

Reply #2 –
I know nothing of said engine,, only the caps that lay on my table,, its up to him to fix,, just wanted to bring this up out of curiosity.

but your point of engine rotation,, and how the keyways are on opposite sides with respect to the rod / caps make sense.

acutally,,can you have a spun bearing and still have the keyway on the bearing itself intact for the most part? i would not think so cause it would have to shear off wouldnt it?

Re: spun rod bearing , second time

Reply #3 –
Quote
made me think that the keyway was full of debris from the past two spun bearings.

These rods have already had bearings spin in them??? If that's the case they need resizing(and are possibly junk). Once a bearing spins, the the next bearing will not crush properly due to wear in the rod.

Re: spun rod bearing , second time

Reply #4 –
For the bearing to spin it ether needs very poor oiling or as TurboCoupe50 said need resizing.  A very easy way to tell a rod is bad is when u go to take the end cap off.
If it slips off with no prob then rod should still be ok.  if u haev to tap that rod cap off then there is something wrong.  Also crank it self will get eag shape wear and will need to be turned down to 10/10 maybe 10/20. 

Who did the rebuild?  what was done.?  how high do he rev the 400M?
Were rod bolts torked to spec?  There are alot of things i can ask.
Stock oil pump or Hi flow?

Re: spun rod bearing , second time

Reply #5 –
for as much of a novel im sometimes accused of writing,, i sometimes feel like i forgot to mention anything. :giggle:
 

Re: spun rod bearing , second time

Reply #6 –
i drove down the hill to check on david who owns this truck.
One look in the oil pan tells me another story so i ask,
"where are the old back two bearings cause you only brought up number 4"
he says
"there were none" :shoothead

this is possibly the second worse situation ive seen for an engine.  Im sure this engine would need more than just a rebuild.  Im talking contaminated oil ports everywhere.  There was a gray film in the oil pan like you would imagine to be the texture of graphite.  The oil pump sump screen would not mind passing all that  out to everyone in the whole engine and every single lifter, pushrod, block oil ports ect ect.

I told him to toss a petty good size magnet in the oil pan before he puts it on. 

I also told him that when it starts knocking again, just cut up a thick leather belt and make his own bearings and buy some time like that cause he's waisting his time.  Money is the issue here so thats why he only bought three bearings.  The crank was the texture of a record but deeper cuts.