[DSRE455]

Not it wasn't ground correctly

["QUICK-SILVER"]

Originally Posted by redhawk44

Is the chatter from the bearings not sized right? Loose in the journal?

Chatter marks on a crank do not transfere into the babbitt material.
Rotating chatter mark cranks work like a milling machine and mill the babbitt away.
The bearing pic does show evenly spaced, end to end, ridged lines in the base metal of the bearing. That's under the babbitt. The smear in the babbitt shows the uneven coating over the ridged lines. That smear looks fairly even, end to end, front to rear. Not quite the same up high as it is in the center. With bad taper the smear would be the same high and low.

Lines on the bearing do "favor" what chatter marks on a crank looks like.

We really need more info on what led up to this 5K mile bearing refresh:
Original bearing clearance
Clearance now
New and now oil pressure
Oil type and weight being used
What was the build in general; stroke, compression, use, etc...

Clay

[DSRE455]

Id bet money it was cut that way but had enough clearsance to live a little while

[redhawk44]

Originally Posted by "QUICK-SILVER"

Chatter marks on a crank do not transfere into the babbitt material.
Rotating chatter mark cranks work like a milling machine and mill the babbitt away.
The bearing pic does show evenly spaced, end to end, ridged lines in the base metal of the bearing. That's under the babbitt. The smear in the babbitt shows the uneven coating over the ridged lines. That smear looks fairly even, end to end, front to rear. Not quite the same up high as it is in the center. With bad taper the smear would be the same high and low.

Lines on the bearing do "favor" what chatter marks on a crank looks like.

We really need more info on what led up to this 5K mile bearing refresh:
Original bearing clearance
Clearance now
New and now oil pressure
Oil type and weight being used
What was the build in general; stroke, compression, use, etc...

Clay

Okay Clay,
A fresh build used a 400 bored and stroked to 461. Original main clearances were .0025 when built. Last summer I lost oil pressure while driving home, usually around 60 lbs but it dropped to 20lbs . I thought as long as I showed some pressure I would limp it home. when I got home at idle it showed 5 lbs of pressure. I thought it was the sending unit ( electronic gauge ) so I hooked up the old manual gauge and it show 0 lbs. So my next thought was oil pump check valve. Pulled motor to inspect and thought I would see signs of oil starvation but not this. With plasti gauge it still has .0025 clearance on the rear main. I run 20w50 oil. Compression ratio is 10.5 - 1 .

[DSRE455]

Yeah pressure dropped as it ate that bearing, the journal is not round so you won't get a consistent clearance measurement and although plastic gauge it just ok its not the correct way to measure bearing clearance fyi, bottom line is crank comes out, gets ground, use the bearings i mentioned, crankshaft could have came that way in a kit, either way it will not live like that, must be redone, period

[redhawk44]

Originally Posted by Formulas

Redhawk the pic of your rear main bearing what does the other half look like?

Can you feel the high low spots on your bearings or crankshaft if the crank caused them you should feel it on both if your bearings were faulty you would just feel it on the bearings

If you could watch the glint from a light off your crank surface while its turning you would be able to detect chatter the light would flicker off the crank surface instead of being steady

.

I can see some marks on the upper rear main but I can feel anything.

[redhawk44]

Originally Posted by DSRE455

Yeah pressure dropped as it ate that bearing, the journal is not round so you won't get a consistent clearance measurement and although plastic gauge it just ok its not the correct way to measure bearing clearance fyi, bottom line is crank comes out, gets ground, use the bearings i mentioned, crankshaft could have came that way in a kit, either way it will not live like that, must be redone, period

My plan is most definitely to get it done and right but I just need to find out the reason why/how this happened .

[DSRE455]

I stand by my statement it needs to be redone., 400 mains are all 1/2" studs, they are all 110lbs with arp moly big main blocks had 9/16n the rear cap, this may be your confusion

[DSRE455]

Originally Posted by redhawk44

My plan is most definitely to get it done and right but I just need to find out the reason why/how this happened .

It wasnt anything u did, thats how it was made

[gtofreek]

Originally Posted by DSRE455

I stand by my statement it needs to be redone., 400 mains are all 1/2" studs, they are all 110lbs with arp moly big main blocks had 9/16n the rear cap, this may be your confusion

Actually, the 326-400's also had 9/16" bolts in the rear main, and they are 140 with ARP Ultra lube.

[DSRE455]

Paul you are absolutely correct just looked at a block and yep 9/16 on number 5 main cap of all blocks my mistake

[chiphead]

My 400 had the same chatter marks in the mains upon teardown. I figured it was detonation, due to the copper showing on the upper rod inserts. Clearance on build was .002/.002". Stock crank was turned .020/.050". Main studs without line hone.

[hurryinhoosier62]

Originally Posted by redhawk44

So your saying its 2 problems? Taper in the journal and improper crank finishing.

Sorry for the delay. Yes, I am. Bottom line: your crank needs to be reground by a COMPETENT crank grinder.

[redhawk44]

Originally Posted by hurryinhoosier62

Sorry for the delay. Yes, I am. Bottom line: your crank needs to be reground by a COMPETENT crank grinder.

I honestly didn't even think a brand new crank could be part of the problem. Gonna run up to the machinist today and see if he can get me in.

[taff2]

Get a good machinist or engine builder to look at it all, half the advice you're getting on here is given by people who don't know what main studs sizes are in a Pontiac ,ffs!

[hurryinhoosier62]

Originally Posted by redhawk44

I honestly didn't even think a brand new crank could be part of the problem. Gonna run up to the machinist today and see if he can get me in.

One thing I had drilled into my head over and over by my engine mentor was “New does NOT mean good.” Just because a part is new does not abrogate a builder’s responsibility to check EVERY part to ensure it falls into spec.

[hurryinhoosier62]

Originally Posted by taff2

Get a good machinist or engine builder to look at it all, half the advice you're getting on here is given by people who don't know what main studs sizes are in a Pontiac ,ffs!

taff2, how many cranks have you personally ground? How many blocks have you machined? Be very careful where you trod....I’ll wager you 20 pounds Paul and I have far more experience in machining engine components than you.

[taff2]

hurryinghoosier62, go back and read my post again -particularly the part about Pontiac main stud sizes -can you see now that it was not directed at you or Paul? You should read the posts properly before you jump in with both feet.
And no, I have never ground a crank or bored a block - I am not a machinist.

[hurryinhoosier62]

Originally Posted by taff2

hurryinghoosier62, go back and read my post again -particularly the part about Pontiac main stud sizes -can you see now that it was not directed at you or Paul? You should read the posts properly before you jump in with both feet.
And no, I have never ground a crank or bored a block - I am not a machinist.

My mistake...sorry, bloke.

[taff2]

That's ok mate.