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Username Post: Wiped half bearing thrust surface... Should replace crank?        (Topic#354224)
Chevytu 
Senior Member
Posts: 240
Chevytu
Loc: Ushuaia, Tierra del Fuego...
Reg: 12-29-02
12-05-18 09:28 AM - Post#2753474    

Been a while since I don't post... meaning I did not break stuff...

Disassembled my engine this winter to change some parts I bought and found half of the thrust bearing surface was almost gone (on the flywheel side of the motor).

Luckily the bearing did not spin (I would've known from the awful noise). There is no damage to the rest of the bearing(s) or crank journals, or anything, just the bottom half the thrust surface on the bearing.

The crank thrust surface itself is OK. I lightly went with 600 grit cloth to wipe it clean and found no damage or scrathes. It has of course blueing that is more present on the opposite (un machined) side of it.. about half of the fillet, meaning of course it overheated... Crank is a forged 4340 steel piece.

Does this mean I should toss it and buy a new crank? Is the hardening compromised or am I just paranoid?

Thanks

1966 Chevy II SS, BBC


 




raycow 
Honored Member
Posts: 27977
raycow
Loc: San Francisco, CA
Reg: 11-26-02
12-05-18 09:51 AM - Post#2753479    
    In response to Chevytu

With a manual trans, some wear is probably normal. When you disengage the clutch, you are putting an end load of several hundred pounds (or maybe even more) on the crank. That's why I don't hold down the clutch pedal at stoplights. Instead, I shift to neutral.

Now with an automatic, I'm not so sure. The oil pressure inside the converter is trying to push it forward off the trans input shaft, but I don't know how much force is involved. If you knew the oil pressure and the cross sectional area of the hub, the thrust load shouldn't be very difficult to calculate. I'm guessing that the load would be less with an automatic than with a manual, but then the load is continuous whenever the engine is running.

Does anyone else here have any thoughts about this?

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17234
grumpyvette
Age: 70
Loc: FLORIDA USA
Reg: 03-16-01
12-05-18 11:54 AM - Post#2753492    
    In response to raycow

if you have a decent knowledgeable local machine shop its a very common repair, they simply weld a bit of metal as required and grind the surface back to spec...including the bearing radias edge area, certainly far cheaper than buying a new 4340 forged crank

https://www.thomasnet.com/products/crankshaft-r epa...



http://garage.grumpysperformance.co...haft-thrust-...

http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.co...tion-of-cran...


IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


Edited by grumpyvette on 12-05-18 12:34 PM. Reason for edit: No reason given.

 
Chevytu 
Senior Member
Posts: 240
Chevytu
Loc: Ushuaia, Tierra del Fuego...
Reg: 12-29-02
12-05-18 01:22 PM - Post#2753502    
    In response to grumpyvette

Thanks for the prompt replies. Checked those links also.

Not sure I explained correctly, the crank itself shows no damage other than being blued on half of the thrust surface filet (very light on the face (where it rides against the oil film), very noticeable on the opposite side.

The thrust bearing half is all broken to the point the metal itself has detached from the shell (but it's still there albeit missing some pieces). Still ran like that for quite a while..

I suspect that the machine shop that bored and honed the mains left the 5th cap tilted at a slight angle, because I remember checking clearance and it was the tightest it could be.

I'm actually in the process of getting a new block because just got tired of dumping money on the old one. Down here no one likes to machine these blocks because they are not the usual stuff and usually mess them up in the process.

My only concern will be using the crank if that event has somehow messed the factory heat treat or something like that, and thus made it prone to cracking or breaking. the journal itself looks like new.

Thanks



1966 Chevy II SS, BBC


Edited by Chevytu on 12-05-18 01:25 PM. Reason for edit: No reason given.

 
Shepherd 
Frequent Contributor
Posts: 1554

Loc: Lake George, NY
Reg: 11-11-15
12-05-18 02:05 PM - Post#2753512    
    In response to Chevytu

The issue here is what is wrong that caused this to occur, wore only 1/2 of the bearing, something is out of line it would seem.



 
Chevytu 
Senior Member
Posts: 240
Chevytu
Loc: Ushuaia, Tierra del Fuego...
Reg: 12-29-02
12-05-18 03:27 PM - Post#2753521    
    In response to Shepherd

Yes you are correct, the cap is not in line or it is tilted, for sure. That's why I'm in the process of getting a new, fully machined, Dart sportsman block and be done with it.

Just want to know if the crank is good to go as it is, or if the problem I had will create issues later on

1966 Chevy II SS, BBC


 
Rick_L 
Honored Member
Posts: 27510
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
12-05-18 06:30 PM - Post#2753537    
    In response to Chevytu

I have had thrust bearing problems in the past that blued the thrust surface. That doesn't cause any problems as long as the metal can be polished where the bearings contact.

I think you'll be fine. I'm sure when you get the new block and do an initial assembly, you'll be careful to inspect this area to make sure everything fits well.




 
Chevytu 
Senior Member
Posts: 240
Chevytu
Loc: Ushuaia, Tierra del Fuego...
Reg: 12-29-02
12-05-18 07:04 PM - Post#2753543    
    In response to Rick_L

Thanks for the input, that's exactly the info I needed.

Since I'm getting a block I thought if the crank needed replacing better do the whole thing at once, as I have to arrange overeseas freight. Didn't want to risk another build just because I did not ask people with more experience. Engine is putting out about 650 at the flywheel so it's not an extreme BBC, but still.

I did measure everything. Actually when bolting the 5th cap down, clearance would get reduced down to the bare minimun spec (just checked my records because I did it some time ago). That should've been a sign something was not correct, but it took so long to get this engine running that I just thought it would be OK.. Wanted to fire it up so bad that I took a chance. Big mistake!

Thanks for all the replies.

1966 Chevy II SS, BBC


 




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