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So I snapped my Crank: Suggestions for a new one.

broncoman6524

broncoman6524

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We will get into how it broke later.:D

But for now, I'm pricing a new one.

What are some good suggestions?

I need a LJ 350 mains crank, 1 piece rear main, internal balance, 3.75 stroke, 5.7 rods.

Cross-drilled mains: Good? Bad? Pros? Cons?

4340? Cast steel? 4140? (I think) Which would be my best solution?



BTW: I was hearing no stranger noises. Driving to work, very casually. I came over a hill, and started to feel a vibration. BAD, then it was gone. Like 75ft later, I had to push the clutch in to stop. It was then, that I felt horrible shaking/clunks in my clutch pedal. THe truck stalled, I cranked it back up. I was making horrible noises, making 2lbs of oil pressure, and would not idle.

Luckily work was only 1/4 mile away, So I babied it along back roads and parked it.

Trailered it home, as I backed it off the trailer, my friend noticed that the balancer was bouncing around. I quickly backed it off the trailer. The balancer was WAY from being straight. So I pulled the belt off, and drove it into the shop. Then we dropped the pan, No metal shavings in the oil. But When I would "tap" the oil filter, silver oil was coming out. (guess it was doing it's job) :) lol

The crank snapped just in front of the 1 rod journals. I'll have pics up later, I'm in school now. lol

Sorry for the long read.
 
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I need a SJ 350 mains crank, 1 piece rear main, internal balance, 3.75 stroke, 5.7 rods.
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First let me say that every 350 built from 1968 and later is a LJ crank. The only SJ 350 was 1967.

So are you looking to build a 383 stroker? The reason i ask is because a 350 has a 3.48" stroke not a 3.75" stroke. Are you looking for an aftermarket crank or just a replacement crank? I think i have a reground stock 350 crank with 1 piece seal in the garage i could sell you. If you're interested let me know and i could dig it out and verify and check on shipping.

Also, ALL SBC engines built from 1986 and later are externally balanced on the rear only.
 
The SJ part was my bad.

The motor is a 87? roller block 383. I originally built it with an internally balaned 1 piece rear main eagle Rotating assy kit.
 
I have a Scat 9000 series crank in my 383... I have driven it like I stole it for 7 years, 30,000ish miles and have had no problems...
 
broncoman6524 said:
The SJ part was my bad.

The motor is a 87? roller block 383. I originally built it with an internally balaned 1 piece rear main eagle Rotating assy kit.
Click to expand...

Well, since it is a 383 and internally balanced at that you have no other option than to replace the crank with the exact crank that broke but MAKE SURE you have the engine rebalanced again since not every crank weighs the same even from the same manufacturer.
 
4X4HIGH said:
First let me say that every 350 built from 1968 and later is a LJ crank. The only SJ 350 was 1967.
Click to expand...


All 350s had large jorunals, 67s used a sj 327 block (4" bore, same casting as sj 327) but the mains were drilled out, still two bolt, so the main caps had less material, hence why they went to the large jounral size. Dont mean to thread highjack, just putting that out there.



Look up that model of crank you had, there was some stroke crank snapping in that area, seemed to be a fault in the materials, if so STAY AWAY. but, if its not the one alot of the circle track guys were having trouble with, if it gave you some dependable service id go back. Was it forged or cast? Whats the other specs of your motor? you may want to go forged if you had cast before, since your gonna want the engine taken apart checked and rebalanced. 2lbs of oil prsesure isnt good on anything.
 
is this the same motor you had big problems with before ? if it is just my opinion get ride of it. its cursed. :eek1:
 
sweetk30 said:
is this the same motor you had big problems with before ? if it is just my opinion get ride of it. its cursed. :eek1:
Click to expand...


Yes it is, whole different set though!! haha, this time I put 2800 miles on it.:eek1:

I'm 95% positive this is the exact kit I had my machine shop order.
http://www.summitracing.com/parts/ESP-B13455L030/

and according to the link the crank was a Forged 5140 steel crank.

Strangest thing was that when I started it to get it off the trailer/pull it into the shop. it had a steady/solid 45psi of oil pressure.

I showed my dad what happened, and he also thinks it was a defect or something. I did plan on checking into whether this had happened to these cranks before or not.

I had never really heard of a SBC breaking a crankshaft before...especially at the snout.
 
This might be a stupid question: But, Since I'm needing a new crank now. Would there be any problem to going to a standard 1 piece rear main crank?

What I mean is, go to how it was "stock" Neutral balanced snout, with a counter weight on the end?

Aside from me needing a new flywheel, would there be any problems with this?
 
Subscribed, I just bought an eagle rotating assembly to build my 355. Crank is the same but with the standard 3.48 stroke.
 
1967 350 WAS definately a small journal crank and the ONLY year for one. The block WAS NOT a 327 block (casting number was a 350 with small journal). Yes the 327 and 350 share the same bore diameter but it IS NOT the same block. I have been building engines for 31 years and can say this with 200% confidence. :deal:

KansasTwister said:
All 350s had large jorunals, 67s used a sj 327 block (4" bore, same casting as sj 327) but the mains were drilled out, still two bolt, so the main caps had less material, hence why they went to the large jounral size. Dont mean to thread highjack, just putting that out there.



Look up that model of crank you had, there was some stroke crank snapping in that area, seemed to be a fault in the materials, if so STAY AWAY. but, if its not the one alot of the circle track guys were having trouble with, if it gave you some dependable service id go back. Was it forged or cast? Whats the other specs of your motor? you may want to go forged if you had cast before, since your gonna want the engine taken apart checked and rebalanced. 2lbs of oil prsesure isnt good on anything.
Click to expand...
 
broncoman6524 said:
This might be a stupid question: But, Since I'm needing a new crank now. Would there be any problem to going to a standard 1 piece rear main crank?

What I mean is, go to how it was "stock" Neutral balanced snout, with a counter weight on the end?

Aside from me needing a new flywheel, would there be any problems with this?
Click to expand...

If your engine was a 383 then you cannot install a factory 3.48" stroke crank without changing the pistons (well i guess you could but the pistons would drop down the bore .135" and drop your compression ratio considerably) and rebalancing the assembly and using the proper externally balanced flexplate.
 
4X4HIGH said:
1967 350 WAS definately a small journal crank and the ONLY year for one. The block WAS NOT a 327 block (casting number was a 350 with small journal). Yes the 327 and 350 share the same bore diameter but it IS NOT the same block. I have been building engines for 31 years and can say this with 200% confidence. :deal:
Click to expand...

http://www.nastyz28.com/forum/showthread.php?t=140262

Articles i found a while back when i was trying to figure out, few of those guys bought the cars new iirc.
 
4X4HIGH said:
If your engine was a 383 then you cannot install a factory 3.48" stroke crank without changing the pistons (well i guess you could but the pistons would drop down the bore .135" and drop your compression ratio considerably) and rebalancing the assembly and using the proper externally balanced flexplate.
Click to expand...

I think you misunderstood me. I am staying with the 383 base. But instead of replacing my crank with a second internally balanced 1 piece rear main seal crank. Replacing it with a typicaly internal front external rear balanced crank. Such as a "standard" 1 piece rear main 350 would have.

Does that make sense? What I'm trying to say, is get away from a fully internal balanced motor. and go to a more run of the mill 1 piece crank.


UPDATE.

Pulled the motor out, and the first half of the crank also.
CIMG1479.jpg


I feel CONFIDENT in saying that this is/was a defective crank.

As shown by the pictures, there is only a small amount of the crank that was connected. IE the shiny parts of the metal. The rest, I would assume should have been connected. (save for the oil hole)
CIMG1505.jpg

CIMG1508.jpg




It also rubbed the block/cap. But I'm not sure if it is bad enough to really worry too much about. The most I think it might need is line-bored.
CIMG1487.jpg

CIMG1490.jpg


Somehow my cam died?!?!?! The fuel pump cam is flat.:mad:
I checked all of the bolts figured maybe I'm a dumbass and put one it that was too long. NOPE, the fuel pump/plate bolts were from a kit. and the correct size.
Neither of the holes on the face of the motor went in deep enough to even see the push rod?
CIMG1510.jpg

Weird. :mad:


I guess my next move is to contact Eagle and see whats up.:(


FML. LOL. I'm trying to keep me head up, keep telling myself this is all just a big excuse for a bigger cam.:D
 
First let me say that now i understand what you want to do and you will still need to rebalance the engine since being internally and externally balanced means different amounts of weight in different locations.

Also, the shiny portion of the crank is a crack that has been there for a while and has been "working" which is why it's shiny. Eagle cranks are not very good, Scat are better but not by much. I have used Scat cranks in the past with no issues even though they are now China made junk like everything else in this country.
 
Your probably going to think I'm nuts,,,

But I have seen overtightened belts break a crank before.....in the same exact spot.

also too long of a pulley assembly with an overtightened belt will do the same thing....do you have any extra pulleys driving air compressors or things like that on your engine ?

are you using a stock ballancer....I would use a high quality balancer over a stocker...
 
wasted wages said:
Your probably going to think I'm nuts,,,

But I have seen overtightened belts break a crank before.....in the same exact spot.

also too long of a pulley assembly with an overtightened belt will do the same thing....do you have any extra pulleys driving air compressors or things like that on your engine ?

are you using a stock ballancer....I would use a high quality balancer over a stocker...
Click to expand...

This was a major problem of broken cranks in the GM 2.8 V/6 engines.
Yes i also agree that an accessory belt that is too tight can cause undue stress and either wear out the front main bearing or break the crank. :thumb:
 
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