Broken Crank

xlr8ngn

Member
89 TTA, stock engine with new chain springs and all seals, PT-52 running 25 psi with E85, ecu-GN, zero knock, plugs looked safe, 78k miles, Husek trans, ran 7.70's at 92 in the 1/8th. My crank more or less had a clean break in between #1 and #2 rods with no warning. The rods were still on the journals but it did "grow" a little in length pushing the front crank snout forward. The crank locked up tight between the back of the #1 main cap and the thrust bearing. When it broke, I was on the highway at 3/4 throttle. The #1 cylinder quit spinning, and the remaining 5 were still propelled by the transmission. I put it in neutral with all the chaos going on under the hood, and everything went quiet. #2-6 pistons all have dimples from the valves, and the bottom of #1 and #2 piston skirts were battered by counterweights. #1 main cap is loose in the register, but all the webbing and cylinder walls look good.

Good news is I can reuse the heads and block. Bad news is I have to buy alot of new parts and machine work. My general plan is as follows:

Forged rotating assembly
.010 pistons
Front 3 steel mains, studs and line bore (girdle too?)
Clean up deck and heads for mls gasket w/ studs
DIY port and polish heads, intake, and stock headers

My goal is mid 10 capability. I have alot of research to do before I start buying parts, who to buy parts from, and what machine shop to use. I'll see if I can load some pics.
 

xlr8ngn

Member
Pics
 

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Nigel

Well-Known Member
That sucks.
I know this obvious, but get the block checked out thoroughly. I would be worried about the webbing and bearing saddle area. They likely experienced much higher loads than normal when the crank broke.
 

Sweet6

Well-Known Member
damn that is rough. Like mentioned above call Dave Husek If you plan on changing the cam that will be a challenge. But Dave may be able to help you get one. But it will take some time.
 

xlr8ngn

Member
That sucks.
I know this obvious, but get the block checked out thoroughly. I would be worried about the webbing and bearing saddle area. They likely experienced much higher loads than normal when the crank broke.
Yes it does, very much so lol. The front main slides in the register with no resistance, so It definitely egged the front main cap and made it a bit narrower. Fortunately the block and webbing all look good, but I'm going to take a burr and sanding rolls to all the webbing to eliminate any stress risers and inspect for cracks.
 

SCOOBY DOO

I'M NOT A MONSTER, I'M JUST AHEAD OF THE CURVE!!!
I may do this before I get to work with the die grinder. I don't want to cover anything up.
For shits and giggles, check the registers and see if they have a 45 degree chamfer on them and the main caps as well.
 

TIMINATOR

Active Member
I have seen many cranks broken as yours is. All of them were externally balanced.
Some were traced to cheap harmonic balancers, some from loose balancer bolts and SEVERAL were the early design SCAT LS stroker cranks that needed 3 or 4 slugs of mallory metal in each end counterweight to achieve "proper" balance. Scat has finally changed all of the counterweights on the LS cranks, so they will internally balance like everybody elses units.
My new build uses a Scat crank that can be internally balanced, but I had to remove a TON of weight to achieve zero balance prolly because of the Wiseco pistons lighter weight. A lot of the weight savings is from a more normal weight piston pin. I believe anyone building an engine with stock replacement pistons buy a lighter set of pins, as stock ones are waaaay heavier than aftermarket ones. A better alternative is lighter aftermarket pistons anyway.
If you bring a Scat crank in to be zero balanced, expect to pay extra for the time for all of the weight that needs to be removed. I think its worth it in improved performance. Also, dont forget to balance the cast iron pulley spacer deal too, mine was way off, even tho it was factory balanced. It does hang way in front of the balancer, putting more load on the front of the crank.
P.S. I also zero balanced my stock flexplate and balancer rather than buying aftermarket, as mine is a "street car."
TIMINATOR
 

rag231

Well-Known Member
It has been a long time since I have read a story about a broken crank! Years!! Maybe it’s better electronics, oil, less driving, I don’t know. The new build will be stronger I’m sure!
 

Mr.Spool

Well-Known Member
89 TTA, stock engine with new chain springs and all seals, PT-52 running 25 psi with E85, ecu-GN, zero knock, plugs looked safe, 78k miles, Husek trans, ran 7.70's at 92 in the 1/8th. My crank more or less had a clean break in between #1 and #2 rods with no warning. The rods were still on the journals but it did "grow" a little in length pushing the front crank snout forward. The crank locked up tight between the back of the #1 main cap and the thrust bearing. When it broke, I was on the highway at 3/4 throttle. The #1 cylinder quit spinning, and the remaining 5 were still propelled by the transmission. I put it in neutral with all the chaos going on under the hood, and everything went quiet. #2-6 pistons all have dimples from the valves, and the bottom of #1 and #2 piston skirts were battered by counterweights. #1 main cap is loose in the register, but all the webbing and cylinder walls look good.

Good news is I can reuse the heads and block. Bad news is I have to buy alot of new parts and machine work. My general plan is as follows:

Forged rotating assembly
.010 pistons
Front 3 steel mains, studs and line bore (girdle too?)
Clean up deck and heads for mls gasket w/ studs
DIY port and polish heads, intake, and stock headers

My goal is mid 10 capability. I have alot of research to do before I start buying parts, who to buy parts from, and what machine shop to use. I'll see if I can load some pics.
The 78k on the motor have you had that setup since day 1 or did you recently purchase it?
 

Chuck Leeper

Toxic old bastard
Staff member
"The rods were still on the journals but it did "grow" a little in length pushing the front crank snout forward. The crank locked up tight between the back of the #1 main cap and the thrust bearing".
When you are doing the suggestions already made, look very close at the entire ft bulkhead of the block. The hit with the crank side loading the cap bolts could wreak havoc with the threads.
 

xlr8ngn

Member
The 78k on the motor have you had that setup since day 1 or did you recently purchase it?
I purchased it recently and only put a few hundred miles on it. Probably hurt from before. I added the ecu-GN, E85, Husek trans. Also found part of a head gasket in the oil pan when I replaced the timing chain and rope seals.
 

SCOOBY DOO

I'M NOT A MONSTER, I'M JUST AHEAD OF THE CURVE!!!
I purchased it recently and only put a few hundred miles on it. Probably hurt from before. I added the ecu-GN, E85, Husek trans. Also found part of a head gasket in the oil pan when I replaced the timing chain and rope seals.
Not monitoring KR gets 'em every time.
 
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