Will My Crank Break? (need help kinda quick please)

TrickFlow

TrickFlow

Member
Jan 20, 2003
340
0
16
Bossier City, La
#1
I got a call from the machine shop today, and they started taking the shortblock apart. Said that my stock crank and rods will not hold up to the 350-370 hp i will have. Is this true, or are they trying to get more cash outta me?


Its the stock rods and stock crank out of a 1991 302 HO
it has been polished just for the rebuild, and the first machine shop i took it to said nothing about it. He said that the stock ford "lightweight" cranks arent good for stock horsepower, let alone how much i want. i thought there were cars running in the 10's on stock forged cranks.. wtf gives?


Mod list:



-Block Bored and honed to 306
-Trickflow 10:1 forged pistons
-Polished crank
-Trickflow Track Heat Heads
-RPM Air Gap intake
-Holley 600cfm double pumper
-Trickflow 6.700 pushrods
-Trickflow stage II cam ( duration 224*/232* lift .542"/.563")
-FMS lifters
-Mac shorties
 

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#3
You should be fine, I would recommend upgrading to a ARP rod bolt though.

We've made well over the HP with no issues on daily driven cars, that see a lot of mileage.

The stock block breaks first in many cases, the rod bolts are the weak link in the stock shortblock.
 
#4
Rick 91GT said:
You should be fine, I would recommend upgrading to a ARP rod bolt though.

We've made well over the HP with no issues on daily driven cars, that see a lot of mileage.

The stock block breaks first in many cases, the rod bolts are the weak link in the stock shortblock.
Click to expand...


I have the arp rod bolts (stock is 5/16 i think?) and the stock forged rods, stock forged crank. i could swear i read somewhere that people were making decent numbers with stock forged internals, so maybe it was you i was talking to.

But the machine shop wants me to get a steel crank, and H or I beam rods with 3/8 bolts. Ive already spent 3 grand on the motor/heads/intake/carb etc... i dont want to spent another 1100 if the stock one will work for me.
 
#5
stock cranks are cast, not forged.


many, dare i say, most times they are fine with enough hp to split the block...but, i have heard of more than a few 5.0's crank breaking when engine is stone stock, and not even abused. why? i have no fricken clue.
 
#6
nosmatt said:
stock cranks are cast, not forged.


many, dare i say, most times they are fine with enough hp to split the block...but, i have heard of more than a few 5.0's crank breaking when engine is stone stock, and not even abused. why? i have no fricken clue.
Click to expand...



damnit, you gave me my first feeling of doubt :(
 
#8
I run HP numbers above those that you've posted on a stock 86 short block with WELL over 100,000 miles. I'm pretty heavy footed but don't get to the track much and don't go out of my way to beat on it either. My torque numbers are over 400 at peak and 371 ft/lbs at just 2300 RPM (meaning that the crank sees a lot of torque all the time). I've not had any issues with the stock rotating assembly to date.
 
#9
Daggar said:
I run HP numbers above those that you've posted on a stock 86 short block with WELL over 100,000 miles. I'm pretty heavy footed but don't get to the track much and don't go out of my way to beat on it either. My torque numbers are over 400 at peak and 371 ft/lbs at just 2300 RPM (meaning that the crank sees a lot of torque all the time). I've not had any issues with the stock rotating assembly to date.
Click to expand...


awesome, thank you. Hes waiting for me to call him back when i decide.. so guess ill leave it how it is <crosses fingers>
 
#12
well actually the last year for forged pistons was in 92...the 93's started with the hypereutectics sp?. not totally sure bout the rods i could be wrong but im leanin towards cast. they do look a lot different to most aftermarket rods...not just in the geometry but in the texture and casting lines/bumps aswell. maybe someone will throw in and tell us for sure.
 
#13
Yea pretty sure the stock rods are cast. If I remember right, I was told by a machine shop that Ford would take like metal dust and put it into mouldings (sp) under immense pressure and form the rods. Not sure if its true.

I have used stock crank and rods in all my motors I have built and no issues. If this helps, I sucked about 4 gals of water in my motor once (long story dont ask) and only bent a rod did no damage to anything else. The stuff is pretty tough.
 
#14
NosPony said:
I sucked about 4 gals of water in my motor once (long story dont ask) and only bent a rod did no damage to anything else. The stuff is pretty tough.
Click to expand...


:lol:

Ok, so im good with the rods... i know that there are holes in the crank (hell if i know what they are for) but can anyone tell me either how many there are supposed to be, or about how deep they are supposed to be? the way he made it sound, someone took a drill and just went hole happy. i didnt notice anyting wrong when i looked at it.. everything except the polishing looked stock
 
#15
ok, Rods for all the H.O.'s are forged (4130 steel, not the best alloy, but better than cast) and they will take the beating that you're planning to put down...

the powdered metal rods are in the mod motors, and the current ones can handle about as much as the stock 5.0 rods, past that, they give out...

in a nutshell, listen to people like Daggar, Rick91GT, and you'll get the low down on engine tech...

edit: where are the holes in the crank? are they straight into the counterweights? how deep? is the crank being balanced?...or are they parallel to the long axis of the crank inside the rod throws? those are casting holes and are supposed to be there...
 
#16
ninety15.0 said:
...they do look a lot different to most aftermarket rods...not just in the geometry but in the texture and casting lines/bumps aswell. maybe someone will throw in and tell us for sure.
Click to expand...


if you're referring to the nice, pretty, expensive H-beam rods, yes, they look much different, but they are profiled rods. my scat 4340 forged I-beam rods look alot like stock rods...just much beefier and with cap screws instead of bolts and nuts.
 
#17
txstang84 said:
ok, Rods for all the H.O.'s are forged (4130 steel, not the best alloy, but better than cast) and they will take the beating that you're planning to put down...

the powdered metal rods are in the mod motors, and the current ones can handle about as much as the stock 5.0 rods, past that, they give out...

in a nutshell, listen to people like Daggar, Rick91GT, and you'll get the low down on engine tech...

edit: where are the holes in the crank? are they straight into the counterweights? how deep? is the crank being balanced?...or are they parallel to the long axis of the crank inside the rod throws? those are casting holes and are supposed to be there...
Click to expand...


They are on the polished part from what im gathering, i dont know honestly, i didnt pay much attention to the holes in the crank before i sent it to them.... i think they are the holes for the oil pressure or something..... hell, im just going there tomorrow, taking pictures, and seeing what you guys think
 
#19
An even better reason to chamfer the oiling holes is to reduce stress risers.

It seems like this shop either isn't as experienced as you had thought, or they are trying to stick it to you. The guy thinks the crank is gonna fail because of the oiling holes? Uh-Ok.:nonono:
 
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