reasons for snapping rocker arm bolts

1994Vib.RedGT

Member

Aug 19, 2004

585

0

16

Denver, CO

Aug 4, 2006

#1

• Aug 4, 2006

• #1

so in my obscenity laden thread from before I described the hell that me and my car have been experienecing. but for those lazy like me, heres the recap: I finished up my heads/cam swap, combo is: Ported E7s with TFS valve springs which have the inner springs and are good up to .600, steeda 19 cam (.480 lift), and a cobra intake. 200 miles down the road from start up my number 6 cylinder exhaust valve-the rocker arm bolt is snapped in half. I fixed it, and low and behold 30 miles after that, it happened again
my possible diagnoses have been limited to these after doing some investigation:

1. Simple bolt fatigue the stock bolts have 100k on them, they are tired, and dont want more lift.

2. The rocker arms (stock; yes im a cheap ass) suck, and they cant handle the combined stress of the higher lift and those stiff ass springs, and they snap the bolt

3. The heads were milled and I was left in the dark, causing the pushrods to be longer and exert too much force on the rocker, snapping the bolt

4. The springs are too strong, and put up too much resistance against the rocker, and the cam lift is too mild to open them now, is this scenario plausible, Ive gotten one vote for no, so i would like to hear some more so I can get my car back on the road.

 

8

8950HO

New Member

Mar 31, 2005

658

2

0

Aug 4, 2006

#2

• Aug 4, 2006

• #2

The stock 5/16" rocker arm bolts are a joke.

Those springs likely have too much pressure for the weak 5/16" bolts.
Also,the stock rocker arms don`t like high spring pressures...they flex too much.

Should have used the TFS spring kit for stock cast iron heads instead.

 

Zero Signal

Active Member

Feb 24, 2003

2,633

2

46

Tucson, AZ

Aug 4, 2006

#3

• Aug 4, 2006

• #3

With the higher friction of the non-roller bearing fulcrum combined with much higher spring stiffness, you will have a tendancy to put a very slight bending action on the bolt. Especially since the oil will have a hard time lubing up the pedestals with the increased pressure. Figure you bend it a few hundred thousand times and it will snap like a paper clip being bent back and forth too much. That's my theory.

FIY: I had the machinist measure the seat pressure of the stock springs. Mine were at about 60 lbs

 

1994Vib.RedGT

Member

Aug 19, 2004

585

0

16

Denver, CO

Aug 4, 2006

#4

• Aug 4, 2006

• #4

so then should I just go get different springs, and keep the same rockers
get new bolts and keep the same rockers and springs, or should I just get some roller rockers and keep the springs

 

Pokageek

Active Member

Jun 10, 2005

2,767

0

46

MA, USA

Aug 4, 2006

#5

• Aug 4, 2006

• #5

My original (rebuilt) e7's that came with the new motor
b4 the TWS heads had shimmed springs to handle the heavier cam. One of MY rocker bolts snapped.... This could have happened to me again had I kept the heads longer..maybe? So to answer the question, I would just get STRONGER bolts. That's my answer.

 

final5-0

Mustang Master

Apr 6, 2003

6,817

12

79

DFW Texas

Aug 4, 2006

#6

• Aug 4, 2006

• #6

One of the many joys of oem heads is simply that they were not built to stand very much more stress as has been pointed out already.

I'd get some ARP or similar bolts.

Then again ... as has been said ... 5/16 is ... kinda wimpy

IMHO......... That is the main reason the ped to stud conversion for oem heads is kinda lame.

Hope it all works out OK for you

Grady

 

Pokageek

Active Member

Jun 10, 2005

2,767

0

46

MA, USA

Aug 4, 2006

#7

• Aug 4, 2006

• #7

Grady and I agree? I must be getting somewhere! lol.

 

final5-0

Mustang Master

Apr 6, 2003

6,817

12

79

DFW Texas

Aug 4, 2006

#8

• Aug 4, 2006

• #8

Pokageek said:

Grady and I agree? I must be getting somewhere! lol.

Click to expand...

Don't Follow Me ................ I'm Lost

Grady

 

1994Vib.RedGT

Member

Aug 19, 2004

585

0

16

Denver, CO

Aug 4, 2006

#9

• Aug 4, 2006

• #9

is there a way to buy ARP rocker arm bolts without buying a whole head bolt set?

 

Pokageek

Active Member

Jun 10, 2005

2,767

0

46

MA, USA

Aug 4, 2006

#10

• Aug 4, 2006

• #10

It's worth a call to summit. They are usually really good with help line support.

 

8

8950HO

New Member

Mar 31, 2005

658

2

0

Aug 4, 2006

#11

• Aug 4, 2006

• #11

How much stronger are the ARP bolts?
Stock is already grade 8.

Reduced valve spring pressure is likely to solve the problem,but a hassle since the engine is running in the car.

I would definately get some roller rockers to replace the stock junk inaccurate stock rockers.

Crane 1.7`s are cheap and may work if your cam is .480" with 1.6 rockers.
If not get 1.6`s.

If you get roller rockers,set the preload properly.Don`t just bolt them down.

 

1994Vib.RedGT

Member

Aug 19, 2004

585

0

16

Denver, CO

Aug 6, 2006

#12

• Aug 6, 2006

• #12

Im trying to figure out what to do now in the sense of :

new roller rockers
new ARP bolts
change valve springs, or maybe take out the dampener springs on the inside(is that do-able, or not?)

or maybe a combo of all three, because Ive had people tell me to replace all of those parts. Which one, or all?

and with roller rockers which ones clear stock valve covers, because I sold my intake spacer, and second I dont have the money for new valve covers and a new hood to go with that spacer.

 

final5-0

Mustang Master

Apr 6, 2003

6,817

12

79

DFW Texas

Aug 6, 2006

#13

• Aug 6, 2006

• #13

Since the Cobra VC's & GT VC's are the same .....................

You know the Crane Cobra ped rr's would be fine.

Seems like I've seen the Comp steel ped rr's are small in size

I don't see how you could remove the damper from ANY set of springs and not have issues.

I would think most spring upgrade sets by Crane, Comp, etc would be fine.

The most important thing to consider is IMHO ... is the vt geom like it needs to be?

Grady

 

SVTCobra306

New Member

Oct 22, 2005

170

1

0

Ft. Bragg, NC

Aug 6, 2006

#14

• Aug 6, 2006

• #14

Yeah make sure your geometry is good, I agree.

What is your open/seat pressure? Mine are FRPP's with shims, and they have enough open pressure they cracked a pedestal on my stock Cobra rockers... I'm gonna replace them with the right springs for my cam. I think my open pressure was 375... I'd have to look when my paperwork gets here.

oh, and Coba V/C's have a dimple in the baffle to clear the #1 rocker. Whack yours with a hammer or similar hard object and it'll clear fine.

 

1994Vib.RedGT

Member

Aug 19, 2004

585

0

16

Denver, CO

Aug 6, 2006

#15

• Aug 6, 2006

• #15

when you refer to geometry of the valvetrain I assume you mean the angles which the pushrods intersect the rockers and the rockers are to the valve tips and that type thing? Ive got it at my mechanic's shop right now, so he should be taking care of that kind of thing, but im kind of working in conjunction with him to figure this **** out. As for open pressure how do I correlate that to lift, to understand how much lift it takes to open x amount of lbs on the springs.

 

final5-0

Mustang Master

Apr 6, 2003

6,817

12

79

DFW Texas

Aug 6, 2006

#16

• Aug 6, 2006

• #16

1994Vib.RedGT said:

when you refer to geometry of the valvetrain I assume you mean the angles which the pushrods intersect the rockers and the rockers are to the valve tips and that type thing? Ive got it at my mechanic's shop right now, so he should be taking care of that kind of thing, but im kind of working in conjunction with him to figure this **** out. As for open pressure how do I correlate that to lift, to understand how much lift it takes to open x amount of lbs on the springs.

Click to expand...

Yes, IMHO ... you got the jest of it

Most of the time, spring height, open/close, pressure and all the rest of the cam mumbo jumbo spec stuff is supplied by the cam grinder.

In the past, some of the big cam peeps like Comp, Crane and the like had all that kinda info on their sites which would help you see the big pic.

Might wanna cruise over there and take a look

Grady

 

SVTCobra306

New Member

Oct 22, 2005

170

1

0

Ft. Bragg, NC

Aug 6, 2006

#17

• Aug 6, 2006

• #17

Yeah, crane has recommended spring specs on their online "cam cards". (and usually a pn and link to their corresponding spring set

 

1994Vib.RedGT

Member

Aug 19, 2004

585

0

16

Denver, CO

Aug 7, 2006

#18

• Aug 7, 2006

• #18

I think I might have just figured things out a little earlier, and if so, I made a huge mistake. The guy that I bought them from said they are good up to .600; I was looking through the summit catalog today, and for Trick Flow valve spring upgrade kits (they are TF) the set listed for .600 life was for "Standard Twisted wedge heads" which I obviously am not running. The other set with .542 lift was for "cast iron heads", I think I might have the twisted wedge set, unknowingly; because the buyer idid not specify what they were for, just a 94 mustang he had. so could this be what is ****ing me up???