I keep breaking rocker arm bolts...
Thread Starter
Joined: Mar 2010
Posts: 1,704
Likes: 10
From: Harrison City, PA
I keep breaking rocker arm bolts... So I had an issue with a yella terra bolt breaking, and I chalked it up to the bolt problem so many people had, because it only lasted 25 miles.
I bought harland sharp sls17 rockers, they were quiet and the car ran great. I started driving the car last night and it was misfiring ridiculously. Turned around, pulled the valve covers, and the harland sharp bolt had broken, but on a different cylinder.
Here's a little background information on my setup:
Texas Speed Giant cam, 248/254 duration, .615/.622 lift
LS7 lifters
Prc .700 springs
Any idea what is going on?
I bought harland sharp sls17 rockers, they were quiet and the car ran great. I started driving the car last night and it was misfiring ridiculously. Turned around, pulled the valve covers, and the harland sharp bolt had broken, but on a different cylinder.
Here's a little background information on my setup:
Texas Speed Giant cam, 248/254 duration, .615/.622 lift
LS7 lifters
Prc .700 springs
Any idea what is going on?
Thread Starter
Joined: Mar 2010
Posts: 1,704
Likes: 10
From: Harrison City, PA
After some digging I found the specs of the springs:
PRC .700" Lift Spring Specs:
Closed Spring Pressure: 160lbs @ 1.850"
Open Spring Pressure: 460lbs @ 1.150"
Maximum Spring Lift: .700"
Coil Bind 1.080"
Spring Rate: 429lbs/in
PRC .700" Lift Spring Specs:
Closed Spring Pressure: 160lbs @ 1.850"
Open Spring Pressure: 460lbs @ 1.150"
Maximum Spring Lift: .700"
Coil Bind 1.080"
Spring Rate: 429lbs/in
Good bolts like that (grade 8 and up) are extremely strong in tension. It takes a lot of stretch to break them. However, with lateral stress they're kinda brittle and break fairly easily.
Carefully inspect the broken parts to see what isn't fitting correctly. Look for rub marks that don't belong, etc. Look at the tip of the bolt to see if it's bottoming out, and not creating the correct clamping force.
Carefully inspect the broken parts to see what isn't fitting correctly. Look for rub marks that don't belong, etc. Look at the tip of the bolt to see if it's bottoming out, and not creating the correct clamping force.
Thread Starter
Joined: Mar 2010
Posts: 1,704
Likes: 10
From: Harrison City, PA
Thanks for the constructive replies.
I took a few pictures for you guys to take a look at.
The YT bolt is actually a little shorter than the stock one, so I don't think it's an issue with bottoming out.
The H-S bolts say H-K 12.9 USA M8 stamped on the side.
I took a few pictures for you guys to take a look at.
The YT bolt is actually a little shorter than the stock one, so I don't think it's an issue with bottoming out.
The H-S bolts say H-K 12.9 USA M8 stamped on the side.
Not sure if the rocker bolt holes extend into the intake ports of your heads but with my trickflows the stock yella terra bolts extended about .020 into the port. You might try coloring the end of the bolts with a sharpy and then running them in and out to see if there is any contact but I doubt that is the problem. I am running a more aggressive cam and slightly heavier spring than you and I havn't had any problem so far. I use thread sealer on the intake bolts. If a bolt came loose that could cause it to break. Most of the bolts I see break are caused by the bolt coming loose first. Wouldn't hurt to check the calibration on your torque wrench. Good luck.
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Verdad Gallardo Thread Starter
Joined: Mar 2010
Posts: 1,704
Likes: 10
From: Harrison City, PA
no it's a freshly rebuilt and calibrated snap on tech wrench. I think it either called for 22 or 24. Even if I put 50 down on it (which I didn't, I followed the instructions), I don't see how it would break. I could be wrong, though.
I lost my pushrod length checking tool a year ago, and ordered a new one, and put it in my tool box only to find out it was the wrong one
Should have another here tuesday. Guy from summit is even sending me rockers after talking to him about it, which is extra nice.
I lost my pushrod length checking tool a year ago, and ordered a new one, and put it in my tool box only to find out it was the wrong one
Should have another here tuesday. Guy from summit is even sending me rockers after talking to him about it, which is extra nice.
Thread Starter
Joined: Mar 2010
Posts: 1,704
Likes: 10
From: Harrison City, PA
Not sure if the rocker bolt holes extend into the intake ports of your heads but with my trickflows the stock yella terra bolts extended about .020 into the port. You might try coloring the end of the bolts with a sharpy and then running them in and out to see if there is any contact but I doubt that is the problem. I am running a more aggressive cam and slightly heavier spring than you and I havn't had any problem so far. I use thread sealer on the intake bolts. If a bolt came loose that could cause it to break. Most of the bolts I see break are caused by the bolt coming loose first. Wouldn't hurt to check the calibration on your torque wrench. Good luck.
If you know where it was located, check the depth of the hole and also that there is no fluid in it. It almost appears the bolt wasn't fully seated against the rocker, i.e., the assembly wasn't preloaded properly.
With a properly preloaded bolt assembly I would think the rocker would give first, but if the bolt was free to bend back and forth even a small amount, it will break.
Also, as a point of curiosity, is this the same rocker location as the prior YT bolt failure?
With a properly preloaded bolt assembly I would think the rocker would give first, but if the bolt was free to bend back and forth even a small amount, it will break.
Also, as a point of curiosity, is this the same rocker location as the prior YT bolt failure?
Had the same issue once. What a pain to repair. Had to tap the head. No issues since.
used a time sert to repair it.
http://www.gtsparkplugs.com/images/Timesert_1.jpg
used a time sert to repair it.
http://www.gtsparkplugs.com/images/Timesert_1.jpg
Thread Starter
Joined: Mar 2010
Posts: 1,704
Likes: 10
From: Harrison City, PA
If you know where it was located, check the depth of the hole and also that there is no fluid in it. It almost appears the bolt wasn't fully seated against the rocker, i.e., the assembly wasn't preloaded properly.
With a properly preloaded bolt assembly I would think the rocker would give first, but if the bolt was free to bend back and forth even a small amount, it will break.
Also, as a point of curiosity, is this the same rocker location as the prior YT bolt failure?
With a properly preloaded bolt assembly I would think the rocker would give first, but if the bolt was free to bend back and forth even a small amount, it will break.
Also, as a point of curiosity, is this the same rocker location as the prior YT bolt failure?
Thread Starter
Joined: Mar 2010
Posts: 1,704
Likes: 10
From: Harrison City, PA
Thread Starter
Joined: Mar 2010
Posts: 1,704
Likes: 10
From: Harrison City, PA
Yeah, but that's where the bolt broke and the rocker got bounced around pretty good before I pulled the valve covers.
The mark on the side of the rocker in picture #4 looks like a repetitive wear mark, rather than single trauma mark. That's where your laterals stress comes from, and that's what breaks bolts like these.
I'd pull off a few other rockers and inspect them carefully.
I would also be looking really closely at the pedestals. If they're allowing the rockers to move back and forth, that would be bad.
I'd pull off a few other rockers and inspect them carefully.
I would also be looking really closely at the pedestals. If they're allowing the rockers to move back and forth, that would be bad.
What length push rod are you using ? Pushrod length may be too long. Check and make sure that the rocker arm is not binding on the pedestal when the valve is all the way open. The wear spot I circled in red on the attchment is where the rocker arm looks like its binding on the pedestal.