Rocker arm slipped off, GT40 heads

[DJCarbine]

GT40p heads on a 289
Just got my exhaust sorted out, took it out for a long drive.

A few blocks from home I hear a ticking sound that gets louder and louder. I figure its an exhaust leak, and just try to baby it home. A tick turns into a WHACK WHACK WHACK and the engine starts to miss.

I push it home and pull off the valve covers. One of the roller rocker arms slipped and the pushrod was just bouncing off the valve cover and the valve head marred up the rocker pretty good, but it was still fine.

Is there anything I am missing? It seems like its very easy for them to slip off, there is nothing except for the allen head bolt holding it on and that doesn't really ensure that its going to stay aligned at high RPM.

Does anyone have any input? I figure I just make a mistake and it wasn't lined up properly, and it eventually loosened up and slipped off.

 

[2+2GT]

There's always some kind of guide. The 63-66 260/289 had a slotted hole for the pushrod. The 66-up had the "rail" rockers, with little rails on the sides of the rocker tip to stay in place on the valve tip. The BOSS 302 etc. had guide plates for the pushrod. And so on.

Now, if you have non-factory roller rockers, and only the tightness of the retaining bolt holds it in line, this is a really bad idea. Being a great swami, I see a set of guide plates in your future. These are not expensive. They need to be held in place by the rocker studs, so some changes may be required there.

 

[DJCarbine]

They are pedestal mount roller rockers, on a GT40 head. The head pushrod slot isn't a guide, its just an open circle that would allow the pushrod to go anywhere

I don't think I can install a guideplate under the rockers because it would alter the geometry and the pushrods would be too short

Maybe a stud conversion is in my future with guideplates

 

[DJCarbine]

That, or my cam wiped a lobe and the pushrod just raped the rocker and jammed it out of the way.....

 

[57fairlane]

maybe . . . I really haven't seen too many issues with a pedestal setup until you get past ~.550" or so range and just a ton of spring pressure.

How many ft-lbs are you using on the rocker bolt?

Did you setup your rocker geometry correctly?

 

[DJCarbine]

Well they are ford racing rockers and a stock GT40 head, so I just used shims and custom length pushrods to get the preload correct. The roller tips are on the valve heads right in the center, and I took off the offending rocker arm and it looks like the roller tip was also right in the center of the valve.

I go for 1/4-3/4 turns of preload, and then torque it down to 18ft/lb

 

[DJCarbine]

Well I just put the rocker back on and turned the engine over by hand, the cam definatly isn't wiped, there was still the correct preload and lift at the rocker arm. I think it was just a fluke, I didn't center the rocker correctly on the valve or forgot to tighten it down properly. That and a combination of 6k rpm with a decent sized cam and tight springs cause it to happen

 

[65ShelbyClone]

That's weird that one came loose. Usually pedestal rockers are a "set and forget" affair. I'm using them with a .513/.529 roller cam and they have stayed put for probably 10,000mi so far.

Are the rockers 1.6 or 1.7 ratio? If they are the 1.7s, Summit sells them individually for half of what Ford does if you decide to replace the damaged one. They were made by Crane, though, so I don't know how the supply will hold up with them having gone belly-up and all.

 

[DJCarbine]

They are 1.6 ratio, the rocker is OK though. All the important parts are still perfectly fine, the pretty blue paint is a bit scratched up though. I figure I slap the valve covers on and no one will be the wiser

 

[cobra1540]

If they are pedestal mount rockers shouldn't there be a u channel below the rocker that spans the intake and exhaust for that cylinder, and that is what keeps them from turning.

 

[DJCarbine]

There is no channel, its just a flat mount for either a stud or a pedestal rocker. I am beginning to think that there are no guideplates for these type rockers, as ford specifies the use of non-hardened pushrods because of lack of guide plates/slots

 

[cobra1540]

I don't believe there is a guide plate like the one pictured above in this post, but a u- channel that sits on the pedestal ( mounting surface of the head ) and captures the bottom of the rocker ( the piece that makes contact with the head ) and that piece should have a square/rectangle that fits inside of the channel not allowing the rocker to turn.

 

[cobra1540]

If you don't know what I'm talking about ( u - channel ) then you must not have them. I'll look for some pics to explain.

 

[DJCarbine]

I don't believe there is a guide plate like the one pictured above in this post, but a u- channel that sits on the pedestal ( mounting surface of the head ) and captures the bottom of the rocker ( the piece that makes contact with the head ) and that piece should have a square/rectangle that fits inside of the channel not allowing the rocker to turn.

Picture of the heads I found on google

You can see a clean spot where there is no oil from where the pedestal sat, but there are no groove and the pushrod hole is not slotted

 

[cobra1540]

See the square piece I'm talking about?

 

[cobra1540]

These are what you should have contacting the heads first , then your rockers.

 

[cobra1540]

Do a search for "Channel Kit, Pedestal Rocker - Ford " and you should find what you need. these were $20.00 bucks. I wouldn't drive the car until you put them on.

 

[cobra1540]

The guide plates shown in post #2 (I believe ) are for adj. / stod mount rockers and require hardened push rods.

 

[DJCarbine]

These are what you should have contacting the heads first , then your rockers.

This makes a lot of sense. The only issue I am concerned about is raising the height of the rocker messing with the preload. If they are the same size as the shims I am using, then it would be perfect (.030-.060)

 

[cobra1540]

I don't know how thick they are, but you can buy shim kits also. I would check your lifter preload at the plunger, because the 3/4 - 1 1/4 turn after zero lash wasn't correct on my adj. rockers. but that would require removing your intake as well ( I assume you're running a carb ).