Rocker Arm Stud

[mrgem]

I was idling at a stop sign and pulled away in a very sedate (2000 RPM) manner last Friday evening and suddenly my 351 Windsor with fewer than 5k miles on it started knocking and banging. Still had oil pressure -- but it sounded like a small end failure on one of my rods. All I could think about was a 3000 buck rebuild.

I parked the car on the side of the road (nice quiet residential area) and left it there that night. I returned the next morning with my trailer, loaded the car up, and hauled it over to my machinist's house -- which was only about 5 miles away.

My machinist had me start the car and immediately identified the noise as a broken rocker or valve spring...BIG sigh of relief. We popped the valve covers and one of the intake valve rocker arm studs was sheered clean off.

The engine is a 1969 H-code with, stock (ported) 69 heads, with 10.5 compression, a mild performance cam and standard springs, lifters, and pushrods. The studs were the original pressed-in style (a corner I probably shouldn't have cut when we built the motor).

This car, while it has seen some spirited driving, has never been revved over 5k. It makes tons of power down low and the engine was built to make power from 2500-5000 rpm -- something it does quite well. It really doesn't need to spin that hard to be fun.

Because it was built for torque, I really didn't expect I'd need a very exotic valve train.

My question is -- why would the stud fail? Just old, fatigued metal? Flexing/deflecting stock pushrods? I want to put this thing back together so it will last, so I've already decided to go with screw-in studs, but what else can I do to minimize the risk of another similar top end failure?

 

[blue65coupe]

I would say stress on the pressed in stud. Hard to tell though. I'd run screw in studs in it and go for it. Check everything else out before reassembly.

 

[mrgem]

Thanks. Upon closer examination, my machinist tells me he believes that the pushrods were slightly too long and that changed the geometry of the valve gear just enough to put too much sheer stress on the stud.

Since all will have to be disassembled anyway, I am biting the bullet and upgrading to screw-in studs and roller-tipped rockers, although my machinist says his supplier is having difficulty locating a set locally. His supplier tells him that they've been temporarily discontinued because of reliability problems, but will be available again, soon.

 

[blue65coupe]

Discontinued roller rockers? OK. Measure the pushrods and measure again. If you need a pushrod that is "not common" look at Doug Herberts in Lincolnton NC. They have a website, catalog, etc. I've had to go there for two different sets. Good guys and very helpful.

 

[Horseplay]

I want to say it was Comp Cams Magnum roller tip rockers that had some breakage issues not too long ago. I think this was more common on higher lift (heavier spring) cam applications but still a concern. It's not much more cash to go to a full roller piece. As long as you are in there I would think you should really consider it. There are benefits.

 

[mrgem]

That is what my machinist was told by his supplier, any way. Although I had no problem locating them at Jeg's, Summit, and Competition Products.

My machinist called me back last night and told me his local supplier had found a set (Comp Cams rail types) in their Phoenix warehouse and they will be here tomorrow.

He said he'll wait for the rockers before measuring for new pushrods...although Comp Cams says they should work with the factory length (8.152").

Thanks again for the help!

Let's Never Forget Our Buddy JohnPro!

 

[mrgem]

Yep...That is precisely what my machinist was told by his supplier. He spoke to Comp Cams and they told him he'll be fine with my mild camshaft and soft springs.

 

[camachinist]

Hey Glenn, wasup? Sorry to hear about the engine....

Presuming the heads are coming off, he can, when machining for the screw-in studs, machine for guide plates and you can get away from rail-type rockers of any sort.

FWIW, I used the standard length SVO pushrods and the Crane vacuum-cast (read 'cheap') roller rockers on the race car W (about .535 lift) and had no problems at 200 track cycles.

IMO, based on my years of racing, guiding the assembly at the pushrod is far easier on stuff than guiding it at the valve tip.

 

[mrgem]

Hey Pat -- Not too much. Just working to try and pay these bills.

The Comp Cams Magnums are already enroute, so it is probably too late to change course. Willy -- the machinist, believes he can do all the work without removing the heads -- but acknowledges you have to be careful to eliminate even small amounts of metal before buttoning up.

After he removes the Export Brace and Monte Carlo Bar, he will decide if there is enough room to work on the heads in the car. The whole notion of tapping holes in heads that are in the car seems a bit risky, but I have faith in this guy.

He's never done me wrong in the past on this stuff and has been a Ford specialist since the late 1960s. He actually owns 3 427 Cammer engines -- one of which powers a wickedly fast 1956 T-Bird.

I'll post the outcome of my little drama here as soon as I've gotten the car back.