How to turn a 10 second car into an 11 second car.

[KMcCullah]

Bummer about the rocker. I wonder if the lobe beat the lifter to death?

[Jim Comet]

Bummer about the rocker. I wonder if the lobe beat the lifter to death?

Good thought, I will have to remove it and check. The odd thing about this was there was absolutely no ticking or knocking noises when running. Jim

[cjshaker]

When you stop to think that we don't bush pistons, but just run pins against the aluminum, I've come to the conclusion that bushing rocker arms is mostly unnecessary and weakens rocker bodies so that your sort of issue comes up at least occasionally. Just a thought.

KS

Couple thoughts on that; a piston pin has two surface areas to rotate in, the piston pin bore and the rod pin bore. If each is working properly, that cuts the rotation sweep down by half (half being in the piston, half being in the rod). A piston pin is also loaded in one direction, then unloaded and loaded in the other direction, so the pin is only seeing a full load on half of its surface about 1/4 of each revolution, as opposed to a rocker which is fully loaded on one surface the entire time, and at great pressure.

Not saying unbushed aluminum rockers don't work. Guys ran unbushed Dove rockers for many years with success, but every used one I saw had fairly significant gouging in the bore. Although back then, they were about the only option.

[1967 XR7 GT]

Ask T&D if they'll still make their rocker in steel, they'd made their aluminum rocker out of steel before for durability.

Here's the link to the set I saw made out of steel... https://www.youtube.com/watch?v=5EmYsEBuWzw&t=442s

Discussion about the rockers starts about 7 min's in.

I'm going to talk to Harland Sharp and T&D, see what they recommend and go from there.

[Posi67]

Timely subject as I broke a Dove HD Rocker this past weekend. Engine went bad top end of 4th gear and it sounded like a piston with a hole in it. Clicked the thing off and got towed back to my pit. Turned out to be the #1 Exh. and luckily I had a spare. I didn't find any other damage and also didn't have time to run the thing before 1st round. Car went 10.04 on the breakage run and 9.96 after so I guess things are okay, Tach recall said 7700 RPM and I still have plenty of confidence in these old used and abused Dove rockers.

As for Aluminum vs Steel..  Each has their advantages but my opinion is design has more to do with longevity than material. My friends SBF has a Cam with a rather large amount of lift and springs to match and never has rocker problems.

[MeanGene]

Timely subject as I broke a Dove HD Rocker this past weekend. Engine went bad top end of 4th gear and it sounded like a piston with a hole in it. Clicked the thing off and got towed back to my pit. Turned out to be the #1 Exh. and luckily I had a spare. I didn't find any other damage and also didn't have time to run the thing before 1st round. Car went 10.04 on the breakage run and 9.96 after so I guess things are okay, Tach recall said 7700 RPM and I still have plenty of confidence in these old used and abused Dove rockers.

As for Aluminum vs Steel..  Each has their advantages but my opinion is design has more to do with longevity than material. My friends SBF has a Cam with a rather large amount of lift and springs to match and never has rocker problems.

Where did the rocker break? Which cam, and what spring pressures? I have several rollers, a couple a bit under .700, and a .725, and have been told that the Doves are pretty safe up to around .700, then get "iffy"

[Posi67]

/quote]
Where did the rocker break? Which cam, and what spring pressures? I have several rollers, a couple a bit under .700, and a .725, and have been told that the Doves are pretty safe up to around .700, then get "iffy"
[/quote]

Guess I'm in the "iffy" territory. Cam is a custom Comp of just over .700 and the Springs are probably in the 700# open range. Never checked the springs nor know the part number so that's just a guess. More Comp parts though. Rocker broke on the underside a ways below the adjuster. They are non bushed and at least this one showed no signs of galling. I'll try post a picture later.

[427fordman]

I've broke quite a few of those dove rockers too.  I'm switching to t&d for next year

[MeanGene]

Yep, I have a .760 and a .785 that I wouldn't even consider used the Doves on- just have this 454 that's a center oiler that hasn't had the lifter galleries drilled so it could use T&Ds

[Nightmist66]

Timely subject as I broke a Dove HD Rocker this past weekend. Engine went bad top end of 4th gear and it sounded like a piston with a hole in it. Clicked the thing off and got towed back to my pit. Turned out to be the #1 Exh. and luckily I had a spare. I didn't find any other damage and also didn't have time to run the thing before 1st round. Car went 10.04 on the breakage run and 9.96 after so I guess things are okay, Tach recall said 7700 RPM and I still have plenty of confidence in these old used and abused Dove rockers.

If it didn't bend the intake pushrod, you got lucky. I snapped an exhaust rocker on my old engine and it definitely bent the intake. Pushrod was fine on the exhaust that broke. Air and fuel goes in, goes bang, exhaust doesn't open, then something has to give with all the pressure in the cyl., pushrod usually.

[Posi67]

If it didn't bend the intake pushrod, you got lucky. I snapped an exhaust rocker on my old engine and it definitely bent the intake. Pushrod was fine on the exhaust that broke. Air and fuel goes in, goes bang, exhaust doesn't open, then something has to give with all the pressure in the cyl., pushrod usually.
[/quote]

Valid point and not something I had considered. I did however use the intake rocker lash as a reference and suppose I should recheck them all on that side of the engine since the shaft was off. I do have spare pushrods. I'm hoping for 1 more race weekend before seasons end but the weather may decide that for me.

[CaptCobrajet]

I kinda think that there may have been too much pressure on the bushing.  If it is overstressed, it could contribute.  I imagine some HS rockers run and run while some might fail.  I don't usually see that happen, but valvetrain pieces can fail for no apparent or visible reason. 

T&D does not offer a steel option for the single shaft sets, and I really think the aluminum is fine for the application. We use the steel T&D on the paired shafts in some circumstances.  I think we should replace just that one rocker.  It may run for years with no issue.  If it breaks another in short order, the T&D would be the way to go, but I'd give it a chance if it was mine.