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

[Jim Comet]

Took the car to Rock Falls last Saturday. Really good air and my friends were running their best times of the season. I notices some smoke when I first started the car which is not normal. Made my first pass and ran a 10.77 @123.9mph 1.49 60ft. When back in the pits I checked the car over and found a bad needle and seat. I replaced that and the smoke went away. The car sounded good with no ticking so I went for another pass. The car launched and was on a PASS (1.47 60ft) when I shifted to 3rd the car stopped pulling strong so I lifted before the finish. The pass was 10.79 @115mph. I went back to the pits and checked stuff out. I did not pull the valve covers at that time because the car idled great and had very crisp throttle response. I verified float level and timing and made another pass. this time the car just didn't pull hard but ran and 11.45 @ 115mph. I checked things over again including pulling the plugs and found nothing. No ticking, no hesitation or any odd sounds. So, I tried another pass and again ran a 11.53 @115mph. At this point I didn't want to hurt anything so I loaded and went home. When I pulled the drivers side valve cover I found a broken intake rocker. It had fallen off in a spot where it didn't touch anything to make a noise. The pushrod looks straight so I think it was just a rocker failure and nothing more. 550lbs open pressure, I may need to upgrade to T&D's. Being in Minnesota, I guess I have the winter to get this thing fixed and sorted out. Jim

[John67427]

Had a similar situation happen to me but the rocker on #6 let go as I was pulling up to the truck after the run. Heard a bunch of noise and shut it off immediately. Took the hood off and it looked like a hand grenade went off under the valve cover. Pulled the cover and found the same thing you did with the HS rocker. The broken rocker rolled on top of the next rocker and started to pound the valve cover. I replaced the all left side rockers with new HS rockers but left the other side alone. Pushrod was fine and other than a battered valve cover I raced that motor for years with out issue.

[machoneman]

Put in a Chevy LS engine......

[Stangman]

Were those bushed rockers just curious. 11.45 on 7 cylinders not bad thank God you didnt hurt anything. I had a rocker break on me no damage except pushrod.

[Jim Comet]

They are bushed. They are 1.85 ratio which moved the adjuster closer to the shaft. I am thinking that may have weakened the rocker also. I'll check with Blair and see which route he thinks is best. I hate to spend $2000 for new T&D's and pushrods, but I can't have these breaking on me as it sure makes a waste of the weekend. Jim

[57 lima bean]

550lbs open pressure?....That is beyond plenty

[Jim Comet]

Even though it is only 540int and 500exh lift it is a plenty rowdy solid roller.

[57 lima bean]

Even though it is only 540int and 500exh lift it is a plenty rowdy solid roller.

    I was thinking flat tappet....

[Jim Comet]

I am glad these are bushed rockers instead of needle bearings or I would be tearing down the motor completely looking for those suckers!!

[Nightmist66]

I was wondering how they were going to manufacture the 1.85 rockers, when the 1.76 have a small-ish cross section in the pushrod area. Looks like there is almost no cross section at all with those. I know the regular bushed HS "can" handle 700+ open. I guess the only crutch is a smaller shaft and thicker body.

[Jim Comet]

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

[cjshaker]

Even though it is only 540int and 500exh lift it is a plenty rowdy solid roller.

That rocker left precious little meat between the adjuster relief cut and the shaft bore. Excluding the possibility that something caused a piston to valve contact, the rocker bore looks for certain to be the failure point. I don't see any way around that when using that ratio and stock shaft set-up. I don't think I'd trust the design on the rockers with that relief cut, it's just too thin there. Since options are limited, I think I'd go T&D and not look back. Things can get bad (read: expensive) real quick when something breaks in the valvetrain.

[cammerfe]

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

[BattlestarGalactic]

Good point.  I've always wondered why they bushed rockers?  Seems redundant and a source for weakness(as shown).

[Jim Comet]

My rocker set up is a mix. Unbushed Comp/Dove 1.76 on the exhaust and the bushed Harland Sharp 1.85 ratio on the intake. This was done because the Comp rockers did not give the desired intake lift with the cam Blair used. He said the T&D 1.76 rockers always check @ .525 lift but the Comp rockers only came in @.500 lift. Blair thought the motor would benefit with more than .500 intake lift so we had the Harland Sharp 1.85s made. Blair advised me to use the T&D's but due to my budget constraints thought the Comp/Sharp rockers should work and were worth a try. I will talk to Blair and go with his recommendation.  Jim