I can't figure it out, maybe you can?

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bovman

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Broke two rocker arms on my 1973 Dart Sport 340 bracket car.
Pulled the heads and replaced the valve springs, hyd lifters, rocker arms.
Went out and it wouldn't rev past 5200 rpm.
I replaced the orange spark box with a chrome one and went out last night.
Better, but still won't rev past 5500 rpm.

It pulled the wheels on the launch, but just won't rev past 5500 rpm.
This car ran 12:60's before breaking the rockers.
Since then it hasn't run faster then 14:50

I have a thermo Quad on it that's worked really well, but I'm thinking something may have gone wrong with it, making the motor lean out and causing the lack of rpm?

I've checked everything else. When I had the heads off, everything looked good. I've checked the timing and it's dead on. The car starts right up and idles fine.

Any idea's on what the problem might be?

Thanks!
 
It seems the logical thing would be something that you changed out, and not something that is coincidental. Since you changed valve springs, are they weaker than the originals? Are you floating the lifters? Do you have adjustable rocker arms? If so, double check how you set them. Good luck
 
If it were me, first I'd check my (new) rocker arms, lifters, pushrods & make sure THEY didn't break, bind, whatever. Assuming they're all good, I'd re-set ALL my valves to make sure nothing else got damaged/broke. Putting the original spark box back (since it was functioning prior to this) wouldn't hurt either.
The reason I say all this is, I seem to rememebr a story of a guy who had a Max-wedge engine and floated the valves on it so badly he couln't start it. Thinking the motor blew he simply sold the car with a "broken engine". Some guy bought it & while going through stuff prior to tearing it down found the timing chain had skipped a few teeth causing the whole valvetrain to be out of whack. I'm thinking something similiar is going on here and just needs to be re-set.......
 
I had a terrible time with my 340 not revving over 7500, I replaced all kinds of stuff and did a lot of other things. Finally I put valve springs on it with more pressure over the nose (I had the recommended springs on it to start with) and that fixed it, 8500 after that.
 
did you replace the two pushrods? make sure you didnt use em from a 360 they are longer. just a guess
 
Sounds to me like the spring pressures are less than you had before. With a high lift hydraulic cam this would tend to float the valves earlier. JMO
 
When you have the valve covers off check for spring bind. If you broke push rods and now it won't rev, maybe the springs are binding. At full lift you should have clearence between the coils of the spring.
 
Something else to check out is your coil.I had an Accel stock looking unit.Had same problem with my cuda.Wouldn't rev and after awhile of driving would shut off. Let car cool and fire right up.Checked everything and changed orange box,still shut off.Pulled the coil wire off and oil was coming out.Put a stock coil back on it and got my revs back up.Coil was getting hot and wouldn't fire the plugs.Yeah plugs looked crappy.Now has a MSD coil and no problem since.Something to check.
 
Gotta go with RamCharger on this one,bent valve.Keep us posted and good luck.
 
Broke two rocker arms on my 1973 Dart Sport 340 bracket car.
Pulled the heads and replaced the valve springs, hyd lifters, rocker arms.
Went out and it wouldn't rev past 5200 rpm.
I replaced the orange spark box with a chrome one and went out last night.
Better, but still won't rev past 5500 rpm. "



How did the pushrods look? Which rockers are you running?

Sure the springs are rated for the cam?


Strange you broke 2 rockers with a Hyd cam....... are they clearing the retainers?


I would look at the timing chain / gears , also and verify everything is good at TDC.

my old Orange box went to 6200 all day long--i doubt its the ignition---

just throwing some ideas out there...


try a leakdown test for the valves

??
 
Thanks to everyone who replied.
I'll have the motor out this week and will let you know what I find.

Bovman
 
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