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

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bovman

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I race a 1973 Dodge Dart Sport with a low compression 340. This engine has performed really well over the past ten years but recently I had a problem.
At the end of a run the engine began to stutter and upon inspection in the pits it was revealed that two pushrods had broken through the rocker arm cups.
I took the heads off, checked all of the valves (nothing was bent or damaged) replaced all of the rockers with new ones and put it back together. It's starts right up, idles fine, but won't rev past 5000 rpm (I used to shift at 6200). I replaced the ignition box (mopar orange one) with another orange one but it still won't rev. I put in the Mopar silver box (everyone at the track says its ignition related) yesterday and am going out tomorrow but don't have a lot of faith that is the cure. I've replaced the battery with a new one, the compression on all cylinders is fine.

Any ideas?
 
Holly blue pump. pressure a steady 6.5 lbs throughtout the run.
Modified Thermoquad carb.
 
Put a timing light on it. If the timing seems to be moving back and forth at idle, you need a timing chain. It could wear out after only 10 seasons.
 
Sounds like you have a couple of bad lifters. Same thing happened to an engine I had some time ago. Two lifters pumped up hard and sent the push rods through the rocker arm cups. I replaced the lifters and rocker arms and no more problems.
 
You may have hit it on the head.
It never occured to me that the lifters could be bad after that incident.
I knew the problem had to be related to those broken rocker arms.
I'll order replacements today.
Thanks for your input.
 
I thought the same thing. Lifters took a beating. Change the oil and replace the set.
 
hi the motor is 10 years old? you just don't thow lifters on a used cam !!!
I would look at valve spring pressures. they prob have lost seat pressure, thats why motor will not rev. a weak valve spring can let the lifter pump up.
I been through this before on my 340. you need to pull a couple valve springs
and check them for seat and open pressures. I think you will find the problem
 
I don't know,sounds like a bent valve (exhaust) take a compression test first
 
If you have been racing this for 10 years already, this might be a good time to completely go through the engine and refresh everything.:thumbup:
 
I did replace all of the valve springs when I repaired it the first time.
I also checked to make sure that none of the valves were bent.
I'm pretty sure the lifters are the problem.
I ran the old valve springs a little to long but the inside of that engine looks like new, I checked everything when I had the heads off.

I'd like to build a stroker motor for it but it "ain't in the budget" this season.
 
A vacuum guage can tell of a burnt valve,weak springs,worn rings,general engine health,how big an unknown cam is.I used mine last night to remove and replace my distributor without a timing light.
 
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