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70-duster

70-duster

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I have a 1970 duster with the 340 in it. On my build I decided to go with edelbrock rpm performer aluminum heads. I was told I neede a longer pushrod and they offered 2 different sizes. I got the slightly longer pushrods. Needless to say I think I should have gone a hair shorter. They shot through the rocker arms!!!!

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Yeah that's fun! LOL Of course, it could just be that the open spring force is too high and the weak pockets in the rockers failed.

Did the engine run OK for a while or at all? If they were too long then one or more of the lifter's pistons would have stayed bottomed out and hung one or more valves open and it would not have run well at all.
 
Not pretty!

Seen it before on the younger brothers 340 in the late 80's. Gotta wonder why stamped rockers with the eddy heads? What cam and springs are you using.

Back then it was low octane on a high compression 340 and his lack of easing up on the foot when the pinging started. ( likely my bad for not curving his dizzy). This came first then 2 pistons in 3 pieces next. New slugs a little honing and a beat over the head for better fuel and it never happened again (along with re-curve). Brings back old days! Sorry for the misfortune, but speed and knowledge cost money!
 
70-duster said:
I have a 1970 duster with the 340 in it. On my build I decided to go with edelbrock rpm performer aluminum heads. I was told I neede a longer pushrod and they offered 2 different sizes. I got the slightly longer pushrods. Needless to say I think I should have gone a hair shorter. They shot through the rocker arms!!!!
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I tend to think it might not be the length of the pushrods.
I have seen stock (ish) motors with better valve springs do that, and usually too long of a rod will break springs and bend pushrods.
 
Whoa ! Stock deck height ? .... I'm running eddy rpm heads with stock rockers on my 340. Zero issues ..
 
That's not the fault of the pushrod. It's the person's fault who used the stock rocker arms on heads with springs stronger than the rockers can stand.
 
nm9stheham said:
Yeah that's fun! LOL Of course, it could just be that the open spring force is too high and the weak pockets in the rockers failed.

Did the engine run OK for a while or at all? If they were too long then one or more of the lifter's pistons would have stayed bottomed out and hung one or more valves open and it would not have run well at all.
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It ran good for a few hundred miles.
 
Why the longer pushrods? Should likely have stock length if everything is right.

There are TONS of cars running stock rockers with the ede headed spring. It's not that stout a spring unless you are running a 520+ lift camshaft.
 
Did you measure them and figure out what push rod you needed or did you just get longer ones and put them in?
 
When I put Eddy heads on my 340 the instructions stated "must use adjustable valvetrain". Spent $500+ on Comp Cams steel roller rockers. Never had any problems.
 
Are the rockers hitting the retainers? I used Hughes rockers, they lined with good geometry, but that was my heads.
 
1969383S said:
Not pretty!

Seen it before on the younger brothers 340 in the late 80's. Gotta wonder why stamped rockers with the eddy heads? What cam and springs are you using.

Back then it was low octane on a high compression 340 and his lack of easing up on the foot when the pinging started. ( likely my bad for not curving his dizzy). This came first then 2 pistons in 3 pieces next. New slugs a little honing and a beat over the head for better fuel and it never happened again (along with re-curve). Brings back old days! Sorry for the misfortune, but speed and knowledge cost money!
Click to expand...

He punched the same two rockers in stock configuration, only they came through a bit farther and nearly to the covers.
 
MP sells HD rocker arms with a heavier guage pushrod pocket, but for that price Id just get some $150 273 ductile iron mechanicals here on FABO.
 
crackedback said:
Why the longer pushrods? Should likely have stock length if everything is right.

There are TONS of cars running stock rockers with the ede headed spring. It's not that stout a spring unless you are running a 520+ lift camshaft.
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Was on the phone with edelbrock and told them my setup. These were the ones thy suggested. I wish they would have told me that I couldn't use the stock rockers. Would have saved me this frustration. I'm just worried I won't find all the metal pieces and have to tear down the engine.
 
Edelbrock has no idea of your deck height, gasket or any number of other things. If buying pushrods, they should always be measured. Anyone that tells you that something needs to be longer or shorter is just guessing at best.

Absolute BS on the requirement for adjustable valvetrain. That's predicated on lift which increases spring pressures the rockers see. Which camshaft is in this engine?

Unfortunately, the people that have "helped" you did you no favors. Tough lesson to learn.
 
crackedback said:
Absolute BS on the requirement for adjustable valvetrain.
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Really? I'm just trying to help. I followed Edelbrock's instructions and used adjustable rockers. I did not have a problem. Perhaps if the O.P. had followed Edelbrock's instructions, he wouldn't had this unfortunate failure?
 
I think adding adjustable rockers to a Mopar is almost imperative. I know lots of people run the stock ones. Adding adjustable rockers does several good things. One of the most important to me is getting the lifter preload right with hydraulic lifters and with adjustable rockers, you can do that and it does make a difference.

It may or may not have solved the OP's problem, but it is a good upgrade, nonetheless, IMO.
 
70-duster said:
It ran good for a few hundred miles.
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OK, so the pushrods are not too long as to cause immediate problems, though they might not be optimum for lifter preload. So the rockers just are not strong enough for the combination of springs and RPM and cam ramps.

BTW, it is not JUST the spring load that does this; it is also the peak RPM's and the cam lift and cam profile too. With the same spring and lift, a steep ramp puts more instantaneous lifting force on the push rod and rocker than a slow ramp. Ditto for higher RPM's. So saying that one similar setup worked is not proof that it will work on every setup. And used stock rockers are going to be more likely to fail.

The 273 adjustable rockers are a decent suggestion. OP, how much lift does you cam have? And what cam? A high lift might push you towards other rockers.

The bits of rocker are probably in chunks and down in the heads, or have washed down the drain hole in the back of the head and into the pan. I would expect most or all of them to be large enough for the pickup screen to block (but can't guarantee that). I'd pull the pan and see what you find.

And FWIW.... yes, modern tech support in large companies is not so hot.... who knows what experience and knowledge the person at the other end has? It is not like calling a place like LeRoy Engines and speaking with the owners in a family who have flowed heads for decades.... I have called Edelbrock tech support, and the person at the other end did not impress me as being any particular sort of motor-savvy individual. I do sympathize that they get all sorts of questions from customers with all sorts of knowledge levels, and they cannot analyze an individual's setup like we can here.
 
I will add one thing I haven't seen followed up on yet. Did you check the piston to valve clearance on this engine? I see this is a 340, and early 340's have pistons that are proud of the deck. I don't know the engine build specifics here, but Edelbrock sells early 340 specific heads. Are the Eddy's the one's for the early 340's? Usually that's a piston to head clearance issue, and of course again the piston to valve clearance depends on which pistons were used and the cam. But if the valve to piston clearance was marginal it might have been ok for awhile, but if you then ran it a little hotter or a little higher in RPM you could have smacked the valves with the piston, and that could have punched the rockers.

Not sure if that's the case here or not, but it is definitely something I would check before I just changed the rockers and moved on. I had a couple of rockers that were cracked on the 318 in my '71 GT when I got it, that's exactly what happened with it. On further inspection I found a couple of slightly bent valves, a couple of bent pushrods, and a couple of dimples where you could see the valves smacked a couple pistons. On that one it was a timing chain issue, but the result would be similar with insufficient piston to valve clearance. And if the clearance was borderline it might not have happened right away, especially during break in if you were taking it easy on the engine.

dano said:
Regardless of adjustable or not, you still need to measure the length.
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Exactly. You have to measure for pushrod length. The deck heights on these engines are all over the place. Add aftermarket heads, a different thickness head gasket, aftermarket cam, lifters, etc and the only way to really get it right is to measure. Sure, hydraulic lifters can make up for some variance, but you can only know if you're in the right range for the hydraulic lifter pre-load if you measure. The 340 in my Duster and the 318 in my Dart have completely different length push rods and neither one use the stock length, even though the 340 uses stock heads.

The Eddy heads are based on stock geometry. There's no reason you can't use the stamped rockers on those heads. But the stamped rockers weren't designed for anything more than the stock valve springs, so unless you run a stock cam with stock valve springs (or close to it anyway) you should upgrade the rockers. They don't need to be adjustable, but pretty much all of the stronger rockers are adjustable.
 
Maybe these can handle it..............

Fits: 273/318/340/360

These heavy-duty rocker arms from Mancini Racing are quality replacements for your factory originals. They feature thicker cross-sections in the pushrod socket. Left and right refer to rocker offset, not to the sides of the engine or cylinder head.

Includes 16 heavy duty hyraulic rocker arms

............
Mancini Racing Steel Rocker Arm Set, 1.5 Ratio
 
Yes to the above fro 72blunblu. I was gonna ask if the piston to valve clearances had been checked but you beat me to it. Pulling the heads and inspecting piston tops and valves would be wise and good insurance at this point.

BTW, the 2 Edelbrock head models for the SBM have the same rocker and valve geometry. So the piston to valve clearance would not change between the 2 , or anything in the valvetrain action. It would only change the piston to head clearance.
 
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