Factory rocker defeated by pushrod.

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HiFire

HiFire

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The aftermath of freeway speeds on a 68 340 with original rockers. The engine is in a 71 Sweptline. The springs are setup for a purple 484 cam. The cam is now a Howards 710931-12 with the 484 springs. Planning on replacement rockers from Mancini. Would like adjustable rockers but money is an issue. Anybody have pos/neg opinions on there rockers? Thanks everyone for your help.

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I was not aware Mancini sold the stock style rockers. I will say this. If those are original 340 rockers, they have a thicker cross section than all the rest of the stock "paddle" style rockers, so be forewarned. Unless the Mancini rockers are even thicker, you may have a repeat performance. That's a pretty common issue with higher spring pressures.
 
Happen to me a lot in early 70's = Usually @ 6500+

Recommend Adjustable rockers at least stock 273 or better
 
Thanks for the info and the warning. Need to get the truck running and don't have easy access to parts here in Hawaii. The Mancini rockers are $119 for the rockers alone. I guess my saving grace is that it's a truck that doesn't see north of 3000. No race tracks on Oahu.
 
Ideally I would like to get 273 adjustable rockers.
 
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I sold my ol iron adj 273 set. I'm running the ol MP HD rockers on my 340. Have spun er up to 7000 many times, in drive it shifts @ 6500. They are noisy... only thing is I think they killed Mopar Performance, maybe you could find an older set?
 
HiFire said:
Ideally I would like to get 273 adjustable rockers.
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They'll fit in a large flat rate gamebox, shafts and all. A little more than 20 bucks. No reason in the world for someone not to ship.
 
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HiFire said:
Ideally I would like to get 273 adjustable rockers. If anyone has a serviceable set that they are willing to ship to Hawaii I'm in. Thank you in advance.
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Are the factory pushrods compatible with the 273 rockers? I thought the 273's need ball/cup and the OEM stamped rockers are ball/ball? Not to mention the length may be different even if you have compatible adjusters? Still a win to go with the 273's, even if you need to get pushrods. I'd slap a single rocker in for the bad one temporarily and work on fitting out the new adjustables.
 
I ran them years ago and had to buy a set of rockers if I remember correctly. I just changed my stock hydraulics with a set of Echlins on my 68 340. Didn't know about the thicker cross sections though. I'll have to keep an eye open now. Thanks for the info. RRR. I will go to 273 style if I ever decide to change my cam .
 
gzig5 said:
Are the factory pushrods compatible with the 273 rockers? I thought the 273's need ball/cup and the OEM stamped rockers are ball/ball? Not to mention the length may be different even if you have compatible adjusters? Still a win to go with the 273's, even if you need to get pushrods. I'd slap a single rocker in for the bad one temporarily and work on fitting out the new adjustables.
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Correct. 273 rockers need a different pushrod and a different length.
 
Thats a common issue with stock rockers, especially when you up the cam. I have seen 318 2 bbls do it too.
The replacement rockers from mopar performance were beefier in the pushrod cup but I dont think they sell them anymore.
I dont know if stock 340's were thicker but they did have a different shape to clear larger valve springs.
Btw, not all 273 rockers were adjustable. They switched to the stamped rockers around 68 or 69 if I recall.
 
gzig5 said:
Are the factory pushrods compatible with the 273 rockers? I thought the 273's need ball/cup and the OEM stamped rockers are ball/ball? Not to mention the length may be different even if you have compatible adjusters? Still a win to go with the 273's, even if you need to get pushrods. I'd slap a single rocker in for the bad one temporarily and work on fitting out the new adjustables.
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If my notes are correct, this is the part # for the pushrods needed to use 273 rockers with hydraulic lifters.
Summit Racing SUM-G6420 Summit Racing™ Pushrods | Summit Racing
 
Kendog 170 said:
I ran them years ago and had to buy a set of rockers if I remember correctly. I just changed my stock hydraulics with a set of Echlins on my 68 340. Didn't know about the thicker cross sections though. I'll have to keep an eye open now. Thanks for the info. RRR. I will go to 273 style if I ever decide to change my cam .
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Sorry, I meant new set of pushrods !!!
 
HiFire said:
The aftermath of freeway speeds on a 68 340 with original rockers. The engine is in a 71 Sweptline. The springs are setup for a purple 484 cam. The cam is now a Howards 710931-12 with the 484 springs. Planning on replacement rockers from Mancini. Would like adjustable rockers but money is an issue. Anybody have pos/neg opinions on there rockers? Thanks everyone for your help.

View attachment 1715928757
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Would not have expected that with the cam & spring combo at lower RPM. Not a whole lotta lift on that cam... well under .500. Maybe just unlucky, getting enough oil up there?
 
My dad has had that happened to him a few times thru the years but only when he was drag racing. He always just swapped out the rocker for another one. Be sure to check the pushrod as sometimes it gets bent in the process. If they are originally rockers you have to remember they are old and some will just fail randomly. Cheap fit would be to put another one on and keep on trucking. It is werid that if failed at low rpms, but stuff happens.
 
I've only had the engine for about 6 months. No telling how the previous owner drove it. No one carries rockers in my state. Summit wants @ $20 to Ship 1 rocker. I'm going to post a wanted ad for the parts needed. Looking into the future I want to run adjustable rockers with a solid cam. For now I just want to get it running. Thanks everyone for the suggestions and help.
 
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moparstud440 said:
My dad has had that happened to him a few times thru the years but only when he was drag racing. He always just swapped out the rocker for another one. Be sure to check the pushrod as sometimes it gets bent in the process. If they are originally rockers you have to remember they are old and some will just fail randomly. Cheap fit would be to put another one on and keep on trucking. It is werid that if failed at low rpms, but stuff happens.
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Had the same thing happen on one of my 340’s, MP 509 cam with beefier springs, stock rockets, bent the pushrod a little and poked through the rocker arm, replaced it with stock parts I had laying around and went on my way and that was about 10+ years ago now. Luckily I found the piece that broke off the rocker, it was laying in the head.
 
HiFire said:
Thanks for the info and the warning. Need to get the truck running and don't have easy access to parts here in Hawaii. The Mancini rockers are $119 for the rockers alone. I guess my saving grace is that it's a truck that doesn't see north of 3000. No race tracks on Oahu.
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There used to be a drag strip down by Pearl Harbor....did it close? :(
 
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