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Username Post: Broken Rocker Arm and Bent pushrod?        (Topic#263379)
sartobuilt 
Forum Newbie
Posts: 64
sartobuilt
Age: 41
Loc: Camdenton, MO
Reg: 06-05-09
05-22-11 09:35 AM - Post#2093469    

I have a 1960 Impala 348 Tri-Power, Z-11 cam. Last year on the way back from a long road trip the motor started to sound funny, limped it home and found a broken rocker arm and bent pushrod. Replaced the rocker and pushrod. Everything was fine after that. I got the car out for the first time this year went for a short drive and everything seamed fine. Car sat for about two weeks went to leave for a show yesterday and it was running rough again. I pulled the valve cover an I have one broken rocker and a bent pushrod. The broken rocker was on the exhaust and the bent pushrod was on the intake, both on number 6 cylinder. The problem last year was on number 5. The engine was completely rebuilt, it has about 3000 miles on it.

Any of you guys ever hear of this problem or have any ideas?

Thanks

 
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motorman 
Dedicated Enthusiast
Posts: 5170

Loc: south western pa.
Reg: 01-25-00
05-22-11 10:19 AM - Post#2093476    
    In response to sartobuilt

  • sartobuilt Said:
I have a 1960 Impala 348 Tri-Power, Z-11 cam. Last year on the way back from a long road trip the motor started to sound funny, limped it home and found a broken rocker arm and bent pushrod. Replaced the rocker and pushrod. Everything was fine after that. I got the car out for the first time this year went for a short drive and everything seamed fine. Car sat for about two weeks went to leave for a show yesterday and it was running rough again. I pulled the valve cover an I have one broken rocker and a bent pushrod. The broken rocker was on the exhaust and the bent pushrod was on the intake, both on number 6 cylinder. The problem last year was on number 5. The engine was completely rebuilt, it has about 3000 miles on it.

Any of you guys ever hear of this problem or have any ideas?

Thanks


the bent intake push rod is caused because if the exhaust can not open the intake valve is trying to open against a cylinder full of pressure so i would guess the exhaust failed first. if you do not have chrome plated exhaust valve stems they can rust in the cast iron guides when they set for a long time.
retired race engine builder,former NASCAR tech inspector. new corvettes owned 1959,1962,1963,1964,1965, 1966,1997,1999,2002,2005, 2008 plus 30+ other chevy cars and trucks along the way. 2008 corvette sold and waiting on a C-7.


 
sartobuilt 
Forum Newbie
Posts: 64
sartobuilt
Age: 41
Loc: Camdenton, MO
Reg: 06-05-09
05-22-11 10:23 AM - Post#2093477    
    In response to motorman

Cool, Your right online with my thoughts. Do you think if I start adding Lead additive to the gas this will prevent this from happening again?

 
cockroach 
Contributor
Posts: 117
cockroach
Loc: Pforzheim, Germany
Reg: 10-10-08
05-22-11 11:00 AM - Post#2093487    
    In response to sartobuilt

Did you install a hot cam with the old valve springs and rockers and pushrods?

This couly be the cause, too. (Rocker fails and the PR bends...)

Cockroach
1959 Chevrolet Impala 2Dr HT (Jan 1959, Oakland)


 
motorman 
Dedicated Enthusiast
Posts: 5170

Loc: south western pa.
Reg: 01-25-00
05-22-11 11:32 AM - Post#2093494    
    In response to sartobuilt

  • sartobuilt Said:
Cool, Your right online with my thoughts. Do you think if I start adding Lead additive to the gas this will prevent this from happening again?


i am not sure about the lead additive. what type of valve seals do you have on the exhaust?? if you have a positive type i would change to a umbrella type so some oil will get in to the valve guide.
retired race engine builder,former NASCAR tech inspector. new corvettes owned 1959,1962,1963,1964,1965, 1966,1997,1999,2002,2005, 2008 plus 30+ other chevy cars and trucks along the way. 2008 corvette sold and waiting on a C-7.


 
bowtieollie 
ChevyTalk Subject Matter Expert
Posts: 21122
bowtieollie
Loc: See the USA in your Chevr...
Reg: 12-06-99
05-22-11 01:08 PM - Post#2093527    
    In response to sartobuilt

The problem is not related to lead free fuel use.

There are two issues I would investigate.

You stated you are running a Z11 cam.
Are the rocker arm slots deep enough for the added lift?? I have seen the rockers bottom out on the rocker studs at full lift - especially if the heads or block were cut and the geometry is now off.

Are they GM rockers? Or a chinese imposter??

Also inspect the valve spring retainers which were used and VERIFY they are not hitting the top of the guide at full lift.

Worse scenario - you are hydrolocking the cylinder with a potential leaking headgasket??

Those are the areas I would check first.
This is not a common problem on the 348 - but since you have two cylinders acting up - its definitely related to the engine build.
Bowtieollie
Chevytalk.com Moderator


 
sartobuilt 
Forum Newbie
Posts: 64
sartobuilt
Age: 41
Loc: Camdenton, MO
Reg: 06-05-09
05-22-11 08:27 PM - Post#2093706    
    In response to motorman

It has umbrella seals on the exhaust.

 
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