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Old 05-11-2011, 07:09 PM
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Rocker pedestal repair on cast head?

After running a new personal best first run out. I broke my rocker pedestal. Then I Found some more disturbing carnage. aft and middle rocker pedestals are cracked. Strangely the fwd rocker is the one that broke. Think this is something I should try to tig repair on the car? Or is that a bad idea because it's iron? And ideas?

This is the middle, it's not so bad.



The aft is the bad one.




This low rpm 3.8 went 10.24@133mph @ 6200 rpm with a 26" tire. Assuming I can fix the rocker pedestals. I plan on going to a 28" tire to lower the rpms.

Thanks.

Last edited by ForceFed86; 05-11-2011 at 07:15 PM.
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Old 05-11-2011, 08:09 PM
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Quote:
Originally Posted by ForceFed86
After running a new personal best first run out. I broke my rocker pedestal. Then I Found some more disturbing carnage. aft and middle rocker pedestals are cracked. Strangely the fwd rocker is the one that broke. Think this is something I should try to tig repair on the car? Or is that a bad idea because it's iron? And ideas?

This is the middle, it's not so bad.



The aft is the bad one.




This low rpm 3.8 went 10.24@133mph @ 6200 rpm with a 26" tire. Assuming I can fix the rocker pedestals. I plan on going to a 28" tire to lower the rpms.

Thanks.
Ouch, can you say new head. But 10.24 @133 whoa dude talk about thumb's up.

You are discovering that the Chrysler shares a problem similar to the old Ford FE where the end rockers are hanging in space. This overhung load moves the end of the tube too much and it fatigues off after jerking the end bolt around pretty good. The solution is to press fit a piece of bar stock into the tube. Gun drill it lengthwise about 3/16ths inch for oil and drill in the bolt locations. This will stiffen the whole tube which will allow the overhung moments to be shared by all the fasteners.

There's no really good fix for the end pedestals once cracked as they are already overloaded, the "solid" core to the rocker shaft helps a lot but not enough to overcome the already existing crack in the pedestal.

Bogie
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Old 05-11-2011, 08:32 PM
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I was afraid you'd say that... was hoping this eng would stay together a bit longer. If the heads are junk, think a pedestal full of jb weld would hold a season? I could try to tig up the side as well. Working on an ls1 to take its place. Won't be ready till next year. Could also drop boost quite a bit. Just blew $150 on ss shim gaskets that aren't reusable.

Last edited by ForceFed86; 05-11-2011 at 08:41 PM.
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Old 05-11-2011, 08:42 PM
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Quote:
Originally Posted by ForceFed86
I was afraid you'd say that... was hoping this eng would stay together a bit longer. If the heads are junk, think a pedestal of jb weld would hold a season?
No there isn't that kind of strength in JB Weld, that's sending glue to do the job of a welder.

I could venture that maybe if you can get this real clean inside the crack, maybe it could be brazed. Weld is what's really needed but welding on cast iron isn't very often successful. On the other hand you can go ahead and run this with my suggested fix to the rocker shaft and see how long it goes. Or put a band clamp around the pedestal or drill it for a cross bolt with the shaft bolt torqued up might hold it together, talk about a ghetto fix.

Nice thing about aluminum heads is they weld pretty easy. A not so subtle hint for your choice in replacement heads.

Bogie
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Old 05-11-2011, 09:49 PM
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Originally Posted by oldbogie
No there isn't that kind of strength in JB Weld, that's sending glue to do the job of a welder.

I could venture that maybe if you can get this real clean inside the crack, maybe it could be brazed. Weld is what's really needed but welding on cast iron isn't very often successful. On the other hand you can go ahead and run this with my suggested fix to the rocker shaft and see how long it goes. Or put a band clamp around the pedestal or drill it for a cross bolt with the shaft bolt torqued up might hold it together, talk about a ghetto fix.

Nice thing about aluminum heads is they weld pretty easy. A not so subtle hint for your choice in replacement heads.

Bogie
Not trying to discredit your info it's great as usual.

This seems to be the fix all for the buicks. They claim it works better than the hardened aftermarket shafts. These together with some thing similar to what you are talking about would be ideal I'm sure. I could have been running cracked pedestals for the last couple years honestly. I never looked that closely at them.


http://www.rjcracing.com/RJC_Buick_P...ft_braces.html

I like the idea of a cross drilled small bolt. I think I'll try that with a stud setup. And rocker braces. I'm really not cranking out tons of RPM. hoping to keep it around 5800. (3.27 rear gear)

I know it is ghetto, but I am swapping over to LS1 soon and don't want to spend the money/time/labor for another set of heads. I've literally got $600 in the rebuild of this engine. Thanks so much for the input!

The little engine that could!





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Old 05-12-2011, 11:46 AM
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Well i have the studs and braces on the way. Also looking into sliding some stock down the rocker shaft.

Think I should bother with brazing? I have some silicone bronze welding rod that keeps giving me the eye in the shop. Think I should even bother with this? May hurt more than it would help? I'd think there woudl be some old timers on here that have made some "on car" weld repairs to cast heads before?
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Old 05-12-2011, 12:51 PM
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There are guys in my area that can weld that type of crack, but it takes the right type of welder, filler and experience.

Maybe you could add a strut from the boss to the valley area to stabilize the shaft boss???
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Old 07-12-2011, 12:40 PM
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Just thought I'd update this. I installed studs and rocker braces. No problems to date. I've put about 100 miles on the engine and 15 1/4 miles passes. On a side note I went 10.17, and 10.14 on my last 2 passes.

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Old 07-12-2011, 03:45 PM
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Quote:
Originally Posted by ForceFed86
Just thought I'd update this. I installed studs and rocker braces. No problems to date. I've put about 100 miles on the engine and 15 1/4 miles passes. On a side note I went 10.17, and 10.14 on my last 2 passes.

Great going, thanks for the feed back so much we talk about just disappears into the ether so you never know what the results are.

Bogie
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Old 10-02-2012, 12:36 PM
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Still running the cracked pedestals all through this season. I went from a 3.27 to a 3.08 gear and it slowed me down a bit. Still runs 10.3x at 134+ all year. And it cruises much nicer with the 3.08's. With the 28" tires I cam Cruise 50 at 1900rpm.
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Old 10-03-2012, 01:01 AM
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Quote:
Originally Posted by ForceFed86 View Post
Still running the cracked pedestals all through this season. I went from a 3.27 to a 3.08 gear and it slowed me down a bit. Still runs 10.3x at 134+ all year. And it cruises much nicer with the 3.08's. With the 28" tires I cam Cruise 50 at 1900rpm.
ouch man ive had to do the same repair on gn heads except they were aluminum gn1's except the peds didnt crack like yours did, they brocke clean off right below the threads for the bolt.

welding them back together wasnt to bad and to stop them from doing it again i setup the heads in the bridgeport and drilled the holes for helicoils and put them deeper into the pedestal

aparently it was a common thing with the gn1 aluminum heads and most guys would drill out the holes for helicoils and put them in deeper and this would stop the cracking
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