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Help!!! 454 BBC Bent Intake Pushrods

 
mikeyj350
I love my Chevy Chevette!
Posts: 6
Joined: 05/10
Posted: 05/27/10 07:12 PM

Hello guys, new to the forum here and I have a quick question. I've got a 1994 Suburban, 454 TBI that has been rebuilt by the previous owner approx 20k miles ago (so they say anyway, no reason to doubt them, but you know how that goes... :-/ ). The rest of the truck has 167k miles. Assuming it has been gone through, I have no clue what was done during the rebuild, however from an appearance and performance standpoint, I would say it is a stock rebuild if anything.

I've driven the truck for about a year and a half now with absolutely no problems. Yesterday I was towing home my new project car (96 caprice) with it and on the 20 mile highway drive home, it started missing all of a sudden. I made it home and started troubleshooting, and found the #4 cylinder was dead. I pulled the pass side valve cover and discovered the #4 intake pushrod was broken. I started pulling out the rest of the rockers and after pulling the other side also I discovered that ALL EIGHT intake pushrods were pretty severely bent. All eight exhaust rods seemed ok.

My question is, what the hell did I do? I swear I wasn't pushing it that hard while towing, but this is definitely the first significant highway load I have driven this truck with. Of course, I can go ahead and replace all 16 pushrods with new ones, but I'd like some advice as to what I can do to prevent this from happening again? Do I need to measure to make sure I get the correct length pushrods? Since they are all bent or broken, I can't measure to see what the intake rods were originally. Should I doubt the quality of workmanship for the rest of the rebuild job?

Lastly, is there a good way to fish out the remaining ~1" piece of pushrod that is still in the lifter valley? I can't see it anywhere, and I tried with a small magnetic tool but to no avail. I'm assuming my next step is to have to pull the intake?  Frown

Any advice or help from you guys is greatly appreciated! Thanks in advance! -Mike  

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Dave632
I mow my lawn and find Chevys
Posts: 2253
Joined: 07/08
Posted: 05/28/10 01:33 AM

If every intake pushrod is bent there is surely a problem.
Several reasons are possible. Wrong length pushrods, coil bind, valve guides frozen, cam installed wrong, excess timing chain stretch, cam gear broke, jumped cam timing.
The most likely cause is the valve hitting the top of the piston which could be caused by a couple of the reasons above.
Since it lasted 20K its hard to tell what happened.
I would surely at least pull the intake. Heads should probably come off too looking for valve to piston contact. If there is contact all camshaft components need to be looked at.  
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chevelle83
I mow my lawn and find Chevys
Posts: 2280
Joined: 11/09
Posted: 05/28/10 06:29 PM

if he had valve to piston contact I doubt it would have made it home. Yes you need to pull the intake and make sure you dont have any more metal in the valley.  You should go ahead an pull the lifters out one at a time and inspect them too. If valves were adjusted too tight this could have been a problem.  I would probably pull the timing cover to make sure you did not jump timing.  However this is not a valve interference engine.    after you get the engine back together turn it by hand and make sure that there is no binding in the valve train.  

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mikeyj350
I love my Chevy Chevette!
Posts: 6
Joined: 05/10
Posted: 05/29/10 12:18 PM

Alright, so today I got it all taken apart. The timing chain was still properly lined up so it didn't jump time, and I pulled the cam out and mic'd the lobe lift and it appears to be a stock cam. Other than the bent intake rods mentioned earlier, everything else during disassembly looked fine. In fact, it's clean as a whistle in there, I do indeed believe now that the engine was definitely rebuilt recently, or else someone changed oil every 2500mi and used mystery oil additive Smile

I had an idea. Is it possible that when they rebuilt the engine that they milled the heads and/or decked the block, which would have lessened the distance from cam to rocker arm, thus requiring shorter pushrods? Maybe they just used stock-length rods and so it was barely out of whack. Then when I used it for a heavy tow they finally gave way?

One last thing. I am STILL unable to find the small ~1" piece of broken pushrod that _has_ to still be in the engine. I'm wondering if it's possible that it fell down past the cam (since there is a slit opening running the length of the lifter valley over the cam) and into the oil pan? Getting sick of chasing this damn pushrod fragment from the valve cover all the way to the pan, but I suppose leaving it in there is not an option. Mad

I'm planning on seizing this opportunity to replace the cam with a mild cam, low RPM range but more duration and lift than stock (was thinking about this one: http://www.summitracing.com/parts/SUM-K1300) and a double roller timing set. Then I think my next step is to get an adjustable pushrod measuring set (http://www.summitracing.com/parts/CCA-7705) and figure out how long the new rods need to be.

Am I on the right track now? Anything else I should look for or try now that I have this all apart?  

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chevelle83
I mow my lawn and find Chevys
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Joined: 11/09
Posted: 05/29/10 05:49 PM

that sure is a bummer to have to tear that motor down for that.  At least there is no major damage.  If you only use a mild cam you should not need shorter pushrods. It is a good idea to go ahead and check them out though.

I Hope the piece of pushrod is in the pan and didnt get caught in the rotating assembly on the way down, I would pull the pan and inspect everything well, before you re assemble.  

 It appears that you have covered it well. that cam looks like good choice for your engine.  I use diesel engine oil for flat tappet cams.  

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idrivejunk
I mow my lawn and find Chevys
Posts: 5119
Joined: 12/09
Posted: 05/29/10 06:05 PM

I'll jump in and say, since I have nothing to lose, that I dropped a bracket bolt (about 1") down my SBC dist hole one day. Proceeded to put about fifty thousand more miles on it, and when the next owner tore it down he goes "Heres your bolt back". My money says it won't hurt anything to leave a 1" piece of pushrod alone. If you were wheelstanding, maybe. Stick a big magnet on the pan if you want. Just wanted to put that out there, to help maybe make the decision to do all that work. Or not.

Also, I have had an old nylon toothed timing set give out on me (yes I pulled the pan and cleaned it out that time) and found 11 bent pushrods. Ran great after replacing the chain set and pushrods. That was a low-dog 307 though.

+1 Chevelle on using the right oil for flat tappet engines.  
idrivejunk

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gettnlarge01
I mow my lawn and find Chevys
Posts: 3330
Joined: 09/09
Posted: 05/29/10 06:11 PM

LOL,,,too funny idjunk  
luck is when skill and opportunity meet

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idrivejunk
I mow my lawn and find Chevys
Posts: 5119
Joined: 12/09
Posted: 05/29/10 07:14 PM

Hi gettn! Good 2CU Smile I heard it hit the pan, so I knew where it was Wink  
idrivejunk

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Dave632
I mow my lawn and find Chevys
Posts: 2253
Joined: 07/08
Posted: 05/30/10 07:08 AM

Pushrods don't bend for no reason.
Is it possible some severe duty springs were put on the motor when rebuilt?
This could cause stock pushrods to bend.
I ran some stock pushrods with some healthy springs way back and I bent some pushrods that way. I would pull a couple of springs and have them checked for closed and open pressure.
That would also answer the question as to why it lasted a year and a half.
Chrome Moly pushrods are available in different lenghts at reasonalble prices.
If you are using an adjustable pushrod be careful, some are not meant to be used with regular springs. A special light duty valve spring must be used for checking purposes.  
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mikeyj350
I love my Chevy Chevette!
Posts: 6
Joined: 05/10
Posted: 05/30/10 11:40 AM

Ok, I've ordered the cam, a gasket set and the adjustable rods. Dave, I also ordered a set of the low-tension valve test springs and will use those for my test. Do I need to measure all eight cylinders to make sure one isn't different than the others? My gut says pick a cylinder and just use that one for testing. While the springs are out I'll bring them to my local machine shop and see if they can load test them. Then I'll order up some pushrods and hopefully I'll be good to go!

Last thing.. I've heard of using diesel oil before too (rotella?)... why is that? This engine came stock with a flat tappet cam, am I changing anything with this new aftermaket one? I've always used regular automotive Valvoline 10-30 and never had a problem. What's the difference with the diesel oil?  

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Dave632
I mow my lawn and find Chevys
Posts: 2253
Joined: 07/08
Posted: 05/30/10 03:46 PM

When checking pushrod length I only checked one cylinders intake and exhaust.
I am not familiar with using the diesel oil. It must have some additive that helps break in.
I had so much trouble with flat tappets and high spring pressure I stopped using them, went with roller cams and never went back to flat tappets.  
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chevelle83
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Posted: 05/30/10 05:24 PM

diesel oil still has some zinc and phosphorus and is good for flat tappets.  Tractors are still flat tappet too and they need it.  It just makes the cam last longer.  

 As far as emissions go I dont think it is good for catylitic converters.  I have not tested this, all of my old rides dont have any smog equipment.  

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tuffnuff
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Posts: 7841
Joined: 12/09
Posted: 05/30/10 06:04 PM

Icon QuoteDave632:
When checking pushrod length I only checked one cylinders intake and exhaust.
I am not familiar with using the diesel oil. It must have some additive that helps break in.
I had so much trouble with flat tappets and high spring pressure I stopped using them, went with roller cams and never went back to flat tappets.


I agree, all things being equal, checking one will either be a go or no go,,, unless it's a radical cam, and then it's best to check everything from rocker slot/travel, retainer/guide clearance, coil bind and pushrod geometry.
I went to rollers too because I was afraid of the "side load" on the passenger side (lifter bosses)of the block, with BIG flat tappet cams.
High pressure tripple springs and flat tappets are not my choice either,,, but there are guys that get away with it.
I prefer to run a rev kit and take some load off the valve springs.
In fact I even run 7/16" pushrods on my Big Blocks for better load stability and less flexing.
Grin  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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mikeyj350
I love my Chevy Chevette!
Posts: 6
Joined: 05/10
Posted: 06/07/10 07:12 AM

Alright, finally have an update here. Went through a ton of theories and finally figured everything out this weekend. Long story short, the whole motor has been pulled out of the truck and I will be doing a complete rebuild.

It all started when I finally decided to pull the heads off. We couldn't come up with a definitive reason as to why the pushrods were bent, and so to be on the safe side I wanted to bring the heads into my guy at the machine shop and have him take a look. Turns out the heads are completely stock and most likely original. The intake valves were slightly bent from hitting the pistons (still held a marginal seal, enough for the engine to run but not perfectly). This was strange to me though, since the timing chain was still in place and perfectly lined up. Things didn't make sense until I pulled the pan off to try and find that last broken piece of pushrod. Found LOTS of little pieces of broken plastic. Seems now that the previous owner threw the original timing chain and didn't clean up after himself when he replaced the chain.

So the final theory is: Timing chain let loose approx 10k miles ago, right before I bought it. Pistons hit the valves and slightly bent the intake valves and pushrods. Previous owner slapped on a new chain, called it "10k miles on a rebuild" and sold it to me. I drove it for 10k miles myself and the pushrods continued to bend under normal operation. The final blow to it all came while towing home that project car-- the added load, heat, and RPM's were the last straw and one finally broke.

Does this sound like a good theory?

The motor is at the machine shop now and I'm getting the works done to it... going to do this the right way and hopefully walk away with a stout 454 (or 496?  Grin ) that should last me another 200k miles.  

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tuffnuff
Moderator
Posts: 7841
Joined: 12/09
Posted: 06/07/10 07:55 AM

Yup,,,
That exolains the whole story in a nutshell.
Valves and pushrods don't bend unless there is interference of some sort.
Your theory is accurate, from the evidence in the pan.
Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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