Bent/broke push rod

[Mike1973]

1984 GMC 3/4 ton 2WD 454 c.i.

With no signs of trouble in the past I started the truck and right away noticed that the starting sound seemed a little high pitched (like when your flex plate rubs on the tin shield covering the conveter although the sound wasn't quite as screechy.)  The motor had a miss on the way home and I also noticed a popping sound under the truck.  I did some trouble shooting and pulled the valve cover, I found 1 broken and bent exhaust push rod (exhaust I'm pretty sure...it goes E-I-I-E-E-I-I-E right?)  So am I to assume that if I'm correct and it is an exhaust rod then that popping noise that is primarily heard in the pass side muffler (same side as my valve train issue) is due to a bent valve allowing exhaust out at the incorrect time?  Further, I'm a little stumped as to why this happened, 80,000 original miles, very clean and always well maintained truck/motor (the cylinder head rocker area is void of ANY deposits what so ever.  I'm going to do a compression check I just need to pick up the gauge (not something I really ever had much of a call for.)  I'm just a little stumped because pushrods don't just break for no reason.

Thank you for any help, hopefully I'm not omitting anything right off.

[winky]

I've had them bend / break for no apparent reason happend in my mud truck. Used a magnet pulled the broke one out put one in I had laying around and never had another problem. But I'm also replacing a cam right now due to push rods breaking. With yours being low millage I would just throw one in it and see what happens. If it bends or breaks then my guess would be a lifter. Also if it is broke that valve wouldn't open at all. Your correct on eiieeiie but I would double check. A broke exhaust rod usually doesn't allow pressure to escape untill the intake opens again causing a cough or knocking noise threw the carb

[Mike1973]

Thank you Winky, I'm going to try just buttoning it back up and giving things a try.  Here is a question, everyone sells stock length 3/8 pushrods but I'm not finding narrower rods (these are as narrow as a SB it looks like anyway.)  The big pushrods won't clear my guide plates of course.  Any idea on a quick place to order a basic pushrod set for this application?

Thanks in advance...Mike

[VileZambonie]

Check lobe lift and valve adjustment. What type of cam is it? Did you adjust the valves? Is it stock?

[Mike1973]

100% origional motor Vile.  A friend brought over a BB pushrod but it was 3/8th (larger than what is in there and... "I'm not sure where this came from dude but I know it's big block Chevy") and it didn't fit through the guide plate of course.  Another question, thoughts on leaving a 3" piece of pushrod in the lifter valley?  I'm not opposed to pulling the manifold of course just looking for thoughts.

[Mike1973]

I'm actually a bit confused, the exhaust pushrod (which should be longer) measures 8.250, isn't that one suppose to be 9"+?  I took this pushrod out under the first rocker at the front of the motor.....The next one over is 9.375??  there also seems to be a fairly large amount of bluing (heat) through the middle 2.5"-3" of both pushrods.

[VileZambonie]

what's the casting # on the heads and block? Either way you need to run the engine and ensure your oiling is making it up to the valve train. If it is pull the heads and yes remove the broken pushrod. The pushrod bent most likely due to a sticking valve or a piece of carbon in the combustion chamber etc. Bottom line is you should pull the heads and rebuild them or upgrade them.

[Mike1973]

1984 GMC 3/4 ton 2WD 454 bbc 80,000 miles

After some quick trouble shooting I've found that an intake valve was stuck and it took considerable pressure to move it down through the guide after I removed the spring.  I tried the old trick of making a cup, siliconing it over the guide and filling the little cup in this instance with PB Blaster.  I tried that for about 48 hours with no luck.  I removed the head and after having it on the ground I can see that the intake valves are heavy with varnish...and not just varnish but almost to the point of being gummy and somewhat thick.  With the head on the ground and access to both end of the valve it took about 10 minutes with PB blaster to get the valve free to the point of normal operation.

Here's the million dollar question, What happened or what caused this? 

the truck is in amazing original shape and the motor has never been messed with, the inside of the motor is spotless.  The truck ran totally fine up until the point of breaking the push rod.  I would like to avoid pulling the other head but I can see down to the intake vales on the head of course and they are equally gummed up (although not stuck at this point.)

thoughts?  PB Blaster the crap out of the removed head and PB blaster down the runners of the head on the still installed head?Thoughts on the idea of getting it loosened up button up the motor and slowly drizzling transmission fluid down the carb while running?  Drizzling water down the carb while running? I guess at the end of the day like I stated above is why did this happen so that I can avoid it happening again.  I bought the truck not too long ago so I don't know as far a oil what the guy used but I switched over to Rotella 10/30. 

[VileZambonie]

Read the post above. Ensure you have oiling to the valve train and if it's good you're safe to replace or recondition the heads. You have a 30 year old engine - It's bound to need a valve job by now even if you think 80K is low miles

[Mike1973]

Well low miles considering the year anyway.  yeah doing a valve job would probably be good practice no doubt.  Of course it's against my better judgement but I'm probably going to forgo that, I don't know...my Dad has a 454 in a pristine 76 Suburban with 180,000 miles and nothing....nothing has ever been touched.  I'm going to go ahead and disassemble and clean it up.  Let me ask this, Replace the lifters while keeping the cam that's in it, bad practice or reasonable? (I am replacing the timing chain.)

[zieg85]

I am going to throw my $.02 in... May be that one oil or more oil changes were beyond the oils life??  I know in my air cooled engine on my garden tractor I made the mistake of not changing the oil soon enough, it was fairly clean but it gummed up the valves, bent a pushrod and same thing basically.  454's work hard and run hotter.  Not saying the proper PM's weren't done according to the book... Just sharing what happened to me.

[Mike1973]

I am going to throw my $.02 in... May be that one oil or more oil changes were beyond the oils life??  I know in my air cooled engine on my garden tractor I made the mistake of not changing the oil soon enough, it was fairly clean but it gummed up the valves, bent a pushrod and same thing basically.  454's work hard and run hotter.  Not saying the proper PM's weren't done according to the book... Just sharing what happened to me.

Couldn't agree more, although everything seems to be in great shape the gumming up can certainly be an indication.  Like I said, I'm fairly new to the truck, an old guy owned it and although seems to be well taken care of he could have used up the oil pretty good.

[VileZambonie]

You have to u understand it's not about miles as much as how much it sat, moisture, fuels, carbon, oils especially the oils it used in its early life etc.

You can replace the lifters just ensure you coat the feet of the lifter with moly lube and treat it like you are breaking in a cam. After your break in, change the oil and add an engine oil supplement like EOS

[Mike1973]

You have to u understand it's not about miles as much as how much it sat, moisture, fuels, carbon, oils especially the oils it used in its early life etc.

You can replace the lifters just ensure you coat the feet of the lifter with moly lube and treat it like you are breaking in a cam. After your break in, change the oil and add an engine oil supplement like EOS

Vile...Darn you...Darn you!  After wringing my hand about it the last two days I know if I buttoned this thing back up without having a valve job done I'd regret it about the time I torqued the last head bolt.  Thank you for the guilt intended or not   I have a quart of EOS and I'll use it.  Your thoughts on head gaskets, I'm going with Fel-Pro, should I just go with the "blue" standard lower end one?  The gaskets I pulled off where all metal, suggestion and part # for the Fel=pro I should use?  I'm switching out the guide plates (5/16th to 3/8th) rocker stud torque 50 lbs?  Lastly, thoughts on new aftermarket head bolts?  I don't know, I've cleaned the bolts/holes on motors in the past and reused but I've found a new set for 30 bucks...Could the "gummin up" issue be due to sludge-like crap at the bottom of the fuel tank?  The motor ran perfect so I would have thought I would have had carb issues before this happened if good gas mixing with crud at the bottom of the tank was the issue.  I'm still a little nervous as to what the cause of the sludge on the valves is.  If the inside of the motor had looked the same (old oil issues) I could roll with that but it's totally spotless.

Thanks for continuing to follow this thread, you've been very helpful. 

[VileZambonie]

Use the good Felpro gaskets don't bother with steel gaskets and if you are replacing the headbolts ARP is good. Liquid Teflon is good too on the bolt threads