Bad Luck is Better Than No Luck; Right?

[cook_dw]

Last Friday I had the exhaust installed on the car which took all day but thats wasnt a big deal. Car sounded great (sorry no video yet) so I pulled it off the trailer and into the garage. Saturday morning I started having issues with idle and backfiring through the carb and dying. Figured it was just where it had been sitting for so long so I took it for a short ride around the neighborhood. As I am pulling back into the drive it acts like it is flooding and dies. Get it started back and pull into the garage, get out and pop the hood to rocker arm noise. I pull the valve cover and this is what I find. 4 of the 8 exhaust pushrods are destroyed on the rocker arm side. 3 on pass bank and 1 on drivers. I did not build this engine and what little I know about it doesnt give the enough info to determine the cause. So first things first is to check pushrod length and go from there. I really dont want to pull the engine out before I have a chance to drive it at least 100 miles.. Awesome luck dont you think...

[Mike S]

What size motor and who assembled it?

Mike

[cook_dw]

396 & the guy who had the car previously

[ko-lek-tor]

Many things come to mind. Very hard to give opinions from far away though. I have seen old gas, more so with newer type gas blends, cause gumming and sticking valves. This could have caused the valves to hit piston tops and an interference that caused damage. I have seen one head milled more than another causing geometry problems. I would use an indicator to determine Cam dimensions by setting the plunger on the retainer and setting lash to zero (may have to bottom out Hyd. lifter). If cam seems to indicate a high lift (.550 or larger) I would use a rocker mounted spring compressor  and install a set of light springs using indicator you can check for valve to piston clearance. Lastly, while the original two springs are off, have them tested for spring rate. Floating a valve on Big Blocks are more common, since the components are heavy and springs lose tension quickly. It could be floating the valve and damaging pushrod.

[Mark]

How long has that engine been running since it was done being assembled?  Looks like there is some kind of heat discoloration just below the current end of the pushrod.

[cook_dw]

Already thought of all that as well.  Just irritated and wanting to vent.  lol  I will figure it out just not what I wanted to do on a fresh (8 year old built) engine..

Engine was broken in back then and had sat unstarted since 2006.  I would turn it over from time to time by hand.  Engine sounded fine when I fired it for the first time since and just a few weeks ago I noticed rocker noise and adjusted them then.  Now I know why there was noise the first time.  Its just odd it was only the exhaust and no intakes...

FYI the pushrods that were pulled out are 1010 mild steel.  Comp Magnum roller tip rocker.  Cam I am guessing by ear is either a .520 or .570ish lift cam (I am leaning to the more .570ish lift due to the radical sound).  Hyd flat tappet (that I do know).

Odd thing is the lifter side of the pushrod is fine.  Just the rocker side is damaged.  Almost like it was starving for oil.  Right now I want to make sure the geometry is correct and look for coil bind (which I do not think it has).

As far as runtime...  Other than break-in it has run maybe an hour if that.


No smoke and plugs look good except for the ones that had the issue which were a little fat but nothing major.

[Mike S]

I had a feeling it was a BB being they have two different size push-rods. You may also want to check for any bent rocker studs.
I recommend to drop the pan to check for metal chips in case some are small enough to get pulled past the oil pump intake screen.

Mike

[ko-lek-tor]

I had a feeling you were just venting as I think you are about as savvy a Chev guy as they come. I also know you already had thought of all I suggested too. Some of those P-Rods have one end hardened for the guide plates. May have been installed wrong? I had a P-Rod shatter on the lifter end once. Usually, gasoline or geometry causes bent P-rods. I have also seen some Sm. Blocks P-rods go through the rocker. Are the P-Rods 5/16, 3/8 or 7/16 in.?

[janobyte]

Ever wipe a cam out ? same symptoms---strange only 4 of ehaust push rods. Checking your timing gear set.


400 68 GTO I had---nylon timing gear set ,severe carb back fire ,guess what??

 one of my SBC's severe carb back fire---cam wiped out ,a few bent push rods.

Both spit up raw fuel through the carb. Both I shut down ASAP with minimal damage. On the chevy, dropped the pan checking for shrapnal, minimal ,most caught by the filter ,changed the cam push rods etc ,ran it hard after that for about 10 years. Blocks now at home in the Anglia ,rotating assembly boxed up.

Really what else could it be but bad cam timing ? Only the upward force of the piston would be strong enough to bind those pushrods and big blocks are ,er ,BIG. Let us know--steve.

[cook_dw]

I had a feeling it was a BB being they have two different size push-rods. You may also want to check for any bent rocker studs.
I recommend to drop the pan to check for metal chips in case some are small enough to get pulled past the oil pump intake screen.

Mike

Ill see how it goes.  No plan of dropping anything at this point.  If I do drop the pan the engine will come out first.  

I had a feeling you were just venting as I think you are about as savvy a Chev guy as they come. I also know you already had thought of all I suggested too. Some of those P-Rods have one end hardened for the guide plates. May have been installed wrong? I had a P-Rod shatter on the lifter end once. Usually, gasoline or geometry causes bent P-rods. I have also seen some Sm. Blocks P-rods go through the rocker. Are the P-Rods 5/16, 3/8 or 7/16 in.?

3/8" and case hardened..

[cook_dw]

Ever wipe a cam out ? same symptoms---strange only 4 of ehaust push rods. Checking your timing gear set.


400 68 GTO I had---nylon timing gear set ,severe carb back fire ,guess what??

 one of my SBC's severe carb back fire---cam wiped out ,a few bent push rods.

Both spit up raw fuel through the carb. Both I shut down ASAP with minimal damage. On the chevy, dropped the pan checking for shrapnal, minimal ,most caught by the filter ,changed the cam push rods etc ,ran it hard after that for about 10 years. Blocks now at home in the Anglia ,rotating assembly boxed up.

Really what else could it be but bad cam timing ? Only the upward force of the piston would be strong enough to bind those pushrods and big blocks are ,er ,BIG. Let us know--steve.

Already checked timing.  Cam lobe was the first thought until I saw the pushrods.  After finding 4 I doubt its the cam.  One I would have thought that but not 4..  But I have been wrong before..

[z28z11]

Darrell,

What compression ratio and piston are you running ? Any specs left by the builder ? I remember hearing this engine run on a couple of occasions - sounded great then, but maybe when you actually got to drive it, the higher RPM got some valves into the pistons ?

I doubt oil starvation would have taken them down this quick - more likely impact. Could be wrong piston/valve relief for the cam lift -

Regards,
Steve

[cook_dw]

They are 11 to 1 TRW pistons and its oval port open chamber heads.  As for actual compression I am guessing 10 or 10.5 to 1 with the heads.  I dont think valves have hit the pistons (might be wrong).  Ill be doing a leak down test later in the week along with a compression test just to be on the safe side.  Most RPM this motor has seen is 5K.  At least with me.

[ko-lek-tor]

My experience with 11:1 slugs (closed chamber) are they were meant for square port heads. The corner of the dome will hit the combustion chamber on oval ports. Are the pistons made for oval ports? Not that this would cause your problem, just an observation and my knowledge of these engines. Back when I was a teen, a guy (kind of a butcher, I will add) told us he did this piston swap all the time and just revved the engine to shave off that little corner that hit. I have a set of pistons that had "gone through this treatment". Like Janobyte, I am suspect of a timing problem or a geometry problem. Can you take a pic of all affected PRs along with an undamaged? It might shed a little more light?

[z28z11]

The remark earlier about the weak spring installation might be a good crosscheck to see just how much lift you can get away with. Piston at TDC, depress the valve until it makes contact, and measure. What ratio are the rockers ? Cam could be stout enough (and I remember the idle) to play hell with the pushrods if the valves come anywhere close to the pistons.

At least it's apparently just pushrods - I've seen BB internals when you hydraulic a piston - rods look like corkscrews, or grenade through the motor.

Regards -