# BOOOOOM says the gto



## tyler t (Aug 15, 2010)

took my 69 to the DMV 40 miles away. longest trip so far. shut the baby off and she diesels for i a good 5 or 6 seconds. come out of the dmv 40 minutes later. fire her up and she went boom. crank case back fire. blew the valve cover gasket out and the vally pan seal out. smoke was every where.drove the same as befor execpt for the pungent smell of. oil get it home. take the intake and vally off and what do i see? 2 broken / bent push rods. one lifter came apart and the other is dented and the little piston on the lifter is cockeyed and stuck in there. *I* think the pushrod might have been pluged with who knows what. and the rocker arm seezed. any body have this same problem before? is there another reason reason it would do this? keep in mind this is a built 1970 455 HO with less than 100 miles on it


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## freethinker (Nov 14, 2009)

tyler t said:


> took my 69 to the DMV 40 miles away. longest trip so far. shut the baby off and she diesels for i a good 5 or 6 seconds. come out of the dmv 40 minutes later. fire her up and she went boom. crank case back fire. blew the valve cover gasket out and the vally pan seal out. smoke was every where.drove the same as befor execpt for the pungent smell of. oil get it home. take the intake and vally off and what do i see? 2 broken / bent push rods. one lifter came apart and the other is dented and the little piston on the lifter is cockeyed and stuck in there. *I* think the pushrod might have been pluged with who knows what. and the rocker arm seezed. any body have this same problem before? is there another reason reason it would do this? keep in mind this is a built 1970 455 HO with less than 100 miles on it


its not from a plugged pushrod. you probably have clearance problems. need more info and a picture of the rocker would help.
when you say built what do you mean?whats been done?


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## Rukee (Feb 8, 2007)

It drove the same way as before?? Even with those broken parts?? If so, then they must have been bent up before the trip. 
After fixing the broken parts, you need to address that dieseling issue. That can cause excess gas to pool in the cylinders. Might be due to a high idle, carb issues, improper timing, running too hot, etc.


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## freethinker (Nov 14, 2009)

i would be careful driving it until i figure it out. thats serious breakage. if its a valve clearance problem the engine could self destruct.


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## ALKYGTO (Mar 29, 2010)

Was the car running rich or any problems previous to this with starting or drivability? 

The cylinder could have filled full of fuel and it could have hydro-locked the motor hence the bent pushrods.


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## dimitri (Feb 13, 2009)

When was the engine rebuilt?? Has it been sitting around long?


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## Bensjammin66 (May 12, 2009)

When you or whoever first fired the engine did you adjust the rocker arms hot or cold? Looks like you did them cold and never went back and set them hot and when they pumped full of oil they bent and broke those push rods. Thats serious boom. Unreal you drove it home. Rukee is right, the damage has been there all along.


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## tyler t (Aug 15, 2010)

:shutmeits not a clearance issue. ive checked all my clearances. and i torques the rocker arms while it was warm. it was built in the early 90's and sat untill my grandpa gave me the car. i went threw it checked clearances. and put it in the car. i broke it in and tightened the rocker arms. i had to pull the intake and vally before cause of a minor leek and everything _*looked *_ perfect. the motor is a 455 HO bored 60 over, with ram air 3 heads, a mild cam, sodium filled valves, and hardened exhaust seats. its been ported (i think thats the right term when they inlarge the intake and exhaust ports), it also has a Elddlebrock performer series intake and carb. and i'm using the MSD 6A box. i was told that it has 10.5-1 compression timing is set at 8 Degrees


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## tyler t (Aug 15, 2010)

it dosent like starting warm but cold it fires right up* and you can see it in my video in my signature


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## dimitri (Feb 13, 2009)

You adjusted the rockers wrong. To correctly adj the rockers you do them cold would have been zero preload plus 1/2 turn. Also did you squirt any oil in the spark plug holes and let it sit for a few days before you bar it over? If you did not the rings could be shot and this is causing your blow by. 

Maximum engine compression ratio with premium pump gas is no more that 9.5 to 1. If it does have 10.5 to 1 you can do some real damage to the engine running pump gas.


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## tyler t (Aug 15, 2010)

yes i lubed the cylnders. i only have one vent from the vally. i dont think it was pulling enough out. im going to buy another breather. is 8 degerase the proper timing? thats what my caM box said. rocker arms were torqued to 20 ft lbs. there not adjustable


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## dimitri (Feb 13, 2009)

Get a new set of steel locking nuts for your rockers. Go to Comp Cams website and you can find instructions on how to properly adjust your rocker arms. It is important that you use steel locking nuts for the rocker arm adjusting nuts.


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## tyler t (Aug 15, 2010)

ok thanks for your advice


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## PisnNapalm (Aug 28, 2010)

I'll vouch for the Comp Cam adjustable locking nuts. Very easy to install. I also put the Comp Cam roller tip rockers in my engine.

Good luck to you in getting it running properly again.


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## BearGFR (Aug 25, 2008)

tyler t said:


> yes i lubed the cylnders. i only have one vent from the vally. i dont think it was pulling enough out. im going to buy another breather. is 8 degerase the proper timing? thats what my caM box said. rocker arms were torqued to 20 ft lbs. there not adjustable


 Definitely WAY too tight! That's not how you do it, and that's probably what caused your backfiring problems and also to bend and break things. You didn't say whether you have a hydraulic or a solid lifter valve train, so I'm assuming hydraulic here. With the factory rocker balls the correct procedure is to 1) make sure the cam is on the base circle for the valve being adjusted, 2) slowly tighten the rocker nut until you can feel that all the slack has been take out (just barely to the point where you can no longer "spin" the pushrod with your fingers) 3) tighten the rocker ball nut an additional 1/2 turn. Do all 16 valves that way, rotating the engine a little bit at a time for each one to make sure the lifter is on the cam base circle. Completing the sequence requires two complete crank revolutions. Those nuts are 'crimped' so that they shouldn't loosen. If they do, then they're worn out and need to be replaced. If replacing the nuts doesn't do it, then the studs themselves are worn out and must be replaced also.

Running a solid lifter valve train REQUIRES fully adjustable "poly lock" nuts as a previous poster mentioned. Poly-locks can be used with a hydraulic valve train too, but the adjusting procedure is the same as for the factory rocker nuts. The only difference is that the poly-locks are easier to keep the setting "locked in".

Also, cam timing and ignition timting are two completely different things. The best way to set ignition timing is to set TOTAL advance to 32-36 degrees (engine running at 2800 rpm or more, vacuum advance disconnected, while you're setting it). Cam timing (which is what the cam manufacturer was probably referring to) is set at the time the cam is installed. Doing it correctly requires a degree wheel, dial indicator with mount, and either a selection of offset crank/cam keys or an adjustable timing set.

With damage like you described, there's a good chance that you've also damaged some of the lobes on the cam itself. The only way to be sure is to check each lobe profile with a dial indicator set up to verify that the lobe lift and timing events still match the cam manufacturer's specs, and also visually inspect the lobes themselves for physical damage/gouges. I'd also inspect all the lifter bores to make sure you haven't cracked or otherwise damaged any.

Bear


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## Indecision (Oct 24, 2010)

BearGFR, great post!


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## tyler t (Aug 15, 2010)

dont mind me i dont know what im talking about. there adjustable and thats what i torqued to 20 ft lbs. the cams fine and so is everything else. the back fire was caused by the lack of crank case ventilation and not having a pcv valve . and the pushrods were bent from the improper valve lash adjustment. its all good now. its all back together in the car. my fault for not reading the torque specs correct. it says 20 ft lbs for (non adjustable rockers) so how it that "Way too thight"?


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## BearGFR (Aug 25, 2008)

tyler t said:


> dont mind me i dont know what im talking about. there adjustable and thats what i torqued to 20 ft lbs. the cams fine and so is everything else. the back fire was caused by the lack of crank case ventilation and not having a pcv valve . and the pushrods were bent from the improper valve lash adjustment. its all good now. its all back together in the car. my fault for not reading the torque specs correct. it says 20 ft lbs for (non adjustable rockers) so how it that "Way too thight"?


It just doesn't make sense that even severe crankcase pressure would cause a backfire. I'd be very suspicous of whoever is telling you that.

Where are you getting your information about "torque to 20 ft lbs"? That's suspect because any torque reading you're able to get on the rocker ball nut is going to be influenced by valve spring pressure and the "tightness" of the crimp on the nut itself. What you're trying to accomplish by setting the "lash" on a hydraulic lifter isn't really "lash", it's lifter preload. You're trying to set the lifters so that the small hydraulic piston inside each lifter is adjusted so that it rides on a cushion of pressurized oil throughout the engine's rpm range - tight enough so that it doesn't bump into the snap ring at the top of the lifter's outer body (so it runs quietly and doesn't "tick"), but not so tight that it bottoms out inside the lifter body (and in so doing screws up valve timing, bends pushrods, and damages other valve train parts). The spring inside each lifter and the various oil holes are calibrated to allow this internal piston to "float" on a cushion of oil at a constant height, provided that the spring preload is properly adjusted. The proper way to adjust them is to follow the method I posted previously. Trying to use a torque wrench won't give you a consistent and reliable result, cylinder to cylinder.

The fact that you were getting backfiring and also bent pushrods is what tells me you had them adjusted "way too tight". You were driving the valve springs into coil bind, meaning that the valve springs physically could not compress any further, and still trying to push them more so something had to give - in this case, that meant the weakest link in the chain - the pushrods bent. Having them that tight also meant the intake valves were closing extremely "late" in the cycle, perhaps even not completely closing at all, by the time the spark plug fired - and that's what caused your backfire.

Bear


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## tyler t (Aug 15, 2010)

Pontiac 265 307 326 350 389 400 421 428 455 V8 Engine Specs-Torque Specs-Cylinder Numbering-Firing Order-Distributor Rotation the back fire did not shoot out of the carb. it happened in the CRANKCASE from not having any ventilation. how could improper timing cause a crankcase back fire? i completely understand how it could cause a, more common backfire with flame shooting out of the carb . im sure your right about the torque specs and ive now learned the hard way how to "properly" adjust vale lash. thank you for your expert engine advice. im glad somebody with your knowledge and experence would chose to share it with others on this site


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## BearGFR (Aug 25, 2008)

tyler t said:


> Pontiac 265 307 326 350 389 400 421 428 455 V8 Engine Specs-Torque Specs-Cylinder Numbering-Firing Order-Distributor Rotation the back fire did not shoot out of the carb. it happened in the CRANKCASE from not having any ventilation. how could improper timing cause a crankcase back fire? i completely understand how it could cause a, more common backfire with flame shooting out of the carb . im sure your right about the torque specs and ive now learned the hard way how to "properly" adjust vale lash. thank you for your expert engine advice. im glad somebody with your knowledge and experence would chose to share it with others on this site


I'll have to check my Pontiac Factory service manual when I get home and see what it says... Over the years I've learned to be veeeery careful of non-factory information sources.

I'd never heard of a crankcase backfire before, so I did some research. One of the things I found was pretty alarming. Pull your dipstick and see if you can detect the smell of gasoline in your oil. Having a leaky fuel pump diaprhagm and gasket can allow the pump to dump fuel into your oil pan (so can a stuck/misadjusted carb float, cracked carb body, etc.). Needless to say, having gasoline in your crankcase can be pretty dangerous - and is something that you'd want to fix immediately.

Bear


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## tyler t (Aug 15, 2010)

i tore the motor down and there was no gasoline in the oil. i think it sucked fumes in from not running a pcv valve and went off like a bomb in the crank case. its all back in the car and now im running a new breather and a pcv valve. havent started it yet tho


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## BearGFR (Aug 25, 2008)

tyler t said:


> i tore the motor down and there was no gasoline in the oil. i think it sucked fumes in from not running a pcv valve and went off like a bomb in the crank case. its all back in the car and now im running a new breather and a pcv valve. havent started it yet tho


Thinking about it, I guess that makes sense. "Usually" there's vacuum in the manifold that's going to be pulling air/gasses out of the crankcase and into the manifold. At WOT or extremely low manifold vacuum (or perhaps when the engine isn't running) I can see how gas vapors could get into the crankcase --- gasoline vapors are heavier than air so they'll tend to run "down hill".

Bear


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## tyler t (Aug 15, 2010)

yeah and im sure the deiseling didnt help


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