Misfire 1971 Pontiac 455 YC Block

PontiacJim said:

OK. Then my money would be on the poly lock being incorrectly adjusted just a little too tight and holding the valve open just enough so it does not seat tightly.

When you back the poly lock nut off on the #7 intake and test for an air leak,and that does it, I would "zero lash" all the lifters/rockers on that side and then do the other side to ensure whoever installed them knew what they were doing. This is done while the engine is running for the best results - in my opinion & experience. Others adjust the lifters differently than with the engine running.

You also want to make sure you have the correct length body on the poly lock - they can be long or short. Look at the allen screw. It should not be sunk into the poly lock, nor should it stick way up and out. You want the allen screw to be somewhat flush at the top or just a thread or 2 above.

Here are a couple posts to read through that will help.

torquing rocker arms

I am putting my 326 back together and I have question on torqueing my rocker arms. The manual says to torque to 20#. Do I just go down the line and torque them all to 20 or doe the need to be preloaded and if so how do you preload.

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Compress lifters by hand - normal?

Hi gang, long time no post. I had my motor re-built quite a few years ago (2012). It sat till I finished my resto in 2015. Strong running, no leaks, plugs burning clean. I have been getting considerable lifter tap from the left bank and was preparing to do a cold engine overlap adjustment using...

www.gtoforum.com

Rocker Arm / possible collapse lifter??

Hello all - I have a conundrum here. My new complete rebuilt motor for 68' GTO, 400 MT came back with ticking noise I attributed to a loose rocker arm or bad lifter. After numerous consults, I adjusted all the rocker arms per the "twist push rod until tension and snug down 180deg. - NOT the...

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PontiacJim said:

OK. Then my money would be on the poly lock being incorrectly adjusted just a little too tight and holding the valve open just enough so it does not seat tightly.

When you back the poly lock nut off on the #7 intake and test for an air leak,and that does it, I would "zero lash" all the lifters/rockers on that side and then do the other side to ensure whoever installed them knew what they were doing. This is done while the engine is running for the best results - in my opinion & experience. Others adjust the lifters differently than with the engine running.

You also want to make sure you have the correct length body on the poly lock - they can be long or short. Look at the allen screw. It should not be sunk into the poly lock, nor should it stick way up and out. You want the allen screw to be somewhat flush at the top or just a thread or 2 above.

Here are a couple posts to read through that will help.

torquing rocker arms

I am putting my 326 back together and I have question on torqueing my rocker arms. The manual says to torque to 20#. Do I just go down the line and torque them all to 20 or doe the need to be preloaded and if so how do you preload.

www.gtoforum.com

Compress lifters by hand - normal?

Hi gang, long time no post. I had my motor re-built quite a few years ago (2012). It sat till I finished my resto in 2015. Strong running, no leaks, plugs burning clean. I have been getting considerable lifter tap from the left bank and was preparing to do a cold engine overlap adjustment using...

www.gtoforum.com

Rocker Arm / possible collapse lifter??

Hello all - I have a conundrum here. My new complete rebuilt motor for 68' GTO, 400 MT came back with ticking noise I attributed to a loose rocker arm or bad lifter. After numerous consults, I adjusted all the rocker arms per the "twist push rod until tension and snug down 180deg. - NOT the...

www.gtoforum.com

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PontiacJim said:

OK, not sure why the change in the leak down with/without oil. Intake gasket seems odd as I am trying to figure how air can get past the valve and pressurize the intake passage. Still could be a cracked head?

You should have had oil pressure the pretty much the second the engine fired. Things to consider would be clogged oil pump pick-up screen if the engine had the nylon coated cam gear and the nylon bits began to deteriorate and fall off into the oil pan - it can clog the pick-up screen, faulty/wrong oil filter, oil too thick, worn oil pump, worn bearings having too much clearance, lifter bore restrictors, pushrods with the smaller holes to hold back oil, rocker arms too loose/too tight, collapsed lifter.

Did you think to observe the pushrods to see that they were all spinning with the engine running?

Have you checked your oil pressure? New oil filter? What brand? What oil weight? Most likely if the engine has never been rebuilt, you have the factory 40 PSI oil pump. So don't expect to see 55-60 PSI. If your oil pump is failing, or not pumping enough oil from the pan, then it would not provide the needed oil pressure going to the lifters and if the lifters were not being fully oiled, this could affect the opening of the intakes and exhaust valves.

What about the wet spark plug & misfire?

Post a photo of your rocker arms/poly locks with the valve cover off. I want to see what you have. Heads should be #66?

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PontiacJim said:

The attachments did not take, as I got an "Ooops!" message.

10W-30 should work and the Lucas stabilizer should not have any affect. Anytime I add anything thicker to an oil, I add it when the engine is hot and running so it flows better and then mixes thoroughly. I used the STP oil treatment in my brother's old truck which calles for 40W oil, so a can went in with the Rotella 15W-40.. The STP also has some ZDDP in it according to the label.

When you "zero lash" the rockers, you tighten slowly until the clicking stops, BUT, give it about 15-20 seconds for the lifter to adjust itself as the oil has to bleed down and find its correct level. The lifter may start ticking again, then you tighten just enough to stop the ticking and let it "normalize" again. You may only have to make 1 adjustment or it could be 3 adjustments until the ticking is gone and the valve lifter where it wants to be, Then turn 1/4 turn, tighten the st screw, and hold the set screw and with the wrench turn another 1/16 of a turn just to cinch the poly lock down.

If you have the correct poly lock length, the allen set screw should be just slightly above the nut. If it is sunk too deep, the poly lock body is too long and you could be loosing adjustment as the allen screw bottoms on the threads and not the stud. If the set screw shows a lot of thread, then the poly lock is probably too short and you are not grabbing enough of the threads inside the poly lock and you can strip out the set-screw or it can go out of adjustment because it is not getting a good enough "bite" to hold it secure on the stud.

Put a dab of white paint or something on the tops/side of each pushrod so you can see the rod spinning. Sometimes you cannot tell as some rods will spin very fast and others may just sit there and not spin and you think they look like they are. The ones that are not spinning are a problem. This can mean too tight, or see if you raise the RPM's a bit if they begin to spin. You should be able to grab the pushrod and spin it by hand with the engine running. If not, it is too tight and you want to back off the rocker arm to see if that gets it spinning.

The looser the rocker arm, the more oil will flow out the rocker arm spurt hole - this is what you want. The oil might be a little sluggish at idle RPM's, but still flow fairly well. I always go 1/4 turn on the poly lock after the clicking stops on my last adjustment. Some will say 1/2 turn or 1 full turn. Who knows? I go 1/4 turn and this has always worked, and the pushrods spins nicely and oil flows out the rockers. Too tight on that last lock down turn, 1/2 or 1 full, can compress the valve plunger too much and add too much pressure on the pushrod and the oil doesn't seem to flow as well and the pushrod labors to spin. Pushrod spinning means the valve lifter is spinning on the cam's lobe as it was designed to do or the lifter would simply sit on the cam lobe and wear the bottom of the lifter/cam lobe out - that is how they are designed.

I don't think a lean condition would damage the intake as it is the exhaust that takes all the heat as it goes out, so a lean condition would more likely do damage over a period of time and some hard running like a long pull up a mountain with a 40-foot camper behind you and a tractor trailer on your butt intimidating you to go faster (no that was not me, or was it? LOL). The soap bubbles could be simply from a bad gasket that is bad enough to allow the incoming intake charge to have enough force/pressure to allow air to escape. Bigger cams with more overlap can have revision characteristics where some of the intake charge is pushed back up into the intake during overlap - which gives the cam that nice idle sound we all want to hear.

If it is an intake problem, then there could be a number of reasons from a poor valve job on the seat, a poor cut on the valve, or a poor machining of the valve guide where it affected the valve placement or angle. So I don't think end of the world problem, might be real simple and a machining error that can be easily fixed. Hopefully you have all new stainless steel valves and the heads were not rebuilt with the stock valves as the stainless being new would give better/wider margins for a better seating/sealing. If the stock valves were used and re-ground, the margins could be thin or the valve sunk deeper into the head if the shop was trying to make what they had work because the owner did not want to spend the budget to do the job correctly. Heads could have been purchased on Craig's List already done up and at a good price and were not rebuilt well (or some scumbag pulled them off his engine because they were cracked and sold them as recently rebuilt and he was installed E-heads instead), so all kinds of scenario's.

All part of this hobby, and if you don't like working/tinkering on a car, then this hobby is not for you, OR you had better have the wallet to pay another to work/maintain your car and not squawk when the bill arrives (I don't have the wallet, just some loose change). I am not a motorcycle rider, but it has always been told me that if you own a Harley, you want to keep a tool bag with it and you own it knowing you like to adjust/work on them. So same principal.

Just keep at it and don't let it get you frustrated. It's a learning process that you can later share with others who may need your experiences.

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PontiacJim said:

OK, let's recap what has already been done.

Delco Remy HEI. It ran fine when I bought it.

1.) Changed wires, plugs, cap and rotor

2.) Compression check on All the cylinders and it’s at 180- 185 psi across all cylinders. Number 7 cylinder was 183.

3.) Changed (swapped) plugs that I know that were firing into the number 7 cylinder.

4.) Changed (swapped) wires that I knew were firing to the number 7 cylinder

5.) Engine still sounds the same with the same misfire. When I pull the plug in cylinder 7 it looks wet.

6.) Took the valve cover off and turn the engine over and watch the valves open and close. Both intake and exhaust are opening and closing properly. Valve adjustment looks good.

Single cylinder won't fire, all others do.

If bad electronic module, it would be bad and all cylinders affected.
If bad coil, it would be bad and all cylinders affected.
If bad rotor, it would affect all cylinder.

Bad cap - cracked, poor quality where brass electrode is not extended far enough to make good contact with the rotor, drilled/positioned too far away from rotor to make contact.
--When you re-attached the coil to the top of the cap, did you use the same screws? Make sure none of the screws have gone through the top of the cap and are not sticking through causing a short.
---Check the center electrode in the cap - should have a curved surface that makes contact with the rotor button and should be able to move in/out against the spring - you did replace this with a new one, right?.

Since it was running well with the old parts, install the old cap and try that.

Rotor. May be bad. Make sure the contact that connects with the center electrode in the cap is making solid contact with it. I have had to lift up on that rotor contact because it was a cheap thin strip of metal and did not have a good enough bend in it to make solid contact with the cap electrode. Some of them can have the metal contact that signals your spark to the cap's electrode be too short and the gap can be too large for the spark energy to jump it and fire the plug.
---Check the distributor shaft that the rotor sits down onto. It could be bent or have a bad bushing causing a wobble and possibly creating a large air gap that the spark can't jump - so check the distributor shaft for wiggle/play.

The Reluctor wheel that triggers the plugs to fire could be bad or grounding out. There are 8 "teeth" and do the same thing as points do in a points distributor. One of them could be bad/bent/grounding or who knows what - I know nothing about factory HEI's.

You checked the rocker arms and the valve adjustment looked good. Looking good is not the same as the adjustment is good. The valve could be hanging open just a hair and you would not be able to see that. With the engine running, "Zero Lash" number 7 cylinder to make sure the valves are fully closing. Do a forum search and you will find how to "zero lash" your lifters. Watching the valve operation could also show a lifter not working correctly. Put a white mark on each pushrod where you can see it. When the engine fires up, the pushrod should be spinning and the white mark will be easier to see. It could take a little more than idle to get it to spin, but not much. If the pushrod is not spinning, this can mean the valve lifter is not spinning on the cam lobe - which is should do. No spinning could mean a bad cam lobe.

Just an odd problem to be sure since all other cylinders are firing. Do a few more checks/tests and give us the results.

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PontiacJim said:

Yep, always a good thing to have some tools if you can use them. It is also nice to have a few parts that you may not be able to readily get at a parts store if you get stuck out on a drive.

Ignition and fuel are the two culprits that can leave you stranded. If points, extra set of quality points/condensor, if electronic, extra module and heat sink grease. I usually save the cap/rotor/couple spark plugs from any last tune-up and toss this in the trunk. I also like to keep an extra coil-to-distributor wire if I change out wires - these have gone bad on me, but very rare. I know they worked, just time to replace them, so I hang on to them. You can source a coil easy enough.

An extra fuel filter is a good idea. If the fuel pump or anything else major goes bad, then you are most likely not going to be swapping it out on the side of the road.

With a Pontiac, I used to keep and extra starter solenoid with me. The heat can cook these and I have replaced my share in parking lots. A manual shift car is not quite a problem as you can push start the car easy enough.

I keep a tire plug set in the car - Walmart sells these. Have a set of needle nose pliers if you get a nail in the tire and have to pull it out. Then just plug the hole with the tire plug kit. Another handy item is a hose coupling kit that has several sized plastic tubes where you can cut a leaking/busted hose, insert the coupler, use the hose clamps, and be on your way - providing you have some anti-freeze in the trunk. A can of Instant Start.

And lastly - AAA or some other break-down/towing service.

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Bopman said:

Sounds like a bad relucter had the same thing happen on a 350 buick, drove it a while with a miss then later a second cylinder went to missing......put a point distributor in it and all cylinders went hitting like they were supposed too !

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Muranator66GTOCNVT said:

Yep I keep adding different things to my tool bag. I have tied if down just in case Someone does a dumb maneuver in front of me…like having to swerve. Happened to me. Had a small battery pack fly around and put an ever so small of a dent in the rear quarter panel that i could see from the outside. Body shop was able to massage it out thank goodness.

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geeteeohguy said:

I have been spouting this same information for years to the masses on pretty much all the car forums. It goes mostly unheard and ignored. That said, I never have suffered ignition problems with all my points and condenser cars and let the guys who 'upgraded' theirs enjoy the tow truck and pissed off wife. 👍

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