# Massive backfires and now I have a tapping/knocking noise



## HemiGTO (Jan 11, 2017)

Hi, I have a 67 Pontiac GTO with a 400 motor. I was having problems with my old points and coil, which was resulting in massive backfires. The backfires came out the rear exhaust and there was no flame or smoke from the engine compartment. The backfires were so loud, it would set off my neighbors car alarm. I had a bad run of bad points, a couple of burned out coils and my own ineptitude of having the distributor #1 located wrong. I probably had a dozen or so of these backfires.

I bought an MSD 6A ignition kit, which includes a distributor, rotor, electronic points, coil (MSD 2), spark plugs and spark leads. Once I got the new ignition system installed, she fired right up and we tuned & timed it in. However, I noticed a tapping noise coming from cylinder 2. Not loud, but I know its not supposed to be there. At idle, I can hear it with the hood closed. When I drive, I feel like i'm missing a cylinder - when I accelerate I can feel a miss where there should be consistent acceleration.

I pulled the spark plugs and they are all evenly colored and no buildup of fluids. And minus the miss, the car runs great and there is no discolored exhaust, leaks or smells. 

Is it possible that the back fires have caused a larger problem with the cylinder, rods or valves? 

Any suggestions on how to identify this? Has anyone used tappet stop noise solutions in these engines?


Very much appreciate your help.
-Hemi.


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## PontiacJim (Dec 29, 2012)

Could be a number of things, but am going with your observation of the ticking from #2 cyl. A rocker arm can loosen up if the rocker arm nut backs off, or even go sideways and fall off if it backs off a bunch - had it happen. Pull the valve cover to check, and you want to torque the rocker arm nuts to 20 ft lbs.

Next, could be a bad cam/bad lifter. Cam lobes do wear out and round off. The type of oil needed in the older engines (non roller cam/lifters) needs zinc to act as a lubricant within the oil. For a while, many oils had most of the zinc removed to meet new EPA standards. From what I now read, many of the oils have put zinc back in where they will meet the needs of the older engines. If in doubt, you can add a zinc additive or buy oils specifically formulated for older engines. If your engine has been run with the low zinc oils, it is possible it could have caused some wear, but if it is an older engine anyway, the cam/lifter may have wear due to high miles. A collapsed lifter will also "tick" and create problems.

So observe the rocker arm action on #2 as compared to the other arms while it is running. Have rags ready 'cause it will get messy and spray oil - so you don't need to run it long.

If any damage has been done due to the backfiring, ie broken ring, or even broken piston, you can do a compression test. Do all cylinders to get a good comparison between them. You want the engine warm, not hot. Pull all the spark plugs so the engine can spin freely/easily. Pull the coil wire as you don't want any sparking. Open the carb wide-open so air will get into the cylinders. Then put your gauge into each cyl and record the numbers. Once done, now go back and repeat the whole process except this time, get an oil can/squirter, and give each cylinder a couple of squirts of oil. Get the oil can nozzle to the back of the cylinder so the oil will run down over the top rings. Put your gauge back in and record the compression. If you see a big number change, rings/pistons are worn as the oil will act as a seal to give you higher numbers. If you see any big difference between #2 and other cylinders, you have a problem.

You could also have burned valve. A burned intake valve will typically backfire through the intake. Never had an exhaust valve get burned, but suspect they do. A vacuum gauge can typically detect this. It is not too complicated to do/use and I believe You Tube has a great tutorial on using a vacuum gauge as this question has been asked before and it might be easier to check it out than to be explained here.

Again, going by your observations as a "miss" could also be a number of other related things like carb, vacuum leak, worn out timing chain/gears, dirty fuel filter, etc.. :thumbsup:


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## HemiGTO (Jan 11, 2017)

Thanks so much, PontiacJim. This is great info and thank you for the detail. I'll get going on it this weekend and let you know how it goes.

thanks man
-hemi


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## 1968gto421 (Mar 28, 2014)

PontiacJim said:


> You could also have burned valve. A burned intake valve will typically backfire through the intake. Never had an exhaust valve get burned, but suspect they do. A vacuum gauge can typically detect this. It is not too complicated to do/use and I believe You Tube has a great tutorial on using a vacuum gauge as this question has been asked before and it might be easier to check it out than to be explained here. :thumbsup:


Just for the record, Jim, had a Ford 302 in the early '80's get a burned exhaust valve. It was my wife's car, so not sure what preceded the exhaust valve burning. Had to replace the valve and do a valve job on the other 15 valves...did restore some "zing" to the 302.

Hemi...please keep us posted on your findings...Thanks!


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## geeteeohguy (Feb 2, 2008)

I had two burnt exhaust valves in my '67 GTO when I pulled the engine down for an overhaul at 173,000 miles back in '88. I have seen other GTO's in CA with burnt exhaust valves, too. Never intakes. Fuel formulation differences? It sounds to me like you have a dead cylinder. A quick way to check is to simply crank the engine with the coil disabled. If it cranks over evenly, no worries. If it cranks with a speed-up on each revolution ( na na na na NA na na na) you have a dead cylinder. As Jim said, could be a rocker arm, pushrod, valve, etc. If you have a dead cylinder, you can pull the valve covers and have a look. If you see nothing, it's time for a compression and a cylinder leak-down test to pin-point the problem. I have seen backfires bend pushrods.


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## HemiGTO (Jan 11, 2017)

Thanks so much for replies. I was so excited when I bought this - the engine was newly reconditioned and I was driving it work once a week (about 70 mile round trip). Then it started spluttering, so I had a buddy come over and he insisted the distributor #1 position points towards the #1 cylinder (I guess this is a chevy thing?). Anyway, smash cut through two blown points and coils and the brutal backfires, I just hope I havent screwed my baby. I had just named her too: "Buckskin Annie." 

Anyway thanks guys. Love love this forum. Hope I can return the help - Maybe steer someone away from my idiot buddy.


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## 64GTOConvertible (Aug 28, 2016)

I doubt your backfire caused engine damage, but I guess I've been fooled before. BTW, you can't just torque your rockers, IIRC you have to do it in sequence. Gotta make sure the valve is closed when you torque it.

My dad used to do it while the engine was running - he was amazing...


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## chuckha62 (Apr 5, 2010)

64GTOConvertible said:


> I doubt your backfire caused engine damage, but I guess I've been fooled before. BTW, you can't just torque your rockers, IIRC you have to do it in sequence. Gotta make sure the valve is closed when you torque it.
> 
> My dad used to do it while the engine was running - he was amazing...


You are not familiar with Pontiacs, I take it. If he has a stock valve train, you post certainly do torque your rockers. This is not a Chevy. The rocker train may look the same, but it's not.


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## geeteeohguy (Feb 2, 2008)

A co-worker sold his mint 4 speed 40,000 mile tenth anniversary Trans Am to our service writer in 1984. Silver with a black interior. NICE car. New owner decided to spiff up the ignition wires and cross-wired it. When it backfired, it blew the cap off a con rod and destroyed the engine. 577 block, but still. When you ignite mixtures against heavy rotating parts at the wrong time, sometimes bad stuff happens. In any case, time to inspect it and get back to us.


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## 64GTOConvertible (Aug 28, 2016)

chuckha62 said:


> You are not familiar with Pontiacs, I take it. If he has a stock valve train, you post certainly do torque your rockers. This is not a Chevy. The rocker train may look the same, but it's not.


Hmmm, made me second guess myself. But since I am a lifelong Pontiac guy I thought I was right. First Google hit proved it. Just saying...

Pontiac Rocker Arm Adjustment


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## chuckha62 (Apr 5, 2010)

????? Your link seems to more prove my point. Torque to 20-25 Lb.ft. with stock rocker train, hydraulic lifters, factory specs.

Now, change things up and yes, the procedure changes.


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## 64GTOConvertible (Aug 28, 2016)

Maybe you didn't see this: "BTW, you can't just torque your rockers, IIRC *you have to do it in sequence*."


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