Can't find misfire

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76Scamp

76Scamp

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Bradenton, Fl
Recently out of nowhere, I have a really bad misfire. It was driving fine, I stopped and shut it off, came back and it as misfiring really badly. It does it at idle, cruising, and light acceleration, but if you put your foot in it, it clears up and runs great until you let off. I've replaced the distributor because the advance didn't work on the old one, set the timing, did an HEI conversion, moved the fuel filter to the other side of the engine, adjusted the valves to spec (while idling), and tuned the carburetor as best I could. Now, to me it sounds like it's ignition related, but I'm not sure. The carburetor was rebuilt a few months ago by a friend of mine, but he really didn't know what he was doing. He only did it because it was stuck in a parking lot because it filled it up charcoal from the canister. Now also, it's not always doing this. Most of the time it'll misfire like it's not running on all six, but sometimes it'll run just fine. But turn on the air and that extra load makes it worse. Any ideas would be greatly appreciated before I start ripping into something else. Oh, and if it means anything, I have the Holley 1945 carburetor, idle is set around 800rpm, advance is currently sitting at about 10 degrees (doesn't change anything but idle speed and quality, misfire still exists), stock distributor, valves around 10 and 12 thou for intake and exhaust respectively, I don't know what compression or manifold vacuum is at because I don't have the tools to check at the moment, and the carburetor was tuned by turning the screw back and forth until it ran its best. If I can, I'll re-tune tomorrow with a vacuum gauge and check compression.
 
I hade this once ....stumped me for a looooong time... Take a good look at the distributor bushing in the block. The bushing can be seen after the distributor is pulled out, just look down the hole for the distributor and you will see it. If you have sloppiness in this bushing it can toss the timing all over the place. It wont generally do it under load because the bushing becomes "loaded up" with torque, but free wheeling it will do it as you explained. It may not be the issue but worth a check, cheap check, cheap fix if it works. I had one worn so bad it wore out the distributor cam drive...crazy! Hope it works!
 
Im pretty sure that the valve clearances should be ten and twenty. I think your exhausts are too tight.I would back them up first.If theyre too tight, combustion pressure can upset the intake vacuum, and subsequently mess up the low speed carburetion .So thats #1 on the to-do list.
However, since this problem existed before the valve adjustment I think theres more to it. I believe that another problem exists and it is in the lowspeed circuit.I have a feeling your float level is too low, and in an effort to keep it running, the idle speed was increased to 800rpm. This puts the T-blade too far up the transfer slot, and it may run dry. This could be aggravated by a plugged idle air bleed. I would be almost undriveable if the timing was stock. But at 10*, advance its helping.
So the next thing to do is set the float level. And while the top is off blow out the airbleeds. Then after its back together see if you can bring the idle speed down some.They usually idle sweetly at 650ish.
I know your not too interested in resetting the valves.But sometimes you gotta back up to go forward.
I suppose theres no harm in doing the carb work first. I just know .012 is too tight and if they continue to run there,say at highway speed, they will overheat and burn. Then you will be spending money that you also dont want to do.And after years and years and years of doing this kind of work, I have found that my time and therefor the customers bill, is best served by starting with compression.But since you dont have a compression tester, we can at least make sure the valves are closing. Later, if Im wrong about the float level/airbleeds, and the engine fails to respond, then a compression test will be required.
So, happy Easter
 
AJ/FormS said:
Im pretty sure that the valve clearances should be ten and twenty. I think your exhausts are too tight.I would back them up first.If theyre too tight, combustion pressure can upset the intake vacuum, and subsequently mess up the low speed carburetion .So thats #1 on the to-do list.
However, since this problem existed before the valve adjustment I think theres more to it. I believe that another problem exists and it is in the lowspeed circuit.I have a feeling your float level is too low, and in an effort to keep it running, the idle speed was increased to 800rpm. This puts the T-blade too far up the transfer slot, and it may run dry. This could be aggravated by a plugged idle air bleed. I would be almost undriveable if the timing was stock. But at 10*, advance its helping.
So the next thing to do is set the float level. And while the top is off blow out the airbleeds. Then after its back together see if you can bring the idle speed down some.They usually idle sweetly at 650ish.
I know your not too interested in resetting the valves.But sometimes you gotta back up to go forward.
I suppose theres no harm in doing the carb work first. I just know .012 is too tight and if they continue to run there,say at highway speed, they will overheat and burn. Then you will be spending money that you also dont want to do.And after years and years and years of doing this kind of work, I have found that my time and therefor the customers bill, is best served by starting with compression.But since you dont have a compression tester, we can at least make sure the valves are closing. Later, if Im wrong about the float level/airbleeds, and the engine fails to respond, then a compression test will be required.
So, happy Easter
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Thanks for the info. Once I get it running again (probably out of gas) I'll pull the valve cover and reset the clearances. I'm also going to be buying both a compression tester and a vacuum gauge tonight and I'll mess with it tomorrow since I have the evening shift at work.
 
Couldn't wait, had to play with it. It turns out that I wasn't getting spark while cranking, so I just wired straight to the battery temporarily. I checked vacuum and I'm getting about 18" with the idle screw all the way out and with the mix to where I have the most vacuum. I went down the line and pulled the plug wires while running, and number six made no change in how it ran. I pulled the valve cover and both valves are moving, and I did my research and it is supposed to be 10 and 12. I put a compression tester on it and I'm getting a little under 100 psi in that cylinder while the rest are roughly all around either 120 or 150 (don't remember which). So, going with another old trick, I held a thing piece of paper (bubble wrap actually) close to the exhaust and it didn't show any sign of a burnt exhaust valve. Until I was right up to the pipe, it wan't to just blow it into my hand. Once I was about an inch or so away, it wasn't exactly sucking it in, but more blowing it back and forth. I'm not too sure, but I am leaning towards a burnt exhaust valve, and I really don't want to pull this engine apart. I will say, that when I got it I mentioned I wanted to adjust the valves so it would run right and be quiet, but the brother of the old lady I got it from told me not to because she had been running so long without doing it. She had driven the car for 15 years and 50K miles without ever having a valve adjustment done. Then three years ago it blew the head gasket and her husband fixed it and did God knows what else, but I know his work, and it's pretty terrible; kinda surprised it still runs after him working on it. So, unless there's anything else that someone can think of, I guess I get to do a valve job.
 
Well, watched the Chrysler master tech video just to be sure, and the book I have is wrong. You are right, the exhaust valves are too tight, so I more than likely have to pull the head due to a burnt valve.
 
Before you pull the head. try opening up the exhausts. Its worth a shot.
And while the cover is off check the spring pressures. If the valves have receded far enough maybe theres not enough seat pressure to keep the valves closed at idle.Since its fine under load and rpm the valves are not yet burned. Perhaps you can shim the springs up and get another few years out of her.
 
AJ/FormS said:
Before you pull the head. try opening up the exhausts. Its worth a shot.
And while the cover is off check the spring pressures. If the valves have receded far enough maybe theres not enough seat pressure to keep the valves closed at idle.Since its fine under load and rpm the valves are not yet burned. Perhaps you can shim the springs up and get another few years out of her.
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Never heard of such a thing, but why not? How would I go about checking the pressure and how/what would I use to shim the valves? I'm good with engines, but (even though it really doesn't matter) most of my knowledge is with Chevy. Everything I've worked on has had hydraulic lifters, so someone's stupidity really can't mess something up like this. Since it seems like I can't get valves for this engine, I may end up just replacing the head since I can get it for $267 before tax instead of $296 because of my employee discount. Either way, I would like this car to be a driver and I would like to be able to roll the odometer over again. Right now I'm showing about 1500 miles and I'd like to see it do that again. Thank you for your help.
 
76Scamp said:
Since it seems like I can't get valves for this engine, I may end up just replacing the head since I can get it for $267 before tax instead of $296 because of my employee discount. Either way, I would like this car to be a driver and I would like to be able to roll the odometer over again.
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I don't know why you think valves are not available for this engine but they are. Check Rockauto for one.
Ironically, I just picked up my rebuilt head yesterday from my machinist. (Yep, on Easter Sunday!) Due to a miscommunication (I thought he knew I was going to do the assembly) it is complete and ready to go. He checked all the springs in a spring checker and re-used them. I was just going to replace them as they're 51 years old but he said they are good. He checked the spring installed height and shimmed them as needed. he also reused the valves. I have not unwrapped it from the plastic shrink wrap yet but the head looks great! I had him install hardened exhaust seats and new valve guides. He used cast iron because he says the iron wears better than bronze. Whatever, I trust this guy explicitly as he's been doing this since 1962.
At first he did not want to mill the head for fear of screwing up pushrod and valvetrain geometry but I had him do it anyway. I chickened out somewhat so we agreed on 0.080. I really want this engine to be right and very dependable so I'm OK with spending the $ for a complete rebuild. I know I won't have to worry about it later on.

If you suspect a burnt valve, it wouldn't take much to pull it and get a valve job.
If only one hole is low on compression, you can do the old trick of squirting oil in through the spark plug hole and see if that brings the compression up in that cylinder. The oil will temporarily seal the rings to the bore so you could eliminate bad rings for the low compression.
 
KosmicKuda said:
I don't know why you think valves are not available for this engine but they are. Check Rockauto for one.
Ironically, I just picked up my rebuilt head yesterday from my machinist. (Yep, on Easter Sunday!) Due to a miscommunication (I thought he knew I was going to do the assembly) it is complete and ready to go. He checked all the springs in a spring checker and re-used them. I was just going to replace them as they're 51 years old but he said they are good. He checked the spring installed height and shimmed them as needed. he also reused the valves. I have not unwrapped it from the plastic shrink wrap yet but the head looks great! I had him install hardened exhaust seats and new valve guides. He used cast iron because he says the iron wears better than bronze. Whatever, I trust this guy explicitly as he's been doing this since 1962.
At first he did not want to mill the head for fear of screwing up pushrod and valvetrain geometry but I had him do it anyway. I chickened out somewhat so we agreed on 0.080. I really want this engine to be right and very dependable so I'm OK with spending the $ for a complete rebuild. I know I won't have to worry about it later on.

If you suspect a burnt valve, it wouldn't take much to pull it and get a valve job.
If only one hole is low on compression, you can do the old trick of squirting oil in through the spark plug hole and see if that brings the compression up in that cylinder. The oil will temporarily seal the rings to the bore so you could eliminate bad rings for the low compression.
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I haven't been to rockauto, but every other place I've looked does not have a listing. With the valve cover off and both valves closed, I pressurized that cylinder and I could hear it in the exhaust pipe. I went to where I was told was an old mopar graveyard, and sure enough, there's an old mopar graveyard about 5 miles away from me that I never knew about. I pulled a cylinder head from a '64 Dart. The guy said it drove to the spot where it was sitting, so I did a compression check jumping it off of my truck and it had full compression in every hole. They had already sold the manifolds, so I just had to pull the head. $65 later and it's sitting in the trunk of the car, hoping to be dealt with this weekend if I can get it off.
 
Wouldn't you know it? Things actually turned my way for once. I was talking to a guy that came into the store about the car, and he said he had a running slant 6 from a 1980 D150 that I could have for $100. So now, I'm thinking I'll do an engine swap and build up the one that will come out of the car for later use.
 
I decided to just take the valves from the head that I got in the junkyard because I got to thinking and I don't want to do an engine swap in an apartment parking lot. Already have the manifolds off and I found the exhaust leak. When the head gasket was done a few years ago, the bolts that hold the manifolds together were broken off. So now, I just have to get the alternator and a couple of other things out of the way and I should have the head off in maybe an hour.
 
I've taken the head off three or four times in my appartment parking lot. I also built my entire slant six turbo setup there. The head usually takes about an hour, I take the top bolt out of the alternator bracket, loosen the bottom one, take the belt off and slack the alternator, and then pull the manifolds. Make sure you replace that little bypass section of hose when you put the new head on, it's a good time to do it. Also stick a wire down the cooling passages while you have it off.

.010 and .020 are slant six respective settings on valves, and you should set them basic static, then fire the engine up, and reset while it's running. It's a lot of fun, and super quick.

Did you try backing the valve off a little? Say .040 and seeing if the misfire straightened out?
I've dealt with the burned valve in the past, which had me pulling the head the first time, but then it also had a broken in half pushrod so I only had 4 cylinders for a minute...
 
Serj22 said:
I've taken the head off three or four times in my appartment parking lot. I also built my entire slant six turbo setup there. The head usually takes about an hour, I take the top bolt out of the alternator bracket, loosen the bottom one, take the belt off and slack the alternator, and then pull the manifolds. Make sure you replace that little bypass section of hose when you put the new head on, it's a good time to do it. Also stick a wire down the cooling passages while you have it off.

.010 and .020 are slant six respective settings on valves, and you should set them basic static, then fire the engine up, and reset while it's running. It's a lot of fun, and super quick.

Did you try backing the valve off a little? Say .040 and seeing if the misfire straightened out?
I've dealt with the burned valve in the past, which had me pulling the head the first time, but then it also had a broken in half pushrod so I only had 4 cylinders for a minute...
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This isn't the first bit of engine work I've done here, this is the same job I did to my truck, but for a different reason and it was a V engine so the head was smaller and lighter. But, I don't have a lift and I want the car back on the road sooner. I tried backing off the valve, but it didn't change anything. With the head off, it looked fine to me, but I could hear hissing in the exhaust pipe when I pressurized that cylinder. So I'm already done putting a new valve in and I installed new valve steam seals on all of them since most were gone or hard. The head is sitting on the block, but I'm waiting to pick up the other engine tomorrow because I want to use the manifolds that are on it. I found that my exhaust leak was not a cracked manifold like I was told. Whoever had replaced the head gasket a few years ago had broken the bolts that hold the intake and exhaust together. And before I finish putting everything back together, I'd like to clean up some wiring I did and maybe install an oil pressure gauge as well as an added temperature gauge. The oil light on the car does work, but I would prefer a gauge so I now what it's doing. The temp gauge on the cluster works, but the new one came with the oil gauge because it's the standard set of three: oil, temp, and volts. So, it should be back running tomorrow evening.
 
Well, manifolds are back on and it at least idles. Still need to hook all the hoses back up, fill the radiator, change the oil, put the alternator on, hook up the exhaust, and adjust the valves properly this time. I also need to find the plug wire for #1. I took it off so I would know where it was on the cap, but it seems to have walked away. Even so, I'm gonna go back out after I cool after and do a compression check on six and see what happened.
 
76Scamp said:
Well, manifolds are back on and it at least idles. Still need to hook all the hoses back up, fill the radiator, change the oil, put the alternator on, hook up the exhaust, and adjust the valves properly this time. I also need to find the plug wire for #1. I took it off so I would know where it was on the cap, but it seems to have walked away. Even so, I'm gonna go back out after I cool after and do a compression check on six and see what happened.
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Well, I did a compression test and number six is still down at 90 psi. At first, I checked and it was at 30 and I had no clue what I could've done. I pulled the valve cover and found the pushrods didn't make their way under the rockers. I finally found a place to get valves for this, so I ordered them and they should be here Thursday. The other engine I bought, well, it's a mess all it's own. It's been sitting with no oil pan and no manifolds, and it sat in the rain at least once. It's not beyond repair, but it'll take more work than I was hoping. So now, I'll have a friend of mine tank the head and lap in the new valves, and if it's still not up to the other cylinders, I guess I get to drop the bottom end out of it.
 
If the head is still on, retest compression in #6 dry, then put about a teaspoonful of oil in #6 and retest and see if the compression level comes up. That may tell you something about the ring condition in that cylinder; if the compression rings are worn, the compression should go up with the oil added.

You should reuse the later head; the casting is better; you can read up on that in the 'Articles' on www.slantsix.org. You can find the proper procedure for manifold tightening in another article there.
 
nm9stheham said:
If the head is still on, retest compression in #6 dry, then put about a teaspoonful of oil in #6 and retest and see if the compression level comes up. That may tell you something about the ring condition in that cylinder; if the compression rings are worn, the compression should go up with the oil added.

You should reuse the later head; the casting is better; you can read up on that in the 'Articles' on www.slantsix.org. You can find the proper procedure for manifold tightening in another article there.
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Well, sure enough, I did that and #6 went from 90 to matching the other five at 120. So, it's rings. Kinda as a "just to see what happens", I added a bottle of the engine restore "six cylinder formula." I've also been soaking the top end in Marvel Mystery oil every night after it cools off and I can touch it without burning myself. I'm doing this because I don't see a set of rings wearing that bad on only one cylinder. It makes more sense that they are stuck to the piston. I've been doing the Marvel and driving with the engine restore in it for about three days now, and although I haven't had time to do a compression check, my misfire is almost undetectable. It is running much smoother and stronger. The new valves came in and I went ahead and ordered a set of cam bearings because the other engine needs them. I went to a local machine shop and to do everything I want, he said $671. That is to fully refurbish the head with my valves, clean the block, bore it 30 over, hone it, polish the crank, install the cam bearings, and I think something else. Right now, since it's still in the back of my truck, I haven't removed the crank so I don't know if it just needs polished or if it needs to be ground. I'm also debating on boring it. I think it'll come back with just honing it, but I'd like to try and make a little bit of power, but I may end up saving myself that extra $145 on boring it out and just go stock on it.
 
Sticking rings is a very good possibility, especially with the older oil with limited/no detergents used in years past, and the car perhaps sitting a bunch. So, continue with the clean up. It may still be a worn ring/groove/bore, especially in #1 and somewhat in #6; the end cylinders run cooler on an inline 6 and tend to wear faster. I had over .020" wear on #1 versus under .010" on the rest.

Interesting way to do it with the MMO. You may also be freeing up a sticky valve guide; the stock valve springs are pretty low pressure so the /6 stock valves stick kinda easily.

You can do a simple crank polish at home. Cut strips of wet-or-dry sandpaper the width of the journal and long enough to wrap around and overlap the ends. Then double wrap a long leather shoelace around the paper and rotate back and forth, moving the leather from side to side of the journal to keep wear even. 220 grit for faster work and 400 for a fine finish. I have taken .001' or more off with patience.

The need to bore is for taper and out-of-roundness in the cylinders; you won't know 'til it is measured. And you should get the ring ridge out, especially if new bearings are going in.

New cam bearings are a very good idea. I got the same machine work (less crank polish but with piston R&R and 6 valves done for around $450 at a great shop so maybe you can find better pricing in your area too. (But I live in a pretty rural area where things are cheaper than in the big city.....)
 
nm9stheham said:
Sticking rings is a very good possibility, especially with the older oil with limited/no detergents used in years past, and the car perhaps sitting a bunch. So, continue with the clean up. It may still be a worn ring/groove/bore, especially in #1 and somewhat in #6; the end cylinders run cooler on an inline 6 and tend to wear faster. I had over .020" wear on #1 versus under .010" on the rest.

Interesting way to do it with the MMO. You may also be freeing up a sticky valve guide; the stock valve springs are pretty low pressure so the /6 stock valves stick kinda easily.

You can do a simple crank polish at home. Cut strips of wet-or-dry sandpaper the width of the journal and long enough to wrap around and overlap the ends. Then double wrap a long leather shoelace around the paper and rotate back and forth, moving the leather from side to side of the journal to keep wear even. 220 grit for faster work and 400 for a fine finish. I have taken .001' or more off with patience.

The need to bore is for taper and out-of-roundness in the cylinders; you won't know 'til it is measured. And you should get the ring ridge out, especially if new bearings are going in.

New cam bearings are a very good idea. I got the same machine work (less crank polish but with piston R&R and 6 valves done for around $450 at a great shop so maybe you can find better pricing in your area too. (But I live in a pretty rural area where things are cheaper than in the big city.....)
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I did a compression check on it today, and amazingly all six cylinders are at 120 just like they should be. I'm very amazed that it actually worked.
 
Run it a while and let us know the compression readings after a few hundred miles. That would be cool it you got it freed up. Keep an eye out the back when accelerating; sometimes, sticking rings will show some smoke out the exhaust under acceleration.
 
nm9stheham said:
Run it a while and let us know the compression readings after a few hundred miles. That would be cool it you got it freed up. Keep an eye out the back when accelerating; sometimes, sticking rings will show some smoke out the exhaust under acceleration.
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Will do. Obviously, it smokes like crazy when running MMO in the top end, but otherwise, this car has never smoked. I'm gonna take it out on the highway later and let it run to clear the cobwebs out. Last time I had it over 50 was about a month or so ago when I drove it up to Tampa. Around town, I can't do much better than that because nobody knows how to drive and there's still too many people in Florida to go around them. Last time I tried to take the highway, it was moving at 30mph and I just got off at the next exit.
 
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