First off sorry about the length.

Well, for background on my situation you can read the last couple of posts in this thread. https://www.thirdgen.org/techbb2/sho...04#post1545104

Here is an overview. I have had my setup running w/ the computer controlled carb for a while. I had it to the track a few times this way. I had a slight fluttery feeling up high, but nothing major. I thought maybe I was running out of fuel w/ the stock LG4 fuel pump. Well recently I got a speed demon 750 dp and a 120 gph carter pump. I installed these along w/ a non comp distributer. It ran fine for normal driving, but when I would get into the high rpms I would get kind of a pop or thunk. Well, I was afraid that I was getting spark knock because of the 58 cc heads so I tried retarding the timing. This seemed to make it worse if anything. I found that it seemed that the farther I advanced it the better it got but never went completely away. The way it ran best the starter couldnt hardly turn the motor over because of the advance. I put it back to a reasonable timing setting. I will mention that when I had the cc quadrajet I ran a snap on scan tool on it and it didnt show any knock under accel even w/ a base of 12*. If I free reved it it would show a slight amount of knock.

Anyway, I tried several things. I cleaned the plugs, I changed coils, and ignigion modules, and checked the cap and rotor. I noticed that it seemed that the problem was getting lower in the rpms a bit. It started out only having problems up high. but got to the point it would have problems even above 2000. Well, I was under the hood and noticed that I could hear it even free reving so I took the air cleaner off and it seems to be coming from the carb. I was told that it could be valve lash. I reset the valve lash, and took it for a test drive. It actually seemed a lot better. The problem didnt seem completely gone but much better. Well, it seemed to come back within a day or 2 and started out being in the high rpms, but worked its way down again.

Well, tonight I decided to mess with it again. I swapped out the pushrods, for another set i had in the garage that were the same length. I also decided to put my roller tiped rockers on instead of the stock ones. They are non self aligning, but I was under the impression that that is what 416 heads used(correct me if I am wrong) because they had the non self aligning stamped rockers as oposed to like the L03 which has a grove that aligns it on the valve. Well, I set the valve lash, and took it for a test drive. It seemed better like last time I reset the valve lash. I was on my way back into the neighborhood to park it and call it a night and it started poping real bad even at light throttle. So I parked it and got out and you could hear it even at idle. I took the air cleaner off and it was coming from the carb. It had never happened at idle before. I have not pulled the valve covers to see if there is a visible problem this time yet but I will before it is drivin again.

I am really at a loss as to what the problem could be other than it started when I put the carb and dist on(or at least became noticable). I did also put an open element on at the time so stuff is more audible. I was told that the xtreem energy cams are not supposed to have over 9.5:1 compresion so that kind of worried me but I remembered that I wasnt getting knock according to the computer w/ the previous carb. I have set the total timing as low as about 18(accidentally because advance kit was installed wrong) and it still had the problem, and I doubt that the LG4 had less timing than that so I think that is not the issue. Valve lash seems to effect it but it seems to revert, and this time it is worse than it has been before.

Thanks for the help.

Ben

 

Have you recently done a compression check per cyclinder, almost sounds like a valve maybe hangin open.

 

Sounds a bit like a valve spring issue. What springs are on your heads?

 

The springs are the comp 981's I believe.

Ben

 

I have not recently done a compression check per cylinder. I may do that. I have to borrow a gauge though. I think I will check under the valve covers to make sure everything looks fine first though.

Ben

 

Another thing that will cause "popping at idle" is an exhaust valve that doesn't open.... like if the rocker nut backed off.

What kind of rockers are these? If they're something that doesn't use Poly-Locks, try adjusting the valves, and add a jam nut on top of each one.

 

yeah, those springs are more than suffient for that mild of a cam. I wonder if a lifter may not be an issue if the valve lash checks out. maybe internally the spirng in a lifter has gone bye-bye and causing slop in the cam profile and affecting this. Also, when you pull the covers off double check to make sure all the rockers studs are where they are supposed to be, possibly one/more is pulling out. Should be obvious signs if this is a problem, if they all check out have a buddy turn over the engine while you observe eack rocker going through the motion-place your finger on the end of the rocker by the vavle spring and hold pressure on it. Maybe lost some seat pressure, which brings up did you have the heads checked out after you installed these new springs, maybe there is'nt enough seat pressure and you might have to shim them.

 

Well, I looked at the studs last night when I changed pushrods and rockers and it seemed that they were all fine. I have not had the heads checked out with the springs on them. I am not using poly locks on these, but when I have pulled the valve covers before, I never found any rockers with slop in them like the nut had backed off. I will see about finding some jam nuts though. I actually have most of a set of poly locks but am missing a couple so I didnt use them.

What exactly am I feeling for when you say to hold pressure on the rocker by the spring while the motor is being turned over? Can the seat pressure be checked w/ the heads installed? I dont plan on taking the heads off until I put the sportsman II's on so maybe I should get to work on those I guess.

Thanks

Ben

 

When you got your cover off, while spinning the motor over-not starting, it's to watch the lifters to make sure they are all opening/closing the same amount. All the pressure on the lifter does is to help ensure the rocker is following the valve/cam and you should be able to feel slop on one side or the other f there is some sort of misadjustment. They have a tool to check seat pressure while on the head so maybe call around for a buddy or a machine shoip that may have one so they can double check while they're on the car to make sure it's right. It'll take some time for the dissambley and reassembly but it's well worth it so you know exactly what you're dealing with.

 

I doubt I will know anyone with the tool. What all is involved in checking?

As far as feeling for the slop should I have the motor turning over quick with the starter, or are you suggesting that I should feel while it is moving slowly by hand?

Thanks

Ben

 

ttt

 

just check it turning the motor slowly checking each lifter/valve/lobe. I'm not sure on the finer tuner points of valves trains, but with these heads you have, they are all stock and you just replaced the springs, no after market valves or anything, if that's the case with aftermarket valves I wonder if the stem height is off a little not allow a full seal when closed? Think I'm diggin too deep on that one though. The only other way to check springs is to take one cyclinder apart-springs off, and have the rate check, for open/ close pressure and double check coil bind.

 

I am still kind of lost on the whole thing about feeling to see if there is any slop in it when turning the motor over. would think that if I adjusted the valve last that the springs should at least have enough pressure to close the motor while turning by hand even if it doesnt seal it when it is running. Am I missing something.

Thanks again.

Ben

 

No sense in over-mystifying something that should be simple.

Stem height isn't the problem. Seat pressure probably isn't the problem, if it does it at low speeds. The issue at hand here is either an intake that doesn't close, or an exhaust that doesn't open.

You should be looking for a broken intake valve spring or a rolled exhaust cam lobe. Either of these would be typical results of shimming the springs too much. They're already being operated right at their limit; and the addition of an extra shim might have pushed the over the edge.

A broken spring would be pretty obvious. A rolled cam lobe would show up as one valve, probably an exhaust, that opens much less than the rest, while the engine is running.

 

Well, hopefully I will have a chance to check it out tonight. If it was an exhaust lobe would there be metal in the oil. I havent noticed any, but if it would be a clue I might change that also. I will check the springs and look to see if I can tell if there is an exhaust valve that doesnt open all the way.

Thanks

 

Unfortunately I didnt have time to check tonight. I have classes till late tomorrow so it will probably be thursday before I get a chance.

I do still plan on checking for any broken springs or to see if any rocker seems to lift less than the others. Are these problems that would seem to mostly go away when I set the valve lash, but come back shortly after? Could a lifter cause this sort of problem?

One thing that I dont think is the problem, but I was wondering about is do valve springs have a definate top and bottom. I was talking to a friend, and he said that one of his instructors in tech school told him that there was a top and bottom to a valve spring. He didnt know how to explain it over the phone though. Is this true, and if it is what difference would it make?

I think that if I dont find any visible problems I am going to try resetting the valve lash and putting jam nuts on like suggested and see if that helps.

Ben

 

Ben,
If you want you could probably bring it over to Alex's shop and the three of us could look at it by using some of the gauges and tools that you may not have. The shop is not to far from Greg's house. On another note, I found a 400 big block that might fit in your firebird, and Alex might know where a 400sbc is.
Mark

 

Thats cool. As of right now, the motor search is on hold though. I have to put the money toward getting the car painted. After that I will probably resume my quest for cubes. lol.

Anyway, any help would be greatly appreciated. I am sure it is just something that i messed up on or something, but I would like to find out what it is so I can fix it. If you can shoot me an email or something maybe we can work something out.

Ben

 

Oh, and out of curiosity, by 400 bb are you referring to a pontiac motor or something like 396 or 402?

Ben

 

actually it might not fit but it would be worth a try. it is a complete running 400bb Mopar. That could be a "weld in a different craddle" project. There also might still be a 400sbc out of a truck w/a powerglide transmission for sale by a friend of mine.

 

Lol, I am not into putting motors made by different companies into different cars. The reason I have been looking for a sbc 400 is because I already have a good set of heads and headers to work w/ one. If I was going to go w/ something else it would probably be a bbc. I guess let me know whats going on, or what a good time to bring the car out would be.

Ben

 

I was told that it may be a burnt valve. Would that make since? I know that a burnt valve can cause my symptoms, but I just dont know if it or any of this other stuff would get better with setting valve lash and get worse again.

Ben

 

Well, I think I found my problem. I will have to verify though. I pulled the valve covers to check on some of the stuff that was suggested. I looked, and all of the springs looked ok. So I checked to make sure all of the rockers felt tight. All of them at least felt like there was no up and down movement. I rotated the motor some and checked again, and the number 8 exhaust valve was loose as crap. I looked, and it appeared to still have the about the same amount of threads showing as the rest if not one more. I strongly suspect that that at least that rocker stud is pulling out if not more. The car has only been driven about 10 minutes since I set the valve lash and it seems that it pulled out a lot so I am thinking that it would have came clear out if I would have driven it much. I am going to pull the other rockers off and check the height of them w/ a straigh edge to see if that one is higher than the others for sure.

Ben

 

Well, I just checked to see if the one seemed pulled up higher than the rest, and all of them were within 1/8 of an inch from each other and it was one of the short ones. I dont know what would have caused it to be loose and the nut not seemed to have backed off. If anyone has any ideas, I am still open to them.

Thanks

Ben

 

A floating valve paired with detonation is my guess. Well than it's probably time for your new heads, unless you want to tap a new hole for it to go back in.

 

Uh, you just lost me. What do you mean. I think I have either a messed up cam lobe or stuck lifter most likely. I am going to try to check the cam lobe with a dial gauge tonight to see if that is the problem. If it is not I am going to have to pull the intake and inspect that lifter. If I get to the point of pulling the intake it probably wont go back together till I get the other heads ready. At this point I am betting that I have a problem that I wont be running the motor until I get the other heads ready no matter what. I might end up with a new cam too.

By the way what are you referring to tapping? I have a set of screw in studs for these heads that are designed to work without guide plates. I am not so sure that I am pulling a stud now anyway because it doesnt seem higher than the rest. But in order put them in I am going to have to tap the holes obviously, and I dont really want that metal in the motor. If the heads come off they arent going back on this motor.

Ben

 

Well... I figured it out. Good call RB. It is an exhaust not opening. I tried setting the lash on that one that was loose, and the nut was down a long way before it set. It must have ground away at the base circle too. Anyway, I show a total of approximately .150 lift at the valve. I am thinking that is not a good thing. lol Well maybe. Now I can get a new cam, or have to I guess. Anyway, thanks for the help.

Ben