Alright...here's the situation....

First, I replaced the heads with a set of built up heads. After 40 miles or so, I started getting a mettalic, intermittent rattling noise I could hear through the carb. My vac at idle was all over the place and steadied out when it was given gas. The verdict after a lot of pondering was that I broke a valve guide somehow. i.e. the heads were built badly and were basically garbage.

Fast forward 2 weeks. I replaced the heads with the 041's that came with the car. These ran fine on the car before and are known good heads. After finishing, the car ran great and once tuned, ran even better. The vacuum held stead at idle and everywhere else and all was good.

Now, fast forward 3 days from that. I drove the car to work and then home. I went to the local speed shop with it to pick up some different rods for the carb. Ran fine there and back. I got in the car to take it to get something to eat. All of a sudden, the car ran horrible, wouldn't idle and generally ran awefully.

After fussing around a bit, I got it to idle fairly normally, although in drive, with a load on it, the idle bounced around about 50-100 rpm or so. I got the old vac gauge on it, and once again, the vacuum was bouncing all over the place at idle and steadied out once some throttle was given to it. The metallic rattling is back again, although not as severe as before.

The motor's never been over revved, which makes a broken valve guide hard to swallow, but, given my bad luck, I figure it's possible. But twice? I highly doubt it.

What do you guys think? What else could cause a vac reading and poor idle/driveability like that? This is the second time the intake's been set and all the vac lines are hooked up right. Anything with those shouldn't give a reading like that anyway.

I'm lost, and I'm not about to try to go out and find a 3rd set of heads, since most likely, the same thing will happen 30 or 40 miles after I put them on too.

Chris

 

Maybe a stuck lifter.......pull the valve covers and check things out. G/L

 

I thought about that too. When I adjusted the rockers a few days ago, everything moved the way it was supposed to. I haven't pulled the valve covers since the car took a dive on me.

Some stuff to add.....

I did a few tests. The first was with the vac gauge and a timing light. I checked each cylinder against the vac gauge with the light. On every cylinder except the #4 and #8, the gauge shows normal vacuum(about 10"...sounds low, but I live in a part of town that's 6500ft above sea level and the cam's a magnum 280). On the 4 and 8 cyls, it's showing just 4".

Don't know what that proves, but that's some more info to ponder.

I did a compression check and everything looked ok, well low, but normal for this motor's setup, at least when I first got the car, with the new heads and now again with the old heads back on.

Chris

 

You didn't say how many miles you have. The guide thing is strange. Did you check any of the lifters for ware when you changed the heads?

I doubt this but I have seen lifters get holes worn into the bottom of them.
Of course if this happens they loose the oil pressure. As I said I doubt this but thought I'd throw it out there.
I'm sure you checked all the normal places like wires ,plugs, cap, points, distributor run out, so if none of those things are off try removing the valve covers and checking the valve operation with the timming light. It may give up the cause. Good luck.

 

Everything under the valve covers seems to be working right.

The motor supposedly has less than 1000 miles on it since its rebuild. I was not the one to rebuild it, and I don't entirely trust any work that was done on it.

I did notice a miss at low rpm or under load at low rpm. The plugs look terrible now, very black/sooty, but that may be a bi-product of something else and no the cause. Yesterday afternoon, the plugs looked perfect.

Pulling one wire at a time, the same 2 cyl(4 and 8) make no difference in the idle and all of the others make it idle badly if at all. The miss goes away at rpm off idle.

Would an ignition problem cause the vac to read like it does? Or are the fouled up plugs(all of the ones I pulled look like the 4 and 8 ones) the result of the other, bigger issue?

Just seems strange that the car ran great for 30 or 40 miles after both head swaps.

The lifters looked good and I pulled and inspected each one after both head swaps.

Oil pressure is good, as is the level.

I doubt anything in the heads is really the problem, since I swapped the rebuilt ones out for the known goods that came off the car before.

The ignition is a mallory distro with a pertronix ignitor module in it. The coil is near new and was swapped out when I was troubleshooting this same problem with the last set of heads.

The wires look good, but I'm not ruling anything out.

What gets me is that everywhere you look, a vac reading like I have is listed as worn valve guides. There has to be something else that can cause this.

Chris

 

I would check the cap and rotor, look for any hairline cracks in there. Check the distributor too while your in there. Just out of curiosity are you still running points and condenser or have you converted over to HEI? Double check to see if the distributor is in correctly. Bring #1 up on compression stroke and remove the dist cap. Does the rotor point to the #1 wire on the cap? You may be off a tooth.

 

I'm not off a tooth. I just reset the distro when I did the heads and it was fine for a week or so. Timing is exactly as I set it after the swap.

I mentioned it above, the distro is a mallory, with a pertronix ignitor ignition module. It's not points or HEI, per se. Sort of in between.

I'm really not sure how an ignition issue can cause the vacuum readings I'm getting. Can someone explain that to me? I can see the ignition issue as a result/symptom of something else, though. Just don't know what.....

 

If the valve timing is off, then your vacuum readings would be low. Valves would open and close at the wrong intervals, giving you a low vacuum reading.

 

I don't just have a low vac reading. I accepted that with the cam shaft that's in there and the high alt I live at.

The problem I have is that I have an erratic vacuum reading all of a sudden. To me, that indicates that some of the cylinders have issues. Using the timing light on the vac gauge, it shows cylinders 4 and 8 to be the problem cylinders.

The car ran great after both head swaps for a short time, then one time, I go to start the car up and it idles terribly. After a few tries, it'll idle ok, but has a metallic rattling sound and the vacuum is erratic at idle, but calms down as soon as you hit the gas.

If it's valve timing, what would cause the valve timing to be fine, then all of a sudden screwed up, then fixed with a head swap, then all of a sudden messed up again?

I'm not trying to be condesending or anything, I'm just having a hard time wrapping my head around a problem that comes and goes with each head swap.

 

Do you have a stock exhaust system? Could the heat riser butterfly be sticking? Isn't it usually on the right side where #4 and # 8 are? Just a thought...

 

i don't think this is mechanical......look at ignition and carburetion...i wonder if you have a egr valve sticking open

 

It's a 72....no egr. The exhaust is an aftermarket dual with headers...no heat pipe.

What ignition-wise would cause the erratic vacuum at idle?

That's the biggest symptom. My vac at idle was normal before yesterday afternoon, about 10"(because of the cam and altitude, that's normal compared to similar setups out here), but now it's very erratic at idle.

After swapping heads, the symptoms weren't there, but came on after 30 or 40 miles or so. I swapped the old heads back on and the same thing....ran great for 30 or 40 miles and the symptoms came back.

It's the same vacuum symptom that most places like chiltons, haynes, and online show as a worn valve guide. Erratic at idle but steadies at higher rpm.

Chris

 

why not misfiring

 

Because it didn't start the noticeable misfire until after the car started running badly. It doesn't take much to foul the plugs enough to cause a misfire.

The vacuum is easily the biggest symptom because it indicates something else is wrong. A misfire wouldn't cause a vacuum problem. But whatever's causing the vacuum issue could cause the car to run bad, foul the plugs and misfire.

Chris

 

Cylinders 4 and 8 are next to each other on the cap. As others suggested, you should not discount ignition so quickly. GL

 

How does an ignition problem cause a vacuum reading to change from steady to erratic????

I've seen some strange stuff on a car, but that really shouldn't make the vacuum have an erratic reading at idle, should it?

Chris

 

????

The only instance where the distributor is off by a tooth is when the vacuum cansiter is hitting something when trying to get the timing where it belongs.
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Since you re-installed another set of heads, did you examine the pair that were on the car? If they are fine, then the broken vavle guide theory goes out the window.

 

It's a mallory mechanical only distro anyhow.

Timing is right on, as said before, too.

Chris

 

OK...I am just going to throw some crazy stuff out here.

I had a similar problem...erratic idle and metallic noise. Turned out that the tach drive gear broke and was causing a slight rattling noise...it also caused the distributor to stick which made if feel like it was missing. At one point, it even caused the engine to stop. Needed a new shaft and gear which solved the problem.

Could it be multiple unrelated problems?

Fouled plugs indicating a too rich carb condition? Bad carb settings, etc. I didn't see what kind of carb, but if it is a q-jet, could it be that you have a vacuum leak around the shafts?

What about a misaligned intake gasket? Oil being sucked in? Vacuum leak?

Metal noises can come from just about anywhere...water pump, bearings, etc, broken valve springs? Sounds like you narrowed it down to 2 cylinders as the possible problem. Can you hear the metallic sound coming from those cyliders? Kind of wierd looking, but I have narrowed down metellic moises by attaching a small length of hose over a funnel end and then putting funnel to my ear as i went arround the top and bottom of the engine....I have found a main bearing failure, vacuum leaks, exhaust leaks (some which sounded metallic), waterpump noise, bad rocker arm, bad lifter, etc. just by "listening" to my engine this way.

Good luck and hang in there...you'll eventually figure it out.

 

OKI, I would be all over that ignition like stink on tschit.....

I had a crazy problem with my TPI hotrod '72 here.....those two wires on #5&6 cyl would ONLY break down when HOT, not when cold...headers...go figger....had a raggedy assed idle and terrible running habits.....cold start the damn thing was fine....
I put on a full set of Jacobs ceramic plug covers/ends.....cured THAT damn problem for sure....now to figger to scratch me *** over why NOT COLD, just HOT???

another thing....pertronics?? that coil....their gear has a terrible rep...you may want to change it out for something else....frankly, I would get a green grass common HEI and have over with it all....