LiveandLetDrive

Some specs:
383 based on 350 LT-1 block, Al heads.
Comp Cams 286XR solid roller, 1.5:1 roller rockers
Accel 7 DFI, sequential MPFI, dual-synch distr.


So here's the story to date: The car started to run extremely rough and did not want to stay running. Eventually the valve covers were pulled and #6 intake pushrod was broken (the rocker-end tip had actually been bashed down about 1/2".) I thought it must have snuck past QC with improper hardness. No wear on the sides of any pushrods. That valve stem tip (and to a lesser degree a couple others) were a bit flattened out as if they'd been slapped hard. I figured I had probably let it go too long without adjustment as it only has a few thousand on it since its build.

So, I replace all 16 pushrods (correct length) and the damaged roller rocker, reassemble, ... and the poor running is essentially the same as before. I did compression and leakdown tests, all cylinders (most notably #6) are stellar. Replaced all plugs, wires are newish and look good.

[[Intermission for several months sitting and not running, shame on me...]]

Today, determined to finally find the problem, I go looking for a bent valve and take the springs off. Nope, travels smoothly. Rotates easily at all points of travel including closed. This was my best guess as being "downstream" in the valvetrain from the source of force it best explained the busted pushrod. Ok, so my final theory is wiped cam or busted lifter. Took off the guide plate and pulled the pair of lifters out through the head ... Nope, lifter looks practically new, cam lobe the same. As far as I can tell the valvetrain is in perfect health.



At this point I am out of good ideas and moving on to bad ones. As much as House MD has taught me not to accept coincidence as a diagnosis, I'm wondering if the running problem may be unrelated to the mechanical failure.

I have not changed anything in the EFI setup to date but my next plan at this point is to put everything back together and hook up the new work laptop and see what I can see. No idea how to use it but presumably it should put out some useful OBD2-esque codes? Any better ideas anyone?

LiveandLetDrive

Damage:







Pulled lifters, no damage:



Poor shot of an apparently undamaged cam lobe:

myk7

If the plugs and wires are good, I'd be thinking when the push rod came out of it's cup and was riding on the face of the rocker arm, it pushed the valve too far and tagged the piston, but the compression/leak down tests would have been wonky.

What do the spark plugs look like?

Also wonder if that lifter is shot.. I'd probably run the car with the valve cover off just to see how things are working.

LiveandLetDrive

I haven't had a good look at the plugs since I replaced the pushrod, once I get it running again I will take a look. Of course back when the pushrod was broken #6 was wet with fuel. The others looked okay.

I don't think there's anything in the lifter to be shot. The roller feels fine and that's the only moving part. Oil passages seemed to be clear as far as I could tell.

-Chris

SmokinBBC

Just wondering if you have the accel dist in there. Did you have to change the gear on it? How's the timing?

LiveandLetDrive

It's a Mallory, or at least the cap is. I didn't build it so I'm learning as things break... I should be able to comment on the timing once I run it with the laptop plugged in.

LiveandLetDrive

Well today has been a mixed bag. I got everything back together and went to fill the coolant back up... and it poured right out onto the ground! I thought I'd left open the block drain plugs open but it turned out to be two freeze plugs that had pushed out. One behind the starter (plug AWOL), and one behind the driver motor mount The H2O %age must have gotten too low while I was still in NY. It certainly hasn't happened since I've been in CA. So now I have that to tackle...

On the plus side, I got everything back together and decided to run it for ~30 seconds without coolant just to see if anything had changed and to grab some data onto the laptop. Despite seemingly nothing changing, she ran beautifully and throttle response was perfect! No sign of the misfire, though without knowing where it went it could very well come back at any time...

If it wasn't for the damned freeze plugs I would be out driving it now for the first time in nearly a year!! Soon... very soon... Off to the autoparts store now to at least get some rubber type plugs until I can get some proper replacements in!

FYI: From what I've seen so far, these look like the dog's bollocks for hard-to-reach freeze plug replacement:

http://www.dormanproducts.com/p-1011-02483.aspx


Data logging via CalMap. Unfortunately it limits you to the values seen here, no temperatures or any of the rest it is capable of seeing from the car but apparently unwilling to record... Still useful information though.

LiveandLetDrive

You see, the funny thing about things that seem to good to be true is...

Water in the oil.

It "magically" ran so well suddenly when I recklessly ran it for a minute without coolant. I filled it up again and suddenly the oil level doubled. I started it and the oil turned to milk and running was back to rough again. I'm hoping it is just a head gasket, which will see me back on the road in 2 weeks. (Next weekend is a rock festival.)

This explains the blown-out freeze plugs (compression pressure was getting to the coolant) and the rapidly filling oil catch-can. And of course the rough running. This does not explain why I never saw milky oil before, compression and leakdown tests were good, etc. For the compression test it could be that I didn't listen in the right place to hear the air escape as I was mostly expecting piston, ring, or valve problems.

Anyway, another step closer...

LiveandLetDrive

Further analysis:



It's been pointed out to me that the "freeze" plugs do not necessarily protect in freezing (they're intended to get out casting sand) so if the plugs came out due to freezing I may well have a cracked block. When I have the heads off I will take the oil pan off and fill the block with water to see if anything finds its way out the bottom. If so then my original LT-1 block is scrap.

Considering that A) the oil pressure gauge still reads high and B) the oil is milky but not the water suggests that the water must be getting somewhere low-pressure. That is probably bad and less likely to be head gasket...

Does it sound realistic to anyone that cylinder pressure into the coolant circuit could have blown out freeze plugs? (Only 2 popped.) Whenever they went it was not while parked in my possession, though it could have been while on the transport truck being moved out here from NY in December. They didn't report anything but who knows. I never had a puddle or found the missing plug. If it happened while running then obviously it wasn't a freeze.

Another symptom: when the radiator is filled to the brim, it slowly drains back out again to about 4" from the top. I think this is about head gasket height, though it could be something else high in the engine! Definitely not low enough to be low in the water jacket/cylinder wall.

I will post up what I find when the heads come off.

LiveandLetDrive

Cracked block

Mmm, bisquick:


Snap, crack(le), pop.


Fortunately I picked up a low-mile, original bore, 010 '70 Camaro block 7 years ago for $20. Who knows how long it will be until I can get it prepped and the whole thing rebuilt though... On the other hand, the stockpile of original '70 LT-1 parts just became rather redundant for a car that no longer has its original block. Potential funding source?