On Monday my car just starting running bad. I pulled off the freeway and it wanted to quit at the next light. I feathered and kept extra gas into it, it would idle at about 1100RPMS. If I just let off the gas in gear it would quit in a hurry. The engine is a rebuilt 1969 4-bolt main 350. New .060 pistons, rings, all bearings, crank turned .020 and the block was decked. We re-used my 1 season old double-roller timing set, XE268 cam and lifters and oil pump. I have the Summit brand cast iron heads just now on their third season. HEI ignition with new wires. I have been running this for about 6 weeks now.

Many of the plugs were fouled and after searching through here I decided to replace the intake and gasket. It seemed there was a lot of oil up onto the intake gasket when I pulled it so I figured I had found the problem. It is just as bad now so I was pretty disappointed. My vacuum gauge is bouncing violently between 5 and 10 which could be a bad head gasket. I plugged all the vacuum lines and sprayed carb cleaner while running but found no vacuum leaks. I checked some of the valve adjustments and they were fine, about 3/4 turn more after clacking stops.

I am going to try a different HEI I have just to verify spark or spark jumping. I will try a different carb I have as well. I am also going to pick up a compression tester tomorrow and start that process. I still feel like it is something little and not a bad valve, head gasket or piston/rings but you never know so for now I need to get to bed. Three nights of troubleshooting has worn me out.

My questions are:

How do you do compression testing?

What do you think my problem is?

Suppose to be headed to the race track Friday, hope I make it!!!

THANK YOU!!!

With a vacuum gauge bouncing, I would look at valve train. Pull the valve covers check your rockers etc. Maybe a busted valve spring,,, is it popping out the exhaust or carb?

Dave

Check Scenario 6 through 9 on this site: http://www.secondchancegarage.com/public/186.cfm

Seems like Dave may have hit the nail on the head.

yeppers, a broken valve spring is a prime candidate here, along with other valvetrain stuff like broken rockers, pulled studs, bent pushrods, flat lobes, etc. I get the valve covers off and crank it without starting while inspecting all 16 valves for movement.

I did have the valve covers off already and adjusted a few valves. I didn't notice anything odd about the rocker arms and the push rods were spinning. I will go through every valve now. The PCV valve, which is connected to the base of the carb, was violently bouncing up and down as well. Scenario 5, 6 or 8 fit my problem. The compression test will help me narrow this down.

Here are the findings of a compression test:

1 - 180
2 - 180
3 - 180
4 - 189
5 - 180
6 - 185
7 - 170
8 - 170

I guess I will swap out the distributor. If no change then the carb. If no change then ???

Did you check out the spark plug wires for cross firing?

I think I would check to see if there was any dirt in the needle and seat of the carb. If the plugs are black and wet, could be something got in there is holding the needle off the seat, letting in too much gas and causing it to flood. Is the tailpipe wet and excessive fuel running out? Pull the dipstick and smell the oil. Does it smell gassy? I would suspect something like that before a broken valve spring or something of that nature. Pretty easy to check too.

I only know how to check for cross-fire on plug wires at night and watch for the arching, how do you do it in the light? I am swapping the carb next but I will smell the oil too before I do that. If it does have a gas smell should I change the oil and filter?

Just a thought, are you running vacuum boosted power brakes?? If so did you pull & plug the vacuum line to the booster while checking?

I do not have power brakes so that rules that out. When I pulled the carb there was a lot of oil in the runners just below the carb. I think I am still pulling oil from the lifter valley so I am headed to TNT to get the thicker gaskets and try that trick again!

Ok... Your symptoms & evidence seem to indicate to me a vacuum leak somewhere. The compression test results rule out the lower end & valve sealing.

If you were sucking oil into the intake passages my next guess would be you lost the intake to head seal somewhere.

You mentioned the block was decked. This will change the angle/clearances between the intake & head sealing surfaces. Before doing anything with the new gaskets, dry-fit the intake without gaskets on the block. Take a look at the intake to head seam. You should have a reasonably equal gap (the gap that the gasket seals) with the manifold centered - If it's a severe taper (nearly pinched at the top or bottom) you'll have a tough time getting it to seal... you may have to have your manifold milled to match the new angle created by the block decking.

If everything seems to be OK, just do the intake install by the book. Just be extra careful setting the intake in place as to not shift the gaskets. Don't rush, clean/scrape everything, wipe the mating surfaces with acetone or laquer thinner, and use the correct sealants.

To check for cross firing, with the car running, I take a mister bottle with water and spray (mist) around the wires where they they cross are run together. You will hear the sounds of a 'short zap' (best as I can describe it) and may also see it.

I found I had cracked insulation jacket on a wire. The crack was so fine that you would not have spotted it unless you flexed the wire back.

It is all back together, will know in the morning if the double thick gasket will do the trick!

No difference, I am going to have to get another set of fresh eyes to look at this thing.

More info:

The vacuum is better but still bounces between 3 and 7. The PCV valve also reflects that as it is rapidly going up and down. When I plugged the nipple on the intake to the PCV valve it made no difference. If I let the rpm's get down to 1,000 it sounds like an old washing machine which can be heard from the carb. I do also get occasional lifter noise after I rev it up a bit and the rpm's are coming down. I am sure there is still oil in the intake just below the carb.

STILL GOING CRAZY

3 to 7 inches vacuum? How big a cam do you have in there?

I use to have a steady 12 or so prior to this thing freaking out this week. I only have the CompCams XE268 so not even .500 lift! I am going to try a different PCV valve as I have one in the drawer but I am sure it won't change anything. Starting to lose heart here...

One guy said the 1" carb space is cracked, removed that but no change. The guy that assembled my engine is coming by tomorrow. He wanted me to pull the intake off again and is sure there is a fitment problem with the intake. It is possible the block was decked previously which adds the the issue.

Here is a link to the picture I took last night after removing the intake. I only applied sealant to the bottom.

http://209.98.143.150/engine1280.jpg

Pic from link above.

http://209.98.143.150/engine1280.jpg

It looks like you are drawing oil into the head on the passenger rear side.

Does the pcv valve hose dump into the intake manifold over that intake runner or connecting at the base of the carb?

Are you using any type sealer/sealant between the intake gasket and intake manifold?

Try a different carb and intake manifold?

Maybe the intake manifold warped or carb has a crack in it?

Thanks for changing the thread John so the picture just shows up. I agree with your diagnosis. The PCV is attached at the base of the carb. For this installation, the double-thick intake gasket) I completely covered the intake gasket on the head side with sealant but none on the intake side. The previous install using a standard intake gasket I used some around the ports on both sides. I bought a brand new intake and tried a different carb ... to no avail.

The circles are probably the ports that leak...
The arrows point to the "witness" marks where the intake was sealing...
The rectangle is probably the area not getting gasket compression, and sucking oil.
http://www.chevelles.com/showroom/data/500/medium/Leakspots.jpg

Go back to the previous larger pic...

See the imprint on the gasket? Imagine that imprint in a port shape to the lower sealing surface. You weren't getting a seal.

Darren,

Here is an idea.

Put a small thin but wide bead of rtv on the intake manifold gasket (between the gasket and intake manifold) and let it start to setup. Then put the manifold on and lightly tighten. Let it set up some more and then tighten to final spec.

I just re-did all that last night with a new Fel-Pro 1204 gasket. Not exactly as you said but close. Still runs bad. I drained the oil thinking I would find metal from wiped cam lobes, nope. I replaced the cap and coil on the HEI as that is the only electrical thing that wasn't touched, nope. Another new finding is that the exhaust on the drivers side is cold, passengers side OK! I have full dual exhaust on each side with glass-packs so nothing funky there.

Ready to give up here...

Still runs bad. I drained the oil thinking I would find metal from wiped cam lobes, nope. I replaced the cap and coil on the HEI as that is the only electrical thing that wasn't touched, nope. Another new finding is that the exhaust on the drivers side is cold, passengers side OK! I have full dual exhaust on each side with glass-packs so nothing funky there.


Let's stop throwing parts at this thing, and figure out what's wrong....

Known:
1) Car was running well until whatever happened, uh, happened.... no bangs, clunks, crunches, or other nasty noises.
2) All cylinders have good compression, +/- 10% of eachother = good head gaskets, no stuck valves, good valve seal.... rules out bottom end and cylinder side of heads.

Unknown:
1) Ignition. Why change the coil & cap? They were working before the incident. Go back to known parts.
2) Plugs. Plugs could be fouled from the oil, or one cracked on the suspect cylinder bank. Change the plugs to new or good known used.
3) Wires. Double check that all plug boots are firmly clicked onto the plugs. Inspect for cuts or burns.
4) Cold exhaust on driver's side. Is this at the tailpipe, or by touching each header tube on the "bad" side?

I still think you've got a bad/not getting an intake seal.
Referring back to those "witness" marks on the gaskets, it looks like your manifold is seating/bedding-in higher on the ports than it should be - and the lower surfaces between intake ports aren't getting enough sealing surface or clamping force. If you'll look closely there are no witness marks on the bottoms of the ports.
This all points back to the block being decked, which is going to narrow the distance between heads, which will cause the manifold to sit higher in the "Vee" created between the heads. The thicker gaskets are double-edged sword. By being thicker they may seal an excessive gap... but in your case (I think) they are narrowing the "Vee" even more - compounding the problem.

Did you try "dry-fitting" the manifold? What were the results of the inspection?

We dry fitted the manifold last night, no obvious issues. I don't know how I missed it before but #7 intake valve spring is broken! Checker has a set CCA-981-16 on the shelf. I should replace them all but am going to be lazy and just do the broken one. I hope to have it done yet tonight!!!

I am sure you found it, a broken valve spring may not cause bad compression during cranking, but idling it could be floating.

Dave

Thank you John D for stopping by last night and helping me replace the valve spring! The push rod was bent as well, probably as a result of the valve spring breaking. I am grateful for all the new knowledge I gained, couple of new tools in my tool box and the blessing of you all!!!