Continuing with Wilson's problematic 72 Skylark

On the possible issue of a wiped lobe, you'd hear ticking/clacking I would think.
You hear ANY mechanical cacaphony

 

Mark,

Definitely on my list to check but there is no discernible mechanical noise at all. Only abnormal noise I hear is a header leak right at the head that I need to address.

Chris

 

Well guys... did some digging this evening on the 72.

Checked spark plug wire resistance. It went as follows:

#1 - 1.1k ohms
#2 - 1.5k ohms
#3 - 1.1k ohms
#4 - 11.6k ohms
#5 - 3.6k ohms
#6 - 9.3k ohms
#7 - 1.1k ohms
#8 - 1.4k ohms


Replacing wires, coil, and module just so I know they are new.

Also found 2 pushrods where the jam nut for adjustment was loose. Tightened those up as well; keeping preload the same.

I then decided to dive into what I was hoping would bring good results and drained oil and removed filter. Oil had a grey tint to it but looked clean. Thought it may have been remnants from Zinc additive.


Well, then I cut open the filter and found what I didn't want to find...metal in the oil filter.



I am now pretty confident a cam lobe is wiped out; probably #6. (that was the cylinder that original owner had some issues with in his OP) It definitely looks like cam or lifter material. Material is ferrous.



I was hoping that it wasn't a cam lobe or lifter but my experience and gut to my otherwise. This would explain my issues I'm having.

I am going to pull intake and see if I can't pull lifters to find the culprit... even though the proof is already there.

Sigh...

Chris

 

That's not un common to see on a fresh build, that's what filters are for to catch that stuff and keep it out of your bearings, don't pull that intake until you do a compression test, you can see a wiped lobe from looking at the rocker arms, you have not found enough of a problem yet, for the symptons your describing

 

No? The rebuild was about 10 years ago. I don't think last owner put a lot of miles on the car since then. The more I thought about it, I wonder if the grey tint I saw in oil was Zinc additive...?

There are some signs of small metallic pieces on the plastic Rocker guides but I have seen those on my GN motor and it runs fine.

How would one see it from just looking at rocker arm? If I try to measure the lift from rocker arm by turning it over by hand, the lifter isn't pressurized and will bleed down from spring pressure resulting in possible false measurements. Only way I could truly check actual cam lift would be to measure travel on the rocker skirt, correct? To do that, I would have to pull intake.

 

Here are some pics the last owner sent when he found#6 cylinder rockers had "become" loose. He didn't tear out the pushrods and check the lifter/mating cam lobe though.





Doesn't look like anything out of the norm here but still concerned due to excessive material.

 

have no problem doing that, just gonna be messy. Oil coming up the thru the pushrods...

 

Fairly new to BBB. Are they prone to any cam/misfire issues?

I know that last owner said that Wildcat performance out of GA built the motor. Hear that they are pretty reputable.

Just a turbo Buick guy that wanted a BBB.

 

If you have no issues with any mechanical noises such as lifter tick or rocker clack, AND your compression /leak down test turned out fine, look closer at the ignition/timing.
Can you post a video of the engine idling?
The way an engine idles usually tells a lot, a "rumipta rumipta" is a decent cam.
A "duh duh duh" is usually a hard miss, from a dead cylinder, and WILL NOT smooth out as RPM increases as it will when a decent cam with a lope at idle will.

 

Mark,

I still need to do cylinder compression/leak down test.

video that I have is attached in this:

https://youtu.be/N1IwxPTH868

The idle in the pic sounds like its a lumpy cam, but its a TA 212 cam; which doesn't have a real aggressive idle.

I feel I am getting the "duh duh duh". It definitely continues when I throttle the car all the way up the RPM scale. RPM increase is not smooth and car has no power.

Chris

 

More news....

Got a little time to work on the 72 this weekend (most was working on the brake upgrade on the Grand National).

I did a compression test on the motor. All 8 cylinders yielded 120-125 PSI. (test done on a cold motor) Replaced my ignition module and coil with ones from Davis Unified Ignition since they were stock GM ones and I figured what the hell.

Didn't get a chance to put wires on.

Fired car up (even though I know it was gonna run the same) and it started right up; and then shot a fireball out of the carb. Seems to run a little better but still not good. I am now certain that there is an issue with timing; either cam or actual. Still thinking the cam has a worn lobe....just need to yank intake to verify.

I spoke with the original owner and he stated that the car ran great for a little while and then start to slowly develop this problem. This has me thinking that one of the cam lobes slowly started to wear down and eventually fully affected the running condition.

And to top it off, the heater core decided to $hit the bed too. :-(

I will continue to keep everyone in the loop as to how things are going.

Chris

 

Being all cylinders were nearly the same psi, I seriously doubt a flat lobe.
Do a leak down test, that will tell all, especially if the valves are sealing.

 

I will tackle that here in the next few days. I planned on doing it this weekend, just ran out of time and my son was having way too much fun working on my GN with me.

Hoping to find something. If the leak down yields good results, the intake is coming off and I am gonna start pulling lifters.

Chris

 

All,

I wanted to touch base and let all involved in this post where I am with the 72.

I finally got a chance to do the cylinder leak down test on the 72. Of course, the motor was dead cold which can yield slightly higher leak down percentages.

So, with that said, listed are my leak down percentages per cylinder.

#1 - 18 %
#2 - 20 %
#3 - 20 %
#4 - 20 %
#5 - 18 %
#6 - 20 %
#7 - 20 %
#8 - 20 %

I am not too concerned about the higher leak down percentage (Harbor Freight LD tester and motor with low miles (rings still not seated)) as I am more of the fact that my cylinder leak down balance correlates to 2%. :TU:

The only slight leak I heard was from the crankcase on all 8 cylinders. no leaks in intake track or exhaust. No signs of leaks in the radiator or antifreeze being pushed out.

With that said, I feel pretty confident that the lower rotating assembly is good.

So, I decided to pull intake and check the cam lobes/lifters for any potential issues.

Pulled both rocker arm assemblies, push rods, and lifters.

All 16 push rods were the same length (adjustable push rods) and all 16 lifters spun in bores and came out very easy. All lifter bottoms had a mirror finish and the cam lobes looked perfect.

Can honestly say that the motor does not have a cam issue in terms of pre-mature wear.

I did notice that all 8 of my spark plugs are black as coal and 3 of them were actually fuel soaked when I pulled them.

I am thinking that the issue is definitely carb or ignition/timing related now. I am planning on trying a known good carb and seeing how that pans out. I already replaced the cap, rotor, ignition module, and coil. Still have to put the new wires on it. Definitely going to verify base timing and following Larry's Power timing your Buick procedure. :Brow:

The carb that was on the car is a Holley Street Demon carb. I don't have any experience with these. Most of my carb days were either old school Holley or the Edelbrock.

As always, feedback, questions, concerns are welcomed and appreciated!

Chris

 

Given the condition of the plugs, maybe the float in the carb isn't set right
and you are getting extra fuel seeping in? If the float is stuck open
maybe it is really flooding when the fuel pump is in action. Any gas in the oil?
I think you are making good progress, carb swap to get it running
again and really examine your timing and verify all cylinders are firing.
With the compression numbers you've posted there's no reason
for misfires. New plugs should be in order. Put the timing light
on each wire to verify they all fire off - if the plugs are all black
then they all work fine - your mixture is way too rich then.

 

Could be a blown or incorrect power valve. The power valve should be open only at high engine loads and thus throttle most of the way open to WOT. With the power valve open at idle and cruise, it will be pig rich and idle rough. If you engine idles in drive at, say, 10.5 inches of vacuum, you should have an 8.5 or slightly smaller power valve. Try a new one with the proper rating and make sure if there is a secondary power valve that it is the same rating and in working order too.

 

That was my thought. Never played with these Street Demon carbs. Thinking of just getting one of Mark's QJets and calling it a day.

I think that may be the case. Oil did have a little fuel smell to it and within 30 seconds of running, my entire garage is filled up with raw fuel smell.

Wanted to verify both compression, leak down, and upper valve train before moving to fuel and spark delivery. Pretty confident now.

 

That's the thing puddle, I don't even think that this carb has a PV in it. It looks to me like it replicates the Edelbrock Performer. Speaking with others on the board, sounds like my best bet is to run a Holley or get one of Mark's QJet.

Idle was terrible and vacuum was at like 12". Would run like $hit all the way through RPM range too. Never really cleared up.

 

Too much fuel like that will keep the rings from seating properly too.
I'm thinking a proper quadrajet is in order. If I remember correctly
Larry runs a Holley but only for racing, otherwise he recommends
the quadrajet and verify you have the proper distributor
for your engine as standard operating procedure.