Help needed from SBC Experts (1 Viewer)

[fzr400guy]

I'm running a gen 1 SBC 350 Crate motor
MSD 6A
MSD Pro Billet Vacuum advance Dist
Rochester Quadrajet

It's running rough like it's mis-firing or missing a cylinder and makes 1 tick from the valve above the number 1 cylinder when I shut it off.

I have replaced the plugs
plug wires
cleaned out the cap and rotor
checked the impedence on the magnetic pick-up
checked the MSD 6A
checked the timing (nothing has changed)

What have I missed?

The cap and rotor still looked serviceable after I wire brushed the contacts. Would replacing these possibly fix my issue?

 

[inkpot]

If the misfire is a constant pattern, then the problem is one particular cylinder. If it is random, then it could be about anything. Have you checked for vacuum leaks? You could try pulling off one spark plug wire at a time to isolate each cylinder to see which one does NOT make a difference. John

 

[nick1860]

pull the valve cover off and check your rocker arm, pushrod, and valve spring

 

[DAD2SIX]

If you are hearing a ticking noise when you shut it off that's not normal. A broken rocker arm / stud or pushrod or other valvetrain issue would cause a miss and a noise. I would take the valve cover off and check it out.

 

[fzr400guy]

The tick and misfire is definately in the # 1 cylinder. Looks like I'm popping of the valve cover tomorrow morning.

 

[pb4ugo]

What's the history of the "crate" motor? Did it run good b4?

 

[fzr400guy]

It ran perfectly before then all of the sudden it went to crap. Was hoping it was an ignition issue but I've now ruled that out. Very anoying since the damn thing only has 60,000 miles on it.

 

[crashn]

Pull the valve cover first and look for problems. If you find nothing wrong then do what Inkpot said, he is right on. A sticky lifter will make a noise and cause problems also. Good Luck

 

[fzr400guy]

Well pulled off the one valve cover and the rocker, lifter, and valve spring are fine. Ran out of daylight today so I will pull off the other side tomorrow and just in case do a full valve adjustment. Maybe they got screwed up some how.
Any suggestion on what adjustment process I should use?

 

[Cdaniel]

The hydraulic valve train really shouldn't need any adjustment unless there are a bunch on miles on it. If you find something loose it could be rocker stud pulling out or a cam lobe going flat. Might explain a tick, but maybe not explaining the miss so much. Is it missing always? Only at idle? A compression check on your suspect cylinder might give a clue too. Intake manifold gasket leak on paritcular cylinder?

 

[nspctr1]

The ticking could be a misfire from a plug wire making contact with a metallic surface. Pull the wires and see which cylinder doesn't respond, check that wire. If you have gone thru deep water recently, it is possible the distributor cap cracked.....02

 

[msapers]

SBC Valve adjustment: With the cylinder at TDC on the compression stroke (both valves closed, loosen both rocker nuts, grasp one pushrod between your thumb and first finger. Slowly tighten the rocker nut while rolling the pushrod between your thumb and forfinger until it no longer spins freely. Then give the rocker nut an additional 3/4 of a turn. Repeat for each valve.

 

[Weber Sarge]

Also, check to make sure none of them are overtightened , it happens a lot . Compression test as mentioned is the best idea , at least narrow the problem down to a specific cylinder .
Sarge

 

[1 Bad FN FJ]

I'm assuming that you are running an HEI distributor? You said you clean the cap and rotor, but you have 60,000 miles on the ignition? When you took your rotor off did you notice any rust like material under the cap, and around the pins holding the weights for the mechanical advance? If you did the rotor is bad and the spark is shorting out to the pins. Common problem on Hei. Try simple things first. Just installed an 383 crate motor in my cruiser with new dist. Had a miss fire and the rotor was shorting out. Use dielectric grease on coil contact, rotor contact, and grease the pins for mechanical advance.

 

[ibinazbass]

You can also do a running valve adjustment which makes a mess but is more accurate. Idle the engine with one valve cover off at a time. Loosen one rocker arm at a time and tighten it again until the ticking stops. Once the ticking stops, tighten the nut another half turn.

 

[Plowboy]

You can also do a running valve adjustment which makes a mess but is more accurate. Idle the engine with one valve cover off at a time. Loosen one rocker arm at a time and tighten it again until the ticking stops. Once the ticking stops, tighten the nut another half turn.

I always cover the top of each rocker with a small piece of aluminum foil. Cuts down on the oil squirting out of the head

 

[pbgbottle]

I took an old rocker cover and cut part of the top off of it to try and keep the mess to a minimum when adjusting rockers on a running motor.

Sent from my iPhone using IH8MUD

 

[fzr400guy]

Ok, so after all the hassle of checking the timing, replacing the plugs, plug wires, checking the valve train, and doing a fresh valve adjustment, the mis-fire issue still persisted. So finally I replaced the MSD cap and rotor and bam everything is fine. It figures the last and simplest thing would be the problem!!!!!

I guess 60,000 miles with some water exposure was all the old cap and rotor could take.

 

[35snmud]

Shoot, I have had 500 miles on a new cap and rotor and it wouldn't start. Checked everything besides that because I knew it was fairly new. Finally replaced, fired right up.

Glad you got it sorted out.