Burnt Valve?

[MOPARJ]

Im thinking that after I tune up the 273 I spoke of previously(273 Options) and swap back to a 2bbl carb, and it still misses, it may be a burnt valve. Its an even miss it seems, not a severe miss. What would be all of the symptoms of a burnt valve?

 

[ValiantMike]

One sympton thats easy enough to check, would be a compression test. If you do test and one cylinder is lower than the others, this could indicate a burnt valve or burnt valve seat. Mike

 

[ramcharger]

Pull your plug wires one by one at the distributor cap until you find which cylinder is missing (no drop in rpm). Push the distributor end back in and check the wire for spark. If you have spark, check for a cracked plug. If the plug is not cracked, do a compression check. If your compression is good you do not have a burnt valve. If your compression is low, bring the missing cylinder to TDC on the compression stroke and load the cylinder with compressed air. If you hear air rushing out the exhaust, you have a burnt exhaust valve. If you hear air rushing out the carb, you a have burnt intake valve. If you hear air rushing out the valve covers, your rings or pistons are smoked. If the cylinder holds air, you might have a bent pushrod, collapsed lifter or flat lobe on the cam.

 

[MOPARJ]

Pull your plug wires one by one at the distributor cap until you find which cylinder is missing (no drop in rpm). Push the distributor end back in and check the wire for spark. If you have spark, check for a cracked plug. If the plug is not cracked, do a compression check. If your compression is good you do not have a burnt valve. If your compression is low, bring the missing cylinder to TDC on the compression stroke and load the cylinder with compressed air. If you hear air rushing out the exhaust, you have a burnt exhaust valve. If you hear air rushing out the carb, you a have burnt intake valve. If you hear air rushing out the valve covers, your rings or pistons are smoked. If the cylinder holds air, you might have a bent pushrod, collapsed lifter or flat lobe on the cam.

All distinct possibilities, although the only noise is the normal light valve tick from the solid cam. I still think there may be a vacuum leak from the bottom of the 4 bbl adapter that someone installed on the 2 bbl manifold, not to mention the #1407 750 Edelbrock carb drowning the motor! The guy, for lack of better words, must have been quite uninformed about overcarurating a motor of 4.5L/273"! I think throwing a 2bbl back on it that I have on the shelf may help somewhat. The exhaust smells of unburned fuel, which leads to my suspicion. I would try it today, but the local damn parts house can't get a base gasket for 3 days!! Maybe there is a 2bbl base gasket below the 4 bbl adapter that I can reuse for now? Or no gasket at all??!!! Haha. :sad1:

 

[ramcharger]

Maybe there is a 2bbl base gasket below the 4 bbl adapter that I can reuse for now? Or no gasket at all??!!! Haha. :sad1:

No joke! I've seen crazier stuff when I was a professional mechanic. Someone came in with their brake pads installed backwards. Metal on metal brother!

Oh yeah, pretty hard to collapse a lifter on solid cam motor! My duh. :sign6:

 

[66dartgt]

If after the 2bbl is on it and you follow all the recommended checks above, and find nothing wrong - maybe the valves need adjustment. Perhaps one of the adjusters backed off, the oem rockers use a friction adjuster, in other words no lock nut to hold the adjuster in place. Maybe that might be part of the story. worth checking after the other stuff. You can replace the friction adjusters with standard locking types btw.

 

[mr.318]

here's one my uncle said they use to check burnt vavles by putting a dollarbill at the tailpipe if it wants to suck the bill up the pipe it's a burnt vavle if you have duals you can tell which side

 

[racyroy1]

mr.318 that is funny as all get out,,,, i was just scrolling down to suggest the same,,,,, I've done it and it works lol!!!! Plus you also hear a sssst, sssst sound out of the exhaust

 

[moper]

My old plow has several burnt valves...lol. And yes, the vaccum has a unique note/pop to it because of it...