Hey all...new guy here. I've been a SB/BB guy my entire life and I just recently picked up a nice '67 FB Barracuda with a /6. It runs GREAT on 5 cyls. I've pulled the valve cover and adjusted the valves hoping that #6 had a valve being held open or something. I have good spark to the cyl. Bad thing is, I can hold my finger to the spark plug hole (with the spark plug removed, of course) and there is hardly ANY compression on that cyl. The motor makes NO noise and again, runs great on the other 5 cyls. I'm thinking of pulling the head this weekend to see if I have a bent valve or something, but any time I've had a bent valve on an 8 it ticked or knocked because of it...this 225 makes no noise, just purrs and does not fire on #6. Standing behind the car I can hear that cyl missing every beat..."pack pack pack". Any ideas what I'm facing?

...broken compression rings, wah wah. (I'd bet).

What's the crankcase pressure like? Is it blowing out the oil fill when you take the cap off, even with the PCV hooked up?

D/W

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If it ain't broke, fix it!

Bad valve guides?

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Bet you anything its a burned exhaust valve. I'm assuming that all the rockers MOVED when you were adjusting them- it might also have a wiped-off cam lobe so that a valve isn't opening. But I'd bet on a burned exhaust valve. Its a pre-unleaded engine, and although most slant-6 engines tolerate unleaded fine, a lot of highway driving, high-RPM driving, or hard driving WILL burn a valve occasionally on any engine not designed for unleaded. I had it happen on my '66 383 when I started using it for a 27-mile daily highway commute back in '91. It had survived fine on unleaded up to that point, but not with routine highway driving.

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...the bets are in.

D/W

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If it ain't broke, fix it!

Not gonna be that. Those just cause clouds of blue smoke, not dead cylinders. I'm putting my bet on bad exhaust valve.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Sweet...thanks all. I'm pulling the head this weekend.

BTW...I don't have any blowback through the breather tube that I can tell. I'll check again this evening when I get home from work.

That would make the case for a valve. Either way, you're gonna be pulling the head, so get to it!

D/W

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If it ain't broke, fix it!

THANKS Dennis!!

Well...it's running on all 6 now. I don't know WTH I did , but it's runnning smooth on all 6. I took it for a drive this morning and it was running semi-rough. I went out tonight to mess with the lights (couple of bulbs, adjust headlights, etc...) and when I started it, it sounded smooth. I was like, WTH? Took it for a spin and it's been running on all 6 since. I guess it was the threat of tearing it apart...

I had a similar expreience early this year. mine was running on 4cyls. for a week then got back to 5 for about a week and on Friday of the third week the thing began to gain #6 in the morning and on the drive home fully recovered. I believe some crap got stuck on the valve head causing misfire until it burned off.

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ifyoubegintothinkyou'relosingcontrol...it'salreadygone

Glad you got the cuda back to running on 6, Our '73 duster was running
on 5 to. I dunno what happened but we pulled the rocker arm shaft and
discovered it had a bent pushrod on the #3 cylinder This
was on a little old lady car with 82k on it. But you never know what
will go wrong with a car that sits for a long period of time. Which was the case with this car, lots of sludge and build up....

When I first got my Dart the same thing happened to it. The first thing I did was check the spark plug...the tip had been broken off. I pulled the head and found so much carbon in there that it would make the baby jesus cry. Turns a large bit of it had gotten loose, broken the spark plug, and then wedged itself in the exhaust valve. Luckily, nothing else was damaged.

-josh

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64 Dart 170 /6

If it had been sitting a long time before you got it, it might have just had a stuck valve (although I'd expect that to make a tapping racket since the pushrod/rocker would be pretty darned loose). My '49 Plymouth flathead six gets sticky valves when it sits for a long time, but its a lot more common on flathead engines than OHV engines.

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