Idle went nuts.

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Trevor B

Trevor B

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I took my wife for a drive in the new family member, a '68 Barracuda (225, most likely rebuilt but possibly by someone with even poorer mechanical skills than me) and after about 25 miles of highway, advancing at a stop sign, it suddenly felt like the throttle got stuck halfway open. Luckily the little slant six didn't overpower the brakes. Anyway, I pulled over and towed her home but now it's time to try to figure out what happened. Here's what I know:
1) I don't know very much about slant six engines.
2) The carb that came with the car was a weird Holley 2209 from an AMC so...
3) I replaced it with a Holley 2280, as I saw recommended as on the Slant Six forum. No choke.
4) The throttle linkage is not exactly straight but after some tinkering, got it to work fine
5) There was no stud for the air filter so I fashioned one with a piece of 1/4 20 and a few nuts and a washer. (I've driven this car a few hundred miles with no problems)
6) After today's episode, when I popped the hood at the side of the road, the nuts and bolt holding the air cleaner had disappeared. The throttle is in idle position.
7) If I start the car, she jumps up to what sounds like 2000+ rpm, and I hear something like an intermittent clatter (but shut it off pretty quick, fearing the worst)

Before I remove the intake and look for carnage:
What might make this happen?
Is it possible that the washer (or nut, or stud) could have gotten sucked into the intake?

Also... totally embarrassing when some dudes are admiring your car in a parking lot and a tow truck shows up.
 
Disconnect your throttle cable from the carb and see if the carb returns to its normal rest position. If that doesn't do it, pull the carb to see if somethings going on with the carb. If your idle is still too high whatever it is is still there. It is quite possible that something may have fallen into the carb, the carb is stuck somewhere, or something fell behind the gas pedal pivot.
 
Trevor B said:
I took my wife for a drive in the new family member, a '68 Barracuda (225, most likely rebuilt but possibly by someone with even poorer mechanical skills than me) and after about 25 miles of highway, advancing at a stop sign, it suddenly felt like the throttle got stuck halfway open. Luckily the little slant six didn't overpower the brakes. Anyway, I pulled over and towed her home but now it's time to try to figure out what happened. Here's what I know:
1) I don't know very much about slant six engines.
2) The carb that came with the car was a weird Holley 2209 from an AMC so...
3) I replaced it with a Holley 2280, as I saw recommended as on the Slant Six forum. No choke.
4) The throttle linkage is not exactly straight but after some tinkering, got it to work fine
5) There was no stud for the air filter so I fashioned one with a piece of 1/4 20 and a few nuts and a washer. (I've driven this car a few hundred miles with no problems)
6) After today's episode, when I popped the hood at the side of the road, the nuts and bolt holding the air cleaner had disappeared. The throttle is in idle position.
7) If I start the car, she jumps up to what sounds like 2000+ rpm, and I hear something like an intermittent clatter (but shut it off pretty quick, fearing the worst)

Before I remove the intake and look for carnage:
What might make this happen?
Is it possible that the washer (or nut, or stud) could have gotten sucked into the intake?

Also... totally embarrassing when some dudes are admiring your car in a parking lot and a tow truck shows up.
Click to expand...


If there was an air cleaner on it the whole time and the nuts disappeared, thee is only one place they could have gone.
 
Yes.
Idle screw is snug against stop on carb.
This makes total sense - I'll pull the carb and look inside - if something got caught in the throttle blade at the intake it would definitely keep it open. Now why didn't I think of that? Tomorrow we'll see what's in there and pray it's everything!
 
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It's not your fast idle cam that the carb is stopped on? It might be stuck there. If your plate is closed you should be able to see that from the top with a flashlight.
 
I just pulled the carb. The nut/bolt is nowhere to be found and one of the throttle blades has been bent partially open - the high idle is explained. So the hardware certainly got sucked in. Could that kind of thing clear an intake valve? I'm guessing the next step is to pull off the intake/header. Happy New Year or something...

I really hope this engine is not toast.
 
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Trevor B said:
I just pulled the carb. The nut/bolt is nowhere to be found and one of the throttle blades has been bent partially open - the high idle is explained. So the hardware certainly got sucked in. Could that kind of thing clear an intake valve? I'm guessing the next step is to pull off the intake/header. Happy New Year or something...

Is this engine toast?
Click to expand...

It might just be bouncing around on top of the intake valve. So, yeah, pull the intake and check. If you can't find it, off with it's head and pray the damage isn't too bad. Good luck.

Al
 
Good chance the bolt is dancing on the back of an intake valve...or stuck into a piston. if it hiccuped ...it went through or was between the valve and seat momentarily. If it runs as well as it did before this with the throttle blade fixed, then when apart you can't find the bolt, then likely it passed or is in the piston. Listen at the muffler or exhaust butterfly for it.
 
I bought a USB endoscope for $17 on ebay. Works great. I know it will fit thru a spark plug hole because I used it to go thru an O2 sensor hole (same thread) to view a catalytic converter. You can also snake it down the intake runners.

Don't remove the intake manifold before reading the detailed write-up on slantsix.org. If you don't orient the triangle and cone washers correctly, the exhaust will later crack, and don't assume the last guy knew how.
 
I actually just bought a (much) more expensive camera at the local parts store. "Looked" in the intake and didn't see too much. But I used the little magnet attachment and pulled a small, and totally unidentifiable, piece of metal out of the #1 cylinder intake. There is no doubt that the bolt and nut went into the cylinder(s). I've been reading the slantsix.org stuff - thanks! I'm also taking a bunch of pictures of everything. This engine has a header on it and some kind of frame-harness over the intake and header that does not appear in any of the pictures in the manual.

Unfortunately, it's been raining cats and dogs for the last two days so I haven't gotten to pulling the intake or looking in the spark plug holes. But I have almost zero doubt that the head's going to have to come off. If there is damage to the head and/or cylinders, it's going to raise some questions about what to do next... replace the slant six or go with a small block.

If, on the other hand, I get really lucky, I have another small Holley 2 bbl carb that should be available to raid to replace the damaged throttle blade.

Will update as soon as I have more info.
 
Well - here are the results in pictures:
1) you can see the damage to pistons #1 and 3 - there are scraps of the washer in #1 and the entire nut in #3. The scraps in #3 are bits of spark plug. I found the bolt, complete and undamaged in the intake behind #4
2) cylinder #1
3) cylinder #3
4) plug from #1
5) #1 chamber
6) #3 chamber
20170104_122054.jpg
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20170104_122203.jpg
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20170104_122222.jpg

Is there hope or am I shopping for a new engine?
 
Ouch...
Had very similar issue with my Merc 470 boat motor.
Put new head gasket in it and it still runs today.. 8+ years.
 
Trevor B said:
Well - here are the results in pictures:
1) you can see the damage to pistons #1 and 3 - there are scraps of the washer in #1 and the entire nut in #3. The scraps in #3 are bits of spark plug. I found the bolt, complete and undamaged in the intake behind #4
2) cylinder #1
3) cylinder #3
4) plug from #1
5) #1 chamber
6) #3 chamber
View attachment 1715004396 View attachment 1715004397 View attachment 1715004398 View attachment 1715004399 View attachment 1715004400 View attachment 1715004401
Is there hope or am I shopping for a new engine?
Click to expand...
Check the valve seats and valve face on the effected cylinders, then if they are good and the cyl walls aren't all gouged up, put it back together and drive it.
 
MOPAROFFICIAL said:
Check the valve seats and valve face on the effected cylinders, then if they are good and the cyl walls aren't all gouged up, put it back together and drive it.
Click to expand...

Should I take the head to a machinist to check for cracks? Also, if the valve seats are beat up, is that something that can be repaired?

Do you think I should pop out the #1 and 3 pistons to make sure a rod didn't get bent? I'm thinking especially about #3, where that not-compressible nut was bouncing around.
 
Does it look cracked ?
The head/rod are stronger than the nut.
Go ahead and have it checked, I mean.. it would be a great time to re con it if the valves are low set, sunk anyhow.You're just a drive away from a shop at this point.
Oh and think hard on if you are going to stick with a slant before dumping money into big valves and the porting to make them work.
 
I pulled the intake valves from #s 1 and 3 (exhaust valves won't come out - does this mean the valve guides have been "knurled"?). Valves don't look too thrashed. There are a few little marks on the #1 intake valve seat but nothing too awful.

MOPAROFFICIAL said:
Does it look cracked ?
The head/rod are stronger than the nut.
Go ahead and have it checked, I mean.. it would be a great time to re con it if the valves are low set, sunk anyhow.You're just a drive away from a shop at this point.
Oh and think hard on if you are going to stick with a slant before dumping money into big valves and the porting to make them work.
Click to expand...

I do not see any cracks. It will go to the machinist for checking tomorrow. So don't bother trying to pull the pistons to check?

MOPAROFFICIAL: It's a really good point you make about dropping $ on the six. On one hand, it's kind of a cool engine (I think) and it's not gutless or anything. And my Duster is where I've been concentrating on power and speed. On the other hand, I'm building a 360 for the Duster, which would leave me with a decent 318 that could go in the Barracuda. But then I'd have to deal with a transmission and probably a rear end. Argh!

By the way... anyone who has read some of my posts may come to the conclusion that I am, in fact, an idiot. Believe it or not, there is nowhere else in my life where these kind of incredibly dumb and costly mistakes happen. Yet I love these cars and cannot give up what has become the most satisfying and fun thing going.

Thank you, in any event, for your help. Will update when I have more information
 
Okay - engine is coming out. There is scoring in the piston walls. Also, the water pump, which was disconnected from the leaking heater core, was so gummed up with deposits that it leads me to believe there is more going on with this engine than I had thought. I want to take it apart and get everything right.

Does anyone have any advice for balanced lift points with the head removed? Also, do I need to support the transmission in any way?

Thanks.
 
Trevor B said:
By the way... anyone who has read some of my posts may come to the conclusion that I am, in fact, an idiot. Believe it or not, there is nowhere else in my life where these kind of incredibly dumb and costly mistakes happen. Yet I love these cars and cannot give up what has become the most satisfying and fun thing going.

Thank you, in any event, for your help. Will update when I have more information
Click to expand...

Here's what strikes me. within the past couple of weeks,,,, I don't recall what was the thread title or topic, I posted a memory story about a friend and his Camaro. The little piece of all thread that had held the breather on dropped into and fecked his engine. That incident was more than 30 years ago.
Then I see this/your thread and think, "Speak of the devil".
Maybe knowing this kind of thing has happened to others helps in some way. Good luck

p.s. Damned if I do? Damned if I don't? For anyone reading here...
Cement blocks crack and drop cars on people. Buy and use jack stands!
 
Trevor B said:
Okay - engine is coming out. There is scoring in the piston walls. Also, the water pump, which was disconnected from the leaking heater core, was so gummed up with deposits that it leads me to believe there is more going on with this engine than I had thought. I want to take it apart and get everything right.

Does anyone have any advice for balanced lift points with the head removed? Also, do I need to support the transmission in any way?

Thanks.
Click to expand...
are you keeping the transmission in the car?
if the driveshaft stays in, the transmission crossmember will hold the transmission in place just fine

as for lift points, i would try to bolt the chain into the block with two of the driver side cylinder head bolt
(it may still kick, but with the intake and exhaust removed, there is plenty of room for that)
 
I think you are doing the right thing here. Machine work (well around here) should run you about $800 that includes the head being done. Here's a great article on a slant 6 rebuild. Keep us posted.
Slant Six Engine Build
 
Alrighty, got her pulled. I mounted the chain at the rear lower head bolt hole and used a hole for the power steering pump mount in front. With the front jacked up, it came out without even removing the hood.

AND... a friend and fellow FABO member (and one of the most generous guys I know - his handle is IW378) is hooking me up with a spare engine he pulled from his 1968 Valiant when he swapped for a V8 so I can drive the car during the rebuild!

Thanks to everyone for the help. I'll be doing a ton of research and will surely be back with more slant six questions during the rebuild.
 
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There are two tapped holes on top of the head, meant for lifting the engine. I recall an AC bracket arm and BATT- cable often bolt there. Many have stated the FSM said to use the fwd hole for lifting engine alone and aft hole for engine + tranny. But, others found that probably refers to holes on a (rare) factory lifting plate that bolts to those two holes (someone posted a photo of that plate). Regardless, they are there to use and can take the load.
 
Yup - works good if you have the head on!
When trying to install the 170, I used both holes and then just moved the hoist hook a link back or forward to get it flat or angled how I want. But that didn't work so I get to do it again:
Different size torque converter knob 170 vs 225?!? Are you kidding me?

Once that puppy's on the stand, however... hope a strong neighbor is walking by if you've made the decision to flip the engine upside down with the head on and want to rotate it upright again. It took about 6' of cheater bar and everything I've got to get her to come around.
 
Dam i think i have the same problem i can drive mine but i do here this little rattling sound here and there not every second but every couple of seconds and i cant seem to get it to idle right haha dammm also slant six hahah man time to get a small camera i did pull out the spark plugs the other day dont damaged but dam hhahaha
 
man this place is so helpfull nooo i berly got her running after like three years of sitting mann
hahahahahah i want to drop the 225 i have the smaller slant six but might as well go for a 318 or 383 yee yeee
 
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