Slant 6 Vibration

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Poboyross

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I recently picked up a 72 Dart 4 door with a 225 /6, 50k original miles, with a 904 and 8 3/4 rear, all stock. I've recently replaced the Holley 1bbl with a professionally rebuilt one, and got a Pertronix upgrade on a new distributor. It has new plugs, plug wires, high output cool, and an oil change. The car runs far better than it did when I got it, but it still held onto this annoying vibration once it gets warmed up. When I start it up in the mornings, it runs fine, and with no vibration. However, after it warms up on the way to work, it still runs fine, but has this annoying vibration that rocks the whole car! The only other things I notice about the engine in general are that there's a faint ticking that is always there and increases with RPM, but not in volume. I also hear a little clatter when it's under load. My check list includes everything from a compression test, EGR valve, PCV valve, timing, and emissions control system all the way to the power brake booster causing a vacuum leak. Does my description lend itself to creating any type of order to which I should organize my list, or do any of them seem more likely than the others? I have attached a link to a video of the motor after it warms up.

 
Did you adjust the valves?
Is either motor mount worn out, specifically the passenger side one?
 
Gettin good and hot and setting valve lash would be good idea first, then,

Are all of the plugs clean? No fouling? Does your mix screw need to be out alot of turns? Float level? Choke open all the way when warm ? Id rule out spark for now with all those new goodies.

Good call on pcv check. Ignition should be okay set at 3* btdc.

Vacuum guage reading might be good too, should be nice and steady. Check things like advance pod too and whatnot for vacuum leaks

My 71 valiant was about that bad, replacing the Chinese junk rotor an cap with good ole fashioned made in usa nos ones really helped. I also run electronic iggy. I still does it a little when warm and i tried a new metering block and popping a plug and cleaning the idle passages in it with nil difference. But i have an oily plug on 6 that stays somehwat clean and fires so i quit chasing it till i rebuild.
 
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"Ticking" could very well be an exhaust leak, which would get louder under greater load. Could also be misadjusted rocker arm. Clatter under load could be excessive ignition advance.
 
Tune-up parts and technique suggestions are in this thread, with a link to the valve adjustment article. I agree with the others; a valve adjustment is your step № 1 here.

There is no EGR valve on a '72, the first year for the EGR valve was '73. California-spec '72s got a severely nasty no-valve EGR "system" involving a hole in the floor of the intake manifold that allows exhaust to flow (full time, always) into the intake tract. The list of badness this causes is long: rough idle (necessitating very high idle speed to stay running without shaking you off the seat or stalling), poor driveability and performance, lousy fuel economy. Swapping on an intake manifold not equipped with the '72-only "floor jet" screwed into the intake floor (or installing a a solid plug in place of the floor jet) would be a very fine idea.

Update: Watching your vid, I hear what sounds like an underhood exhaust leak. Likely one or more blown exhaust manifold gaskets. Your '72 exhaust manifold has three gaskets: one seals the intake and exhaust manifolds to the head, one seals the intake manifold to the exhaust manifold, and one seals the choke thermostat cup to the exhaust manifold. That last one is no longer available; see here. For the others, it is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.

Faulty brake booster or booster check valve is certainly worth checking for, since it will essentially kill (lean out) cylinder № 6.

Eventually you'll probably want to do the Fuel line mod and the HEI upgrade , and you may also want to take a look at this post.
 
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Thats good to know about 72 manifolds! Crazy way to do it..

It was quick and cheap and it squeaked the '72s past their emissions type-approval tests so they would be legal to offer for sale in California. Those were the priorities for a list of reasons other than the obvious ones; at that time the American automakers were generally complying with safety and emissions regulations in the nastiest ways possible, just about openly trying to spur public backlash sufficient to get Congress to repeal the regs. Ridiculous crapmess of five buckles and uncomfortable, clumsy, pain-in-the-nuts separate lap and shoulder belts…crude emission controls that made the cars run poorly…they won a few minor battles this way ('74 ignition/seatbelt interlock), but they lost the war. When dealers and zone reps shrugged and said "Not our fault, the government made us do it", instead of writing to their congressional representatives, consumers tried out foreign cars whose makers spent their efforts and funds complying with the regs instead of fighting them. Many never returned to American-made autos.
 
Tune-up parts and technique suggestions are in this thread, with a link to the valve adjustment article. I agree with the others; a valve adjustment is your step № 1 here.

There is no EGR valve on a '72, the first year for the EGR valve was '73. California-spec '72s got a severely nasty no-valve EGR "system" involving a hole in the floor of the intake manifold that allows exhaust to flow (full time, always) into the intake tract. The list of badness this causes is long: rough idle (necessitating very high idle speed to stay running without shaking you off the seat or stalling), poor driveability and performance, lousy fuel economy. Swapping on an intake manifold not equipped with the '72-only "floor jet" screwed into the intake floor (or installing a a solid plug in place of the floor jet) would be a very fine idea.

Update: Watching your vid, I hear what sounds like an underhood exhaust leak. Likely one or more blown exhaust manifold gaskets. Your '72 exhaust manifold has three gaskets: one seals the intake and exhaust manifolds to the head, one seals the intake manifold to the exhaust manifold, and one seals the choke thermostat cup to the exhaust manifold. That last one is no longer available; see here. For the others, it is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.

Faulty brake booster or booster check valve is certainly worth checking for, since it will essentially kill (lean out) cylinder № 6.

Eventually you'll probably want to do the Fuel line mod and the HEI upgrade , and you may also want to take a look at this post.

Wow, thanks for all the great info! I'll go ahead with the valve adjustment first chance I get. I already did the Pertronix electric ignition upgrade, along with a new distributor, as the vacuum pot on the old one was shot.

Speaking of manifold gaskets....WHAT MANIFOLD GASKETS?!??! I just realized this when I looked closer....

OVHFxOm.jpg
 
SOOOOOOO..... I'm now dead in the water. I only had a little time to troubleshoot today. I went out and played with the timing, which with only a little adjustment did seem to help the vibrating some. I took it literally around the block and got home only to find a pinhole had opened up in a freeze plug, half of which is obscured behind the exhaust manifold. GO FIGURE. Looks like I'm tearing it all down now :/
 
From the looks of it the manifolds need to come off anyways. I double up on the felpro gaskets for manifolds to head. some use remflex there which you need longer studs for so for now i avoid it.. I used a remflex for the one between the manifolds where the intake sits ontop of the exhaust, well worth it for no leaks.

I just pulled the factory block heater last winter for that reason, leaking coolant
 
Longer studs are not usually needed for the Remflex gaskets, and the Fel-Pro items stand you about a 50/50 chance of having to pull it apart and do it again.
 
Squirt water along the intake manifold gasket. That is how I found mine was leaking in my 1996 2.4L. I knew I had a vacuum leak since it idled too fast, even with the IAC port plugged shut. When I sprayed water there, the engine rpm suddenly decreased. Pulled the manifold and the gasket was hard and cracked, with chunks missing. What do they use today? Cardboard? The replacement Victor-Reinz looked like the same thin black stuff that failed.
 
I replaced my gasket with a Remflex because of an annoying exhaust tick. The car ran super after that so I figured it probably had an intake leak too which was cured by the Remflex gasket as well.
 
BTW, and exhaust leak by itself usually does not cause engine vibration like you show; an intake leak or valve misdajustment are better candidates for that, among other things.

Since you have compression test on your list, I would do that first as a baseline of what you are working with inside; no sense in doing everything else and then finding you have a burnt valve and having to tear the manifolds off again.

Run the compression test with the throttle propped open, pull all plugs first, and run each cylinder 4-5 times around and take readings. Post here.
 
Do the remflex gasket! I fought leaks for awhile on my slant. My manifolds didn't appear to be warped but new gaskets always failed quickly. Even doubled up gaskets failed. I cleaned to engine off and painted it up in the engine bay, painted the manifolds and installed the remflex gasket knowing it wouldn't leak. It held up perfectly until I pulled the slant for a V8 swap. Slants are pretty quiet little engines when sealed up and tuned up properly. A valve adjustment and basic ignition tune up is cheap and makes an incredible difference on a neglected slant.

AAAAND yeah that's ford blue, I know. I knew it would one day be pulled and replaced so special ordering Chrysler paint seemed like a waste of time. The high temp black exhaust paint help up perfectly with daily driver abuse also. Kind of wish I left the slant in place instead of having the car sitting in the garage while I chase parts for the V8.
downloadfile-1.jpeg
 
Ok fellas....time for some good (minimal), bad (possibly a lot), and the ugly (all signs point to yes.

While I have all the mainifolds off for replacing bad freeze plugs, I decided to do a compression test on all cylinders. Yes, I know it's ideal to do it after the engine is warmed up, but I wanted to get an idea of what I was looking at, at the worst.

Here's my readings:

Cyl 1: 95
Cyl 2: 35-40 (Why God, Why?!!?)
Cyl 3: 115
Cyl 4: 118
Cyl 5: 100
Cyl 6: 100

On Cyl 2, I got a 5lb jump just using some fogging oil I had on hand, I need to go get some standard oil and try again, but I'm not expecting much more. One weird thing when spinning over the engine on Cyl 2 is I can hear either a clicking noise or a degassing noise like a "PSSS" when doing the compression test. I didnt hear that same noise on any of the other cylinders. Not that I want it to be more than needing valve adjustment, but at worst, I'd rather it be a burnt valve over lower end problems like the cam. When the oil was changed last, the oil looked worn but fine, no sparkles or flakes in it. Any thoughts? I've considered getting a cheap borescope to check out the valves without having to pull the head....yet.

EDIT: just FYI, before all of this it ran ok, decent power, good pickup, no smoke but had a bit of gas smell from time to time. It did have the "clackety clack" when I tromped the gas, which was variable (it seemed) based on my experimentation with timing.
 
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It can -- if the exhaust is getting into the intake tract.

Hey Dan,

What do you make of the results I posted above? BTW, I've also followed your advice from some other threads and picked up an electronic choke from Carbs Only, which turns out literally to be 2 blocks from my house!! He also was the one who replaced my worn out Holley 1bbl with a newly rebuilt NOS one.
 
BTW, and exhaust leak by itself usually does not cause engine vibration like you show; an intake leak or valve misdajustment are better candidates for that, among other things.

Since you have compression test on your list, I would do that first as a baseline of what you are working with inside; no sense in doing everything else and then finding you have a burnt valve and having to tear the manifolds off again.

Run the compression test with the throttle propped open, pull all plugs first, and run each cylinder 4-5 times around and take readings. Post here.

Results posted two above this one. Thoughts?
 
Typically, if you add a teaspoon of motor oil, and the readings don't go up significantly, it is a bad valve or head gasket. I am not sure what fogging oil would do to seal up bad rings in this type of test, so I would reccommend repeating the tests with a tsp of motor oil in each cylinder.

Normally your valve train wears so that the valve lash (looseness) gets bigger and so that would not hang a valve open. But, if a valve pounded badly into the valve seat, then it could close up the lash and hang the valve open a bit.

Next time see if you can determine if the 'psssss' is coming out of the intake port or out of the exhaust and that would confirm a bad valve. Putting air pressure into each cylinder from a compressor with a park plug adapter would show this right away.

And the lower than average reading in cylinder 1 could be valves or cylinder wear; front cylinders in inline sixes often show more wear.
 
Typically, if you add a teaspoon of motor oil, and the readings don't go up significantly, it is a bad valve or head gasket. I am not sure what fogging oil would do to seal up bad rings in this type of test, so I would reccommend repeating the tests with a tsp of motor oil in each cylinder.

Normally your valve train wears so that the valve lash (looseness) gets bigger and so that would not hang a valve open. But, if a valve pounded badly into the valve seat, then it could close up the lash and hang the valve open a bit.

Next time see if you can determine if the 'psssss' is coming out of the intake port or out of the exhaust and that would confirm a bad valve. Putting air pressure into each cylinder from a compressor with a park plug adapter would show this right away.

And the lower than average reading in cylinder 1 could be valves or cylinder wear; front cylinders in inline sixes often show more wear.

I reran the test with motor oil on cylinder 2 only (battling a head cold at the moment and in the CA hear that's all I could muster) and the reading only topped out at 45. I didn't hear the hissing noise this time, however. Maybe it was nothing. So that indicates most likely a head/valve issue? I was considering getting a cheap borescope to look at the valves without taking the head off, but I suppose that's inevitable now.
 
Here's my readings:

Cyl 1: 95
Cyl 2: 35-40 (Why God, Why?!!?)
Cyl 3: 115
Cyl 4: 118
Cyl 5: 100
Cyl 6: 100

Gross. Time for some engine work.

On Cyl 2, I got a 5lb jump just using some fogging oil I had on hand

Not enough of a jump to write home about.

when spinning over the engine on Cyl 2 is I can hear either a clicking noise or a degassing noise like a "PSSS" when doing the compression test.

Engine is sick pony. Remove/rebuild.

Not that I want it to be more than needing valve adjustment

It's not that.

I'd rather it be a burnt valve over lower end problems like the cam.

1. It's not the cam.
2. It's not a burnt valve (wouldn't jump with fog oil)
3. You wouldn't actually want what you think you wish, because then you'd go spiff up the head and plop it back on the block, whereupon it would quickly finish off the tired bottom end.
 
Gross. Time for some engine work.



Not enough of a jump to write home about.



Engine is sick pony. Remove/rebuild.



It's not that.



1. It's not the cam.
2. It's not a burnt valve (wouldn't jump with fog oil)
3. You wouldn't actually want what you think you wish, because then you'd go spiff up the head and plop it back on the block, whereupon it would quickly finish off the tired bottom end.


For an engine that only has 50k miles, those miles must have been rough as hell. This is my first Mopar...what a welcome mat. I've got a lot of family stuff going on at the moment, so I won't be doing any major work to it until this time next year at the earliest...at which point I'd probably drop in a magnum/V8 for the cost of a \6 rebuild. I will just button it back up for now and either let it sit or run it till it dies. Sheeesh....that's depressing.
 
For an engine that only has 50k miles

Well…maybe. Remember, these cars have only an odometer that reads up to 99,999.9 miles, then it's back to all zeroes. It's hard to prove an old vehicle reading "49648.2" or whatever doesn't actually have 149648.2 or 249648.2, etc.

Maybe the 50k miles is correct, and if that's the case and it is some valve-related failure, and the bottom end's in fine condition, then you stand better odds of getting away with just a head repair (it's the guys with high-miles engines who want to do just the bottom end or just the top end who find themselves having to do both anyhow).

But even if the 50k miles is correct, it's still reasonably possible this engine needs major work of one or more kinds. Prolonged under-use (i.e., short trips and long periods of sitting unused) causes its own kinds of deterioration and failure in engines and parts. And while the Slant-6 and these cars were sturdier and better-engineered than most of their competitors at the time, by today's standards every step of the manufacturing process was primitive and poorly managed, so the spread of durability in individual old cars and engines is much wider than in individual units of more recent or current car and engine designs. Cars just didn't last as long then as they do now. The average age of a car on American roads in 1979 was 5.7 years, and that was up from a lower figure in 1969. The 2016 average-age-of-car-on-the-road figure is 11.6 years, that is a little over double the 1979 figure. All of which is to say there were a lot more early failures back then—even among the generally more durable engine designs like the \6. If it's not failure due to usage or non-usage, it could easily be just plain old bad luck.

I'd probably drop in a magnum/V8 for the cost of a \6 rebuild.

»yawn« Boring. Your car, of course, and my vote doesn't count, but…»yawn« Boring.

Now having said all that: What if it's just something easy like a faulty head gasket? I mean, you'd usually expect to see some other symptoms (violent radiator overboil, coolant smoke in the exhaust, two adjacent cylinders with similarly low compression readings) but sometimes they fail less dramatically.

What'll it hurt to pull the head and take a look? It's not very difficult.
 
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Well…maybe. Remember, these cars have only an odometer that reads up to 99,999.9 miles, then it's back to all zeroes. It's hard to prove an old vehicle reading "49648.2" or whatever doesn't actually have 149648.2 or 249648.2, etc.

Maybe the 50k miles is correct, and if that's the case and it is some valve-related failure, and the bottom end's in fine condition, then you stand better odds of getting away with just a head repair (it's the guys with high-miles engines who want to do just the bottom end or just the top end who find themselves having to do both anyhow).

But even if the 50k miles is correct, it's still reasonably possible this engine needs major work of one or more kinds. Prolonged under-use (i.e., short trips and long periods of sitting unused) causes its own kinds of deterioration and failure in engines and parts. And while the Slant-6 and these cars were sturdier and better-engineered than most of their competitors at the time, by today's standards every step of the manufacturing process was primitive and poorly managed, so the spread of durability in individual old cars and engines is much wider than in individual units of more recent or current car and engine designs. Cars just didn't last as long then as they do now. The average age of a car on American roads in 1979 was 5.7 years, and that was up from a lower figure in 1969. The 2016 average-age-of-car-on-the-road figure is 11.6 years, that is a little over double the 1979 figure. All of which is to say there were a lot more early failures back then—even among the generally more durable engine designs like the \6. If it's not failure due to usage or non-usage, it could easily be just plain old bad luck.



»yawn« Boring. Your car, of course, and my vote doesn't count, but…»yawn« Boring.

Now having said all that: What if it's just something easy like a faulty head gasket? I mean, you'd usually expect to see some other symptoms (violent radiator overboil, coolant smoke in the exhaust, two adjacent cylinders with similarly low compression readings) sometimes they fail less dramatically.

What'll it hurt to pull the head and take a look? It's not very difficult.

You mention boil over. I have only had the car for 2 months, and driven it sporadically. However, I've had several instances of it boiling out of the overflow tube, so I decided to do a radiator flush since what was leaking out was brown. It hasn't boiled over since, but it does get hot really quickly, like I'm my other post about the freeze plug failing. That was after it only running for 15 min or so. I hadn't made any possible connection to the head gasket for some reason.

Good point on the odometer, and I never knew that about the expected lifespan of cars at the time.



I'll pull the head and report back.
 
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