.
cars

Jump to content


Hello, Allpar Forums member or visitor! If you were an active member (more than two posts) or subscriber, you would not see this ad!

Register for a free account or Sign in (see top right of page for Facebook/Open ID login icons).


Photo
- - - - -

Rough Idle - 225 Slant Six - Sharing Several Fixes That Cured Mine


This topic has been archived. This means that you cannot reply to this topic.
15 replies to this topic

#1 66DartConvert

66DartConvert
  • Inactive
  • 18 posts

Posted July 23, 2009 at 09:35 am

Have a 1966 dart with 225 slant six engine. I took the car to two mechanics neither of which could figure out the cause of my rough idle, poor starting, and rough running after hot start (which I thought might be vapor lock but really wasn't). I'm guessing the mechanics didn't want to take the time/effort to figure out and fix the problems. So I decided I needed to fix the problem myself and after much internet research and a lot of tinkering/testing/fixing I cured the problems. Here are the issues I found/fixed (in order) that now have my car running and idling smoothly. With each fix the car ran progressively better. Hopefully this list will come in handy for others troubleshooting this same problem (rough idle, poor hot start and running rough after hot start).
1 - Valve lash adjustment too tight - My valves were surprisingly quiet for a slant six. Plus hooking a vacuum gauge to the intake manifold showed that gasses were leaking past my valves -- the gauge needle shook rapidly over 2 or so inches as the engine idled. The prior owner apparently set the values too tight. Adjusting the valves to the proper lash significantly improved how the engine ran. However vacuum gauge showed that vacuum was a little lower (15-17 inches) than it should be (about 20 inches) indicating I was loosing vacuum somewhere.
2 - Loose carburetor mounting bolts - This was one source of vacuum leak. I had the carb rebuilt and when I reinstalled the carb the bolts were not tightened enough and I was loosing vacuum at the base of the carb (this one was my fault!). Significant improvement in run/idle.
3 - Loose manifold bolts - Another source of vacuum leak. A mechanic recently replaced the exhaust manifold and apparently didn't tighten the bolts correctly. Be sure to check ALL manifold bolts -- especially the one in the very center of the manifold that is difficult to reach/see. Good improvement in run/idle.
4 - Loose carb screws - Another source of vacuum leak. Apparently the shop that rebuilt my carb did not screw the carb back together tightly. The carb body screws were surprisingly loose. Tightening the screws significantly improved idle and eliminated the hot start problems.
After doing the above, recheck timing and readjust the carb and you're in for some smooth sailing.
Happy slant sixing!

#2 Bill R

Bill R
  • Inactive
  • 1,728 posts

Posted July 23, 2009 at 11:09 am

In the end , smaller details count. As to setting the valves, I used to do it hot and idling. I would set the idle speed way down and have the engine just rolling over and oil wouldn't splash all over - believe I laid something over the manifold. I think the adjustment screws were self locking. You would just slide the feeler gauge in and out and get a slight drag ( at correct setting) when the valve was in the closed position. After doing one you will get the hang of it. I would set them all and then go back and recheck. You can do the valves faster this way. Gives a very smooth running engine assuming everything is up to snuff. I did a 273 V8 in a 1966 Valiant I once owned - super smooth idle after that. Good report!

#3 Bob Lincoln

Bob Lincoln

    "CHECK FAULT CODES"

  • Supporters (L2)
  • Others:Forum Leader
  • 25,317 posts

Posted July 23, 2009 at 01:21 pm

Welcome to Allpar, and thanks for the tips!

Yes, the previous owner most likely set the valve clearance with the engine off. This doesn't work on this engine - it cools down too fast and the clearance will be set too close. How do I know? :blush:

In my case, the car woud start and immediately stall with a sigh. I set the clearance with the engine off because I didn't think I could keep a wrench on the moving rocker arms. But you have to, to be successful.

Hope you caught it early. Tighter valve clearance = burned valves. But this is a rugged engine.

Intake/exhaust manifold bolts should only be torqued to spec - 10 ft-lbs. I tightened them too much, to about 30, and broke 3 of them. Luckily the seal was so tight all around that there was no vacuum leak.

Do as much as you can yourself, today's mechanics tend not to know or care to know how to work on these cars. Happy motoring!

#4 66DartConvert

66DartConvert
  • Inactive
  • 18 posts

Posted July 23, 2009 at 01:58 pm

Welcome to Allpar, and thanks for the tips!

Yes, the previous owner most likely set the valve clearance with the engine off. This doesn't work on this engine - it cools down too fast and the clearance will be set too close. How do I know? :blush:

In my case, the car woud start and immediately stall with a sigh. I set the clearance with the engine off because I didn't think I could keep a wrench on the moving rocker arms. But you have to, to be successful.

Hope you caught it early. Tighter valve clearance = burned valves. But this is a rugged engine.

Intake/exhaust manifold bolts should only be torqued to spec - 10 ft-lbs. I tightened them too much, to about 30, and broke 3 of them. Luckily the seal was so tight all around that there was no vacuum leak.

Do as much as you can yourself, today's mechanics tend not to know or care to know how to work on these cars. Happy motoring!


Agreed that too tight valve lash does not allow the valve to seat fully (letting gasses by) and more importantly NOT allowing the valve to transfer its heat to the metal of the engine -- resulting in burned valves. From the looks of the vacuum gauge results on my engine (steady needle at idle) the valves appear to have survived the heat.

I tightened my manifold bolts by "feel"-- didn't go crazy tightening -- but I'm guessing they are tighter than 10 ft-lbs. Will keep this in mind and be gentle on them.

#5 cass

cass
  • Active Member
  • 849 posts

Posted July 23, 2009 at 02:28 pm

...As to setting the valves, I used to do it hot and idling. I would set the idle speed way down and have the engine just rolling over and oil wouldn't splash all over - believe I laid something over the manifold. I think the adjustment screws were self locking.

Brings back memories of my 1974 Dart with the 225. I used to hurry to get the valves finished before the splashing oil completely coated my glasses. My motor did have the (interference thread) self-locking adjusters. Can't imagine doing the job without them. I recall that I installed Chrysler's electronic ignition on the car. That was a simple bullet-proof sweet-running six.

#6 TWX

TWX

    DO NOT FEED THE TROLLS!

  • Supporters
  • Others:Forum Leader
  • 8,871 posts

Posted July 23, 2009 at 02:58 pm

I could see it now, a mechanic not having any idea what adjustable lifters are, or how to set valve lash...

Glad that all of your problems were relatively simple, even if there lots of them.

#7 Bill R

Bill R
  • Inactive
  • 1,728 posts

Posted July 23, 2009 at 05:57 pm

Cass - if you had slowed the idled speed down, you wouldn't have been splashed with oil. As was pointed out, exhaust manifold would break if the 2 end nuts on the studs were overtighted - I think the torque setting for the end bolts was shown with raised letters on the exhaust casting near each end. I had a landlady that was on her third manifold when she talked to me - I checked the end bolts and they were very tight - I slacked them off and she never replaced another exhaust manifold. Cass I had a 1974 Dart as well - bought new. It had the electonic ignition on it - just carried a spare ballast resister.

#8 cass

cass
  • Active Member
  • 849 posts

Posted July 23, 2009 at 07:12 pm

Cass - if you had slowed the idled speed down, you wouldn't have been splashed with oil. Cass I had a 1974 Dart as well - bought new. It had the electonic ignition on it - just carried a spare ballast resister.

Now that I think of it, mine was a '71. I bought it from my dad in '74, and he originally bought it from Chrysler's executive trade-in lot at Highland Park Engineering, so we're talking ancient history here. Kind of gives away my age! Anyway, I know that it had ignition points when I got it, because I swapped it over to electronic on my father's recommendation. He gave me the parts that a guy in the engine lab gave him. He (my father) was an engineer at Highland Park. In regard to the valve adjustment, I was quite young then, so I didn't know all the tricks of the trade! In any case, I learned a lot working on that car.

#9 Trailmaster

Trailmaster

    Move Over Plymouth Aproaching Rapidly

  • Active Member
  • Others:Forum Leader
  • 2,061 posts

Posted July 23, 2009 at 07:27 pm

Yes, the previous owner most likely set the valve clearance with the engine off. This doesn't work on this engine - it cools down too fast and the clearance will be set too close. How do I know? :blush:

I'm glad I found this. I've never adjusted the valves on my slant, how often are you supposed to do it? Is there any posibility of doing it like I used to on my 216 Chevy, set them hot the first time and then let it cool overnight and measure to get a cold reading for future setting? Cool engines without oil splashing all over are much easier to work on.

#10 Wizard

Wizard

    Stready as Tulip goes will win.

  • Active Member
  • 5,109 posts

Posted July 23, 2009 at 07:31 pm

Crank the engine rpm low enough that engine turns over without stalling during hot valve adjustments. This way splashing oil all over is much less.

Also check out slantsix.org as well.

Cheers, Wizard

#11 Bob Lincoln

Bob Lincoln

    "CHECK FAULT CODES"

  • Supporters (L2)
  • Others:Forum Leader
  • 25,317 posts

Posted July 23, 2009 at 10:12 pm

I'm glad I found this. I've never adjusted the valves on my slant, how often are you supposed to do it? Is there any posibility of doing it like I used to on my 216 Chevy, set them hot the first time and then let it cool overnight and measure to get a cold reading for future setting? Cool engines without oil splashing all over are much easier to work on.

Wiz is right, it can only be set while hot and running. But the idle being slow will minimize oil splash. Other than that, wear gloves or a long sleeve shirt. It's not that bad. This really is an easy task. Use a 3/8" box wrench, so that you don't drop a socket down in the engine. And recheck your measurement several times after adjusting, to be sure it's dead-on.

The book says to check it every 12K miles, but you can easily triple that interval. By then the cover will be leaking oil and need a new gasket, anyway. LOL.

Make sure you don't pinch the alternator wiring under the valve cover when you reinstall that. A friend did that on his 318, and the car's main fusible link fried. It never charged right after that, because he had 3-4 strands of copper to solder the new one to.

For a little higher compression, more power, but slightly rougher idle that must be set faster to stay running, you can back off to about .012" intake and .022" exhaust. It just won't idle at lower speeds and must be turned up. But you can measure the increase in compression, and feel more power by doing so. It will have more chatter, though. Just a tradeoff if you want to make more power. Not sure how much it will affect gas mileage.

Edited by Bob Lincoln, July 23, 2009 at 10:13 pm.


#12 68RT

68RT
  • Active Member
  • 4,595 posts

Posted July 24, 2009 at 02:23 pm

A couple of shop rags (CLEAN SHOP RAGS!) laid over the rocker arms not only stops the splashing but also keeps the rocker arms and pushrods closer to hot temerature combined with a low idle speed works best. Just expose the area you are working on and keep the rest covered.

#13 66DartConvert

66DartConvert
  • Inactive
  • 18 posts

Posted October 7, 2010 at 06:02 pm

Update on loose carb mounting bolts and carb body screws...
They apparently loosen themselves after a while. I need to check mine every now and then and tighten them. When they get loose, I get a whistle sound when I give it a fair amount of throttle (up hills, etc.). Plus it doesn't run as well when unmetered air from the loose bolts/screws gets sucked into the intake (vacuum leak). So my advice is to check your carb bolts & screws every once in a while.

#14 edselehr

edselehr
  • Inactive
  • 1 posts

Posted November 14, 2011 at 01:59 am

Thanks everyone, this thread helped me out a lot. I had the same problem, turns out I adjusted the engine while hot but not running. It must have cooled enough to make my clearances just a hair too tight, resulting in an intermittent drop in vacuum and "pop" from the exhaust at all speeds. I increased the valve last 3-4 thousandths and now the engine runs a lot better. I've gained a very little bit of valve train noise, but well worth it for the smoother running engine and increase in power.

#15 KOG

KOG

    KOG

  • Active Member
  • 5,836 posts

Posted November 14, 2011 at 06:15 am

One tip with the self locking adjusters. Always finish by turning them in the tightening direction (clockwise), never loosening (counterclockwise). If you get one too tight, back it off at least 1/4 turn and try again to get it right. Setting valves looser than stock will increase low end torque slightly and reduce top end power slightly on any engine.

Electronic ignition is a real winner on the 225 as it avoids your having to fight timing with the limited range strap on the distributor.

The later models with small oil filter can still use the longer Purolater 3001, but will need a longer center tube from an early model to match the longer filter.

Larger diameter exhaust (2-1/4" all the way to the rear) as found on the Feather Duster/Dart Lite improves both mileage and power very slightly, but it's a pain to install and can be loud unless you add a resonator (440 C body part) at the rear in addition to the muffler (340 A body). Any muffler shop can bend up the tubes for this.

Go back and torque the manifold bolts correctly or you will have a cracked exhaust manifold. Another tip to be aware of: make sure the hear riser flap is operating freely. If it sticks in the closed position it will boil gas out of the carb and warp the carb body from excess heat. Getting the float level tight can be tricky. It's not unusual for ti to be too high when set dry using a gauge. It can be checked running by taking the power valve out and measuring with a dial caliper through that opening with the engine running. I forget what the wet spec is (it's been 20 years since I did this), but setting the float that way has solved some carburation issues on a couple of my 225s.

225 got a cam with slightly more duration beginning in '73, same power rating (110 net), but actually has slightly more top end. For quite a few model years they would outrun 260/289 (105-120 net HP) Fords and 283 (125 net HP) Chevys in Falcon/Nova. The 225 had both a broader torque band (peak torque at 1200) and a three speed automatic vs. the two speed of the other pretenders. Got better mileage too. And would outlast the Fords at least 2:1 and the Chevys at least 1.5:1.

I had a 74 Valiant which would run a clocked 117 mph (as opposed to "my speedometer says my car goes 150MPH"! b.s.) with a stock 1bbl 225. Car also had the rain gutters removed, large air dam, narrowed bumpers (to match body instead of hanging out), lowered front suspension and narrower front tires to reduce drag. 2.45 gear in a 74 318 axle to improve top end and mileage, but that's not really a good move overall as it does hurt acceleration from a stop and doesn't help mileage under about 70. A typical A body 225 will run 105-107 dead stock with automatic. 318s have trouble getting to 117.

If you ever want real power, a 340 or 360 used to be the only way to go. I've still got a 73 Valiant 360 which is fairly rapid. If you were doing it now a Gen III Hemi will outperform any of the LA V8s though.

#16 chuzz

chuzz
  • Active Member
  • 5,049 posts

Posted November 14, 2011 at 11:32 am

You can use a little dab of blue thread lock on those screws and carb mounting bolts. That way, they'll stay snug, but you can still loosen them if you ever need to service or replace the carb. Great tips on the vacuum leaks, BTW. I used to have slant 6/s back in the 70's, and had one in 1994, but have not had one since then.


.
Allpar

Home · Cars · Engines · Repairs · People
Tool and Car Reviews · News

Please read the terms of use and privacy policy. We are not affiliated with Chrysler Group, makers of cars, minivans, trucks, and Mopar (TM) parts. We make no guarantees regarding validity or applicability of information, opinions, or advice. Posts may be edited and used in other parts of allpar.com and affiliated Mopar (Dodge, Chrysler, etc) car related sites. We have the right to remove or modify any message, and to ban or suspend any user without notice. Logos and site-specific information copyright © 2001-2013 Allpar LLC; Chrysler PR materials remain property of Chrysler Group.