Normal idle???

[mach0415]

Hello all. I am in the final stages of a long overdue process of putting the 47 P15 on the road. But, I am noticing a running characteristic that i am not sure is normal, as I have read through some of the tune-up spec threads. The engine seems like it has a random misfire at idle and at higher rpms.

Here is some history:

It has a 218 from a 1939 Dodge D11. I recently had the Stromberg carb rebuilt, replaced the plugs, wires, distributor cap, rotor, points and condenser.

The engine runs tons better than when I started. I set the points at .020" and set the dwell at 39. I checked the distributor advance and found working just fine. Also, vacuum timed with approx. 20 in/Hg vacuum at the wiper port. I made sure it has good fuel in the tank, as well.

I initially thought it could be a vacuum leak, but I cannot find one at the intake gaskets or wiper and distributor advance ports.

Do these engines tend to have a very smooth idle with no movement when set up correctly?

I have not checked valve clearance, as of yet. And, I have not checked compression. Do you all think improper valve adjustment could cause all of the random misfiring? Any ideas are greatly appreciated.

Edited December 19, 2011 by mach0415

[TJM70's_48]

I had a very hard to detect in daylight short from a spark plug wire to oil filter line...but I'm not a very experienced mechanic...it was random though - as you have described.

[mach0415]

I will check that too. I though I was very thorough when I installed them. I will look in the dark to see if I can detect any stray sparks.

[greg g]

make sure that all your spark plug wires and center coil wire are firmly seated. Also run you car at night and open the hood, look for any stray arching. like between wires or down a spark plug or down on the the dist cap.

If the miss is prevailant at idle, use a pair of insulted pliers to pull off one spark plug wire at a time. If the engine runs worse with one plug wire off its is nto that plug that is missing, so keep pulling wires oe by each till you find the one causing the miss.

You migh also have a sticky valve that isn't seating all the way. Have you done a compression check?

[mach0415]

I have not done the compression check. It is not a dead miss, just an intermittent, random misfire detectable by exhaust sound and engine shake. If I find one to be low, I will do a cylinder leak down test to see what gives. Are these things supposed to run like a sewing machine? It seems like I remember barely being able to see other flatty Mopar engines shudder, while running, at previous car shows. Fact or Crap?

Edited October 26, 2011 by mach0415

[greg g]

They are inherently a smooth engine especially at idle. I have a slight miss in mine, the wierd thing is i had the same miss in the engine I removed, this one is rebuilt, has a different distributor (checked on a machine) different coil and dual carb intake. So the miss transferred to a new engine with new accessories. It doesn't occur pulling or cruising. It does show up at lowspeed closed throttle coast down. I chased it new tuen up parts, new wires and plugs, changed the coil, still there living with it.

[mach0415]

Sorry to hear that. I hate it for you, especially after all the expense. Lots of these parts are Chinese crap. There is a lot to be said for quality these days. We should keep each other posted. My engine does not seem to miss under load. I wonder if borderline valve spring tension has anything to do with this issue.

[garbagestate 44]

The 48 Chrysler that I had as a kid almost ran smooth enough to balance a nickle on the head Not too long ago on this forum, someone said that induction misfires can happen between wires due to the fact that they all pass through the routing tubes and are bunched together pretty tightly. I guess it's not likely in your case since you stated that you replaced your wires but it's something to think about.

[mach0415]

Oh I dunno. I have replace new wires on other cars too:rolleyes:

[james49ply]

Mine does the same thing, irratic miss at idle or a no load condition, every thing is good mechanicaly, have detumined that it is caused by the 10% alcahol in the gas. no miss under load, runs smooth and has plenty of power, people ask what engine I have and they are surprized when I tell them it is bone stock.

[Desotodav]

It is interesting to find conversation of shorting spark plug wires as I just experienced a similar problem on my 218 long block. After having my carburettor re-built (which was probably needed anyway), I still found that my motor would have a miss or splutter on acceleration. I found that the problem was actually getting worse over time and it was just by chance that I saw the #4 wire arching out on the coil bracket one day when I had the bonnet open. I wish that I had thought to run the engine at night in the early stages of my problem. The engine certainly idles and runs smooth now!

Desotodav

[Don Coatney]

With your engine running at low idle hold a dollar bill flat side to the tailpipe. The exhaust should push the bill away. If it sucks the bill towards the tailpipe you may have a valve hanging up.

If I lug my engine (as in trying to accelerate at a low speed in a high gear without down shiffting) I will get a slight burp occasionally. Does this once and then clears up. I believe this to be from over carborating as I am running dual carburetors. My engine runs smooth but does have a slight lope at idle due to my lumpy cam.

Edited October 26, 2011 by Don Coatney

[mach0415]

Thanks. I sprayed carb cleaner around potential leak areas and found none. Then I sprayed windex on the plugs and boots, working my way down the wire tubes and distributor. As soon as I hit the distributor, the sucker cut off and did not restart until dry. I did not see any arcs, but it was in a lit shop too. I also think I have a dud compression tester. I stopped after I found the first three cylinders tested at 50 psi. I will try another one to see if this one was screwing with my head.

[greg g]

make sure you compression tester head does not extend further into the head thann the spark plug.

[mach0415]

Well, I think I have found the source of at least some of the low compression readings. I put a vacuum gauge on it while running and it pulsed while running between 20 in/Hg and 15 in/Hg. My suspicions were that I either had a burned valve, or a broken valve spring. I was leaning toward a broken valve spring, since there was never an intake backfire, or sticking valve(s) I drove my P15 home and back last evening - first on the highway since 1984. When there was a load it ran great. On decel and idle, was a stumble/skip.

So I decided to pull the head and do some investigative work. (The head gasket was leaking through the laminate, as I observed bubbles coming out of the passenger side while running.) I also found that I could lift #1 intake valve 1/2 way with my fingers, confirming my suspicion - broken valve spring.

BUT I also found the #3 cylinder upper compression ring land at the top of the piston broken off. The ring appears to be okay, though. I checked all cyinder walls and found all beautiful with no significant wear ridge or scratches. So, I will replace the valve spring on #1 and Replace #3 piston and rings. The valve seats and valves all look okay. The cylinder bore mics out right at 3.25 - stock! I am shocked at how little wear this thing has.

My questions are these:

1. Am I headed in the right direction, in terms of repair, not rebuild?

2. Anything else to look for?

3. Is there any difference in piston type from a 1939 Dodge 218 and a 1947 Plymouth 218, since the engine was out of the Dodge and placed in my P15?

Thanks!

Edited February 9, 2012 by mach0415

[Young Ed]

I think your plan should net you a decent runner. Its probably not the "proper" way to do it but I've seen it work before. LMK if you need a decent used valve spring.

[mach0415]

so, would you re-ring the entire engine too? or Can I get a complete piston with the rings for one cylinder only? I am leaning toward re-ringing it. But I should break the glaze, which means removing the engine to keep the crankshaft clean, right?

[TodFitch]

Decades ago during a low budget "shade tree overhaul" I decided I could just replace one piston. Turns out that there was a significant weight difference between the new piston and the other five. Way past the weight variation limits given in my '33 Plymouth's Operator's Manual's standards of adjustment section.

Just saying, you shouldn't replace one piston without at least seeing if it's close enough in weight to the others in your engine. Probably just easier to get a matching set of pistons and rings....

[mach0415]

Yeah, I am finding a discrepency in certain places between a 1939 D11 piston and a 42-48 P15 piston, in terms of part numbers. I am assuming there is a difference in either pin location, relative to the top of the piston, or the gap in or number of ring lands (3 vs 4 ring pistons).

Can anyone shed any light on the differences in piston design from late 1930s Dodge vs 1940s Plymouth 218s?

[T120]

Regarding pistons -check #38...

[mach0415]

Thanks for the info. The print is small, but it appears they interchange. Is that correct by your copy?

[T120]

It appears they should interchange.Tod brought up a good point about replacing as a set.Years ago because of circumstances at the time,I have replaced individual pistons.

..To enlarge the scanned page left click on it and then on the lower right of your screen change the Zoom level to 150% - should make it easier to read...

Edited February 10, 2012 by Ralph D25cpe

[mach0415]

okay. Thanks! I may pull another as I am replacing rings just to check the weight vs the replacement

[ptwothree]

I was faced with a similar problem.....replace one piston or the set. After measuring the ring land gap, I bought a new set. If you have a broken ring land on one then the others will follow.

Btw, if you still want to replace just one let me know...I have a brand new Sealed Power std. bore piston and pin all boxed up and ready to go......

[james49ply]

Back to the origional problem, intermttent miss at idle, I also have this problem. I have traced it to the vacuum port for the dizzy, if I back the idle down far enough (300 rpm) the miss stops, I checked the port for the dizzy and had 0 vacuum, raised idle to 500 rpm and had full engine vacuum at that port. right now I am congitating a solution to this problem:confused:, have several thoughts but haven't had time to experimant with a solution. Also note that engine bone stock, but have the HEI dizzy in it from Stovebolt. the dizzy gave awsome performance improvement:eek:.