strictlyballroom

Misfire Teaser - straight flathead 6

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My new 1950 Nash Rambler is only firing on 5 cylinders. Confirmed by when you remove the lead to cylinder 1 it makes no difference. By contrast, remove any of the others and there is a noticeable difference.

 
There is a good spark at cylinder one - tested with inline tester and the more traditional way of holding plug to earth (really strong Blue spark).
 
Looking into the spark plug hole, the valves seem to be opening when the engine is running.
 
The real mystery, the internet tells me the firing order should be 153624. However, it's set-up as 142635. I did try and put the leads as they should be, but the car would not even start. The fact is the car runs quite sweetly with the incorrect firing order, save for missing on one cylinder.
 
The engine is the correct 1950 Nash Rambler straight 6.
 
I performed a Compression test (I only tested 3 cylinders)
1.   105 (the offending cylinder)
2.    90
6.   90
 
More mystery, the offending cylinder has good compression.
 
I have tried to test the timing, but I could not get my hands on a timing gun that would work with 6 volts, but seeing as she runs pretty well apart from a slight misfire I don't think the timing has anything to do with it.
 
When you remove the plug after running the car for a short-while, the plug is wet so there is fuel getting to the cylinder and you can see it down the plug hole.
 
Yes, I know I should take the head off and see what's happening, but I have just bought this car and I am not near my workshop and hoping I have missed something really obvious.
 
All suggestions welcome.
 
Mike

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Did you happen to swap the no. 1 plug to a different cylinder to see if the problem is the plug or the cylinder?

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3 minutes ago, joe_padavano said:

Did you happen to swap the no. 1 plug to a different cylinder to see if the problem is the plug or the cylinder?

Yes I did, the plug is fine.

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turn the engine over till you are on TDC #1, is the distributer pointing to #1?

 

On the timing light just use a 12V battery to power it, should work fine.

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ballroom

believe firing order 153624     I think you are looking at firing order on dist in reverse direction

                  Bob

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Is there any sort of vacuum port along the intake trough near cylinder #1? (It would probably look like a fitting right into the head.)

 

Regarding the firing order, crank the engine with the cap off and see which way the rotor turns. The firing order will go around the cap in the same direction the rotor turns..

 

Edited by Bloo (see edit history)

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Interesting point---somewhere online is a fascinating piece about possible alternative firing orders, but all I find in my notes is one small note, that late 1920s Buick 6s were 1-4-2-6-3-5, and that Wisconsin water cooled truck/ind'l 6s were the same...

Can't comment re' the Buick, but have a little Thonpson "manual" (more like a pamphlet) that verifies the Wisconsins...

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Try swapping a couple of plug wires to see if the problem may be a bad wire.

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The same web site that gave me the firing order also stated the direction of the dizzy was CW, but I should have checked, which I will do tomorrow. I really don’t think the leads are a problem given I am getting a really strong spark.

 

i don’t remember a vacuum port, but I will look tomorrow also.

 

it would appear based on the replies so far there is nothing obvious for the cylinder not to be firing.

 

mike

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Just checked my Canadian Service Data Book for 1954. It covers all foreign and domestic makes sold in Canada from 1942 to 54. It says all six cylinder engines firing order is 1-5-3-6-2-4.

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An old mechanic friend of mine used to say "too young (1-5), too old (3-6), just right (2-4)"

 

I am getting old enough they are all too young....but I never forgot the firing order

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An easy way to tell which way the distributor turns is to look at the vacuum advance, it points in the direction of rotation. Or to look at it another way, it pulls the points towards the rotor.

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Just wondering why you didnt compression test #5 ? 

 

Ok misread your original post, so as suggested have you swapped the offending lead, had a good look at the distributor cap ?

Edited by hchris
Rearranged (see edit history)

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Verify the engine's firing order with lose plugs and that compression weeps out in the correct order. Maybe someone put the plug wires into the cap in the wrong order. With all the references to the ignition firing order mentioned here and yours doesn't match seems to be a root cause. Is this an original engine or was it rebuilt at some time? Could the distributor be installed a few teeth off? #1 plug is wet because its not firing at the right time (during compression stroke). Go back to basics.

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The dizzy does turn ACW so the firing order was a red-herring. 

 

The engine is original, but recently rebuilt.

 

The plug and lead is good - all checked three times.

 

The mystery continues.

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4 hours ago, strictlyballroom said:

 

 

The engine is original, but recently rebuilt.

 

 

 

This should be a HUGE contributing factor.

As suggested, back to basics.

My money is on a valve problem.

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The engine is original to the car, and it has been recently overhauled  prior to my purchase.

 

I too thought it was probably a valve, but the good compression threw me. 

 

Mike

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The plug and lead you say are OK. You say you have a good spark. Hopefully, it is equally as strong as the other five sparks. You have checked them 3 x so any further checks on them must be in a completely different (independent) way to any done up to now.

 

Back to static timing. Make sure it is set up correctly, as @Friartuck said. Can you can try another distributor cap - you might have a track or other electrical leakage in the cap disturbing spark timing to number 1.

 

Is it possible there is fuel in the cylinder but not enough? e.g. a partial blockage of the port, such as at the manifold gasket? There has already been mention of a vacuum offtake on that leg of the manifold that might be taking fuel. Just an off the wall thought - did it take more strokes to work up the compression pressure in that cylinder than the others? This might happen if the inlet is blocked, meaning the volumetric efficiency of that cylinder was reduced.

 

Is it possible the spark to number 1 is leaking out of the cable somewhere? i.e. a short. When you remove the plug or lead to test, you move the lead away from any possible short.

Edited by Spinneyhill (see edit history)

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 A professional engine builder friend of mine tells me that, these days, he prefers using a "leak-down" tester instead of a compression tester, because it can reveal more problems. 

 

Personally, I would clamp the plug from the non-firing cylinder to the head somewhere with a  good ground connection, attach the spark plug wire to it as normal, turn off most shop lights so I could readily see the spark when it happens, and cover the spark plug hole with my finger or thumb. Then have someone crank it over with a ratchet or breaker bar, and see if the spark occurs just as my finger gets pushed out of the hole by compression stroke. That will isolate answers about timing issues to just that one problematic cylinder. 

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You said that the plug on the duff cylinder was wet. That suggests that it is not sparking in the cylinder. Can you not confirm sparking in cylinder using a strobe light? I know they need 12v, but you could use a spare battery beside the car to power the lamp and put the inductive clamp onto each lead in turn whilst the engine is running. The flashes will soon tell you if a spark is occurring at each cylinder. Definitely worth a try before you lift the cylinder head. Also, look for escaping sparks in a darkened garage with the engine running (but mind the rotating fan!!!). 

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