One cylinder in my new engine not firing...any thoughts?

[Chris]

Just fired up the 21 stud flathead in my 33 pickup today. It had a load POP out the drivers side exhaust...further investigation showed that the rear cylinder (number 8) was not firing. It has compression, spark and fuel...so why would it not fire? After running for 20 minutes the plug was wet, but not a hint of firing. I put another plug in it (thinking it was bad), it made no difference. Any thoughts??

[Mike in AZ]

pull the plug and look in plug hole to see if valves are moving correctly....and closing all the way.....might have broken a valve....collapsed lifter??....good luck....Mike

[Russ/40]

When you say you have compression in 8, I presume it was normal. Look for a shut to ground somewhere in the ignition to that cylinder. LIte it up in the dark and you should be able to see where your spark is going.

[Chris]

Thanks guys. Yes, I pulled the plug and everything looks to be moving correctly. As far as compression, I don't have a gauge handy so I was just going by cranking it over with my thumb over the hole and feeling the compression. Cheezy, I know...but it's all I got

I fired it up in the dark and could not see any spark exiting anywere. I did pull the distributor/wires and am planning on replacing that stuff. It's a 46-48 distributor and I wanted to change to a crab I had anyways. So I'll pick some wires up for that tomorrow, button it up and see what happens.

[Ken Crans]

Chris, What kind of headers are you running? Hope you get the spark issue resolved. Ken

[Frank Miller]

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A long shot but if you accidentally set the clearance of a valve on the open part of the camshaft you will not get proper air flow to make the cylinder run. I would pull the intake and inspect the valve operation as well as lifters and springs. I am assuming you grounded a screwdriver to the top of the plug to make sure the spark is getting to that point.

[Terry,OH]

plug wire not installed in the proper position in the distributor.

[41ford1]

Chris,

I would beg or borrow a compression gauge to do a real test before opening up the engine. On Terry's lead could a pair of plug wires be crossed or an insulation break inside the harness tube. If there was a break inside the tube it might not show up running in the dark.

[ford1]

the easiest way to see if the plug is getting spark is to hook up and induction timing lite to that cylinder, if the lite blinks then its geting spark, another thing to check is the dist lobe on #8 cylinder, ive seen them worn so much that the points wouldnt open

[ford1]

while im thinking about your problem check inside the cap for carbon tracking, maybe a cracked cap

[Cecil/WV]

And take the plug out and ground it to the head to see if it fires.

[rotorwrench]

What kind of load popped out? Oil? Or was that just an after fire (loud pop) like too rich a mixture getting into the exhaust. I hope nothing got left around to get into the intake to block the port.

[Russ/40]

DON'T pull it apart! As suggested, you need a compression test. Your thumb will not cut it. Also do as suggested by pulling the dead plug hook it up to the wire and lay it on the head, does it fire? You could also hook up a timing light to the wire with the engine running to see if there is any high tension there. Reprt back...

[Mick/mo]

Like has already said .Check to make sure you don't have 2 wires crosed.

[BIG MIKE]

yopu got the same motor as in my tank! (bren Carrier) I wonda how much faster it would go if I did the same thing as you did Double carbs, I think you #8 wire is shot!

[BIG MIKE]

And who sayz your your thumb will not do the trick? it worked for me. best feeler even

[Chris]

Originally Posted by Russ/40

DON'T pull it apart! As suggested, you need a compression test. Your thumb will not cut it. Also do as suggested by pulling the dead plug hook it up to the wire and lay it on the head, does it fire? You could also hook up a timing light to the wire with the engine running to see if there is any high tension there. Reprt back...

I'll get a compression tester tonight and check. Yes, the plug gets spark when grounded out and running....maybe no spark under compression? I have the distributor and wires off now checking everything. Will report back if/when I find something.

Thanks everyone so far, been a great help

[Mr 42]

Swap the plug and see if the problem follows the sparkplug.
If not swap sparkplug cable to see if the cable is the problem.

[[email protected]]

I hate to admit it but when I built my '46 flathead I got some gasket shellac or loctite or something on one of the valvestems and the valve hung-up just enough to keep it from closing all the way. It acted just like your describing your engine. Though it only took about 30 minutes to pull the intake, clean the valvestem and put the intake back on it was still a little embarrassing because I had a smarta$$ friend here to help me fire it and he never let me live it down. After cleaning the valvestem the thing purred like a kitten.

[paul2748]

Try a new plug - it wouldn't be the first time that a new plug is bad