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I have a +/- '57 chevy 235 that started to misfire on #5 after a 200 mile trip. Plugs are clean, rotor and wires are fairly new and I'm getting a spark. I don't have compression tester, but I am not getting any blue smoke out the pipe. Any suggestions?

Thanks.

tlorber,

When you say misfire, you mean that cylinder isn't firing at all...all the time, it's dead!

The obvious first step would be to replace the plug and look closely at the cap. It might be as simple as sticking a new plug in it.

If things get serious, the next step would be as you alluded to, and that would be a compression check.

It's easy to swap wires and plugs and see if the problem follows either of those items, but the no-brainer first thing to do would be to replace the thing that doesn't' seem to be working, and that's the plug! Keep us posted.

Stuart

atomarc, thanks for the reply. I would say the miss is somewhat intermittent-maybe a couple times per second at around 1500 rpm. I'll try to change the plug gap and see if that helps.

Inspect the distributor cab for a crack , Are the plug wires clean and neat ? wires plugged in tight ? If they are tied together you could have a crossfire going . Check rotor and points also. I know these are basics but sometimes I overlook the obvious and try to make things more complicated than they need to be .

The wire could have a broken conductor near one of the terminals. Try swapping wires between #5 and say, #7.(to see if it is a wire)
Swap plugs arround (to see if it is a plug)
Check the distributor cap for crud on the terminals, or carbon tracing.

Had one do that, tried everything,finnally I had the valve cover off to adjust the valves and found that when I held my finger on the side of the valvespring when running it would run smooth as silk.well the valveguide was worn so the valve wasn't seating.My neighbor was there and wanted the car for awhile so I sold it to him.He fixed er up and may still be running it.

Scott - if it's the #7 wire on his 235 six cylinder then that is likely the problem, HA.

Your right Dave, I keep thinking everyone here is running V8's. Either way, the point was made.

Scott

Would a bad valve guide cause blue smoke?

tlorber,

Yes, bad valve guides could cause blue smoke, typically not at a idle, but usually after accelerating following a closed throttle, high vacuum condition. The classic example is the car or truck cruising down the long, steep hill on compression. When it reaches the bottom of the hill the driver gives it some gas and out pours the blue smoke.

Unless one guide suffered a failure, all intake guides would wear with accumulated engine mileage.

Stuart

I hate to ask, but how do you know that its #5? I assume that you pulled the #5 plug wire and the engine RPM didn't change?

There are a lot of obvious, and not so obvious reasons why this could happen. For instance, did you check you intake manifold for bird's nests?

What I would suggest is that you borrow a distributor cap from a fellow bolter, preferably one whose engine doesn't miss on #5, and see if it makes a difference.

OK I have a follow up here:

After performing compression and leakdown tests, checking distributor & plugs, valve lift & duration, (none of which were spectacular by the way)my problem ended up being that the manifold gasket had shifted and was permitting air to leak into the intake. This was causing #'s 5&6 to run to lean and stumble.

I'd like to take credit but it was a Porsche tech I know that located the problem.

I hope this can help some of you down the road.

Have you looked for vacuum leaks? There should only be one vacuum port on your engine. Disconnect the vacuum hose and make sure the fitting is not cracked at the manifold. Make sure the manifold bolts are tight. Does this misfire change with acceleration or engine speed? Yes/no and how it changes or doesn't change makes a difference as to the cause- fuel, ignition or something mechanical.

Harvester